Pride and Priority

Knowledge, power and control in the early aerospace industry


David Musker, 2009


"The best dividends on the labour invested invariably come from seeking more knowledge rather than more power"[1]


This is the story of the battle for priority to the invention of the slotted wing, fought on the battlefields of science and law using publicity and power as weapons.  Patented by Sir Frederick Handley Page in the 1920s, it was widely applauded at the time: “it is the only real aerodynamical discovery of the last decade, and was undoubtedly a brilliant invention” wrote aircraft engineer and mathematician John Dudley North (1893-1968)[2] in 1926.  According to Handley Page Ltd[3] it was “hailed throughout the world as the greatest achievement in the realm of aeronautics since man first conquered the air.”  In the UK it was adopted as standard equipment.  "I think it will be a great satisfaction to the House that this British invention should now be in process of adoption throughout the whole of the Royal Air Force", the Air Minister, Sir Samuel Hoare[4], told the House of Commons in 1928.  Imperial Airways, the major British civil carrier, adopted it too. 

The slotted wing saved many lives, and is still in widespread use as part of today’s multi-element wings.  It was heavily patented.  The patents earned Handley Page Ltd, and Sir Frederick Handley Page personally, a great deal of money and were largely responsible for keeping the company afloat long enough to play a part in the Second World War.  Abroad, "practically every important government has acquired for its nationals either the patents or the right to use the Handley Page slots"[5].  However, many others also claimed to have invented the slotted wing, amongst whom the most persistent was Dr Albert Peter Thurston, aeronautical pioneer and patent agent, who took on Handley Page but found himself thwarted and silenced.  "I remember well that Thurston used every possible opportunity in discussion at R.Ae.S lectures to claim that he anticipated the invention of the slotted wing" wrote Gustav Viktor Lachmann[6] (the person with the best claim to priority, to whom we shall shortly return), but "I do not think these claims were ever taken very seriously by anyone."  In fact, many did take Thurston’s claim seriously, but not until the 1960s, after both combatants were dead, did they go public; Thurston’s obituary in Flight magazine[7] stated baldly that “Dr Thurston anticipated Handley Page's invention of the slotted wing …”, and shortly afterwards, aviation writer Oliver Stewart[8] claimed that it would be “unjust” not to mention him; “References to the wing slot and its great success would be incomplete without acknowledgment to the far-sighted work of Dr Thurston[9] who “must be given his proper ranking”.

The website of the Newcomen Society[10] for the study of the history of technology holds an article by Professor Alec Young,[11] Thurston’s friend in later life and successor at Queen Mary College, and two by Thurston himself.  Young's paper (after Thurston’s death) discusses Thurston's dispute with Handley Page without reaching definite conclusions, but several of the contributions in the following debate reveal the extent of Thurston's bitterness.  Thurston's own articles are, surprisingly, silent about Handley Page, but refer to a cancelled lecture and the destruction of all but two copies ([12]) of a paper to be read before the Royal Aeronautical Society.  The Science Museum Library holds a not-for-loan copy of the paper at Swindon, with a typescript letter from Thurston tipped in facing the title page, stating that the paper was not read and all copies were withdrawn.  The R.Ae.S file on Thurston (marked “To Be Kept Very Confidential”[13]) contains another copy of the cancelled paper, marked “ONLY COPY - KEEP CAREFULLY”.

Priority is often debated – television, radio, the telephone and practically every other important invention have a host of fathers.  However, suppression of a technical paper by a learned society is rare.  Thurston was undoubtedly an aeronautical pioneer, and a long-time member of the R.Ae.S (and other learned societies).  Was he a liar, or a hoaxer?  Had he become a crank?  Or did his paper contain something dangerous? 


Slotted Wings – what they do

The earliest aeronauts pursued three goals: power, stability and control.  Many early kite, glider and aircraft designs were stable, but stability was bought at price; stable aircraft[14] were less manoeuvrable, and became sitting ducks in the First World War for less stable, more agile fighter planes.  These, however, suffered stability problems – stalling, and then spinning into a lethal crash.

Stalling is caused when aircraft wings cease to generate enough lift.  One trigger is low airspeed, often a problem for the underpowered early aircraft.  The airflow over (and under) a wing normally forms a thin “boundary layer”, hugging the wing, across through which the airspeed varies in a transition from that of the wing to that of the free air.  Increasing the angle of attack of the wings increases the lift, up to a certain critical angle of attack at which the boundary layer can detach from the wing, and an area of turbulent, chaotic flow spreads over the upper surface of the wing in the detached region (typically from the outboard ends of the wings).  That increases drag and reduces lift, resulting in a low speed stall.  If the conditions were not identical on both wings, the drag was asymmetric, causing one wingtip to drop and initiating a nose-down spin, whilst rendering ineffective the outboard ailerons on which the pilot would have relied for control. 



The stall angle or “burble point”, from the Wrights’ 1921 split–flap patent US 1504663


Increasing the lift of a wing makes it able to fly safely at lower speeds, or at higher angles of attack, without stalling.  Breaking one wing into two in tandem, with a small aerofoil or “slat” separated from the front of the main aerofoil by a slot running lengthwise along the wing at its leading edge, can be remarkably effective in increasing lift (though at a cost, as it also increases drag and therefore slows the aircraft).  It also makes the stalled aircraft more controllable.  When it was introduced, crash deaths plummeted.  Even modern high-speed aircraft continue to deploy leading edge slots on takeoff and landing (together with flaps at the rear of the wing), to allow safer flight at slower speeds which in turn allows use of a shorter runway. 

A slotted wing therefore permits a short take off and landing (STOL) plane.  An example was the Fieseler Fi 156 Storch, with which Otto Skorzeny, Hitler’s favourite commando, rescued deposed Italian dictator Benito Mussolini from a mountain top surrounded by troops near Monte Cassino, and in which, in April 1945, Hitler’s last visitor, the famous Nazi test pilot Hanna Reitsch (1912-1979),[15] landed on a shell-shattered street in Russian-invested Berlin.

The slot principle can be applied beyond aircraft wings.  Something similar was used by Fauël on windmills to enable them to rotate at low wind speeds,[16] and may have earlier been used on windmills on the English East Coast.[17]  It has been claimed that the “fenestrated rudder” used on Chinese junks uses the same principle.[18]  Sailors will recognise that in the Genoa rig developed in the 1920s, the large overlapping foresail defines, together with the mainsail, a slot which improves performance to windward before the onset of a stall[19]


And how they work

Most sailing books suggest that the foresail and mainsail define a slot, which creates a “Venturi effect”, accelerating the airflow over the mainsail and hence improving its windward performance; many books on aerodynamics say the same of aircraft wings.  This widespread view is, however, incorrect.  The five mechanisms by which slots work were only finally explained in 1974, by which time computers had made it possible to solve the complicated equations of fluid flow around aerofoils, by Douglas Aircraft engineer Apollo Milton Olin Smith (1911-1997)[20].

A wing moving forwards generates a circulation current around it, contributing to its lift; air rises around and over the front edge of the wing, and descends around the rear edge.  With two aerofoils in tandem, the downdraft part of the circulation behind the rear of the small, auxiliary forwards wing interacts with the updraft part of the circulation in front of the large, main wing, slowing it and therefore reducing the peak negative pressure (i.e. suction) on the forwards part of the upper surface of the main wing.  That reduces the steepness of the pressure gradient along the top of the wing, so that the separation of flow from the upper surface and resultant formation of vortices (which is what causes a stall) does not occur until the wing is at a higher angle.  It also reduces the lift generated by the main wing.

Conversely, the updraft around the front of the main wing affects the circulation around the rear of the auxiliary aerofoil, increasing its lift to an extent which outweighs the reduction of lift suffered by the main wing, so that the overall effect is an increase in lift. 

However, this latter mechanism was not understood until Smith[21], and is still sometimes misunderstood (as Smith (1974), Gentry (1981) and Marchmann (1991) point out).  In 1904[22], the great aerodynamicist Ludwig Prandtl (1875–1953)[23], postulated the existence of a thin "boundary layer" of air hugging the surface of the wing, creating a smooth laminar airflow he described as “live air”.  The boundary layer explained, amongst other things, the stall phenomenon.  The wing changes direction and narrows towards the rear, creating a pressure gradient above it which affects the boundary layer.  When the wing is held at too steep an angle of attack, the boundary layer peels off at some point of discontinuity to create eddies (described at the time as “dead air”), sharply reducing the lift of the wing and causing a stall.

Prandtl’s followers at Göttingen Aerodynamic Institute showed both that applying suction through holes in the surface could pull the boundary layer down onto the wing, and that blowing high-speed air currents up from within the wing could “re-energise” it, in both cases deferring detachment of the boundary layer.  Many eminent aerodynamicists (including Prandtl[24]) assumed that Handley Page’s slot was itself a kind of boundary layer blower which had the same effect – that the progressively narrowing slot shape accelerates the air passing through it due to the Venturi effect (whereas in fact, the air flow is slow), and that the addition of the auxiliary wing increases the lift of the main wing (whereas it does the reverse).


The Inventor’s Apprentice

Albert Peter Thurston was born on 31 October 1881, the eldest son of Peter Thurston and Annie Elizabeth Thurston (née Hanking).  His father was an umbrella maker, employing a small workforce.  Albert Peter was born and grew up at 64 Clarence Road, close to Hackney Downs, off the lower Clapton Road.

Umbrella-making is a skilled trade and, structurally, umbrellas have much in common with kites[25].  It is, therefore, no surprise that Thurston and his father (who he referred to as a born engineer[26]) should have made and flown kites in his childhood.  He studied engineering, and was working by 1901 as an engineer’s draftsman.  In 1902 or 1903, he joined Hiram Maxim (1840-1916) as designer and chief assistant.

From an upcountry New England background of great poverty, Maxim was a self-taught, self-made prodigy, “A breezy extrovert, and very strong physically, he was intolerant of those who did not think as fast or accurately as he, so his autocratic manner was often regarded as bumptious, and led to difficulty with many associates[27], but Thurston was able to work easily with him.  He had a complex and dubious private life, involving three sequential but overlapping marriages each of questionable validity, which drove him from the US to make his home in the UK.

He is still famous for the "Maxim gun", the first fully automatic weapon (which became the British Army's favoured machine gun, and for which he was subsequently knighted), but he invented across many fields, amongst them flight.  A January 1901 congratulatory note on Maxim's knighthood in Flight magazine speculated that "Sir Hiram Maxwell has worldwide renown for the automatic gun which bears his name but perhaps it is his Flying Machine that will secure him a more enduring fame."  However, time and the achievements of the Wright Brothers have erased his aviation contributions from popular memory; aviation historian Gibbs-Smith (1966) branded him “the most wasted talent in aviation history … a victim of his mental inflexibility, overweening conceit, and lack of humility which, where aviation was concerned, perpetually baulked his undoubted talent: he later made grotesque claims.”[28]

A common view nowadays is that manned powered flight was impossible before the petrol engine because steam engines were too heavy, but Maxim proved that wrong.  His 1891 paper "Aerial Navigation: the power required"[29] showed that he had thought through the lift required for a propeller-driven aeroplane, and he went on to build a huge biplane driven by two high-powered steam engines, each generating around 160 horse power, running at pressures of 320psi.  The wingspan was over 100 feet, the weight was over 8,000lb and the propellers (one of which still rests in the Science Museum) were each over 17 feet in diameter.

This plane was just a technology demonstrator, lacking control mechanisms; it ran on a lower set of tracks and was constrained from rising too high by an upper set of tracks.  Maxim gave demonstration flights to important visitors, including the future King George V and the Admiral of the Feet.  Following these private flights, Maxim went public on 31st July 1894.  After some lower powered runs, he went to full throttle, the plane broke through its restraining rails to fly free for over 600 feet, and three men (including Maxim himself) became the first to take off unaided in a heavier-than-air flying machine before it crashed[30].  It was never repaired.  According to Gibbs-Smith’s jaundiced view, “This giant 1894 test-rig proved nothing new, broke no new ground, and influenced no one; it represented the greatest amount of wasted money and effort in the history of flying.”

When Thurston joined him, Maxim was attempting to raise funding and also public interest for more aviation experiments, through "captive flying machines", a fairground attraction which involved whirling captive pods around a central pole.  Thurston acted as test pilot, becoming the first man to experience high-G accelerations, and losing consciousness at 6.5G.  Contractual and safety legal issues thwarted their success, but one of the machines is still in operation at Blackpool's Pleasure Beach. 


Thurston’s pre-War career

In the meantime, Thurston continued to study at East London College (now Queen Mary, University of London).  The college became able, in 1905, to grant University of London degrees and he graduated that year with First Class honours.

He applied for a job at the Patent Office and, after an open competition, was awarded the post of Assistant Examiner on 22nd February 1905.  He arrived in a period of change for the Patent Office: the Patents Act of 1902 had introduced novelty searching for patents, requiring a prior art search covering at least UK patents over the preceding 50 years.  The Office had therefore vastly expanded its technical examining staff.  The turbulence caused by the new arrivals was recalled in a paper by Beaumont (1924):

“Into this comfortable equilibrium was suddenly introduced the turmoil of the search and the Office was filled with a large number of young men fresh from college with new, keen intellects and overwhelming zeal, who were suddenly let loose upon the work that was being turned out by the profession, with the sole duty of exercising their critical faculty—which youth invariably thinks it is specially fitted for and pursues with the greatest delight.  …

The profession doubtless thought that the young men did not understand what they were talking about, … and the young men certainly thought that too large a part of their efforts was spent in the correction of faults for which there could be no adequate excuse.”


With the agreement of the Patent Office, Thurston continued to assist Maxim, taking a major part in designing and building a new, petrol-powered biplane using hollow metal spars and aluminium construction; this, however, crashed in 1910 never to be rebuilt, and his employment by Maxim seems also to have ended around that time, although they evidently remained on good terms until Maxim’s death in 1916.  Through Maxim, Thurston also met Maxim’s friend and compatriot, the legendary aviation pioneer and showman Samuel Franklin Cody.

From 1907 he also lectured regularly at East London College and occasionally elsewhere.  His courses were evidently high-powered.  In 1909, in three successive lectures, he hosted Sir Hiram Maxwell, Sir Cornelius Neale Dalton (the former Comptroller of Patents) and Sir Baden Powell (brother of the founder of the Scouting Movement, balloonist and longstanding advocate of military aviation).

He became very friendly with Patrick Young Alexander (1867-1943) astronomer, balloonist and aeronautical pioneer, the “Patron of Aeronautics”, a man who knew everyone in the field and who ultimately would spend his fortune in the cause of aeronautics[31] - Alexander’s epitaph was Something Attempted Something Done.  Alexander’s support allowed Thurston in 1908 to set up an aeronautical laboratory with a wind tunnel at East London College (the first in a UK academic institution).  Ackroyd et al (2008) give a detailed account of his work there.

He recast his lecture notes into his practical and readable 1911 textbook, "Elementary Aeronautics: or the science and practice of aerial machines"[32], in which the analytical approach to the historical development of the subject shows his Patent Office training.

In 1913, he was awarded a doctorate in aeronautics, the first such in the UK.  He joined the Research Committee of the (soon to be Royal) Aeronautical Society[33] and, later, was co-opted onto the Council of the Society.  Later that year he went on Alexander’s meteorological expedition to South America, and then to the West Indies in June 1914 to study tropical bird flight as well as ocean currents[34].  Despite these wide-ranging adventures, however, he remained on the staff of the Patent Office up to and during the War.

When war broke out, although in his mid thirties, Thurston rushed back early from Jamaica in 1914 to enlist (his ship, the SS Patuca, having to evade enemy cruisers en route), joining the London Electrical Engineers (R.E.) as a private on 22nd October and transferring by July 1915 to the Royal Flying Corps where he served as a Lieutenant and later a Captain, and learned to fly.  Although he went to France, he was too valuable a munition to expend in combat; he was appointed an Inspector in summer 1915, and later became head of the Safety of Design Section of Military Aeronautics Directorate, responsible for safety aspects in the design of all British military aircraft.[35]  By the end of the war, he was investigating all-metal aircraft construction.  He was awarded his Pilot's Licence on an Avro Biplane on 4th October 1918.


Captain Thurston



Thurston in the aftermath of War

In 1918, Thurston lived at the Author's Club in Whitehall Court, and after the war, until demobilised in late 1919, at the RFC Club in Bruton Street.  Metal aircraft construction was still on his mind, for on 18th January 1919 he filed a number of patent applications[36] with Major Hamilton Neil Wylie, with whom he had served during the War.  Wylie later designed the metal-winged military plane which in 1924 became the Armstrong-Siddeley Siskin, the RAF’s standard fighter. 

Around then, Thurston suffered a very severe illness, apparently caused by overwork during the war; he left hospital shortly before 14th May 1919 when he struggled to deliver his paper “Metal Construction of Aircraft[37].  At that time, his reputation as an innovator was high; he had "started more researches, which were now huge specialities, than any other man present" according to Major Low in discussion after that paper.  Two weeks later, on 30th May 1919, he was awarded an MBE for his wartime work.  He was commissioned to write a Ministry of Reconstruction pamphlet, "The Future of Aerial Transport",[38] which predicted many advances[39] that subsequently occurred, together with a few[40] that have yet to materialise. 

In November 1919, he filed a number of further patent applications on metal aircraft construction[41] and one more in March 1920[42] (by which time he was back in Kingston, Jamaica, returning to Bristol on 13 June).  He also brought out the 1920 second edition of his book Elementary Aeronautics – less well received than the first, as some felt it had not moved with the times.  Initially, he worked as a consulting engineer, moving briefly to 186 Evering Road, Clapton before taking offices in Bank Chambers, 329 High Holborn where he would remain in business for the next three decades. 


The move to patent agency

Peace brought shrinkage in the aviation industry, and rather than return to academia or struggle along as a consultant, on 24th November 1920 Thurston took a sideways move, joining CIPA, the Chartered Institute of Patent Agents (the smallest chartered profession, with only 202 Fellows).  He passed CIPA’s qualifying examination in 1925, and was elected a Fellow in 1930. 

From that time until the late 1950s Thurston had an active patent practice, first on his own account and then in partnership as Thurston Edwards & Co, remaining a Fellow of CIPA until his death.  His aim was to use his technical skills not merely in patenting but also in perfecting other people's inventions.[43]  He advertised in aeronautical journals, and much of his practice as a patent agent must have been in that field, but his non-aeronautical clients included Marie Stopes, Franz Moller (inventor of the Zenit air pistol), Babcock & Wilcox, the American Radiator Company, Owens Corning, the DryIce Corporation of America, Ford Instrument Corporation, and Snyder Multiform Corporation.  He sold his practice to Messrs W. C. Blatchford & J. M. Wilson in 1956.


Thurston’s character

Thurston was a sociable man, who founded or joined a wide range of organisations and played an active part in them.  Model aircraft were a natural extension of his wind tunnel research, and he was a founder member and early President of the Northern Heights model aircraft club and the Society of Model Aeronautical Engineers (SMAE) to which he donated a trophy, the ‘Thurston Cup’.  He and his wife were regulars at the popular Northern Heights Gala days held at RAF Halton near Aylesbury.

He often attended meetings of the Institute of Mechanical Engineers, the Royal Aeronautical Society, the SMAE and CIPA, and was a Fellow of the Meteorological Society.  He joined the Pattenmakers Company, a City of London Livery Company, in 1943, and was a vice President of the Poetry Society, and a member of Council of the Kipling Society.  He and his wife were active in their local Gardening Society, to which he donated an annual prize. 

He was historically-minded, and – unlike his patron Maxim (who, Thurston wrote,[44]never troubled to find out what other people had done or had invented”) – his training as a Patent Office Examiner both inclined and equipped him to recognise and give credit to contributions of predecessors.  Close to his heart was the Newcomen Society, founded in 1920 by a group of historians, curators and Patent Office Examiners (including many of his former colleagues).  He joined in 1927, was elected to Council in 1928, and remained there for 36 years serving twice as President.

Characteristically, in his introduction to the 34th Edition of Molesworth’s Pocket-book of Useful Formulae and Memoranda for Civil and Mechanical Engineers, he saw it as “his privilege to serve his brother engineers”.  According to his wife, "He was a brilliant man but not commercially minded and the only reward he sought was that his work should be acknowledged."[45] 

In total, over his long career, he published well over 50 books and articles (several of which were carried by two or more peer-reviewed journals).  He was clearly proud, and desired recognition, of his technical achievements, and perhaps not only for personal reasons; his reputation as an aeronautical engineer was important to his practice as a consultant.  A relative recalls that he was “a lovely man – a touch eccentric but very kindly”. Young (1966) portrays an active man, small but strongly-built, kindly and good humoured, "courteous and charming”, “who retained... the zest and idealism of his youth” and was “revered and loved by a wide circle of friends[46].  Certainly, some degree of courtesy and charm are essential to success in practice as a consultant and a patent agent.  However, "to some of his contemporaries Thurston seemed unduly contentious and sensitive to slights.  Perhaps he was; he was a courteous but proud man who found it difficult to accept discourtesies from others.” 


Alulas and Rider Planes

Thurston was an excellent photographer, having learned the craft from his father.  According to his own account[47], from 1910 on, he studied pigeons and seagulls in flight, using photographs to analyse their motion.  He had also heard or read Frederick Webb Headley's[48] 1910 R.Ae.S paper[49] which contained a discussion on the role of the pinion feathers; Headley’s view (contested in the discussion which followed his paper) was that separating the wingtip feathers stabilised the bird's flight.  Headley’s book, around the same time, discusses the “alula”[50] or bastard wing – a feathered “thumb” possessed by most modern birds (though not by proto-birds such as Archaeopteryx) forming a secondary wing that can be retracted or deployed relative to the main wing.  Observations of the deployment of the alula also featured in a lengthy series of articles on bird flight by a Dr Hankin carried in Flight magazine over 1911.[51]

Thurston says he noticed that "the alula forms a gap between itself and the top edge of the wing when a bird glides at a steep angle and is in danger of stalling", and deduced that "if the functions of an alula could be applied to an aeroplane wing, valuable results should accrue."

In an apparently separate line of research Thurston, considering the stability of the Wright Brothers designs (which were “canard” machines, having a control plane in front of the wings[52]), explored what he termed “rider planes” for stability.  He appears to have coined the term, and it seems to have been used only by him or in relation to his work. 

His 1911 book Elementary Aeronautics concluded that small planes placed in front of the main wing plane should have a large aspect ratio and a long span, should be set as far as possible from the main plane, and should have a positive angle with respect to the main plane.[53] 


From Thurston’s book Elementary Aeronautics


He expanded on this in a 1911 paper[54] which suggested three methods of stabilisation: providing a rider plane at a positive inclination in front of the main wing, or a negative inclination behind it, as far away as possible from the main wing (as in his book); shaping the front or rear control planes; or (crucially for what was to follow), using the wake of the front plane to affect the one behind it.  His paper notes that "too little attention has been paid to the utilisation of the "wake effects" for increasing the stability of a machine."  He mentioned the same three options in discussion after a paper by Baden Powell on 11th April 1911[55].  This work was reproduced (in thinly rewritten form, and with only a cursory acknowledgment) in a book by Hayward (1912:443-449). 

Between January 1912 and June 1914[56], a series of wind tunnel tests on the effect of mounting a small auxiliary plane forward of the main wing were performed at East London College, under his instruction and supervision.  He presented his results in three College lectures, for one of which he retained the notes.  The results were also communicated to "the Military Aeronautics Directorate".  He obtained "official sanction" (presumably from the Directorate) to publish in Flight magazine in November 1914[57] - but only "a few" of the results were included because of wartime restrictions.  These were to play a crucial part in the disputes to come. 

The 1914 paper explained that “The arrangement of the aerofoils chosen was that employed on the " canard" type of aeroplane, as at the time the experiments were commenced, the form of machine which now predominates had not become so common.”  “… the elevator [i.e. the rider plane], which was mounted in the course of the investigation in a number of positions relative to the main aerofoil, and of which only five are shown in the diagram in Fig. 2, was capable of being rotated, and the pressure distribution over the surfaces of both the rider and the main aerofoil was ascertained at each position”.


Figures 1 and 2 showed the rider plane in a variety of positions and orientations at each position, including negative angles of attack (i.e. sloping upwardly and backwardly) relative to the main wing.  At Position 6, the rider plane is located closest to the main wing (but still spaced from it by several inches).  It gave strikingly different results to all other positions.



The paper included the following comments on Position 6:

“As is to be expected, the maximum amount of interference with the pressure distribution occurs at No. 6, when the rider is in close proximity to the main surface …

With the rider in position 6, however, both curves [pressure above and below the main wing] undergo considerable change …

… where the maximum amount of interference is desired for the purposes of stability, position 6 might prove more satisfactory …”


According to Young, "It seems likely that more data were indeed in his possession than were published in Flight and it is probable that much remained to be analysed when War broke out."  This much is certainly true, as the paper itself says; it discusses data for only 5 selected positions (of at least 10) and shows only the pressure on the main wing (whereas the pressure on the rider plane was also measured).  Thurston was later to say that “I suppose not one in a hundred of the experiments which I made at the time were published…”.[58]

The paper does say that “Throughout the experiments, the main surface was set at an angle of 7 degrees”.  If it had remained at 7 degrees to the airflow, Thurston could not have observed stalling behaviour, since this would only occur at higher angles of attack.  However, he was later to explain that the angle was relative to a turntable, which was itself rotated (with the main and rider planes) through a whole range of angles.

During the War, spending all his energies on aircraft construction and safety, Thurston can have had no time to analyse his data although he claimed to have discussed the subject with colleagues.[59]  At any rate, there is no evidence that Thurston thought or did anything more serious about rider planes, alulas or slots from 1914 until at least 1919.  We therefore now turn to the other main protagonist in the slotted wing dispute, Sir Frederick Handley Page.


Handley Page

Frederick Handley Page (1885-1962), son of Theodore Page, a furniture maker and Non-Conformist Minister of the Plymouth Brethren, was born on 15 November 1885, and whilst he abandoned the sect’s strict observances, he maintained throughout his life something of their self-righteousness, together with a wealth of Biblical quotations.  Barnes (1987) and Dowsett (2003) give accounts of his early working life.

Five years younger, Page's pre-War career had run parallel but a few years behind Thurston's.  He trained as an electrical engineer from 1902, graduated in 1906, and worked for a year as chief designer at Johnson & Phillips, but by then he had caught aviation fever, and joined the Aeronautical Society in 1907.

His passion for aeronautics was such that he was dismissed from his job in 1908 for persisting in unauthorised aeronautical experiments, then began working as an aeronautical engineer and started Handley Page Ltd, the first British company specifically for aircraft manufacture (it was incorporated in 1909).  It was rumoured that he won the money to do so in card games[60] - later, in 1913, he lost £500 in a later bet with Noel Pemberton Billing[61] that the latter could obtain his Royal Aero Club certificate within 24 hours of first sitting in an aeroplane[62]

His first plane-building venture was a collaboration with the gifted landscape artist and aeronautical pioneer José Weiss (1859-1919).  Weiss, born in Paris, emigrated to England in his twenties and lived near Arundel in Sussex where he painted landscapes whilst designing and flying kites and gliders, and developing theories on bird-flight.  He sought to build inherently stable wings, and his glider and aeroplane designs[63] were swept back, curved, and tapered with the trailing edges turned upward towards the tips – attractive forms in an age dominated by boxy, Heath-Robinson contraptions.  Handley Page first built a canard-type glider using Weiss’ wing.  His subsequent monoplanes – of which the “Blue Bird” (1909)[64] and Type E “Antiseptic” or “Yellow Peril” (1911) are best documented - clearly owe a huge debt to Weiss which was not acknowledged fully at the time, or at all afterwards[65], though Handley Page apparently took the trouble to secure a royalty-free patent licence (Barnes 1987: 3).  In 1909, Page built a biplane to the design of William Phillips Thompson of Liverpool, a patent agent and aeronautical inventor who, no doubt, gave Handley Page his early education in patents and would later file his first few patent applications for him.

Handley Page was not born rich, and his business initially depended on his teaching and on investments by acquaintances.  By 1911 he was lecturing at Northampton Institute, later to become City University, where he organised courses and set up a wind tunnel, in competition with Thurston’s work.  Throughout his later career, he was a supporter of education in engineering. 

He joined the R.Ae.S and, in 1910, was one of those who mounted a coup to reorganise it into the conventional form of a Learned Society, with Fellows and Associates.  His first R.Ae.S paper[66] therefore came at a time when he was seen by older members as something of an enfant terrible in the push to reform the Society and increase its relevance.  Designed to impress, it was a model scientific paper, mixing experimental results with a review of the work at Prandtl's Gottingen laboratory, and (unlike his future papers) concluding with a list of references.

A disastrous crash in 1912 which killed both Page’s chief assistant and a Navy test pilot put an end to the commercial prospects for his monoplane designs, but 1913 brought a contract from the War Office to supply biplanes.  The firm also started designing a large aircraft – a market they would ultimately corner to the extent that “Handley Page” entered the Concise Oxford English dictionary as a synonym for a large bomber[67].

The War brought great commercial openings for Handley Page Ltd, and in 1915 the Government awarded them a design contract for a large bomber, to meet the Navy's demand for a "Bloody Paralyser".[68]  This became the “O” series, the first effective large bomber in the War.  By the end of the War they had developed the huge four-engined V-type, capable of bombing Berlin from England.  Handley Page’s (largely unpatented) designs were influential worldwide.  They were given by the government to other British manufacturers, and also to the Americans when they entered the War,[69] and a Handley Page bomber captured by the Germans become the basis of their only effective large bomber.  Handley Page eventually received substantial reimbursement for the UK and US use of his designs.[70]  In the immediate aftermath of the War, Handley Page Ltd had grown to an empire employing over 2,000 people, and capable of supplying over 200 planes a year.

Handley Page was “a power in the aircraft industry and ... the air transport industry[71] for decades: as President of the Society of British Aircraft Constructors (1938-39 - he also served as honorary Treasurer andd Chairman); President of the Royal Aeronautical Society (1945-47 – and longstanding member of its Council); vice-Chairman of the Air Registration Board for 20 years; President of the Institute of Transport (1945-46); and Chairman of the Board of Governors of the College of Aeronautics, Cranfield, amongst other aeronautical positions. 

Over six foot, a big, impressive personality, full of energy and immensely determined, his courage was undeniable; he was awarded the order of the Crown by King Albert of Belgium for saving two bathers from drowning at Blankenberge.  He was a risk taker, who gambled on civil aviation after the War and lost massively, even losing control of his own company for a few years.  He was noted for “forthright comments, pungent sometimes daring wit”.  Stewart says he was “one of the finest speakers in the country … an outspoken and effective critic”.  He was a great salesman - the Flight obituary refers to the fact that "he could never resist a spot of timely public relations" and Stewart (1966) to his “powers of technical salesmanship”.  His Flight obituary[72] mentions that he was a "brilliant and forthright extempore speaker" but also refers to his "foibles", his "pride in achievement".  He was described as "a master of repartee, ... always abreast of current technology and objective in criticism" but also as "an autocrat", and "intolerant" by Barnes (1987).  Politically, like many others in aviation at that time,[73] he was of the right.  Pritchard (1962) recorded his surprise at the lengths to which Handley Page would resort in order to get his way.  With one brother a barrister and another a judge, he had no fear of litigation. 

His combination of brilliance, salesmanship, risk-taking and autocracy, mercifully uncommon in the population at large, is normal and perhaps even necessary in company founders, at least in this writer’s experience,[74]  but sits uneasily with scientific objectivity.


Griffith Brewer

Late in the War, Handley Page started to file patent applications, and in the few years after the Armistice, many more were filed.  The earliest were handled by W P Thompson, but to handle his ambitious post-War patent program Handley Page chose Griffith Brewer (1867-1948) of Brewer & Sons.  Handley Page hired not just the services of the firm, but the man – unusually, for patent agency, he paid a retainer (originally £300, rising to £450 per annum) for Brewer's personal attentions. 

In 1892, at the age of 25, Brewer had opened a branch of his father’s family patent agency firm in Leeds.  Work must initially have been light, because he had time to satisfy his passion for aeronautics by preparing (with Patrick Young Alexander) a slim volume entitled "Aeronautics: An Abridgment Of Aeronautical Specifications Filed At The Patent Office From 1815-1891[75].  Moving to London in 1900, he took over management of the firm from his father and was to retain control for the next 45 years.[76]  He was elected President of CIPA in 1930.

Brewer was also an influential man within his wide circle of contacts in aeronautics.  He was an expert on lighter-than-air flight.  He started ballooning every Saturday afternoon in 1891[77], making over forty balloon flights and winning the 1908 Hurlingham balloon race (the largest ever in the UK)[78].  He also made aeronautical inventions, including the "Brewer Rip" for kite balloons allowing a safe emergency descent, and during the First World War he was Honorary Adviser to the Airship and Kite Balloon Services.  He was an early member of the Royal Aero Club, and of the R.Ae.S, becoming President of the latter over 1940-42.  "Never again shall we hear his wise counsel in that soft-spoken voice of his" mourned his Flight magazine obituarist[79] on his death.

When the Wrights first brought their machine to France, in 1908, Brewer was the first Englishman to take a ride with them, and hence the first to fly in a heavier-than-air craft[80].  He was to become their close family friend and regular visitor, but his first service to the Wrights (together with Charles Rolls, of Rolls-Royce fame, a fellow ballooning enthusiast and founder member of the Royal Aero Club) was to introduce them to the Short Brothers, balloon makers to the Royal Aero Club, who ordered a number of Wright machines and subsequently made their own under licence from the Wrights.  In 1909 he selected a site for the Shorts aeroplane manufacturing operation, and the Royal Aero Club’s base, at Muswell Manor in Kent[81].

Nowadays, it is taken as axiomatic that the Wrights invented powered flight, but at the time there were many other challengers for that title.  The Wrights’ innovation was their patented three-axis “wing warping” control system which allowed them to manoeuvre[82] – but their more crucial contribution was the fact of being first in the air, for which they had to design not only their control system but also a lightweight petrol engine and the rest of an aeroplane.  Their first successful flights were said to have been on December 17, 1903, some nine months after their patent US 821,393[83] was applied for.  However, since they published little of their theoretical work and there were few witnesses to their earliest successful flights, their claims were attacked for many years. 

By the time of the first Air Show in Rheims, 1909, the Wrights had serious competition; the winner of the first Air Race was not the Wright machine flown by Lefebvre, but the Curtiss-Herring biplane.  When, in 1910, the Wrights sued Glenn Curtiss under their US patent, Brewer was involved as their advisor, and after Wilbur’s 1912 death, blamed by some on the strain of the patent litigation[84], it was Brewer who founded, as Managing Director, the British Wright Company, deftly handling their UK licensing by extracting a £15,000 lump sum paid-up royalty from the UK Government rather than refusing licences to competitors, or suing infringers (as the Wrights had in the US)[85].  He clearly took a narrow view of the professional conduct rule against conflict of interest – in 1920 Handley Page, by then his client, was sued under the US Wright patents but Brewer continued to act for both parties, and it is tempting to suspect that he managed to get the case settled.

In 1913 he established the annual R.Ae.S Wilbur Wright Memorial Lecture series to commemorate his friend, and he himself gave the fourth lecture, on Wilbur’s life and works.  His friendship and his business interests with the Wrights combined to make him a jealous guardian of their reputation, and particularly of their claim to be “first”, and his own background in lighter-than-air flight may also have informed his views that:

“ …we owe everything to these two American scientists.”. … “In 1892 Maxim built a machine with sufficient power to fly, but all the modern petrol engines in the world would not be able to coax that machine to go up in the air today[86].


Later, he recalled that until the Wrights, the general belief (and his own) was that manned powered flight was impossible:

"ten years after the Maxim engine we were still where we had always been - confronted by a problem held by all to be impossible"[87].


His dismissive view of Hiram Maxim's work reflected by association on Thurston's own reputation, which rested on his years with Maxim as the inventor’s apprentice. 


Brewer and the Langley Fraud

The direct threat to the Wrights’ reputation, and their patent rights, was posed not by Maxim but by Glen Curtiss’ fraudulent priority claim in the name of the late Samuel Pierpoint Langley (1834-1906)[88].  Langley was an American flight pioneer and Secretary of the Smithsonian Institute over 1887-1906.  He had obtained significant US government funding, and some from the Smithsonian (with the assistance of his friend and successor as Secretary, Charles D. Walcott) to build a manned flying machine.  However, Langley’s tandem-winged “Aerodrome” machine was unsuccessful, crashing in 1903.

Curtiss (with the support of Alexander Graham Bell) attempted to invalidate the Wrights’ claim to priority, using Langley’s name.  He negotiated a contract to resurrect Langley’s “Aerodrome” from the remnants of the crash kept in the Smithsonian, to prove it could fly.  It duly did so at Hammondsport in May 1914, and Curtiss announced that Langley’s machine, rather than the Wrights’, had been the first capable of flight – but all was not as it seemed.

Brewer, who happened to be visiting the Wrights (and was not known to Curtiss) travelled over to observe the tests from a rowing boat, and took photographs that demonstrated that the Curtiss rebuild was quite different in significant ways from the Langley original.  He published a letter in the New York Times in June 1914 demonstrating the falsity of the trials.  Brewer's devastating critique raised eighteen points of difference between the reconstruction and the original. 

However, such was the influence of Walcott and the Smithsonian that their favourable November 1914 report of the trials was generally accepted at the time.  In 1921, Brewer returned to the fight, vilifying the Curtiss trials and vindicating the Wrights in a lecture to the R.Ae.S[89], and subsequent newspaper articles.  The Smithsonian would stick to its guns until a public recantation in 1942[90], following which the London Science Museum sent them the original Wright Flyer, denied them by the Wrights.


Handley Page’s development of the slot

The history of Handley Page’s slotted wing is recounted by Barnes (1987: 210) and Dowsett (2003: 50).  Although his company would later[91] link the development back to "early experiments in stability and control associated with the Company's first aircraft" this was misleading, since that early interest in stability rested on Jose Weiss’ specially shaped wing which had no connection with slots.  According to Dowsett (1999: 65), Handley Page was motivated to find a solution to the stall-and-spin problem by the tragic 1912 monoplane crash that ended his monoplane development. 

The only account Handley Page gave of his development of the slot is in his own 1921 R.Ae.S paper.  This is vague as to dates, and there is no evidence whatsoever of any work before 1919 when the original wind tunnel experiments on Handley Page’s slotted wings were carried out by his assistant Robert Oliphant Boswall[92].  Some later experimental work was done by Boswall’s replacement, Captain (later Professor) Geoffrey T R Hill[93].  The earliest point of reference Handley Page gave in the paper was his own earlier 1911 paper[94] dealing with what was then known of stalling.  It refers to having a “live” air stream to break up the “dead” air at the back of the wing – Prandtl’s terminology, though without Prandtl’s deep analysis.  The 1911 paper predicted that the onset of the stall occurred earlier (i.e. at a lower angle of attack) for wings with a high aspect ratio - that is, long narrow wings rather than short stubby ones. 

According to his 1921 account, Handley Page was motivated by this to reach the insight that chopping up a long, high aspect ratio wing by fore-and-aft (“chordwise”) slots to create a series of separated stubby zones might give it the same performance at stall as a wing with a low aspect ratio.  One can perhaps see an electrical engineering analogy – substituting one large capacitor by a parallel bank of smaller ones. 

Unfortunately, this hunch proved wrong – his graph[95] show a shift of the stall point to a higher attack angle by about 1 degree, but only a minuscule improvement in maximum lift.  In the subsequent discussion he claimed to have obtained better lift later on, but that seems improbable – why would he have shown poor figures if better ones were available?  At any rate, “this line of investigation was abandoned in favour of a transverse slot.

Initially Page used a straight-cut slot with parallel sides[96] - he says that he got good results, but if this is the case, he must have benefited from a healthy dose of luck, as some later investigators found slots to give no benefit[97] and others found that straight cuts gave only small lift improvements[98].  He then began to experiment with better slot shapes, and in October 1919, he instructed Griffith Brewer to investigate patenting the slot[99]

At this point, some explanation of the then-prevailing system of patent priority is necessary.  Whilst different national patent systems are complex and diverse, there are some longstanding fundamentals of the priority system:

1 - Priority can be claimed internationally; thus, a first, "priority", application made in any country can be used to support a claim to priority for a later application in any other - provided that the later is made within one year and the necessary formalities are observed;

2 - The priority application must show that on its date of filing, the inventor had made the same invention he later claims as his own[100];

3 - It must also describe how to reproduce and work the invention[101], leaving out only mundane and well-known details, so that the reader can enjoy the benefits without undue burden of experiment, or inventive activity of his own.


At the time of the slotted wing dispute[102], the UK had the egregious priority system known as "provisionals" and "completes".  The idea was to permit an inventor to rapidly file a "provisional" specification document that contained the bare gist of his invention.  The custom was not to include claims defining the invention, or even drawings, in the "provisional" application, then to flesh it out over the following year with a replacement "complete" application (usually professionally drafted) having the missing elements, and perhaps substantially more disclosure of the invention.  Provided that these had “fair basis” in the provisional, they backdated to the provisional filing date.

In the early decades of the 20th century, the practice[103] was to file a provisional "as soon as the invention was conceived, relying on the doctrine of legitimate development to enable all the useful numerical or similar limitations to be found for the first time in the complete specification".  The advantage of that practice was that it enabled a quick and cheap filing which might therefore get the earliest possible priority date, but there were obvious dangers in filing a vague, incomplete provisional lacking drawings -  the unaided assumed that they had a valid date when by filing too little they had established nothing, and the devious “completed” an early filing by adding in someone else’s subsequent invention, achieving a backdated priority claim.

The problem was at its most serious in the US, where high standards of disclosure have always been required.  Dyer Smith (1950: 44-45) refers to various US cases[104] according to one of which “A British provisional specification might well be so vague and incomplete as not to amount to what the American law regards as an application, and a British complete specification may well be so different from the provisional as to be considered under our law as a new application for the first time disclosing the invention.”

Handley Page’s provisional specification filed on October 24th 1919 discusses transverse slots through an aerofoil.  As to the shape of the slot, there are no diagrams (as was customary) but it is stated to slope backwards, to narrow as it runs upward, and to be curved.  The part of the wing in front of the slot could be a separate structure, but there is no suggestion that it would itself be a shaped aerofoil.

The text indicates that "burbling" is due to eddies created by a "discontinuity" between the "live air stream" (i.e. the laminar flow region) and the wing.  It discusses a wing with a transverse "through slot", through which a "live air stream" is introduced onto the upper surface of the wing, "maintaining the continuity of the airflow over the forward or leading edge of the aerofoil." 

This explanation is difficult to follow, in several respects.  Firstly, for the relatively thick aerofoils Handley Page used after the War, the discontinuity and eddies at stall are not normally concentrated at the front edge of the wing, but behind the peak of suction pressure, which in turn is some way behind the front edge of the wing.  Secondly, the air from the slot is not "live air" in the sense of a fast-moving current, but relatively slow air.  Possibly an electrical analogy was intended, with the slot short-circuiting the airflow around the front of the wing like an overvoltage path - but as Smith (1974) points out, that analogy is incorrect and misleading. 

The existence of the slot was first hinted at in The Aeroplane[105], the incendiary weekly aviation industry newssheet, which ran teaser stories on 3rd, 10th & 17th March 1920 indicating that Handley Page had a revolutionary invention permitting flight with a 50% reduction in wing size.  Evidently the details of the slot were known to some in the Forces, as on 24th March 1920 a Captain Wedgwood Benn described it as "a form of shutter which was to vary the wing surface so that when rising from the ground the shutter would open and the wing surface would be reduced ..." - for his pains, Grey ridiculed his description.  The first test flight (internal rather than open), using a modified army surplus de Havilland DH9 with a fixed slot[106], was on 31st March 1920 and a confidential demonstration was given to the government on 22nd April.  All of these activities must have been seen as secret, because it was not until 11th June 1920[107] that Brewer filed the Complete Specification of Handley Page’s patent.  This showed that there had clearly been substantial experimentation (presumably over November 1919 and March 1920) resulting in a complete re-think of the mechanism by which the invention worked: the "slot" had been redefined as the space between two aerofoils, and the fallacious explanation of its effect had disappeared without replacement, except to say that opening and closing the slot has the same effect as switching the wing geometry between a low cambered wing and a high cambered wing.

The Complete Specification also included a paragraph[108] attempting to discriminate the invention from prior proposals:

There have been numerous suggestions for aeroplane construction comprising combinations of wings, arranged in some instances superposed and in others in tandem, and in some cases the multiple wings have been of similar and in others of different dimensions ...”.


Accordingly, by June 1920 Handley Page had realised that the key was not slots, but (to use Thurston’s terminology) “rider planes”, arranged “in tandem”.  The words “wings arranged ... in tandem ... of different dimensions” are peculiarly apt to describe Thurston's 1914 Flight paper entitled “Aerofoils arranged in tandem”

Some time later, the UK Examiner cited four earlier-published UK patents[109], forcing Brewer to amend by adding two further paragraphs to the Complete Specification each respectively contrasting the invention with one of the cited prior patents, and some limiting language to the introduction.  The patent was first published by the US Patent Office on 21st September 1920[110]

The first public demonstration of the slotted wing in the wing of the DH9 was on 21st October 1920, and the first article describing technical details was published in Flight magazine on 28th October 1920[111], after the filing of provisional specifications on a number of improvements.


Thurston’s patent filings

Meanwhile, at some point after the War, Dr Thurston revisited his pre-War research.  He had had models made up by Alex F Houlberg[112] and wind tunnel tests were carried out at Bristol Aircraft Corporation (in return, apparently, for a part-share of some patent rights).  As a result, he found that his rider planes “could increase the total lift and move the burble point”, but “the resistance was increased out of proportion and therefore this device would not be efficient except for control purposes” and for landing.[113]  The timing is unclear, but must have been before the Air Conference on 13th October 1920 (the week before Handley Page’s public slot demonstration), the Report of the Proceedings of which[114] record this contribution from Thurston:

I have not particulars of Mr Handley Page’s wing.  If it is after the principle of something I was after and experimented with before the War, namely a rider plane or planes in front of the main plane, I have no doubt that this would increase the suction on top of the wing and the compression underneath it, and it would also have the advantage that the pressure on the main wing could be distributed more equably than at present …”


Although Handley Page’s US patent had by then been published, it would not have been available in the UK (let alone indexed) until some weeks later.   Thus, before he knew of the public details, Thurston realised enough about Handley Page’s slot to see the similarities with his own pre-War work and to describe its effects. 

Thurston therefore did not attempt to file for what he had invented before the War, but for the use of “rider planes” as control devices (i.e. to replace ailerons, elevators, or rudders) like the control planes in the Wright Brothers’ canard machines which he had analysed before the War.  His Provisional Specification filed on 14th December 1920[115], discloses small planes “on or near the leading edges or tips of the wings[116], used for control, or for slow landing, when an “intense lifting force” is generated (and the accompanying drag would assist in braking).  As was conventional, it was filed without drawings.

Thurston then discussed this invention with officials at the Air Inventions Committee of the Air Ministry, at whose suggestion he wrote on 8th January 1921[117] enclosing a copy of his provisional patent application.  To his eternal chagrin, on 13th July 1921 they replied[118] that "the invention comprised in your Provisional Specification No 135116/20 has now been investigated and it is considered that the invention does not give sufficient promise of practical utility for it to be developed ...".  Specifically, they wrote, “as regards … the addition of surfaces to direct the air along the wing, it is considered that such improvement is improbable”. 


Gustav Lachmann

The publicity generated by Handley Page in 1920 brought out several other would-be inventors of the slotted wing, of whom the one with the soundest claim (sounder, indeed, than Handley Page’s) was Gustav Victor “Gus” Lachmann (1896-1966), German son of Austrian parents, who had served with distinction during the War earning two Iron Crosses.  After being wounded as a cavalry officer, he became a pilot, but stalled and crashed his Rumpler C aircraft in August 1917 and was again injured.  He would later describe how, whilst recovering in hospital, he experimented on the slotted wing concept by blowing tobacco smoke through small handmade wooden models of a slotted wing with a ladies hairdryer[119].

He filed for a German patent on 19 February 1918 through a patent agent, Otto Kattler, but the German Patent Office (which had, in those days, a very high refusal rate compared to the British or even the US Patent Office) would not believe that the structure described in the patent application could work. 

Lachmann’s patent (reproduced below in its entirety) is, by modern standards, ridiculously brief, and one can understand the scepticism of the Patent Office[120]:


Aerofoils whose profile consists of several separate staggered elements, arranged in the form of a Venetian blind.

The lift of a curved plane moving through some medium is composed of a positive pressure on the lower surface and a negative pressure on the upper surface of the plane. The present invention has for its object an increase in the lift of an aerofoil. Fig. 1 To achieve this the thick aerofoil F is divided into auxiliary sections f1, f2, f3. Fig. 1.

The spaces between the auxiliary aerofoils have the appearance, in section, of nozzle-shaped channels, with their narrow ends on the upper surface of the main aerofoil. The air rushing past the narrow nozzle openings on the one hand, and the suction of the negative pressure on the upper surface of the aerofoil on the other, result in sucking air past the cambered auxiliary aerofoils, thus causing the new pressures Pi. PJ. Pt.

The total air resistance W of the aerofoil is therefore composed of the sum of the pressures p1, p2, p3, etc., on the small aerofoils f1, f2, f3, etc., and of the total resistance P of the larger aerofoil F respectively.  These will naturally be somewhat smaller than the resistance P of a solid aerofoil.

In Fig. 2 is shown diagrammatically the constructional application of the invention to a modern aerofoil. In the space between every two ribs are arranged two plates of ply-wood, sheet metal, Cellon, or some similar material, shaped to conform to the aerofoil section. By suitably shaping the plates a smooth run into the lower aerofoil surface is possible.



Supporting Surface characterised by its being divided into a number of tandem components which together form a wing section.

However, when Lachmann (by now a final year engineering student at Darmstadt) read the 1920 reports of Handley Page's practical success in German journals, he went public to the German aviation journal Flugsport[121], and also commissioned his own wind tunnel tests from Göttingen Aerodynamic Institute, the legendary laboratory of Ludwig Prandtl.  The March 16th 1921 issue of the German aviation journal Flugsport published a translation of Handley Page's 1921 R.Ae.S lecture and presented Lachmann’s own wind test results.

His German patent was granted as DE 347884 in 1922.  His patent agent Otto Kattler made applications in Switzerland (CH 95938) on 29th and France (FR 534980) on 31st March 1921, claiming the 1918 priority date;[122] it is unclear why these applications were in Kattler’s name rather than Lachmann’s, but Handley Page acquired these too. 

Lachmann’s 1921 paper[123] admits that the slot described in his original patent was non-optimal.  The French Kattler patent included a new diagram (below), in which shaped slots have given way to spaced aerofoils, transparently based on work carried out after Handley Page’s 1920 and 1921 disclosures and looking very similar to a Figure in his 1921 paper:

From Kattler’s patent


From Handley Page’s 1921 paper



In the meantime, on 24th January 1921 Handley Page’s British application was accepted as patent number GB 157567.  The granted claim defining the invention was in the following terms:

1 In an aeroplane flying machine; providing wing-section main wings to be flown at a positive angle of incidence each with a small forwardly located auxiliary wing of wing-section distanced from and connected to the main wing and set at considerably less angle than the main wing so as to produce a through slot between the under surface of the auxiliary wing and the leading upper surface of the main wing, said slot having its opening on the under surface of the wing in advance of the opening on the upper surface.


The collapse of Handley Page Limited

Over the brief period between invention and grant of his basic slotted wing patent, times had changed, and Handley Page Ltd’s prospects had collapsed[124].  The end of the war reduced the need for new aeroplanes, and the Royal Air Force, then the world’s largest, started selling off its surplus stock, flooding the market.  Many other aircraft companies went to the wall.  Since the War, Handley Page Ltd had bought their premises from the Ministry, floated, diversified disastrously into civil air transport (all in 1919) and cars (in 1920), and sent out hugely profligate but unprofitable worldwide sales missions (in 1920).  Handley Page Ltd’s wage bill halved, from £277,000 in 1919 to £133,000 in 1920, but even so, their reported profits fell from £51,000 in 1919 (half those of the previous year) to a colossal loss of £645,000 in 1920.  1921 was also to be a terrible year, and in April Frederick Handley Page himself was effectively temporarily deposed (though he remained Managing Director) as creditors took control of his company. 


The lifeline

A key element of his survival strategy was the slotted wing.  In many cases, patents are used as discriminators, helping the patentee maintain a technical performance edge in the free marketplace for his own products.  However, the aircraft markets of the 1920s were anything but free - the primary markets were military, and each government was a monopsonist, buying on dictated terms from its own national suppliers. 

In the UK, a ring of tame manufacturers[125] were maintained, on starvation rations – minimal manufacturing orders, supplemented by refurbishment and research contracts – supplying to government design and performance specifications and standards.  The fledgling civil industry was scarcely less chauvinistic in its procurement habits.  Other countries adopted the same policies.  Handley Page could therefore not expect to make substantial export sales outside of the UK and its Dominions, and within them the pickings were thin and at the gift of the Ministry.  His strategy was therefore to sell a technology, rather than products, and his campaign was targeted at governments and at those who influenced their design choices, to push the slotted wing into their procurement specification and pay him royalties for the privilege of use.

Dynamic in business, technically impressive, and masterful in debate, Handley Page possessed in spades what every inventor needs but few possess: the ability to sell his technology.  According to Stewart (1966: 123), he "showed his powers of technical salesmanship to good purpose with the wing slot.  ... The point which Sir Frederick made with his customary energy was that the wing slot was an essential to air safety" and this was a point that played well with the press, Parliamentarians and the public after every major air crash.  "By his wit, his personality and by his wide understanding, he tamed government officials and Service officers."[126]


The 1921 meeting

Following the successful public demonstration in 1920, and the grant of his patent, he elected to further his sales campaign with a major presentation to his peers which would showcase his oratorical skill.  His paper, “The Handley Page Wing”,[127] was presented to the R.Ae.S on 17 February 1921.  The title announced his claim to ownership and made a determined attempt at branding the technology with his name. 

It is generally good form in scientific papers to acknowledge prior relevant work.  Handley Page certainly knew of some by this time, as a result of various Patent Office searches, but the aims of this paper were to reinforce the priority and validity of his patent, so he referenced only his own earlier papers[128], and nothing else, presenting instead his own findings and contrasting them with the poor results he had obtained by hastily testing Lachmann’s patented wing.

In the following discussion, many gave his paper an enthusiastic welcome.  However, it had been circulated in advance, and others had come prepared to contest his priority.  Alfred John Sutton Pippard[129] gently probed Handley Page’s defences; he pointed out that “there was a gap in the lecture as there seemed no logical explanation of the change from longitudinal to lateral slots.  He rather thought this must have been a stroke of genius on the part of the lecturer.  He would like to hear more of the reasons for this change.”  Sutton Pippard had served with Thurston during the War, so his mildly-phrased intervention may have concealed a barbed intent to expose Handley Page.  The answer was unconvincing – according to Handley Page, the fact that the chordwise slots had worked (in fact, they hadn’t) led him to think that air could rush into the dead zone all along the wing more easily from a lengthways slot, and that “was more or less the manner in which the transverse slots were arrived at.” 

One William Cochrane claimed, by communication read out at the meeting, to have patented a slotted wing in 1902.[130]  He later twice repeated his tenuous claims through the correspondence pages of Flight magazine: 

In 1902 I patented the first heavier-than-air machine fitted with slotted planes, the angle of incidence of which could be varied by the aviator in flight for fast or slow flying. This design won the first prize presented by the President of the Aeronautical Society, but was turned down by the official experts.”[131]  “In 1903 I designed a model aeroplane which won the first prize presented by the President of the Aeronautical Society.  The patent embodied the basic idea of the slotted wing[132].


Thurston came to the talk well prepared.  He was now in his fortieth year, when many start to examine their legacy, and wanted credit for his largest and, since he had changed profession, his last major aeronautical research project.  In a lengthy intervention, he showed a number of slides drawn from his 1914 Flight paper, and explained that they showed the forward plane set at a negative angle to the main plane (just as claimed in Handley Page’s patent), and that his apparatus could be rotated through any angle, including the stall angle.  He claimed that "he had worked out, more or less, the whole of the theory, before the War", and criticised Handley Page’s explanation for “burbling”, suggesting that it was due to a wingtip “end effect” as it was less marked at higher aspect ratios.  In the sharp exchanges that followed his intervention, Colonel W. A. Bristow[133] (a former Ministry colleague now turned competing consulting engineer, who within three months would be working on a Handley Page contract[134]) made a telling point against Thurston: this would have had a profound effect on aircraft design and construction, so if he really had known all this before the War, why didn’t he publish earlier? 

Handley Page’s reply as reported, by way of contrast, was weak for such a strong debater – he merely said that wings “in tandem” were not at all the same thing as a slotted wing, which was not the case[135].  Perhaps he meant to imply that a slot had to involve overlap between the front plane and the rear one.  It is true that in Thurston’s pre-War experiments the front plane cannot have overlapped the rear one (because he pivoted the front plane through a full range of angles, so must have been able to swing it past the main plane), whereas it did so in all of Handley Page’s diagrams, and this may have suggested to Page that Thurston’s arrangement was not a “slot”.  However, Katzmayr and Kirste would soon show that overlap is not essential, or even optimal.  It seems that Handley Page carried the day with his audience, but Thurston’s unwelcome challenge was now widely known. 

Thurston's second provisional patent specification[136] was filed (jointly with BAC) eight days after the lecture.  It was directed to wingtip pinions, but contains a reference to Thurston’s 1914 Flight paper, and implies (as he had said in his intervention at the February 1921 meeting) that Handley Page’s explanation of the reasons for the stall is wrong:

This point [the critical stall angle] is incorrectly but widely known as the “burble point”.  The critical angle decreases with increase of aspect ratio and at the same time the intensity of pressure at the critical angle decreases also.  According to the pre-war experiments of one of the applicants, the critical point practically disappears when the aspect ratio is greater than 10, i.e. when the aspect ratio is more than 5 on either side of the centre line.  This fact in itself is a proof that the burble point is due to end effect and not to the air flying away from the front edge as usually believed.” 


There are elements of both truth and error in Thurston’s analysis; it is true that air is not “flying away” exclusively from the front edge, but further back on upper surface, and it is also true that end effects are important, but to ascribe the stall point exclusively to “end effects” is certainly wrong. 

Thurston (with BAC) filed a Complete Specification on 12th July 1921 relating to a control system using a wingtip array of planes resembling a bird’s pinions, and this was granted on 15th May 1922 as GB 180359.   He was also working on alulas, of which “a model was tested at BAC before L G Frise and L D Whistler on 10th August 1921.[137]  On 12th August he filed another application[138] in his name alone.  It claimed priority from 135116/20 of 14th Dec 1920, and described the use of the alulas (i.e. small planes in front of the main wing) for control, combining the function of ailerons and rudder, by varying the separation and the angle of inclination of the alula relative to the wing. 

A few years earlier, a new control system would have been useful as a way of avoiding the Wright Brothers patent, but this had just expired and, patent free, ailerons were (and remain) the control system of choice.  Thurston allowed his patent application to die by not paying the Sealing Fee, "for various reasons, but largely because of official encouragement and for lack of funds to bring the invention to the practical stage."  The reason may have been cost, but, it also seems likely that, some time after filing this application, Thurston became aware of Holle’s patent GB 128341.

Alexander Albert Holle was a Dutch citizen living in London who filed several wing patents, of which GB 128341 was filed during the War, on 14th May 1918, and published on 16th June 1919.  Using the “Jepson” format (which implicitly conceded that aircraft with alulas per se were already known) it claimed:

[“In an aeroplane having combined with the wings or aerofoils bastard wings mounted at or near the leading edges of said wings or aerofoils,] so constructing and arranging said bastard wings that in their normal positions they conform to the contour of the wings or aerofoils and in their active positions they break the contour of the upper surfaces of said wings or aerofoils and thus cause a disturbance of the flow of the air above said wings or aerofoils, and means for controlling the positions of said bastard wings.”



Holle’s “Alula” wing


Holle’s patent says that the deployment of his alulas reduces the lift and causes spinning, so their effect was not the same as Thurston’s (or Handley Page’s).  He was later to form a syndicate to make a high-lift, stable wing called the ALULA wing[139], but it does not seem to have included his deployable alulas.

The Complete Specification of Thurston’s parallel GB 180359 appears to have been amended after filing[140] to include the following words to assist in distinguishing from something that sounds very much like Holle’s invention:

It has further been proposed to pivot a small bastard wing to the leading edge of the main plane for the purpose of disturbing the air flowing over the top of the wing to increase the resistance and at the same time to decrease the lift …


Although it exhibited the opposite effect, Holle’s invention looks superficially similar to Thurston’s and he may well have concluded that the cost of persuading the Patent Office to accept his application as inventive over it would be beyond his means.  However, it does appear with hindsight that he could have obtained a patent on the use of a small auxiliary plane in front of, and at a negative angle to, a wing (i.e. a slotted wing) for control purposes. 

Just a month after the patent filing, a “Marco Polo” (1921) wrote pseudonymously in Flight magazine on “An Immediate Application of Slotted Aerofoils – Their Use as Inter-Plane Ailerons” – the first published suggestion that the slot could be used as a control device.  It was a suggestion “offered for what it is worth”, the writer noting that considerable experimentation would be required, but that it would not be too expensive, and space was made available for future discussion in Flight

An intriguing possibility is that “Marc Polo” was Thurston.  “Marco Polo” was evidently an aviation old-timer and insider, who had earlier written on air resistance[141], as had Thurston, and on wing construction[142], as had Thurston.  Later, he would speculate in the pages of Flight on the use of slots in the Guggenheim race.  Thurston seems to have written anonymously on at least one other occasion, as Archaeopteryx in The Car magazine of 29th May 1928.[143]  A pseudonymous article would have allowed him to assess, and later to reap, any interest stimulated in his invention whilst avoiding further open conflict with Handley Page. 

In 1928, “Wing Tips”[144], another pseudonymous Flight contributor, was to say[145]:

“… the present writer, at any rate, wishes unreservedly to acknowledge his indebtedness to "Marco Polo” for his early thoughts along these lines [on cantilever wings]. The practice of "poaching" other men's ideas without acknowledging their original source is apparently as popular in the aircraft industry as in every other sphere of human endeavour, but while in the universal field of science the only thing that finally matters is the work and not the man, at the same time in the interest of common justice, it is proper to award priority where such is rightly due.”


“Wing Tips” knew who “Marco Polo” was, indicating that it was "a pseudonym which older readers of the paper will probably penetrate."  His pointed comments would certainly have echoed Thurston’s view of Handley Page’s later behaviour.

Over the next few months, Thurston filed a number of further applications, and obtained the following patents jointly with BAC:



Provisional filed

Complete filed


GB 180359

14th December 1920

25th February 1921

12th July 1921

Splayed wingtip pinions

GB 186990

7th July 1921

5th January 1922

A bank of pinions slide out of the end of the wing.

GB 190800

28th September 1921

28th June 1922

Fixed and sliding parallel pinions


Handley Page buys out Lachmann

Meanwhile, comforted no doubt by Thurston’s lack of patent protection for the slotted wing, Handley Page and Brewer were solving the more immediate problem posed by Gustav Lachmann.  Lachmann could only afford patent applications in a few countries, and lacked the money to exploit the invention or even to pay for further research.  On the other hand, he undeniably had an earlier priority date than Handley Page and was in a position both to exclude him from those markets where Lachmann had been able to file his patent, and to embarrass him by undermining his personal claims to scientific priority for the invention.

Accordingly, guided by Brewer, in August 1921[146] Handley Page cut a deal with Lachmann by which each kept his own “home” territory and their exploitation of foreign territories was pooled.  From that point, their efforts were pooled; Handley Page had bought not merely the patent but the man.  On 12th September 1923, Handley Page also bought out Lachmann's US patent rights[147]


A few more contenders

We should not leave this era without briefly reviewing some of the other contemporary claimants to the slotted wing.  Riabouchinsky[148] (1935) makes out a strong case for having discussed and demonstrated slotted aerofoils in 1909, and he credits Thurston with having "foreseen the importance of a like arrangement for increasing the stability of aeroplanes" before the War.  Handley Page was familiar in general terms with Riabouchinsky's work, as he cites him in his 1911 paper.  Sergei Alekseevich Chaplygin[149] had done similar work to Lachmann’s in 1913 and 1921 according to Stivers & Jones[150], but the language barrier posed by publication in Russian kept this from British eyes at the time. 

These were theoreticians, but claims were also made by, or on behalf of, more practical men.  Joseph Cordner (1875-c.1960), a Londonderry engineer who, like the Wrights, ran a bicycle repair shop, built his own pre-War planes and claimed the first powered flight in Ireland, is credited by some with the invention and patenting of the slotted wing.[151]  His patent GB 1911/02521 shows a wing with “channels having suitable throttling devices or flaps which can be raised to open the channels or lowered to close the said channels to any required extent for the purposes of braking, steering and so forth”.  These do not, however, resemble transverse slots.

It has been suggested[152] that Louis Constantin (a Spanish engineer who moved to Paris) took the first practical steps in 1913; much later, in 1928[153], Constantin did patent an automatically opening slot but the 1913 reference may be to his patent[154] which aimed at to reduce head resistance by adding a false bow at the front of a vehicle to change the direction of the stream lines:

This invention relates to devices for reducing the head resistance which vehicles experience when moving through fluids such as water and has particular reference to devices of the kind which have the effect of changing the direction of the stream lines in such a manner as to minimise the effect of same on the main portion of the vehicle.


I Claim:

1. A device intended to reduce the resistance to the progress of a vehicle in a fluid consisting of a screen of section smaller than that of the vehicle and having walls inclined on either side of a ridge or point fixed at such a distance in front of the vehicle that when the latter moves forward the fluid will be divided into divergent streams which will not converge to their normal direction until the main plane of the vehicle is passed.


Another contender may well have been Oscar Gnosspelius, mining engineer, seaplane designer and pilot, who made the first takeoff from a body of water but will be best remembered as "Squashy Hat" in his friend Arthur Ransome's "Pigeon Post".  He wrote on the role of bird feathers, and suggested that Handley Page’s slotted wing improved lift by "constructing a few rough feathers and arranging them in a certain manner."[155]  In response to Handley Page's challenge, he said "When I first found the remarkable results which could be obtained by dividing a wing into a series of vanes I was struck by the fact that a bird's wing also consisted of a series of vanes."[156] 

Over 1919-1921[157], Dr Otto Mader (1880-1944), Technical Director of Junkers during the First World War, also independently developed and tested a wing with a slot (but at the trailing edge), in a wind tunnel and on an aeroplane (later assisted by Theodore von Kármán, Lachmann’s professor at Aachen) and in 1921 applied for a patent[158].  Handley Page sued Junkers in Germany under Lachmann's patent, and a settlement was reached under which Junkers admitted infringement and paid royalties.

In the US, a Mr Martin[159] claimed before a Congressional Committee to have invented the slotted wing three years before Handley Page, and a Mr Naulty likewise.


Early theoretical and practical studies

Lachmann’s contacts at Göttingen and elsewhere were active in slotted wing research, and it is likely that Handley Page had easy access, via Lachmann, to their results.  On 15th June 1921, Lachmann published[160] a paper in Zeitschrift fur Flugtechnik und Motorluftschiffahrt which includes his own data from the Göttingen tests on his wing, a summary by Carl Wieselsberger of the Göttingen tests on Handley Page’s wing, and the experimental results of Richard Katzmayr and Leo Kirste of Vienna.  The latter compared (1) adding an auxiliary wing just in front of the main wing, much like Thurston's pre-War experiments, and (2) cutting slots through the main wing.  They concluded that both increased lift, but the former was much more effective.  The most effective arrangement of two aerofoils was when the front edge of the inclined 29.8mm forward aerofoil was sited 28mm in front of the front edge of the main wing, so that the two do not, in fact, quite overlap.

Lachmann does not discuss theory, but Katzmayr and Kirste quote a 1920 article in Luftfahrt:[161]

"According to one theory, the slot behind the auxiliary wing increases the vacuum over the front part of the wing, as the result of a sort of Venturi action.  According to another theory, the region of strongly diminished pressure is extended further back."


Katzmayr and Kirste reflected Handley Page’s own duality of thought – was the invention truly a slot through one aerofoil, acting to produce a jet of fast air by the Venturi effect, or was it two aerofoils in tandem, their airflows interacting to modify the pressure on each? 

Albert Betz of Göttingen (1885-1968), then a post-doctoral researcher[162], expanded on the latter theory.  According to Handley Page (1921b) in December 1921, Betz argued as follows:

If the simplest form of one plane is considered with a single slot through the forward portion, splitting this plane into two portions, an auxiliary and a main plane, the auxiliary plane, lying as it does with its rear edge on the upper surface of the main plane, tends to have the air at its rear edge accelerated owing to the region of accelerated air flow in which it is placed. In consequence the velocity change between the front and rear edges of the upper surface of the auxiliary plane is diminished, the pressure gradient is reduced, and the tendency to burble lessened, in a similar but reversed way the front portion of the main plane, lying as it does in the region of the reduced air flow of the rear edge of the auxiliary plane, has the velocity of the air flow reduced. There is, therefore, a lesser change of velocity from front to back of the main plane, and therefore a lesser tendency to burble."


However, Handley Page was not himself prepared to abandon the slot analysis:

It is necessary, however, to take into account another consideration, namely the provision of a slot of such an area that sufficient air can be sent through it to clear out the dead air that tends to form on the upper or suction surface of the plane and, by preventing this formation, preventing burbling.”


Betz (1922) himself subsequently wrote at greater length.  His paper gives the dual alternative views of the action of the slot – one analysis as two close aerofoils, one as a single aerofoil with a slot.  In the latter case, “The slots convey new energy to the marginal layer of air retarded by friction on top of the wing ... the air stream flowing out of the slot acts like the jet from a syringe and reinforces the air stream on top of the wing.”  The reader cannot help but gain the impression that Betz preferred the aerofoil analysis, but his conclusion was that “both are equally correct”.  It would henceforth be unnecessary to choose between Handley Page’s initial conception of a slot or his later acceptance of a pair of aerofoils – amazingly, duality was now the orthodox explanation, sanctioned by the high authority of Göttingen’s academic research.

Finally, Prandtl & Betz concluded that “the air stream flowing through the slot lifts or raises up the boundary layer” – an unsatisfactory explanation in several respects, according to Munk (1934: 30).[163]

Although quantitative explanations of the behaviour of the “slot” would not be possible for many years, there was a surprising lack of rigour in this ongoing doublethink.  Practical men will use any analysis that will do the job, but theoreticians are expected to get the explanation right.  Why was Handley Page’s original explanation (abandoned in his Complete Specification, but repeatedly referred to subsequently by him), that the Venturi action of the narrowing slot produced an accelerated jet of “live” air displacing the “dead” turbulent region, accepted so uncritically?  Deference to Page himself, a valuable connection who funded some of the research, might have played a part.  Perhaps, also, the Göttingen research team saw the slot (as Lachmann would do until his death) as a boundary layer control device, giving the clearest possible practical application (and hence validation in the marketplace) of Prandtl’s boundary layer theory, the vital importance of which was only slowly being grasped at the time.

At the practical level, Handley Page had by now more or less abandoned interest in the fixed slot as a high lift device[164], because of the increased drag, in favour of the openable slot which he now saw as a variable geometry wing allowing either normal high speed flight (with the slot closed), or higher lift, lower speed flight on landing or stall (with the slot open).  His own slot designs were therefore a compromise between optimising the lift performance of the slot when open, and achieving normal flight with it closed.  To reduce the drag penalty further, the “wingtip slot” was developed; having slots only towards the ends of the wings, Handley Page’s designs came to resemble Thurston’s alulas even more strongly.


Selling the slotted wing

Handley Page’s campaign continued through the early 1920s.  Naval flying was an early success area; the "Hanley", a torpedo carrier with manually actuable slots designed to take off from a deck, was tested in the UK in March 1922[165] and shown at Paris Aeronautical Exhibition in December, and within a few years, the Japanese Navy had taken a licence.  He did not do all the talking himself.  His test pilots, Captain Tom Harry England and James Cordes, played a part.  So did a Mr R Reynolds, one of the assistants in his Research Department who had tested slotted wings in 1921.  He wrote a 1922 article,[166] and Flight magazine reports that on 29th June 1922,[167] Reynolds went into the lion's den to read a paper “The Handley Page Slotted Wing” to the London branch of the SMAE with Thurston presiding – there was an “excellent discussion” afterwards, with hearty votes of thanks both to Reynolds and to Thurston, so a lively and controversial debate was no doubt involved.  At the First London Air Congress in June 1923, Handley Page gave a talk, followed by a slotted wing demonstration by the RAF. 


Building and buying a portfolio

Handley Page was to work to acquire a portfolio of slot patents, beginning in June 1920, when he filed for a number of minor improvement patents:



Provisional filed:


GB 166428

16th June 1920

A rocking mechanism for opening the slot whilst varying its camber

GB 166429

16th June 1920

A slide mechanism for opening the slot

GB 166430

16th June 1920

A mechanism for opening the slot whilst varying its angle

GB 172109

31st August 1920

Multiple backward-sloping, narrowing slots

GB 176909

21st December 1920

Trailing-edge flaps with slots


In examining Handley Page's improvement patent GB 172109, the Examiner had demanded the insertion of a “statutory reference” to Frank Duncanson's earlier patent GB 167318[168].  Under the then-prevailing patent system[169] the Patent Office could demand the insertion of statutory references, or insert them ex officio, where using the invention would infringe an earlier patent either because the earlier was a broad “master patent”, or where the later re-used the earlier with only a minor improvement[170].

Initially, Handley Page appealed the Examiner's decision.  The appeal was based on Handley Page’s charge that Duncanson's complete specification (dated 15th March 1921, after Handley Page's filing) was not entitled to priority from its own provisional (dated 15th May 1920) which failed to mention slots.  In the intervening period, Handley Page had demonstrated the slot, and presented his R.Ae.S paper[171] and his own basic slot patent had been published – Duncanson had, said Brewer, plainly added backdated references to slots based on Handley Page’s own work.  However, the Patent Office (and the appeal tribunal) refused to examine the discontinuities between the Provisional and Complete specifications.  Handley Page had therefore filed to revoke Duncanson's patent in 1922, on the basis that a reference would not be required “to a patent which was obviously invalid[172], but this application seems to have gone badly, and he opted instead for a commercial solution, buying out Duncanson's rights in the patent on 22nd October 1922 as he had Lachmann’s.


Slots for Control

The next stage of Handley Page’s development was to turn the slot from a safety device to a control device.  The Aeronautical Research Committee had concluded[173] in 1922 that the combination of a slot with an aileron gave better control than the sum of each separately, particularly close to or at stall.  Handley Page filed for two patents to implementations of slots for control, in 1923 and 1925.



Provisional filed:


GB 223292

16th July 1923

Combined slot-and-aileron control (e.g. using a device to intercept the slot)

GB 263290

9th December 1925

Combined slot-and-aileron control connecting the slot on one wing with the aileron on the other


Slot & aileron control was demonstrated on an Avro at Croydon on 15th April 1925, and in March 1927, Handley Page presented a lecture on the topic (modestly, as always, entitled “The Handley Page Slot-and-Aileron Control[174]) to the R.Ae.S.  A slotted Handley Page Hendon was demonstrated at Cricklewood on 20th July 1926, and a Handley Page Hamlet with slots & flaps at Croydon to Dominion Prime Ministers on 23rd Oct 1926.  Handley Page would later replace slot and aileron control by slots with spoilers and other control mechanisms.


The Automatic Slot

Finally, on 9th July 1927, Handley Page applied for an important patent on a mechanism for automatically deploying the slots, so that the slot was normally closed to reduce drag and only opened when necessary to prevent stalling.  The official demonstration of the automatic slot took place on 18th November 1927[175], after several months of speculation, and it was acclaimed as a life-saver (described by Handley Page’s supporter C G Grey as being as important to aviation as the pneumatic tyre to land transport (Barnes 1987:229)).  It is doubtful, however, whether there was anything inventive about the concept of an automatically operating slot per se – in patent law, mere automation of that previously done manually is notoriously unpatentable – and indeed it was sufficiently obvious that Handley Page's patent agent Griffith Brewer[176] had suggested including a general mention of an automatic slot arrangement in Handley Page's basic patent. 

Others had also been there beforehand.  Lachmann (1921) had previously suggested a speed-drop actuated automatic slot.  Armstrong Whitworth applied for a patent for another on 5th April 1927[177].  Ronald McKinnon-Wood of the Royal Aircraft Establishment[178] had filed a UK patent application to an automatic slot on 25 January 1927[179].  He assigned all US patent rights to Handley Page and granted him a UK licence.  Handley Page’s own automatic slot patent was therefore of narrower scope and more dubious validity than the basic slot patent, covering only one way of deploying the slot, but it did usefully extend his patent protection by 8 years.


Handley Page’s Exploitation Strategy

According to Fearon[180] slow growth of UK civil air travel, coupled with sporadic defence orders, and the general economic recession, were responsible for Handley Page Ltd’s poor financial performance – payments on the patents (and particularly the slotted wing patent) of over £700,000 in total were all that kept the company afloat.

To exploit the slotted wing, Handley Page pursued the course followed by Brewer on behalf of the Wrights – settle with governments direct, rather than suing competitors.  He had licensed the US Navy, in return for a downpayment of $125,000 and royalties at 5% on the total price of each plane with slotted wings (the same rate as the Wrights had charged, and a very significant sum bearing in mind that an aircraft might be covered by many different patents) up to a maximum of $750,000.  However, half the downpayment could be repaid, if the validity of the patent were challenged.  There were US Governmental Hearings into the contract.  In 1924, the US Attorney General recommended seeking repayment of half the downpayment, and a court action, United States v. Handley Page, was accordingly started in the UK.

He licensed the Japanese Navy for a total of £50,000 in the mid-1920s, with the prospect of a further licence to the army.  Other governments, including Italy and Sweden, also signed up at 5%, the latter in 1929.  Although these terms were acceptable to governments, they seem to have been too high to be attractive to the private sector on civil aircraft.  Time magazine hailed the lapse of Handley Page’s basic US slot patents in 1939 on the basis that he had “demanded a fancy price for installation: about 5% of the plane's cost (as much as $25,000 for a DC-4). Too costly for most plane makers who hesitated to devise variants lest they infringe on British patents, wing slots were rarely used. Many a flier crashed who might otherwise have been saved. Last week Engineer Page's patents expired, wing slots became available to everybody.”[181]  High rates in the civil aviation markets caused Handley Page to lose potential licensing revenues from competitors.  On the other hand, lowering his royalty rates would have encouraged foreign governments to ask for a corresponding discount, and would hence have resulted in lower revenues from the military markets which, with the slow growth of civil aviation in the inter-War years, would probably have offset any gains from the civil sector. 

One rival who did successfully exploit a licence was Geoffrey de Havilland, on whose DH9 the slot had first been implemented.  He personally acted as a demonstration pilot for the slotted wing, and his Moth, fitted with slots, generated considerable interest abroad, particularly in the US.


The UK compensation claim

Late in 1927, Handley Page applied to the UK government for compensation for their use of slotted wings.  His claim was by now based on a substantial portfolio of patents:



Provisional filed:


GB 157567

24th October 1919

The basic slot patent

GB 167318

15th May 1920

Duncanson’s patent to pivotal opening of the slot

GB 166428

16th June 1920

A rocking mechanism for opening the slot whilst varying its camber

GB 166429

16th June 1920

A slide mechanism for opening the slot

GB 166430

16th June 1920

A mechanism for opening the slot whilst varying its angle

GB 172109

31st August 1920

Multiple backward-sloping, narrowing slots

GB 176909

21st December 1920

Trailing-edge flaps with slots

GB 223292

16th July 1923

Combined slot-and-aileron control (e.g. using a device to intercept the slot)

GB 263290

9th December 1925

Combined slot-and-aileron control connecting the slot on one wing with the aileron on the other

GB 298508

9th July 1927

The automatic slot[182]


The Air Ministry appointed the patent agent with the greatest litigation experience of his day to consider the claim.  Hubert Alexander Gill CMG (1881-1954), founding partner of Gill, Jennings & Every and twice President of CIPA[183], was later to be a Ministry expert in many post-Second World War claims for wartime patent use before the Royal Commission on Awards to Inventors (‘COATI’).[184]

Gill dismissed all but the “basic” patent GB 157567 and the “automatic slot” patent as being either trivial or not used.  As to the latter, the automatic slot had been prior-disclosed to the Ministry by McKinnon Wood, so by time-honoured principle known as “prior Crown record”[185], no payment would be appropriate.

Gill examined the validity of Handley Page’s basic patent over the prior art cited by the British Examiner, as well as Thurston’s 1914 Flight magazine paper (he referred also to Thurston’s contributions to the discussions after Handley Page’s 1921 R.Ae.S paper), and two patents[186] which Alfredo Guillermo Leigh (or possibly Leigh Bañados, a Chilean dentist-turned-aeronautical engineer who claimed priority for the invention of the slot) had notified to the Ministry.  He recommended that Leigh’s wing should be built and tested to determine its performance; this was done[187], and it was found to give a little lift but too much drag to be usable. 

He concluded[188] that Thurston’s Figure 6 test results came closest to Handley Page’s patent, but not close enough since the described position of the main aerofoil meant that there could be no “burbling”, so the slot could not be preventing a stall.  He therefore opined that the patent valid, and was supported by leading Counsel John Whitehead KC.  Negotiations ran over 1927-1929 and, after an appeal to the Committee on Awards to Inventors, the UK government begrudgingly paid Handley Page £100,000 for past and future military use of the slotted wing patent.  This was intended to equate to a 5% royalty, but Handley Page needed ready cash, and preferred the tax treatment of lump sums.


Monetization and litigation

Successive mid-year Handley Page Ordinary General Meetings were reported in the Times, and must have been read anxiously by the shareholders who had seen the company decline since the days of its flotation.  In 1927, Handley Page restructured the shares, writing down their value to one shilling in the pound for ordinary shares and eight for preference shares.[189]

Even now, patents are notoriously hard to value, but in 1927, of Handley Page's total assets of £200,000, the slotted wing patents made up £75,000.[190]  To monetize that value, Handley Page sold off various of the foreign rights to governments; the Canadian patent rights went for $200,000 in 1930, and the Italian rights in 1931 for “a substantial sum”.  The fact that the UK government had agreed to pay £100,000 was announced to shareholders in mid-1929. 

In the US, 16 aircraft entered the competition for the 1930 Guggenheim safe flying prize of $100,000, but only two completed the course – the Handley Page Gugnunc[191], and the Curtiss Tanager.  The winning Tanager used Handley Page’s patented slotted wing, and Handley Page sued for $300,000, thrice the price money.[192]  In fact, of the last four aircraft in the race, three had slotted wings – the third was the Ford-Leigh Safety Wing biplane, which had a fixed slat along the front edge of its wing, designed by none other than Alfredo Leigh the Chilean dentist.  Handley Page’s suit against Curtiss brought an immediate counter-charge of copying from Leigh, which however in the end did no more than muddy the water[193]. Curtiss claimed that his use was merely for experimental purposes, but in the end submitted to a consent decree acknowledging infringement and validity of the patent, and agreeing to a royalty-bearing licence for future use.[194] 


A break from aviation

Over 1921 to 1925, Thurston had moved out of academia and was training to become a patent agent.  At some point before 1925, he moved out of London to Petersbank, a large house just outside the village of Bidborough in Kent on the road to Penshurst (where there was a First World War airfield[195]) which was to remain his home for the next four decades.  On 30th July 1925, he married the indomitable Suzanna Sophia Grece (1887-1966).  She was the daughter, by his first wife Mary Gasson (1854-1897), of Dr Clair James Grece (1831-1905), the learned (though eccentric) liberal lawyer, correspondent of Charles Darwin, electoral reform enthusiast and (for the last 42 years of his life) Town Clerk of Reigate.  After her father’s death, she had studied mathematics at Bedford College, but gave that up to look after her younger brothers, successfully contesting her inheritance in the High Court against her father’s young second wife.  She had moved from Redhill to Speldhurst around 1910, and volunteered as a driver in the First Aid Nursing Yeomanry Corp during the War.

These professional and personal activities kept Thurston away from aeronautical research.  Having previously published at least one technical article each peacetime year between 1909 and 1920, he appears to have written nothing of significance between 1921 and 1928[196], and filed no patents between 1922 and 1927.  Whilst remaining active in the SMAE and regularly attending R.Ae.S meetings, he was falling well behind the rapidly advancing forefront of aeronautical research.  On November 21st 1924,[197] for instance, he gave a paper before the Institution of Aeronautical Engineers on "Some Further Practical Points in the Structural Design of Aircraft" but it was poorly attended, and he was criticised for attempting to use old data on modern machines instead of offering new methods of design. 


The negotiations of 1928

Unable himself to pursue research on alulas or rider planes, he could not have been unaware of Handley Page’s success in selling the slot.  By this time, Handley Page’s designs included wingtip slots actuated for controlling the aircraft – something Thurston regarded as essentially his own invention.  He also thought his abandoned patent application had disclosed an automatic slot.  Early in 1928, it became known that the automatic slot was to be adopted as a UK standard.  That provided the impetus to Thurston to seek a share of the rewards Handley Page would reap.

To strengthen his position, he filed a number of provisional patent applications in February 1928 – two on particular automatic slot mechanisms.  One, granted as GB 310988, was essentially a re-filing of his 1920 application, containing all the same drawings but with the text somewhat reworked, and with claims only of the "omnibus" type of almost no legal effect[198].  Much later, he explained his reason for filing it: "I ... used the method of applying for a patent as the only way in the face of strong opposition of recording my discoveries."[199]  It is also interesting to note that he was concurrently handling a patent application (ultimately published as GB 300782) on an automatic slot with variable closing angle for a Captain Gerald Iredale Newenham Deane, a First World War pilot and inventor. Deane’s provisional application dated back to 9 November 1927, but the Complete was filed on 30th January 1928.



Provisional filed

Complete filed


GB 310988

2nd February 1928

3rd February 1928

Varying width of the gap together with inclination of a swing-out leading edge wingtip alula to augment or replace the rudder & ailerons of conventional control system. 

GB 310989

2nd February 1928

2nd November 1928

Sliding variable length alulas - varying the length of the gap whilst keeping fixed width

GB 313419

2nd February 1928

2nd November 1928

Structure using wind vane automatically opening/closing gap when stall likely

GB 312106

16th February 1928

16th November 1928

Auto-opening slot structure


On 17th February 1928, the day after filing the last of these applications, Thurston wrote to “My dear Handley Page”, asking for a lunch meeting “as I have something which will be of interest to you.”  The two duly met three days later, and Thurston showed Handley Page copies of his 1920 Provisional Specification 35116/20, his 1921 Complete Specification 21496/21, and a letter written to the Air Ministry in 1921.  Thurston's typed notes of the meeting indicate that it lasted over two hours, and that on reading his Complete Specification Handley Page said "You missed something.  You really missed something."

Thurston had another two-hour meeting, this time with Griffith Brewer, on 2nd March, and told him (as Brewer reported to Handley Page) that “this Specification contained all the invention of your Slot patents so far as lateral control was concerned, also that he had other proofs of further inventions which covered practically all your work.”  He also claimed to have a verbal order from the Air Ministry (for experimental work, it seems), on which he would like to work with Handley Page, and said that his abandoned applications (which he had sent to the Ministry and to other firms) gave him an ongoing “prior use” right.  Finally, he told Brewer that he had re-filed his abandoned application. 

Handley Page’s instructions to Brewer were (as they had been with Lachmann, Duncanson, and McKinley-Wood) “to ascertain what he had for sale or negotiation.”   Thurston must, as a patent agent, have known that he had no relevant patent rights to sell, or with which to threaten – the only one which mattered had long since been abandoned.  If he knew anything of Handley Page, he could have had little expectation of charity, particularly after their past clash in 1921.  The few options he had were to:

  1. Offer his services for hire in developing the slot (a pious hope at best);
  2. Offer not to work his prior use right (if he could establish it) in competition to Handley Page; or

3.      Offer to stay quiet and cease to embarrass Handley Page (which would require him to establish either that he had prior-published, or that Handley Page had stolen his idea from him).


Brewer didn’t accept that there were any rights in the abandoned applications, and told Thurston, if he wanted money, to claim it from the Air Ministry.  Handley Page told Brewer on 3rd March that he “did not want to spend money on examining Thurston’s fictitious claims beyond what is necessary to assure myself that there are no steps that we can profitably take”.  He then offered Thurston a further meeting.  The latter in the meantime filed another patent application on 12th March 1928: 


GB 314105

19th March 1928

6th September 1928

Front & rear alulas on the control surfaces e.g. ailerons, rudder


The two met once more on 14th March.  According to Thurston's typed notes, Handley Page said he assumed Thurston wanted money; he would only pay if Thurston had something to sell.  Thurston said he wanted to develop his own inventions, and if Handley Page would let him do it free or for a nominal licence fee, he would in return not challenge Handley Page’s patents.  The reply was uncompromising; according t Thurston’s notes, Handley Page would attack "with the full vigour of the law and would take it up to the House of Lords if necessary.  He said: You know what these things are.  You remember Mooney."


“You Remember Mooney”

The Mooney case would have been familiar to both men, but from opposite sides.  The matter was aired in Parliament in 1920, and must briefly have become a cause celebre.  “Mooney” was D J Mooney, founder of the Steel Wing Company Ltd, who alleged that his wartime invention on metal spars had been stolen and patented by Thurston’s wartime colleague and post-War collaborator Major Hamilton Neil Wylie, and brought an action before the Patent Office but failed to prove his point.  Handley Page was a lynchpin of the Society of Aircraft Constructors who backed Mooney, alleging that there was a prima facie case, and pressed for sanctions against Wylie[200], whereas Thurston had been Wylie’s wartime co-worker and post-War joint inventor.  Handley Page’s message was clear: an inventor claiming his rights against a determined usurper faces a hard and expensive job and is likely to fail.

Wylie and Mooney would return to haunt Handley Page a few years later.  Wylie had developed designs for spars built of strip metal in 1917, when there had been a severe spruce shortage.  The Air Ministry accepted these designs in 1918, and Wylie’s corrugated metal tube spar for use in aircraft construction was patented that year[201].  Ultimately, Wylie (through Armstrong Siddely) and Mooney (through Gloster[202]) pooled their patent interests into a patent holding company called Aircraft Technical Services Ltd[203].  By 1934, many aircraft manufacturers had taken licences[204].  Over 1931-32, Handley Page delivered eight infringing aircraft to Imperial Airways, and ATS Ltd (the then-owners of the patent) sued for patent infringement[205].  Frederick Handley Page gave convincing evidence for the defendants, and Wylie’s patent was struck down on the ground that corrugating metal was commonplace.


The Memorial Lecture

On 19th March 1928, Sir Samuel Hoare announced to the House of Commons the adoption of the slotted wing across the RAF.  Thurston decided to go public.  On 24th April, Thurston wrote to the Society to offer a lecture on rider planes and alulas.  However, he had left it too late for the current lecture season.  Handley Page was due to give a major presentation[206] on the automatic slot, at the R.Ae.S Wilbur Wright Memorial Lecture[207] on 30th May 1928.  On 18th May, Thurston wrote to the Society about the Memorial Lecture, but they wrote back to tell him that the custom for Wilbur Wright Memorial Lectures was to allow no discussion afterwards.  The lecture referred at length to wingtip slots and slots partway along the wings, used for control in conjunction with ailerons.  At the end of his lengthy and impressive paper, Handley Page thanked McKinnon Wood of the RAE. 

In response, Henry Egerton “Harry” Wimperis[208], whilst not stinting his praise of Handley Page, was careful to point out that he had certainly not invented the automatic slot single-handedly: "A platform was built up through a series of years by scientific work carried out at the RAE and NPL ... It was Mr. Handley Page who saw what use could be made of it."  It must have been galling to Thurston to sit through the evening in silence, but he was still in correspondence with Handley Page.  He asked Page to read his Specification and make him an offer; Page wanted to know what Thurston was asking before he read anything.  Finally, on 25th July, Thurston spelt out his demands: “a small royalty plus expenses and a small lump sum to cover past expenses, provided you could pay me a salary during the experimental period to compensate me for loss of time in my own business.”  Handley Page ruled out either a salary or a lump sum; he would consider only an outright purchase or a royalty – if Thurston had any rights to buy. 

His letter stung Thurston into a warlike response on 27th July: “In view of the fact, as you very well know, that I am the first inventor of controlling and stabilising aeroplanes by means of small supplementary or rider planes in front of the leading edge,… and as you have apparently adopted my invention with very great success and not a little financial reward, you should be in the best position to appreciate both the value of my inventions and to assist in development.”  Naturally enough, this merely drew a denial of copying and a refusal to cooperate.  Sensing that he had overplayed his hand, Thurston wrote once more on 14th August in a more conciliatory tone but got a final and categorical refusal on 29th August.  Handley Page’s sales activities went on undiminished in the meantime, the company demonstrating a spectacular remote controlled flying electric model plane with automatic slots in Berlin on October 9th to 28th, 1928.


Thurston’s 1928 R.Ae.S paper

It seems likely that the correspondence over the Wilbur Wright Memorial Lecture finally swayed the Society into offering Thurston a right of reply.  Founded in 1866, the R.Ae.S was and is the world’s oldest aeronautical society.  It became “Royal” in 1918, and by a demarcation agreement with the Royal Aero Club (the leading aviation sporting body) and the Aerial League of the British Empire (the leading aviation lobby group) its role was to be “the paramount scientific authority on aeronautical matters’. 

In 1928, however, the Society was in the throes of mild schizophrenia.  The rival Institution of Aeronautical Engineers (founded in 1919) had been an engineering institution like its more successful sisters the Institution of Mechanical Engineers and the Institution of Electrical Engineers, but declining attendance and dwindling finances forced it into the arms of the Society, with which it merged (against active resistance from Thurston[209] amongst others) on 1st October 1927.  In later years, the Helicopter Association of Great Britain[210] and the Society of Licensed Aircraft Engineers and Technologists[211] would be absorbed in the same way. 

Although there was a degree of common membership between the Institution and the Society, there was inevitably some tension between the aristocratic “gentleman scientist” origins of the Society and the practising engineering focus of the Institution, which would be reflected in differing views as to what kind of papers to publish. 

The then-President of the Society was “Colonel The Master Of Sempill”, William Francis Forbes-Sempill (1893–1965), former RFC colonel and test pilot, and soon-to-be-author of “The Air and The Plain Man”[212], a man of extreme right-wing political opinions who was involved with several anti-Semitic organizations[213]

Sempill was an enthusiast for Japan, who held the rank of acting captain in the Imperial Japanese Navy, having led a three-year “unofficial” British air mission to Japan between 1921 and 1924 that involved supplying British aircraft technology to the Japanese Imperial Air Force, and thereby unknowingly paved the path to Pearl Harbour.  The mission included Handley Page’s chief designer, George R Volkert and, later, S. T. A. Richards accompanied by a slotted wing torpedo plane, and they succeeded in licensing the slot patents to the Japanese Navy.  Sempill remained an active salesman for British air companies throughout the 1920s[214].  It has recently been revealed[215] that in 1928 he was already under surveillance by MI5, by whom he was later held to have spied for the Japanese, supplying them with technical information, for which he narrowly escaped prosecution and was sent safely out of the way to Canada for much of the Second World War.

After some internal discussion, the Secretary of the Society wrote to Thurston on June 21st 1928 that "The Committee are strongly of the opinion that this subject should be properly ventilated."  Captain John Laurence Pritchard (1885-1968), was then the Secretary, a post he would hold for a quarter of a century over 1926-1951, also acting as the longstanding editor of the R.Ae.S Journal.  During his early days at the R.Ae.S, Pritchard ploughed his income from the Society back into their Journal, funding himself by working as a journalist and writer.  He wrote technical books on aircraft and radio, but also adventure and mystery stories (under the nom-de-plume John Laurence), including Mystery From The Air, The Great Aeroplane Mystery, and Murder In The Stratosphere and at least twelve more terrestrially-oriented thrillers, as well as several non-fiction crime books including the definitive study of capital punishment.  According to “FHS”, his obituarist in Flight magazine, “Pritchard was not an easy man to get on with ... He did not suffer fools gladly”, but “he bore no grudge after the particular issue about which they argued was closed.”  Pritchard (with A J Sutton Pippard) had served under Thurston in the Safety Directorate during the War[216], and would therefore show him some sympathy.

Thurston complained that he had offered his talk three times over the past eight years and "on each occasion I have been informed either that my application is too late or that there was no date available...".[217] .  He wanted a firm date "owing to my past very bitter experience".[218]  On 16th July, Sempill wrote to offer him either a talk later in the year, or an article in the Aeronautical Journal, “the earliest form of publicity possible” for “stating your case”.  There was, however, a distant warning note; the text would be subject to review: “Obviously the Council must safeguard itself to some extent in this way, and in fact, in the past, several lectures have had to be turned down where the manuscript has been submitted, because such a lecture would not redound to the credit of the lecturer or the Society.  Naturally, I do not anticipate any paper by yourself being rejected on such grounds.

Thurston presented a paper before the British Association in Glasgow on 11th Sep 1928, an abstract of which was published in Flight magazine two days later.  Taken on its own, the talk was apparently innocuous.  He opened with a discussion of the role of the alula in flight of birds, and then explained his own patented system (but without referring to his patent).  There was a brief mention of his 1914 work, indicating that his pre-War experiments proved:

1.      “That small rider planes or alulas could be used for controlling aircraft.

2.      That the maximum interference occurs with the rider plane near the front edge of the main plane and turned down at a negative angle to the main plane.

3.      That the burble point of a main wing could be delayed and the lift increased by placing the rider plane in front of the leading edge of the main plane”. 


Totally absent was any explicit mention of "slots", or of Handley Page – it was as if the paper had been written in 1920, skipping over the previous eight years as if they had never happened.  There is no indication that the Glasgow paper came to Handley Page’s attention.  But it was only a dress rehearsal. 

Scientific papers are as varied as science itself, but Thurston’s unusual 1928 R.Ae.S paper is best understood as an answer to Handley Page’s own 1921 and 1928 presentations.  Thus, the title “Control of Aeroplanes by Alulas (Apt[219] control)” laid personal claim to the content, as Handley Page’s paper had.  Like Handley Page, Thurston made little attempt to put his own technology into a comparative frame, referring largely to his own work, although he does credit several authors on the structure of bird wings, and cites Eiffel for the discovery of the effect of aspect ratio on stalling (for which Handley Page had cited himself).

The text fell into three parts.  The first nine pages opened with a detailed biomechanical analysis of the bird wing, with emphasis on the alula and the pinions, which were as purely scientific as anything published by the Society over the previous half century.  Without drawing particular attention to his own contribution in discovering this, he presented the functions of these as analogous to those of the slot:

“When the thumb is extended, a gap is left between it and the main wing, which is at a negative angle with the chord of the wing.  The thumb and its pinions are known as an “alula”…. The alula appears to be used in taking off, landing and at the commencement of the down stroke of the wing ….  According to further observations that were made, it would also appear that the alula forms a gap between itself and the top edge of the wing when a bird glides at a large angle and is in danger of “stalling”.


Taken alone, this section posed no threat to Handley Page.  Indeed, Thurston’s interesting (though commercially unimportant) revelation that the slot had a precursor in Nature would, if anything, lend weight to the invention.  Aviation in its entirety had been an attempt to emulate bird flight, and as Stewart says, it was seen as unusual that “the wing slot seemed to have stolen a march on nature, it seemed to be something which the aeroplane had but which birds did not have.” 

The next seven pages presented the methodology and results of Thurston’s pre-War experiments.  In principle, this was still interesting information, since most experimental data on the slot was specific to Handley Page’s openable designs.  It also had a certain historic value since pre-War wind tunnel experiments were already receding into the past.  However, the opening of the section suggested that the experiments were “in order to test the accuracy of these conclusions” (emphasis added) – i.e. the conclusion that the bird’s alula was an automatic anti-stalling safety device, which must therefore itself have been reached before the War.  This was a claim that Thurston had invented the slot before the War, lacking any basis in his published work. 

After presenting some of the data from his 1914 Flight paper together with additional contemporaneous unpublished data, he concluded that “it is clear … that, if rider planes are to be used for stabilising or controlling aircraft, the motion permitted to the rider plane should not allow its “wash” to pass to the other side of the main plane …” – effectively, a requirement for a negative inclination.  Also, “as the phenomenon, known as stalling, appears to be due to the peak of the suction curve becoming too high … it is clear from these diagrams that the “stalling” angle … would be increased by placing the rider plane in front of the main plane at a negative angle …”  Although his various deductions from the experimental data are all expressed in the present tense, he claimed that “All the experiments and conclusions given above were published before the War, particularly at a lecture given at East London College (University of London) on June 10th, 1914.”  This part of the paper was dangerous for Handley Page – if true, Thurston had not only invented the slotted wing before him, but made his results available to the public before the War so as potentially to invalidate his patent.  The paper has a surreal flavour because (as in Glasgow) Thurston wrote as if the past eight years had not happened, and Handley Page did not exist; when he writes on the possible future uses of alulas, the real message is that he had predicted in advance all the current uses of slots.

The final five pages describe the devices of some of the embodiments of his patent applications.  Thurston’s first draft was scrutinised by the Society, who made editorial changes and suggested expansions before accepting the final draft.

The date for the talk was 6th December 1928.  Presumably, if (as Sempill had suggested) the Council had intended to review the content of the paper, this should have taken place at latest by their meeting of 20th November attended by Sempill, Brewer, Pritchard and McKinnon Wood amongst others, but in fact no objections were raised.  The draft paper was circulated in advance, as was customary, and some time in late November it reached the eyes of Frederick Handley Page. 

He immediately understood the coded language as an attack.  According to Lachmann,[220] "HP was very furious about it and called certain statements and claims in this paper 'bare faced lies'.The slotted wing patents (and particularly the first) were now commercially crucial to Handley Page, and were under critical examination by the Ministry.  Suggestions that they might not be valid, or might be the property of another, were extremely unwelcome in view of their potential economic impact. 

But there was also a more personal reason why the timing of Thurston’s paper was extremely unwelcome: the R.Ae.S had decided to award Handley Page the Wakefield Gold Medal[221] for his work on the automatic slot, and the presentation would take place at the annual Wright banquet, barely two weeks after Thurston’s talk.

His immediate reaction (“over-reaction” is perhaps more accurate) was to try to suppress the paper.  He wrote to Brewer on 28th November to ask him “whether we should proceed by way of injunction in the Courts to prevent the paper being read?


Handley Page’s letter made a number of points:

1.      Thurston said that his apparatus was constructed to test bird flight, whereas in Thurston’s 1914 paper appears to discuss canard planes with small elevator planes in front.

2.      There was no discussion of stall in Thurston’s 1914 paper – a 7 degree inclination was a typical flying angle for planes of that era, whereas stall would occur at about 16 degrees.

3.      There was no mention of lateral control in Thurston’s 1914 paper (this point was wide of the mark, as Thurston claimed to have invented that after the War in 1921).

4.      He doubted very much that East London College lectures contained any extra test results.

5.      There was no evidence that Thurston had invented the automatic slot.

6.      Thurston’s 1920 provisional patent application was exactly the same as that of Holle (however, that cannot have been the case: as Holle’s system reduced lift and caused spinning, it was clearly different to the slotted wing and also to Thurston’s arrangement).


Brewer replied on 30th November that whilst Thurston’s paper was “irresponsibly inaccurate” there was no ground for an injunction.  Some of the claims lacked corroborating evidence, but were not demonstrably false.  His advice, founded no doubt on his own experience in defeating the Langley fraud, was that “the only way in which his paper can be dealt with is by the discussion which follows”.  Despite “Dr Thurston’s attempt to use the Aeronautical Society as a cheap Court to ventilate his imaginary wrongs, your strongest way to deal with it is to expose his misleading statements”.

He suggested:

1.      Citing Balassanian’s patent GB 2642/1912 “from whom Thurston probably obtained the information to make his first tests” (this seems improbable given that Thurston was thinking about planes in wakes back in 1911).

2.      “Repaying Thurston in kind” for what Thurston did in the 1921 talk.

3.      Pointing out that Handley Page’s basic patent GB 157567 was published on 24th January 1921, before Thurston’s Complete Specification was filed.

4.      Asking why, if Thurston had already made his patent drawings for the Complete Specification before the 1921 meeting, he hadn’t shown them in his intervention at the time; 

5.      Pointing out that Thurston filed his Complete Specification right after Handley Page’s 1921 talk;

6.      Opposing Thurston’s patents.


That same day, before Brewer’s letter reached him, Handley Page wrote to the Secretary of the R.Ae.S.  His main charge was that “The paper is written not with the idea of advancing technical information but of setting up priority for his alleged development work, which, if successful, could only be detrimental to this company’s interests”.  He was correct, of course, but his interests as against Thurston’s ought not to have been a concern of the Society.  He repeated the substance of his letter to Brewer and added that:

1.      The 1914 Flight paper was in fact itself stated to be a summary of the 10 June lecture referred to by Thurston;

2.      Thurston never used the word alula before 1920; it was “first used by Mr Holle … and the use of alulas was patented by him

3.      Figure 9 “imitate(s) the slotted wing device

4.      Figure 14 “is a copy of an early arrangement of slotted wing used by our company

5.      Thurston gave no evidence of automatic opening.  “The first automatically controlled aerofoil for the purpose of delaying burbling was that covered by patents taken out by this company in 1927” (dismissing McKinnon-Wood’s earlier device as merely something “similar”)

6.      Thurston’s specifications “remained unpublished” (which was untrue in the case of the provisional application) and ultimately became void (which was irrelevant).


He asked for publication to be deferred until Thurston could prove his claims about automatic slots.  Faced with Handley Page’s demands, Sempill, pillar of the military–industrial complex, wrote that same day to Thurston to ask him to let his lecture “stand over for the present”.  Sempill was travelling to Germany, so the Secretary, Captain Pritchard, would explain. 

Handley Page's letter arrived at the R.Ae.S on 1st December, and was opened by Pritchard.  Sempill was uncontactable, so Pritchard rang Lawrence Arthur Wingfield (1898-1989), the Society’s solicitor (a post that was to become official in 1929) and author of “The Law in relation to Aviation”, for advice. To his concern, he was told that there were risks in either deferring or proceeding, so he wrote on 2nd December to McKinnon Wood to ask for his technical opinion – “I have read the paper through and it does not appear to me to be controversial.  It is a matter of policy by the Council to have this lecture given in order that Captain Thurston may have full opportunity to put his ideas before the Society as there has been a certain amount of grouse in the past that he has not been able to ventilate his ideas.  …The Master of Sempill thinks you would probably be able to give a far better independent opinion of the paper than anyone else.” 

McKinnon-Wood was not actually independent.  His own priority for the automatic slot had also implicitly been put in play by Thurston.  He had just sold his patent rights to Handley Page, and was economically linked to his camp.  Nonetheless, he replied on 5th December that “I do not see anything objectionable in the paper, using the word in its popular sense”.  Much of the paper was “words, idle words; the remainder might be interesting and valuable, but one wants more information …”.  It “was not, to my mind, of the standard the Society should demand, but I feel that we should go very carefully about it if we proposed to reject it, and it is probably better to let him “ventilate” in his own way.”  Pritchard thanked him, and agreed, by letter of 7th December.

In the meantime, a Special Council Meeting had been called for 4th December, with the purpose of ratifying Sempill’s action.  In summoning the Council, Pritchard commented that, having consulted the Honorary Solicitor, “the position … appears to be serious from the legal point of view …”.  Wingfield’s advice had been that “the Society’s attitude to the matter must be that it is not responsible for the statements of lecturers and that legal issues between Dr Thurston and Mr Handley Page must be tried by the proper tribunal.”[222] 

As Sempill was abroad, the Vice-President Air Vice Marshall Sir Vyell Vyvyan (1875-1935), a director of Imperial Airways, chaired the special meeting.  It was attended by 15 Council members including Handley Page, Griffith Brewer, McKinnon Wood, Wingfield, Captain Pritchard and his assistant, and:


Mr M L Bramson

Pilot and aeronautical engineer, Wakefield Gold Medallist 1926, later played a key role, with Whittle, in jet propulsion

Major John S Buchanan

CBE, later Sir John Buchanan, of the Air Ministry

Wing Cmdr Thomas Reginald Cave-Browne-Cave (1885-1969)

Consultant, later Professor Emeritus at Southampton University

Alan Ernest Leofric Chorlton (1874-1946)

Wartime Deputy Controller of Aero-engines in the Ministry of Munitions, and member of the Board of Inventions.  Subsequently elected a Manchester Conservative MP.  President of the IMechE in 1933.

Charles Richard Fairey (1887-1956)

Later Sir Richard Fairey.  Aircraft manufacturer and founder of Fairey Aviation, Wakefield Gold Medallist, SBAC and R.Ae.S President; trained as an electrical engineer.

Frederick Thomas Hill

Author of Materials of Aircraft Construction For the Designer, User And Student of Aircraft and Aircraft Engines, Pitman, 1934.

Captain Alfred Gilmer Lamplugh (1895-1955)

CBE, MIAeE, FRGS.  Of the British Aviation Insurance Group, “a man of the greatest integrity

Major Robert Hobart Mayo (1891-1957)

Technical Advisor to Imperial Airways, and well known consulting engineer, also British representative of the Guggenheim fund (which funded the race).  Previously he had been at the Royal Aircraft Establishment with McKinnon Wood, and at Ogilvie’s with Colonel Bristow, for whom he had worked on a Handley Page project in 1923.

Lt Colonel John Theodore Cuthbert Moore-Brabazon (1884-1964)

(Vice President) The first person to fly in England, and holder of the first pilot’s licence.  Read engineering but did not take his degree.  A right-wing Conservative MP and ally of Churchill, wartime minister of transport Minister of Aircraft Production, sacked by Churchill for publicly hoping for the annihilation of Russia, Britain’s then-ally.  President of the Royal Aero Club, president of the Royal Institution, and chairman of the Air Registration Board.

Lt Colonel Mervyn Joseph Pius O'Gorman

Former Head of the Royal Aircraft Establishment, forced to resign by, amongst others, Pemberton Billing over the BE2c.  Consulting engineer, R.Ae.S Chairman. Originally trained as an electrical engineer.


On Wingfield’s proposal, it was agreed to support Sempill’s action by postponing Thurston’s lecture, and to defer the matter to the next Council meeting of 11th December.  Handley Page then wrote to the Society once more, on 7th December, criticising Thurston’s response and then making an analogy with the Rougemont scandal – an outrageous and insulting accusation, referring to the adventures of “Louis de Rougemont” among “cannibalistic” Aborigines in Western Australia, sensationally published in the World Wide Magazine in 1899, which were in fact all found to be tall tales by Henry Grien, a Swiss hoaxer.  Preparing for the worst, he wrote to Holle to provoke him into attending the meeting, but got only a polite reply; he also wrote to Thurston’s co-workers and authors of the 1914 Flight magazine paper, but got no reply at all.

The meeting of the 11th December involved essentially the same participants.  Pritchard, the journalist, "felt very uneasy" and therefore took a full shorthand record.  The cancellation of the lecture was now a fait accompli, the only question was whether to reinstate it at a later date.  Whilst Thurston waited anxiously in the office outside, Handley Page led the attack on him, in the strongest possible terms.  The paper should not be read, as it included untruths; Thurston was thereby branded a liar.  Mayo and Buchanan supported him.  So, though less vehemently, did Fairey and Hill.  On the other hand, O'Gorman argued strongly that the Society ought to consider questions of priority and that Thurston’s paper should be read in full, and Moore-Brabazon had the same view; Branson and Chorlton also had concerns about the cancellation of the paper and supported O'Gorman.  McKinnon-Wood felt that it should not be published if it contained nothing new.  Lamplugh had written in to express his view that although Handley Page could have spared the Society embarrassment, he felt the paper was "not up to the standard the Society expects, and the element of self-advertisement exists to a marked degree."  Vyvyan, in the chair, wanted to "smooth things over", and Wingfield was concerned that the Society should avoid getting caught up in a private dispute.  Despite Handley Page’s powerful debating skills, the meeting was split down the middle.

O'Gorman eventually suggested the chosen way forward; the paper should be reviewed by an independent analyst, and the name he proposed was Sir Richard Tetley Glazebrook (1854-1935).

In the meantime, Pritchard wrote next day to tell Thurston that his paper was under scrutiny as being, essentially, just an amplification of his earlier paper in Flight, it might not contain enough new material to merit publication.  That represented a clear volte face, since the Society had known all along that the point of Thurston’s paper was to justify a priority claim and hence to revisit old ground.

Further, Thurston was asked to provide proof of his claims to meet Handley Page’s objections, as “The Council has recently decided in a similar case that it was in no way their business to question the bona fides of claims made as to priority but that it was clearly their business to satisfy themselves as to the value of the evidence submitted.”

On December 19th, Thurston wrote to make an all too obvious point: "I think it is rather unfair that some of the members of the Council who are naturally liable to have an unconscious bias due to their commercial activities, should be allowed to sit in judgment upon matters in which their commercial interests might influence their good judgment."  That certainly applied to some of those present.  Brewer was Handley Page’s patent agent.  Mayo had consulted for Handley Page and now worked for a Handley-Page related company of which Vyvyan was also a director – Imperial had been formed from, amongst others, Handley Page’s ill-fated civil aviation venture, and Handley Page Ltd supplied the majority of their airliners.  McKinnon Wood was, as we have seen, Handley Page’s licensor.  Sempill’s sales work to Japan had been in collaboration with Handley Page, and Lamplugh’s insurance work would have brought him into business contact with Handley Page.  At a personal level, Moore-Brabazon was a friend of both Handley Page[223] and Brewer, and Handley Page was also close enough to O’Gorman to address him by a nickname.

That same day, Pritchard wrote to instruct Professor Glazebrook but, crucially, did not make it clear what criteria Glazebrook was to apply.  The first director of the National Physical Laboratory[224] over 1900-1919, Glazebrook carried out important research in aeronautics, notably on conditions of stability, and was subsequently Zaharoff professor of aviation at Imperial College, London over 1920-1923. He was knighted in 1917, and was chairman of the Aeronautical Research Committee and the first president of the Institute of Physics; he received the Royal Society Hughes' medal in 1909 and the Albert medal of the Royal Society of Arts in 1918, and would in 1933 be awarded the gold medal of the Royal Aeronautical Society.  Glazebrook read the papers over Christmas and the New Year, and reported on 3rd January 1929.  His report (marked “NOT TO LEAVE THE SECRETARY’S OFFICE) was guarded, and relatively short.  Clearly he did not assess Thurston’s paper as a statement of priority, or a right of reply.  The yardstick he applied was whether the paper “advances Aeronautical Science or adds usefully to our knowledge of the subject.”  On this basis, he was bound to conclude that the core of the paper added nothing new – it was not intended to discuss new, unpublished work but to show that Handley Page’s published work came after Thurston’s published and unpublished work stretching back over a decade, as the Society must have understood from the outset. 

He found the first part of Thurston’s paper concerning birds interesting, but understood that the concerns arose from the later material.  Thurston’s pre-War experiments are described as “for the time, a valuable study”.  However, he pointed out that they had already been published twice; once in the Flight paper[225] and, a second time, in Thurston’s 1921 intervention; the new diagrams were deducible from the data already given.[226]  He concluded that some of the post-War results were “distinctly of interest”, “mainly in connection with the question of rights to an invention.”, but he was against re-publishing Thurston’s lapsed patent applications. 

Pritchard wrote on 18th January to convey the unwelcome news that publication was refused, as the paper reiterated material presented in 1921, although the Society would consider a paper on his “later work” (the unpublished automatic slot closure results).  Understandably, Thurston declined.

1929 marked the Wall Street Crash.  Aviation stocks (with radio, the “tech stocks” of the 1920s) had risen high in the preceding years.  With staggeringly bad timing, on 1st August 1929, just before the crash, a syndicate of American, Canadian and British bankers got together to found Anglo-American Shares, Inc., a trust company to hold shares in Handley Page and other European aviation companies formed, with Sempill as a director.  Aviation shares, like other industrials, plummeted and those of the trusts fell even faster.  The crash marked the beginning of a five year depression in aviation manufacturing.

Perhaps understandably, in view of the widespread wreckage of the crash, the slotted wing dispute remained quiet until 30th July 1930, when Sempill used the occasion of a speech by McKinnon-Wood to point out that the latter had in fact invented the automatic slot before Handley Page.  That triggered a letter a fortnight later from Thurston[227] protesting that he had ante-dated McKinnon Wood.  Sempill and Pritchard both showed signs of guilt, the latter writing " ... I hold no brief for Thurston, but I do feel somehow that he is not being treated fairly."  However, McKinnon-Wood, to whom Sempill copied Thurston's letter for comment, now felt under direct attack himself and acted to close down the debate: "I sympathise with your desire for further understanding of Thurston's position, but it will be an unpleasant and difficult task to clear it up."  With only a little of his term as President remaining, Sempill was persuaded to let sleeping dogs lie.


Lachmann enters the fray

Until that time, Thurston’s quarrel had been with Handley Page, but when Gustav Lachmann returned to the UK, it was perhaps inevitable that he would be drawn in.  After the First World War, Lachmann had studied under Theodore von Kármán at Aachen University, and his doctoral thesis, unsurprisingly on “The slotted wing and its importance for aviation”, was accepted in 1923.  During this period, he carried out paid research for Handley Page at Prandtl’s Göttingen Aerodynamic Institute.  Subsequently, he worked for Opel, then Schneider, then Albatros (where he designed a slotted wing aircraft), and over 1926-1929 he moved to Tokyo where he worked for Ishikawajima as designer and test pilot.  He married the widow of a British diplomat there, and the couple then moved to the UK where Lachmann was hired by Handley Page, becoming his chief designer and loyal friend.

Lachmann (1932) gave an impressive talk on the slot to the R.Ae.S on 17 December 1931 (for which they awarded him the Taylor Gold Medal) in which, amongst other things, he discussed wingtip slots.  However, prepared for battle, Thurston made an intervention in the subsequent discussion.  He had brought a slide carrying a drawing dated 13th July 1921 and initialled by Alex Houlberg, of a wing fitted with an alula; he discussed this, and also the functions of alulas in bird flight.  Lachmann however denied that the alula could have "any noticeable stabilising effect."  "In answer to Dr Thurston, he said that in the picture of the very large birds Dr Thurston had appeared to see only the alula, whereas he had been most struck by the multi-slot feather formation at the ends of the wings." 


Thurston’s Rotary Thumbs

Thurston had by no means given up on aeronautical research.  His next development, dating from early 1929, was another high lift device, but one that owed something to the autogyro (or autogiro), the revolutionary flying machine with freely rotating rotor blades developed in the 1920s by Don Juan de la Cierva y Cordoniu which was immune from “stall and spin” crashes.  Perhaps the most famous example is “Little Nelly”, the Wallis WA-116 Agile machine used by James Bond in “You Only Live Twice”.  In a typical autogyro there are no wings, and the rotors form the main aerofoils providing lift.  However, Cierva’s earliest experimental models retained rudimentary wings and an aircraft chassis, which may have given Thurston the seeds of his own idea: to use rotors (just two blades per wing) not as the main aerofoils (as Cierva did) but as wing-mounted auxiliary aerofoils equivalent to his “rider planes”.  At low wing inclinations, the rotors remained extended along the wing so as to define something like a slot.  At higher inclinations of the wing, the rotors started to spin, providing lift.  If an aircraft stalled, the spinning rotors would control the descent like a helicopter or autogiro.

The development apparently began with some experiments at East London College, the department he had founded two decades earlier.  Young[228] includes a picture of the model plane Thurston tested in 1929.  He filed seven provisional patent applications between 6 April 1929 and 8th July 1929, when he filed a complete specification which was accepted on 30th July 1930 as GB 331283; later patents were GB 377178, and GB 432195.  Meanwhile, he disclosed his line of research to Flight magazine, which published some details over summer 1930[229].  He gave a more substantial presentation at the fifth International Air Congress September 1-6, 1930, The Hague, entitled "The Thurston Rotor Thumb Control."[230] 

His correspondence with the Aviation Ministry from late 1930 to 1933 is available at the National Archives.[231]  Initially he had an unsympathetic reception from some quarters – “it will be clear that Dr Thurston is still harping on his alleged bad treatment in the past”, says a Minute dated 6 December 1930[232] - but his acquaintance with Air Vice Marshall (as he then was) Hugh Dowding[233], to whom he repeatedly wrote, ensured him an audience.  Thurston wanted the Ministry to make comparative lift tests against the slotted wing.  He wanted to be personally involved, and even to be paid at his hourly rate as a patent agent, but neither condition was acceptable to the Ministry; nonetheless, they tested his invention.

The initial results by the National Physical Laboratory[234] concluded that there was not much additional lift, but an undoubted increase in stability - the stabilising effect was similar to a “good tip slot”.  This came at a price since the mechanism was more complex and delicate than the slotted wing.  The Ministry wrote to Thurston on 20th June 1932 to tell him that, accordingly, they planned no further research or development.  There was also a compelling commercial disincentive, as Harry Wimperis said in a Minute of 27th September 1932[235]; having recently paid Handley Page a large lump sum for unlimited use of slots, there was no incentive to spend money on alternatives, and the rotor “appears to have no advantage over [the automatic slot] whilst possessing the disadvantage that we are now free of patent royalties for the latter & should not be for the former”. 

Thurston wrote to Dowding on 15th November 1933 requesting permission to use the Ministry tests to support his public claims for the rotor: “You will appreciate that in view of my past experience, it is necessary to secure publication of the skeleton results at the earliest possible moment but of course with the minimum leakage of information as to how these results have been obtained.”  These results, reproduced verbatim, would form part of his short R.Ae.S paper in January 1934, entitled "Thurston wing-tip rotors; control beyond the stall",[236] – the title was clearly a reply to Lachmann’s paper “Control Beyond the Stall” given two years earlier, but there was no other attempt to raise the old controversy.

That paper warranted a full page report in the Evening Standard[237], but despite the Press interest, the Ministry themselves remained unpersuaded.  Thurston protested to Dowding on 3rd March 1934 (in terms that constitute a disguised criticism of Handley Page’s conduct) that he would make the invention available free: “As a patent agent and late member of the Examining Staff of the Patent Office and also the Air Ministry, I am averse to making a profit out of my inventions, but I should like the Air Ministry to benefit.  I am prepared to make over the rights in the patent to the Air Ministry provided that suitable steps are taken to carry out adequate experiments.[238]  They declined even these generous terms.  Nor was he likely to find private sector interest; although an alternative to the slot would once certainly have been attractive, at this stage it would inevitably have taken some years of development to engineer his inventions to production, whereas Handley Page and Lachmann’s basic patents would expire in the same timeframe, after which the slot could be used free of charge.


Tailless aeroplanes

German rearmament placed Lachmann under suspicion.[239]  Though neither spy nor Nazi, Lachmann was a patriot, decorated in the First World War, who visited Germany and Japan and discussed aeronautics openly there (as scientists and engineers will).  He was certainly in a difficult position; Prandtl (and many others of Lachmann’s German colleagues and friends) were forced to make hard choices during the “Germanisation” of physics and aeronautics, drawing the line at joining the Nazi party, but acquiescing in the removal of Jewish co-workers and cooperating actively with Goering’s Air Ministry during rearmament and war.  All his post was intercepted after 1933, and Handley Page was ordered to remove him from any military work, and ultimately from his post, which (after some years of prevarication and resistance) Handley Page eventually did.  Thereafter, he performed semi-detached research work.

From the mid-1920s, whilst at Westland, Handley Page’s former aerodynamicist on the slotted wing Geoffrey Hill had developed the Pterodactyl, a tailless, stable aeroplane with wingtip controls reminiscent of Thurston’s (Stewart (1966:183-195)). In 1936, Lachmann himself started a tailless aircraft development program at Handley Page, initially in collaboration with Westland but then alone.  This resulted in a design capable of “Autogiro-like descent”, having a canard structure with a fore-plane, with “elevons” functioning both as ailerons and elevators – all features reminiscent of Thurston’s inventions.  The design is described in GB 497969[240].  According to Barnes (1987: 425) Lachmann at that time described the foreplane as a “rider plane”, although the patent refers to it as an “auxiliary plane”. 

When War arrived, Lachmann was taken to Lewes gaol, held in poor conditions and then interned for the rest of the War.  Unsurprisingly, his sympathy for the UK evaporated and he refused to cooperate in the War effort.  However, he evidently continued to think about tailless machines because on 23rd March 1944, from his prison camp on the Isle of Man, he filed a provisional application which was granted in 1946 as GB 575538.  This patent does use the term “rider plane”.  Given that, otherwise, the term was and is used only by Dr Thurston, or in relation to his ideas, influence and borrowing of ideas from Thurston seems the only explanation. 



From the mid-1930s, thanks to the slotted wing patents, Handley Page Ltd were ready to meet the challenges of rearmament and once more became the RAF’s major supplier of heavy bombers, notably the Halifax.  Knighted in 1942, Sir Frederick Handley Page was awarded many honours in his later career, amongst them, Lord Lieutenant ship of Middlesex, 1956-60; Officer de la Légion d'Honneur; Officer de l'Ordre de la Couronne, Belgium; the WGL[241] Ludwig Prandtl Ring, 1960; the RSA Albert Gold Medal, 1960; and the R.Ae.S Gold Medal, 1960.  After the Second World War, he strongly resisted governmental plans (with which McKinnon Wood was closely associated) to restructure the industry, and his company remained independent.  Independence limited their ability to develop new aircraft, however, and in 1970, eight years after the death of Sir Frederick, the company entered voluntary liquidation.  The Jetstream, the aircraft which had in part caused the collapse, was eventually taken over by BAC.  Their voluminous archives, including Sir Frederick’s correspondence, were preserved and are now at the RAF Archives in Hendon.

On Lachmann’s release after the War, he re-joined Handley Page (who had campaigned against his internment), where he worked and published on boundary layer devices, his lifetime interest.  His last favour for his friend was a posthumous appreciation of his life and works[242].


A Dish Served Cold

Through the dispute with Handley Page, Thurston had lost credibility in some quarters, but he had reconnected with aeronautical research and presented and published in the field once more.  Around 1930, he became involved in the massive task of editing Molesworth’s Pocket-book of Useful Formulae and Memoranda for Civil and Mechanical Engineers,[243] a venerable standard reference text, for which he remained responsible over the two decades between the 30th (1931) and 34th (1951) editions.  From it he carved a specialist book, Molesworth’s Aeronautical Engineer’s Pocket-Book, which ran to two editions (in 1942 and 1947).  During his editorship, engineering was in a state of permanent revolution, so that every edition involved expansion and review, and the 34th edition (undertaken between 1944 and 1950), was a complete re-write growing to 1700 pages.  The royalties must have been a convenient stream of income, as he made specific provision for them in his will.  He published a few more articles and patents on aeronautics, but his post-War business was now in patent agency. 

A public acknowledgment from Riabouchinsky (1935) of his contribution to the development of the slot heartened him, and as time wore on he became an object of historical curiosity for his recollections of early aviation, enabling him to publish his version of events at last to a new generation.  He first did so in 1942 before the Newcomen Society.  By that time, most of Handley Page’s patent portfolio was dead or sold, and all his efforts were directed to the War, so that Thurston’s attack drew no response.  He repeated it in 1949 – probably in response to the publication of Forty Years On ..., commemorating the fortieth anniversary of the foundation of Handley Page Ltd – and again in 1953,[244] and in 1954 when he made his complaint explicit at last by naming names – "The above description shows how I came to discover the value of rider planes and automatically opening rider planes thirty five to forty years ago which discovery predates the so-called "slotted wing" of Handley Page."

He outlived Handley Page by two years.  After his death, an editorial in The Aeroplane on 23rd April 1964 suggested posthumous publication of his 1928 article.  Prompted by his widow, and by Sir Hugh Lloyd[245], the R.Ae.S took the suggestion seriously enough to consult various worthies[246], but the consensus was against it.  She died soon after, and the pressure to publish evaporated, but the sympathetic obituary by Pritchard (1965) containing a brief anatomy of the dispute, the acknowledgment by Stewart (1966) which put him on an equal footing with Handley Page, and the balanced articles by Young (1964, 1966) went a long way to restoring his place in the pantheon of aeronautical pioneers – without criticizing Handley Page.  Susannah Thurston left £4,000 to Queen Mary College, to be called the Dr Peter Thurston Memorial Fund.  The couple were buried at Over Wallop, home of the School of Army Aviation and the Museum of Army Flying, and a wide-grassy airfield still used for model aircraft races. 


Thurston redux?

In several areas, Thurston’s views have become accepted.  Whether he deduced the function of the slotted wing from that of a bird’s alula or vice versa, he seems to have been the first to see the analogy between the two (so hotly denied by Lachmann in their 1931 debate).  The slot/alula analogy was shortly to gain widespread acceptance following Graham (1932).  Graham, like Thurston, claimed that both the wingtip pinion feathers and the alula functioned as natural slot mechanisms, and that the latter was pulled into position on stall so as to function like the automatic slot.  Though doubted by some[247], this view has recently been fully validated in wind tunnel tests, by Meseguer (2005), and by Austin & Anderson (2007) – though Thurston has not received the recognition he was due because of the suppression of his 1928 paper.

High lift devices have seen something of a comeback since Smith (1974), with increasing interest in wingtip structures.  Of several similar systems, the Winggrid system[248] (a fanned winglet wingtip with parallel blades) of La Roche & La Roche (2004, 2005) most clearly resembles Thurston’s patented wingtip pinions, and they have acknowledged their debt to him in their papers on the project.


The answers to the priority puzzle

It ought now to be possible to resolve the Thurston controversy dispassionately.  It is clear that he was neither a crank nor a monomaniac, but a man who believed in his claims, pursued them strongly and felt that he had been ill treated as a result.

Some elements of his claims are based on his uncorroborated recollections.  That is not to say that they are false.  According to Young, he had an "astonishing memory"[249], he seems to have been a generally truthful man by nature (“his sincerity was as transparent as his humanity”, according to Air Chief Marshall Sir Hugh Pughe Lloyd[250]), and he was professionally required as a patent agent to be truthful.  His claims were made for personal, not financial, reasons and whilst he stood to gain credibility and esteem if he could make his case, equally he stood to lose them in spades if he seemed to lie.  No one other than Handley Page and his supporters seems to have suggested that Thurston was falsifying his account.  Rather than lies, we have therefore to contend merely with the usual distortions to which memories are subject as the events recede into the past, and the artful vagueness and ambiguity in use of language which a good patent agent acquires in practice.

The narrative theme of his 1928 paper, that he first observed the slot-type behaviour of the alula and then designed his experiments to validate it, is however at odds with the evidence of his earlier contemporaneous papers.  These suggest that in 1911 he was re-thinking canard-type aircraft by moving the rider plane so close to the main wing that the latter lay in its wake; he published nothing concerning the alula, and cited no evidence that he had discussed it, until his 1920 patent filing.  The early deductions on bird flight that he claimed preceded his 1914 paper are vaguely stated and not even vaguely dated, and might in fact have been based on observations made as late as Summer 1914 when he was in the tropics, or even 1920 when he returned there recovering from his severe work-induced illness.  Remembering the date and sequence of thoughts and inspirations is much harder than doing so for events, and it is therefore likely that by 1928 Thurston's certainty that he had priority led him to misremember the sequence of the links in his chain of reasoning. 

As to whether Thurston invented "the slotted wing" (referring in a narrow sense to the anti-stall device so brilliantly marketed by Handley Page), even he said on one or two occasions that he laid no claim to that per se.  Did he invent it before the First World War ended?  It seems most improbable.  It is true to say, as he did, that he would have been in no position to patent such a discovery, but had he known it then he would probably have drawn attention to it in his 1914 paper, and (as Colonel Bristow pointed out in 1921) he was not a man to have allowed wartime pilots to crash had he known how to save them.  Indeed, it seems likely that from the outset he saw his "rider planes" primarily as control surfaces with secondary roles in conferring lift and stability. 

It is certain, however, that he was on the right track to discover the high-lift properties of the "slot", and that but for the War, had his patriotism not drawn him into the Forces, he might have done so before Handley Page and Lachmann.  His theoretical understanding of the mechanism of the stall was wrong, but not more so than Handley Page's, and his mental picture - that the phenomenon was due to two aerofoils in tandem rather than to a slot in one - was the sounder of the two. 

His 1914 paper comes very close to anticipating the claims of Handley Page's broadest patent.  Was the necessary data to be found, unpublished and unanalysed, in his test results?  There certainly was more data than that in the Flight article - the article itself refers to measuring the pressures on the rider planes.  However, he never offered any evidence of having discovered anything of greater relevance than his 1914 paper before the War, and in any event it is questionable whether the accolade of priority ought to be accorded to unpublished, unwitnessed work which gives nothing to the public in return.

As an explanation for the absence of publications between 1914 and 1921, Dr Thurston sometimes implied that he had been precluded from patenting his inventions whilst a government employee. It is certainly true that he could not have filed any patent applications before he left the Patent Office, the RFC and the Ministry.  As the eminent patent barrister Kenneth Swan[251] (1921) explained[252], this required official consent (not usually given).

The President “Supposing an expert in some department of manufacture had been compelled to go into the Army, and the military authorities recognised that they could best use him in the department in which he had the knowledge, and he went on with his own work in which inventions suggested themselves to him, as they would have done had he not been in khaki, what was such an expert to do? He was bound not to take out a patent without the leave of his commanding officer, and the Government had the first claim on the patents.  Assuming that he had an invention near the time of his demobilisation, was he to hold up that invention and wait until he could patent it in his own name?”

Mr Swan … “In the Air Ministry and, he believed, in all the other Ministries, official rules were circulated to the staff telling them upon what terms they were entitled to take out patents, and so long as they remained officials under the orders of the department they were bound to obey such rules.  It might become a very difficult and delicate question as to what a temporary official should do on leaving the service, and as to how far he was immediately released from those restrictions and at liberty to patent his ideas and inventions for his own benefit.”


Thurston was well aware of this position then and afterwards: in 1947[253] he said “Under the Defence Regulations, an officer, a soldier or a civil servant was not permitted to take out patents except under the regulations, and under Regulation No.  6 he must not even employ a patent agent” and in 1955: “The Government Departments forbade, or had in the past forbidden, the inventor to protect his own invention and had even prosecuted him if he had patented his own invention[254].”  He was also still on the Patent Office Examining Staff, and therefore under prevented for that reason also from filing patents.

Finally, there would have been the difficult question of who owned an invention made during his service in the RFC and the Air Ministry.

Dr. A. P. Thurston asked whether an invention which an employee made, having left the service of an employer, was the property of that employer and how many employers a man must be employed by before an invention which he made ceased to be the property of his original employer.

During the war many men with great inventive capacity and perhaps with inventions more or less developed, had joined Government Departments, and it seemed extremely unjust that the Government should claim those inventions because they had been made while the inventor was in Government employment.  What steps should such inventors take to secure the protection of their rights?[255]


However, the fact that he could not have filed patents earlier than he did is certainly no evidence that he was in a position to do so.

Is there anything in the charge that he took inspiration from Handley Page after the War?  The earliest date we have for Thurston's own work is October 1920, by which time some information about Handley Page's wing was available, but had he paid much attention to it, he would surely not have delayed his patent filing until December, nor made it look so different.  At that time he saw his invention primarily as a wingtip device for use in control, and for providing lift only on landing - something different enough in specifics that there is no reason to assume any copying of Handley Page.

As regards two narrower developments, the idea of wingtip slots and the use of slots for control, it is clear that Thurston pre-dated Handley Page.  This was the thrust of Thurston's argument, and he spoiled his strong case on these points by straying into broader claims.  Finally, there is his claim to have invented the automatic slot.  The references in his patent application to the alula or rider plane being mounted in balance certainly do not add up to a disclosure of automatic opening at a stall[256].  However, he supplied evidence of his 1921 work with BAC, supported to some extent by the named collaborators there.  He discovered that the "rider planes", if allowed to pivot, would take up an angle related to the angle of attack of the main wing.  That does not quite add up to the idea of allowing the slot to open at a stall, however.  Again, Thurston's research was work in progress; had it continued, it might have led to the automatic slot, but it did not get there, and whilst it demonstrates Thurston's gift for seeing the right direction, it does not entitle him to any priority. 

What of Handley Page?  Did he actually invent the slot, or did he derive it from elsewhere?  He was certainly technically astute enough according to Stewart, although by training an electrical engineer.  However, he was a self-publicist, who consistently blurred the line between himself and his company, and it is not unknown for research team leaders to over-claim, on the convenient assumption that funding, setting initial objectives, or participating in regular discussions is enough to enable them to lay claim to a whole body of research without acknowledging their co-workers. 

He also had a personal financial incentive to claim inventions for himself to the exclusion of others in the form of the substantial licence fee which he claimed from the company for "his" inventions.  That applied in particular to the slotted wing patents which were undoubtedly the most valuable assets owned by the company.  An indication of the scale of this incentive is given by the fact that when the company was restructured in 1927, he forwent £176,000 (a vast sum in the 1920s) which had been due for use of "his" patents.  He was also personally to benefit from awards made by the Royal Commission on Awards to Inventors. 

In Britain[257], Handley Page held all patents in his sole personal name until around 1919, at which time he and Handley Page Ltd became co-owners (a practice which would be improper nowadays, as a director is assumed to owe a duty to his company rather than vice versa), and every one of the twenty Handley Page Ltd US patents filed before 1930 named Handley Page personally as the sole inventor. 

It is strikingly implausible that such a hands-on head of such a large company should be wholly and solely personally responsible for making so many inventions over that period, whilst employing no one else inventive.  Moreover, during the precise period during which the basic slotted wing invention was apparently made, Handley Page must have been intensely busy in business fighting to revive his ailing company, and was recently married with a young family[258]– was it really possible for him to have personally constructed the theory, done the testing, designed the wing sections?  And in particular, was he personally responsible for the two key changes of direction that took place - firstly, the switch from chordwise slots to lateral slots, and secondly, the redesign of the slot as two close-coupled aerofoils?

As to the first of these, Sutton Pippard had in 1921 highlighted the surprising nature of the leap, and Handley Page's inadequate explanation in reply was phrased oddly impersonally - as if he had no first-hand knowledge of it; as if it were the work of another.  Nor was he more forthcoming later.  Even sympathetic writers have difficulty with Handley Page’s claim to the invention.  In his memorial lecture on Handley Page, Lachmann (1964: 440), who was best placed to know, said "I have never been able to discover in later years what reasoning prompted the drastic change from a number of chordwise slits to a single spanwise slit", and commented that Handley Page’s explanation "always struck me as construed post factum".  Stewart (1966: 114) calls it a “strange fact” that Handley Page’s invention was not inspired by anything in nature[259].  According to Miller & Sawers (1970), “It is not clear who among the Handley Page staff had the idea of trying the spanwise slot.”  Barnes (1987: 210) considers it is unclear whether the idea came “from Handley Page himself or Boswall or one of the carpenters”.  Given the surprising fact that no one at Handley Page Ltd seems to have claimed the credit, inspiration from Thurston cannot be ruled out. 

Young suggested that the change to spanwise slots might have been inspired by knowledge of Thurston's unpublished research, via perhaps the Research Committee of the R.Ae.S on which both sat as members.  That, however, is not the only possibility.  The War led to considerable interchange of information between companies, the Ministry and the Services, of which the Mooney affair, noted above, was one example.  According to Swan (1921: 71),

By virtue of their official position and the all-pervading powers of D.O.R.A[260]., these temporary officials, had access to every sort and kind of manufacture.  To receptive and reflective minds, the new processes and methods of manufacture which they had the opportunity of examining and the technical information placed unreservedly at their disposal in many cases suggested improvements and modifications which were clearly quite good subject matter for patent. …

An official who obtains a patent in such circumstances is exposed in a marked degree to the charge that he has obtained the invention from one or other of the manufacturers whose works he has visited.

… there is bound to be a large number of border-line cases in which it is difficult, if not impossible, to affirm that the invention is not due in some measure to information confidently communicated, or knowledge which the patentee gained from practical acquaintance with some specialised manufacture to which he has had access in his official capacity.


Handley Page was himself the subject of an accusation of this kind[261] by a Mr Mackenzie Kennedy, the inventor of patent GB 166184 of 1918, which described a large aircraft with a hollow tail having a pit for a tail gunner.  Kennedy had been in Russia before the War, where he had seen large aircraft designed by Sikorski.  He offered his idea to the British Government and supplied them with technical information, but got no contract.  Before he filed his patent, the Government had discussions with Handley Page on similar constructions.  Handley Page filed a patent of his own[262], and was subsequently awarded contracts for aircraft that would have infringed the Kennedy patent.

Kennedy (now bankrupt), and Rowlands (his trustee in bankruptcy) sued the Air Council for over £300,000, for both breach of contract and confidentiality and for use of his patent.  To maintain his patent as valid over Hadley Page's, he had to show Handley Page's to be invalid, on the basis that Handley Page was not the true inventor but had taken Kennedy’s idea via the Air Council.  After six years of litigation, Kennedy lost on all points. 

Whether or not such leakage did occur in Thurston’s case (and it is impossible now to know), the possibility would not have been seen as wildly unlikely in view of the Kennedy and Mooney cases.

The second change, from slots to aerofoils, can be dated to between the filing of Handley Page's provisional and complete applications.  The fact that the Complete contains a distinguishing reference to planes in tandem suggests quite strongly that someone was aware in the same period of Thurston's 1914 paper entitled “Aerofoils in Tandem”.  If this is the case, it seems legitimate to infer that the paper was the source of the view that the invention was a pair of tandem aerofoils close enough to form a slot (i.e. "overlapping") that could mitigate a stall.  The author of the patent, in other words, adopted Thurston's analysis but considered he had discovered a special case that was inventive over the general discussion and specific examples in Thurston's paper.  The timing coincides with the departure of Boswall and the arrival of Hill, which may also explain the change of analysis.

There are thus serious grounds for doubting that Handley Page was truly the sole inventor, whilst having ample economic motives for claiming to be.  However, playing fast and loose with inventorship was a high-risk strategy which would have potential consequences for the validity of his patents – not in the UK, where the role of the inventor in the context of patents was (and is) regrettably minimal, but in the US where declarations of inventorship are made on oath, and false statements can invalidate a patent and, potentially, lead to charges against the applicant and his attorney.  If there were something fishy about Handley Page's inventorship of the slotted wing patent, it would explain why he elected to suppress, rather than debate, Thurston's paper.

Handley Page certainly deserves the praise showered upon him for seeing the potential in the slotted wing and selling the technology so single-mindedly and successfully as a safety device.  Without his example and powerful backing Lachmann, like Thurston, would have abandoned his patent applications, and Thurston’s own work would probably also have been abandoned at an early stage.  However, in technical rather than commercial terms, he and his company were beaten to the slotted wing by Lachmann’s patent filing, Thurston’s 1914 experimental results preceded his own, and his contribution to the underlying theory was unhelpful.  Of the three, he therefore has the least claim to scientific priority to the invention he branded with his name.

Outside the narrow context of the patents, does it actually matter who invented the slotted wing first?  Some[263] question the very possibility of individual achievement on ideological grounds.  Others, noting the fact that many great inventions are made independently in the same timeframe by different workers, consider that ideas are just “in the air” and would inevitably be invented by someone.  To the historian interested in broad trends, priority disputes are an annoyance, as Gibbs-Smith (1966: xvi) complains: “The pursuit of minor details is rivalled, especially in aviation history, by the pursuit of “firsts”, which he calls “conundrums beloved of this modern variety of sophists.”  According to Gould (1977: 35), "debates about the priority of ideas are usually among the most misdirected in the history of science."  However, no matter how irksome historical priority claims may be, there is no doubt that priority is deeply bound up with the self-esteem that drives a great scientist or engineer. 

Scientists and engineers are rarely motivated primarily by wealth – almost any other way for an intelligent person to make a living is faster and surer for that purpose.  Original research and development is what attracts scientists and engineers.  Priority demonstrates originality.  Recognition of priority by others is what propels scientists towards publication (to the benefit of the community as a whole), as sociologists of science have long argued.[264]  Where several workers (or teams) pursue the same goal, being first, having the priority, matters to scientists and engineers, as a claim to fame that time cannot tarnish.  As well as being a desired end in its own right, priority has economic implications: recognition attracts sponsorship enabling future research, and thereby reinforces the likelihood of future recognition.

For many classes of engineer, the opportunities for recognition are rare.  Too often, good work is recognised, if at all, only in an obituary.  The self-esteem of technologists, whose work is usually ignored or misunderstood by society at large, is therefore wholly within the gift of their peers, and the embodiment of the peer group is the professional scientific or engineering society.  According to Belden (1991), “Rewarding service or accomplishment is certainly one of the central roles of a professional society. In the process of providing those awards for technical or scientific accomplishment, we validate innovation. We recognize an accomplishment as of major import in the history of its particular technology or engineering. Certainly the marketplace may have already said "this is an important development," but recognition by peers is a completely different kind of reward to the innovator. It proclaims that those who know, those who understand the process, recognize the individual's great achievement.” 

In the close-knit early aviation community, like many at the cutting edge, pioneers knew each other personally and all who mattered were members of the R.Ae.S.  The disputes in 1921 and 1928 were therefore of importance for both the main contenders in this tale.  For Thurston, a proud man, the perceived lack of professional recognition was coupled with implied stains on his honour and honesty, which were keenly felt.  Although Handley Page was also a man of pride, the slotted wing dispute was for him a matter of sales and profits more than science and engineering, as Lachmann (1964) makes clear: “When I reminded HP before his death how successfully we had spread the slotted wing gospel throughout the world he gave me a sad and wistful look and said "But Lachmann, the patents have expired."”. 

It is easy to sympathise with the Society’s 1928 dilemma, but their process left Thurston, and many like-minded sympathisers, with a very long-standing grudge, manifesting all the symptoms of a breach of natural justice.  Even officers of the Society felt that injustice had occurred - decades later, Pritchard (1965) was to write "The situation was one, in my opinion, which did little credit to the Council, an opinion I still hold", and Frank Nixon (a Rolls Royce engineer) added that "...the action of the Council in suppressing it and canceling the meeting was, to say the least, extraordinary." 

Nowadays, we would make a number of criticisms of their process:

         Thurston's paper carried a disclaimer from the Society indicating that it did not represent their views; publication was therefore a matter of editorial judgment with which the Council, like all magazine proprietors, should have been slow to interfere;

         Thurston should have been allowed to present his case with “equality of arms” to Handley Page – as it was, the latter got the first and last word in writing, and dominated the discussions from which Thurston was excluded;

         Handley Page, having declared a purely commercial interest, should not have voted;

         Brewer, McKinnon Wood and others with commercial connections with Handley Page (or Thurston) should have disclosed them, and ought not to have taken part in the decision (as Thurston said at the time);

         Account of the balance of harm should have been taken.  According to Handley Page, the consequence of allowing a discussion would have been a test of credibility between Thurston and others (chiefly himself), of which he ought to have had no fear, whereas cancelling his talk and suppressing his paper would seriously damage Thurston's credibility.

And as it happens, in this case, Handley Page was wrong (and perhaps cared little) about the underlying science of the “slot effect”.  Even his persistent use of the term “slot” (largely for branding purposes) contributed to the longstanding confusion about the underlying mechanisms.  Suppressing critical debate on the slotted wing was not only bad for Thurston but, possibly, bad for science.  It assisted Handley Page and Lachmann's erroneous view that it was a boundary layer blower to dominate for several further decades.  Thurston himself clearly did not know the answers unearthed after his death by Smith in 1974, but years of experimenting with smoke and springs, ribbons and string, close observation of bird flight, and actual piloting experience, gave him a better feel than his opponents, so that according to Stewart (1966: 125), he "had probably understood the slot effects better and more clearly than those who actually introduced them into practical aviation."  In this case, then, measures taken to suppress dissent in the interests of advancing science were, perhaps predictably, capable of having precisely the opposite effect – science is advanced by open discourse and even by controversy.  On this, at least, Thurston was undeniably right.



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Young, Professor Alec D (1961) – "Queen Mary College, University of London: The First in a Series of Articles Describing the Facilities, Academic Curricula and Research Activities in the Aeronautical Engineering Departments of the British Universities", Aircraft Engineering and Aerospace Technology”, Aircraft Engineering, 1961, 33:9, 270-273, DOI: 10.1108/eb033454


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·         Royal Aeronautical Society


·         Handley Page Association   


·         Flight Magazine archive


·         Espacenet free patent database


·         Newcomen Society




Thanks are due to Brian Riddle, omniscient librarian and archivist at the R.Ae.S, for pointing me towards much of the material reviewed; Professor David Bloor of the University of Edinburgh and Ian Whitehouse of Airbus UK for their helpful comments and suggestions; the enormously helpful staff of the RAF Museum at Hendon; Colleen Hunter, the librarian at Elsevier’s Engineering Village, for her assistance in searching the impressive Compendex Backfile; and all those who put the archives of Flight magazine online for free – an invaluable resource.  All errors are, of course, entirely my own.


[1] The Wright Brothers in 1906, quoted in "Back to the Beginning", Flight magazine 28th October 1948 505-507

[2] The Aircraft Engineer, 24 Jun 1926 (quoted in "The Handley Page Slot-and-Aileron Lateral Control", Flight magazine, 10 Mar 1927 150-151)

[3] In Forty Years On …, Handley Page Ltd, 1949

[4] A right-winger forced to resign as Foreign Secretary in 1936 over his plans to divide Abyssinia with fascist Italy; he was sacked as a Minister in 1940 by Churchill.

[5] In Forty Years On …, Handley Page Ltd, 1949

[6] Letter of 2nd July 1964 to Pritchard

[7] Flight magazine, April 1964

[8] Major Oliver Stewart, M.C., A.F.C (1895 – 1977), test pilot, fighter pilot, editor of Aeronautics over 1939 to 1962, specialist aviation writer and broadcaster, and commentator at the Farnborough Air Show

[9] Stewart (1966: 126)

[10] At

[11] Alec D. Young (1913-2005), accident investigator, OBE, FRS, FEng FAIAA Hon.FR.Ae.S, A.F.I.A.S., Emeritus Professor of Aeronautical Engineering and and Vice Principal, Queen Mary College, University of London, Chairman of the Aeronautical Research Council and of the Board of the Von Kármán Institute, R.Ae.S Gold Medallist.  Obituary; The Times February 3, 2005

[12] One in the Science Museum and one in the Patent Office Library, now, sadly, absorbed into the British Library at Euston.  No copy of the paper exists on their catalogue.

[13] Although it was made available for historical research after Thurston's death

[14] Such as the RAE-designed BE2c

[15] Who had made the first practical helicopter demonstration flight in 1938

[16]  referring to The Dutch Windmill, author Frederick Stokhuyzen (1891-1976), trans. Carry Dikshoorn, and Comparative Wind Tunnel Investigation of Sail Profiles for Windmills, Technische Hogeschool Delft (Netherlands) Fauël,P. L., Feb 1975

[17] Young (1966)

[18] McElney (2001), Needham et al

[19] See, for example, Gentry (1981).  Some (McKenna (2003)) give the honour of invention to Sven Salén (1890-1969), 1927 Olympic 6-metre sailor, but it is also clear that Dr Manfred Curry (1899–1953) and Sir Charles Richard Fairey, the aircraft manufacturer, both experimented in 1928 with overlapping jibs in explicit imitation of the slotted wing; see (Curry 1928), and The Times 1st June, 29th December 1928, respectively.

[20] Smith (1974)

[21] See for example Munk (1934)

[22] Prandtl (1904)

[23] for whom the Prandtl number and the Prandtl crater on the Moon were named, see

[24] See for example Prandtl & Tietjens (1934) p153

[25] Most umbrellas harbour secret ambitions to become airborne in a stiff breeze!

[26] See Young (1966), and Thurston (1949b)

[27] Penrose (1970)

[28] He is equally savage about Langley, Adler and almost everyone else who might be considered a contemporary of the Wrights.

[29] Maxim (1891)

[30] Though some give that honour to Clement Ader’s steam-powered bat-wing airplane the Eole, which is alleged (with little independent attestation) to have flown in 1890 - his claims about a subsequent flight in 1897 have been found to be inflated.  Some also make the claim for the Brazilian Santos Dumont’s 1906 “14-bis” flight – see

[31] Aeronautics, 7 Aug 1919

[32] Thurston (1911a)

[33] On which he served together with Major Low, Handley Page, Melvill Jones and Mervyn O’Gorman, who will reappear later.

[34] He was later to return to Kingston, Jamaica, in early 1920

[35] Thurston (1949b)

[36] GB 140531, GB 142895

[37] Thurston (1919)

[38] Pamphlet No. 34 Published on July 26th, 1919

[39] All-metal construction, turbines, use of servo-motors, automatic landing gear, giro control, directional radio (i.e. radio direction finding).

[40] Nuclear aeroplane engines, anti-gravity

[41] GB 153180, GB 154431

[42] GB 163559

[43] Trans. CIPA 16 December 1921 Discussion on Mr O’Dell’s Paper p119

[44] Thurston (1949b)

[45] Letter Susannah Thurston to Sec R.Ae.S 20th June 1964.

[46] obit Newcomen society

[47] Thurston (1942)

[48] (1856-1919), author of the books The Flight of Birds and The Structure and Life of Birds

[49] 18th March 1910 – it followed the Annual General Meeting, so there is every likelihood that Thurston attended the lecture – reported at Aero J XIV Apr 1910 62-72

[50] Latin: “winged one”

[51] Also at Aero J XVI Apr 1912 70-84.  Hankin reached the rather surprising conclusion that soaring birdflight was due to sunlight, trapped in the air and released by the passage of a bird’s wing, in the form of a changed molecular structure he called “Ergaer”!

[52] Rather than at the tail – this design was falling out of favour by 1911 but is now used on high-speed planes and also on modern home-built aircraft – see Thurston (2000) (no relation)

[53] These two last requirements are exactly the opposite of what Handley Page’s slot patent describes.

[54] Thurston (1911b)

[55] Discussion of paper by Major B Baden Powell, Proc. Junior Institution of Engineers, Vol XXI, 1910-11, p350-352

[56] According, consistently, to all subsequent accounts by Thurston

[57] Thurston (1914)

[58] Letter of 3rd December 1928

[59] Thurston (1942)

[60] Doubted, however, by Barnes (1987: 5)

[61] An extreme right-wing pilot-turned-demagogue MP and founder of Supermarine Aircraft, later involved in a scandalous libel case over his article “The cult of the clitoris” – see Edgerton (1991).  The case is brought to life in The Maud Allen Affair, Russell James, Remember When publishing, 2008

[62] Edgerton (1991)

[63] For example, as shown in GB 1908/17150

[64] Described in Flight Magazine 26 Oct 1912 p962

[65] There is no mention of Weiss in Forty Years On...

[66] Handley Page (1911)

[67] Forty Years On...

[68] Forty Years On...

[69] Handley Page v Butterworth (H M Inspector of Taxes) (1935) 19 TC 328 (HL)

[70] See National Archives files TS 28/40, TS 28/41, TS 28/42

[71] Times obituary

[72] Flight magazine, 3 May 1962 "HP"

[73] See Cook (2003) and Edgerton (1991)

[74] See also Jeremy (1984); non-conformist backgrounds and technical apprenticeships were also not uncommon at that time.

[75] Reprinted Kessinger Publishing 2007

[76] The firm itself, founded in 1844, continued until the 21st century (initially under his son), being ultimately absorbed without trace by Harrison Goddard Foote

[77] Brewer (1931)

[78] Turner (1927)

[79] Flight magazine, 11 March 1948, 287

[80] Setting aside Maxim’s accidental flight

[81] Where Charles Rolls died in 1910 flying a Wright plane

[82] Though there are earlier contenders for the invention of ailerons – amongst others, Dr Thurston cited UK patents GB 1868/00392 and GB 1870/01469, and David B Thurston cites Louis Pierre Mouillard’s 1897 patent US 582757

[83] British equivalent patent GB 1904/06732.  The German equivalent was refused as lacking novelty.

[85] Turner (1927); Flight magazine, 3 Jun 1948 "The Outlook"

[86]With the Wrights in AmericaFlight magazine September 3, 1910, see also “Early Flying”, Letter to The Times, Thursday, May 31, 1928; pg. 10

[87] Brewer (1931) - Thurston was almost certainly in the audience, as he was elected a Fellow of CIPA at that meeting

[88] For whom NASA’s Langley Research Centre is named

[89] Aero J Vol XXV Dec 1921 620-664 - the paper generated furious controversy, drawing written interventions from Walcott, Curtiss and others to which he robustly responded; Handley Page supported Brewer and the Wrights although he was at that time being sued under the Wrights’ US patent.

[90] Article in the 1942 Smithsonian annual report, published as Abbot, C. G. “The 1914 tests of the Langley Aerodrome”. Journal of the Aeronautical Sciences, vol. 10, no. 1 (January 1943), pp. 31-35

[91] Forty Years On... "Aeronautical Panacea" Chapter

[92] Handley Page (1921a).  Boswall (1884-) had been a lecturer at Northampton Institute with Handley Page before the War; he left Handley Page to return to academia at Manchester before the beginning of 1920

[93] Later to pioneer variable sweep wings, and to design the Pterodactyl, discussed below, and eventually professor of engineering at UCL

[94] Handley Page (1911)

[95] Handley Page (1921a), Figure 3

[96] Handley Page (1921a), Figure 4 “early type” slot

[97] Klemperer (1921)

[98] Katzmayr and Kirste in Lachmann (1921)

[99] Fearon (1990)

[100] See, for example, EPO Enlarged Board of Appeal decision "Same Invention" G02/98, [2001] OJEPO 413, [2002] EPOR 17

[101] See, for example, the House of Lords’ judgment in Asahi’s Application [1991] RPC 485

[102] Adopted in England before 1852, abandoned there in 1978, but still in use in Australia and New Zealand and, sadly, recently adopted in the US.

[103] According to CIPA's “Blue Book” The Patents Acts 1949-1961 2nd Ed at p22

[104] Including Handley Page v. Leach 35 F. Supp. 856

[105] Edited by Charles Grey Grey (1875-1953), a consistent Handley Page supporter who described him as "one of my oldest friends in aviation" shortly before his enforced resignation (Grey (1939)).  His consistent policies, according to Edgerton (1991), were "support for the dictators, strong rearmament in the air and a gross anti-semitism".  He appears together with Noel Pemberton Billing in The Maud Allen Affair, Russell James, Remember When publishing, 2008

[106] Manually variable slots were only demonstrated later, in 1922

[107] The UK Patent Office did not, at that date, publish or make available the Complete Specification as filed, but since the US and French texts are identical and both lack matter present in the UK text, it is reasonable to infer that they correspond to the originally filed UK text prior to amendment

[108] Present also in the foreign texts and hence probably present on UK filing

[109] GB 20173/09 (William Tattersall), GB 559/12 (George Howard Short), GB 2642/12 (Baronir Hovanes Balassanian, 1876-, an Armenian mining engineer resident in the UK), and GB 13150/13 (Gustave Garnier)

[110] As US 1353666.  Granted in under three months, it cannot have been seriously scrutinised.  See also equivalents FR 521895 and DE 357735.

[111]The Handley Page Wing: first Public Demonstration”, Flight magazine, 28 October 1920

[112] A leading light in the SMAE and other model aircraft associations, and the Modelling Committee of the R.Ae.S, with whom that year Thurston had planned the rules of the Wakefield Cup challenge – Thurston credits him in his 1928 paper with longstanding support and assistance, at which time he worked at Morris Motors.

[113] Letter of 14th August 1928 to Handley Page

[114] Published as Parliamentary Papers (Blue Book) Cmnd 1157, HMSO 1920 or 1921, quoted by Thurston in his letter of 3rd December 1928

[115] 135116/20, published in Patent GB 180359

[116] Corresponding respectively to the alula and to the pinion feathers of a bird’s wing

[117] His letter is quoted verbatim by him in his later letter to the R.Ae.S of 3rd December 1928, discussed below

[118] Under reference 55/772/21/A.IB; again, the letter is quoted verbatim by Thurston in his later letter to the R.Ae.S of 3rd December 1928

[119] DNB entry

[120]The H. P. wing and Germany”, Flight magazine, January 13, 1921, translation of an article in Flugsport magazine

[121] Reported and translated in “The H. P. wing and Germany”, Flight magazine, January 13, 1921, translation of an article in Flugsport magazine

[122] In apparent breach of the 12-month priority term under the Paris Convention

[123] “Zeitschrift fur Flugtechnik und Motorluftschiffahrt” magazine 15th June 1921 translated as “Experiments with Slotted Wings”, NACA Technical Note 71, November 1921

[124] Fearon (1990)

[125] Ibid

[126] Stewart (1966: 124)

[127] Handley Page (1921a)

[128] Handley Page (1911) and another

[129] Alfred John Sutton Pippard FRS, F.R.Ae.S (1891-1969) worked for the Air Ministry during the War, then became Visiting Lecturer at Imperial College, and, in 1922, Professor of Engineering at University College Cardiff, returning to Imperial in 1933 as Professor of Engineering and Head of the Civil Engineering Department; he was President of the Institution of Civil Engineers over 1958-1959.

[130] Referring, presumably, to his patent GB 1902/27027, which shows a wing-flapping monstrosity having variable pitch vanes.  Some more information is in his paper at Aero J VIII Jan 1904, 23-25.

[131] Flight magazine, 22nd November 1922 Correspondence, William Cochrane [2062] “Scrap The Lot

[132] Flight magazine, 13th June 1930 Correspondence, William Cochrane [2316] “Flying Sticks

[133] M.I.E.E., M.I.A.E., F.R.Ae.S, of Ogilvie & Partners, consulting aeronautical engineers, founded by Lieutenant-Colonel. Alec Ogilvie (a pioneer flight enthusiast,under whom Thurston had served).

[134] (Barnes 1987:164-166)

[135] As the discussion in his own patent GB 157567 reveals.

[136] No. 6321/21, published in Patent GB 180359

[137] Thurston (1954)

[138] Number 21,596/21 – never published, and now no longer available from the Patent Office, but it is referred to in the text of GB 180359 and reprinted apparently verbatim in Thurston’s suppressed 1928 paper.  It is also substantially reproduced in Thurston’s later patent GB 310988.

[139] A more attractive trade mark than “bastard wing”, the term Holle used throughout his patent

[140] The text is not in the US equivalent patent, US 1466551

[141] “Marco Polo” (1917)

[142] “Marco Polo” (1920)

[143] A copy of the article, containing reminiscences of people he knew, is present in his R.Ae.S file

[144] From the clues given in his letter, "Wing Tips" himself seems to have been Stanley H. Evans, F.R.Ae.S., A.F.I.Ae.S, a wartime flyer, later an aircraft designer with Koolhoven, Gloster, Handley Page, Douglas and Northrop and chief designer of Folland Aircraft; then dean of the engineering school in the Curtiss-Wright Technical Institute, Glendale, and Director of Engineering at the Ryan School of Aeronautics, San Diego, California; American correspondent of Flight magazine for many years.

[145] Flight magazine, January 26th 1928 Correspondence [2168] The Case for the Cantilever Wing

[146] Fearon (1990)

[147] US 347884

[148] Professor Dimitri Pavlovitch Riabouchinsky (1882-1962)

[149] (Tschaplygin, Tchapliguine), (1869-1941), later to write “On the general theory of a monoplane wing,  A theory of the slotted aeroplane wing”. Paris, Gauthier-Villars, 1929, originally published 1921 – this indicates that his theoretical work began before the war and refers to his 1914 article "A theory of the Latticed Wing" published in “Mathematical Methods” in Russia.

[150] Quoted in Smith (1974), footnote on page 504

[151] Dictionary of Ulster Biography,

[152] Article in the Journal of the Royal Society of Arts

[153] GB 310966, claiming French priority of 5 May 1928

[154] GB 1912/06564, equivalents CH 60669, AT 62329B

[155] Notes, R.Ae.S J XXIX Oct.1925 543-547 at 547

[156] Correspondence, R.Ae.S J XXIX Dec1925 648-649

[157] A History of Aerodynamics, John D Anderson Jr, Cambridge University Press p367

[158] Published as US 1600834

[159] He described the invention as "something that Handley-Page secured more or less through a German prisoner of war".  He also claimed that he "had an adjudication of the Patent Office that my invention was prior".

[160] Lachmann (1921)

[161] Ibid p175

[162] Later to be a professor, and Prandtl’s successor, at Göttingen

[163] Quoting Prandtl & Betz, “Ergebnisse der Aerodynamischen versuchsanstalt zu Göttingen”, Lieferung 3, p9 line 17

[164] As Thurston had previously done, according to his own account

[165]Flight Test of the Handley Page torpedo-carrying airplane” March 8 1922 Editorial in The Aeroplane, reproduced as NACA TM-82,online at

[166]The Case for the Slotted Wing”, Flight magazine 13th July 1922

[167] The previous week had featured Dr Hankin, of “Ergaer” fame, discussed above

[168] Handley Page's Application (1924) 41 RPC 109

[169] See Prior (1953) and Waghorn (1939)

[170] Hopkins' Patent (1909) 27 RPC 72

[171] published in Flight magazine, on 24 February 1921

[172] Brownback (H.L.’)s Application 59 RPC 80

[173] ARC Reports & Memoranda No 856

[174] Reported in Flight Magazine, 10th March 1927 p150

[175] Reported in Flight magazine 24th November 1927

[176] By letter of 7th January 1921

[177] Granted as GB 288027

[178] Over 1914-1934; later, as a civil servant, to champion the nationalisation of the aerospace industry against which Handley Page was to fight so doggedly in the 1970s.  See Edgerton (1991).

[179] No. 2210/27.  It was granted as GB 289517 and US 1806379

[180] Fearon (1990)

[181] TIME magazine, 24th July 1939, “Hot Race”

[182] Filed but not yet granted when Handley Page approached the Ministry

[183] 1925-1926 & 1939-1940

[184] Obituary at Trans. CIPA LXXIII 1954-55, C81

[185] Now enshrined in s.55(3) of the Patents Act 1977

[186] GB 130859 and GB 131252

[187] National Archives file AVIA 6/1680

[188] National Archives file TS 28/178, Report on GB 157567 by Hubert A Gill, 3 June 1927, see also AVIA 8/63

[189] The Economist, 31st August 1929 p399

[190] The Times, Thursday, Jul 28, 1927; pg. 20

[191] Now exhibited in the Science Museum Annex at Wroughton Airfield

[192] Andrew Sellon, 20 April 2004, ; “Prize Fight,” TIME magazine, Monday, Jan. 13th, 1930

[193] New York Times 26th November 1929, "SAYS HANDLEY PAGE COPIED SAFETY WING; AJ Leigh Makes Charge in a letter to judges of the Guggenheim Contest".

[194] Flight magazine, 29th May 1931

[195] It remained an emergency airstrip during the 1920s, hosting an annual air show

[196] Other than a paper on patent law and a paper on structures discussed below

[197] Reported in Flight magazine, November 27th 1924

[198] See Grubb (1974)

[199] Thurston (1954)

[200] Aviation in Parliament, Flight magazine December 9th 1920.

[201] GB 132332

[202] “"Gloster" Metal Construction” Flight magazine, April 18th, 1930

[203] In the Matter of Wylie’s Letters Patent (1934) 51 RPC 377

[204] Ibid

[205] ATS Ltd v. Handley Page Ltd (1936) 53 RPC 99

[206] Handley Page (1928)

[207] The annual lecture series instituted by Griffith Brewer

[208]  (1876-1960), appointed the Air Ministry's first Director of Scientific Research in 1924

[209] Flight magazine 18th June 1925 p375 “Dr. Thurston said he very much regretted the amalgamation, and that the two Societies were of quite a different character. It was because he was so convinced that the Institution of Aeronautical Engineers was devoting its special attention to the practical application of aeronautics that he thought they could do their work as a separate body and without association with the Royal Aeronautical Society which devoted itself to pure science, and he would strongly oppose the proposed amalgamation.”

[210] On 8th January 1960

[211] On 1st July 1987

[212] Elkin Mathews & Marrot, 1931

[214] Edgerton (1991)

[215] British aviation pioneer was a spy for Japan, Peter Day The Telegraph 2nd January 2002, referring to National Archives files KV 2/871-874

[216] Penrose (1970)

[217] Letter of 4th July 1928 to the R.Ae.S

[218] Letter of 23rd July 1928 to R.Ae.S

[219] “APT” were Thurston’s initials

[220] Letter of 2nd July 1964 Lachmann to Pritchard

[221] Awarded for contributions towards safety in aerospace

[222] Letter of 3rd December to Pritchard

[223] Brabazon referred to HP as his “dear old friend” in his Flight magazine obituary, and also wrote the introductory eulogy in “Forty Years On…”

[224] Where much early wind tunnel research took place

[225] Thurston (1914)

[226] As was, of course, Thurston’s intention, in showing relationship between his pre-War work and the slotted wing.

[227] On 13th August 1930

[228] Young Plate XXV(b)

[229] Flight magazine 2nd May 1930 p489, 20th June 1930 p668 and 18th July 1930 p820

[230] The “thumb” is the alula – he was making an explicit link back to his earlier claims to priority for the slot

[231] National Archives files AVIA 8/207, DSIR 23/3084, DSIR 23/3388, DSIR 23/9322

[232] National Archives file AVIA 8/207

[233] (1882-1970), later to head RAF Fighter Command in the second World War

[234] Report of 20 May 1932 by D H Williams, Ae.Tech1.631, copy in National Archives files AVIA 8/207

[235] National Archives files AVIA 8/207

[236] Thurston (1934)

[237] 11th January 1934

[238] It is perhaps too much to say that Thurston was truly averse to making a profit, but he did believe in patenting in the national interest, as his remarks in the discussion on "The Royal Commission on Awards to Inventors", Kenneth R. Swan, Trans CIPA LXXIV 1955/56 B93, Paper at C47, show, he “…considered it essential that when anyone made an invention, whether he wished to use it himself for his own benefit or not, it should be protected by a patent.  He thought that that was a very important matter. …It was necessary for the nation's benefit that the inventor, or someone else in this country, should hold a patent for the invention.  “

[239] See National Archives files AIR 40/2632, AIR 40/2633, KV 2/2733, KV 2/2734, KV 2//2735

[240] Provisional application filed 2nd July 1937, granted jointly to Handley Page and Lachmann in 1939

[241] German Scientific Society for Aviation

[242] Lachmann (1964)

[243] The 1862 creation of Sir Guilford Lindsey Molesworth (1828-1925) railway and civil engineer and President of the Institution of Civil Engineers.

[244] 4th Anglo-American Aeronautical Conference 1953; Proceedings, R.Ae.S 1954; p224

[245] (1894-1981), the former Commander in Chief of Bomber Command

[246] Sir Sydney Camm, David Keith Lucas of Short Brothers & Harland; B S Shenstone

[247] See Videler (2005), p61

[248] For which, see their patents EP 0642440, WO 9422713, US 5823480, EP 1205384

[249] As is also clear from some of his reminiscences, and the consistency of his accounts over several decades

[250] (1894-1981) - Letter in The Times in response to his obituary

[251] Later Sir Kenneth Swan KC, son and biographer of Sir Joseph Wilson Swan (the famous electrical engineer and inventor, simultaneously with Edison, of the light bulb); between 1945 and 1947, he was to chair the Swan Committee which led to the 1949 Patents Act

[252] Thurston, having become an Associate of CIPA only the preceding month, would almost certainly have attended the meeting

[253] Discussion on “An Employee’s Duty in Respect of Industrial Property” Trans CIPA 1947-1948 LXVI 91

[254] Discussion on Swan (1955) B93

[255] Discussion on “An Employee’s Duty in Respect of Industrial Property” Trans CIPA 1947-1948 LXVI 91

[256] Although according to Stewart his paper makes it "plain that ... automaticity was visualised for these rider planes as it was eventually used for slots."

[257] Where disclosure of inventors was not required

[258] He married Una Thynne (1890-1957) in 1918; his first daughter, Helen Anne, was born on 5th November 1919 (m. Manley Walker, d. 2001); his second, Phyllis (Elizabeth “Buffy”), on 10th December 1921 (m. Winfield, d. 1987), and his third, Patricia (Mary), on 14th June 1923 (d. 1992).

[259] Or, one should add, anything else

[260] The Defence of the Realm Act

[261] As described in Rowland & Kennedy v. Air Council (1923) 40 RPC 87, (1925) 42 RPC 433, (1927) 44 RPC 453

[262] GB 139230

[263] At least in the past; in the Soviet era, no Soviet patent named a lone inventor, all listed the entire research group.

[264] See for example Fjällbrant (1997), David (2004), or Stephan (1996), all drawing on the work of Robert King Merton, (1910-2003), father of sociology of science