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The Short Stirling 

The Stirling was only one of three four-engined British bombers of World War 2. As such, it was the only one that was designed as such right from the start, since the Avro Lancaster and Handley Page Halifax were further developments of two-engined bombers.
Alas, since the requirement it was a response to was in some areas restricting, the Stirling was restricted in certain ways as well, and never performed as good as the others. On the other hand, it had other fine qualities, that made the Stirling very comfortable with it's crews, so the scale was probably balanced.

The B.12/36 requirement was the direct cause for the Stirling, and requested a strategical four-engined bomber that could be designed, developed and placed in production with the utmost speed, and yet provide Bomber Command with a high-speed means to deliver a large weapons load over long ranges. The crew would consist of six men, and defensive armament would comprise of multi-gun nose, ventral and tail turrets, and the weapons bay had to be sized for 500 lb (227 kg) general-purpose bombs or 2,000 lb (907 kg) armor-piercing bombs. The maximum take-off weight had to be about 48,000 lb (21.773 kg), although a growth figure of 53,000 lb (24.041 kg) was allowed and a long-term figure of 65,000 lb (29.484 kg) was possible.
Several contenders submitted their designs to the Air Ministry, namely Armstrong Whitworth, Short and Supermarine. Prototypes of the Short and Supermarine types were ordered. Somewhere along the line during the building of the prototypes the Supermarine factory where the Supermarine Type 317 prototype, powered with four Bristol Hercules radials, was being built was bombed. It was only partially complete before the German raid, while after the raid there was only wreckage left. Subsequently, Supermarine then cancelled the project.
Short initially proposed a design with good high-altitude performance provided by a wing spanning 112 ft 0 in (34,14 m) and based in structural and aerodynamic terms on that of its Sunderland maritime reconnaissance flying boat, but it was at this stage that the Air Ministry demanded the ability to fit into the standard hangar. The Short design team had therefore to revise its concept with a wing of reduced span and greater chord, the resulting decrease in aspect ratio inevitably reducing high-altitude capability. Even though this meant a reduction of capabilities of the Stirling, the Air Ministry was forced to continue with the project in the light of intelligence about the German rearmament program, and ordered two prototypes of this S.29 design. Parrallel to this decision the Air Ministry decided to order aircraft even before the first prototype would fly.
Experiences in the past with evaluating new types let Short decide to create a half-scale prototype. To validate the aerodynamics and controllability of the new type the S.31 was designed as the half-scale prototype with a powerplant of 4 × Pobjoy Niagara III radial, rated at 90 hp (67,1 kW) each. The S.31 made its first flight in September 1938 and revealed good handling characteristics. As a result of its test flying of this prototype, however, the Royal Air Force requested greater wing incidence: Short had selected an incidence of 3° for the best possible cruise performance, but the RAF was more concerned with improved take-off performance and asked for the incidence angle to be increased to 6,5°. This was a major redesign, however, requiring time-consuming revision of the central fuselage, so the compromise reached was a considerable lengthening of the main landing gear legs to given a higher ground angle. This change was tested on the S.31 from the end of 1938, when the aircraft was also revised with a powerplant of 4 × Niagara IV radial, rated at 115 hp (85,7 kW) each. Other changes evaluated on the revised S.31 were concerned with longitudinal control, and saw a change to horn-balanced elevators and finally to a larger tailplane with conventional elevators.

The Stirling was to be a cantilever mid-wing monoplane of all-metal construction using a wing structure that was based on that of the S.25 flying boat that had entered service as the Sunderland. The fuselage was of a more or less rectangular section with rounded corners and a raised flightdeck, and carried the flying surfaces which comprised a cantilever tail unit with a single vertical surface, and the wing. This wing was dihedraled, tapered in thickness and chord, and carried the standard trailing-edge combination of outboard ailerons and inboard (Gouge-type) flaps. The airframe was completed by the retractable tailwheel landing gear, which comprised twin tailwheels and main units that retracted rearward into the inboard nacelles of the four wing-mounted engines.
Construction of the two S.29 prototypes continued during the early part of 1939, and the first of these prototypes made its maiden and only flight in May 1939, being written off as it landed. One of the brakes had seized, and the asymmetric strain caused one of the main landing gear units to break. The main landing gear units were redesigned, and the second prototype made a successful first flight in December 1939. Production was already under way, and the first Stirling Mk I bomber made its initial flight in May 1940.

Version list:

• Short Stirling B.Mk III ^(*)
• Short Stirling A.Mk V ^(*)
• Other Short Stirling versions
• Short S.29 versions
• Short S.31 versions
• Short S.34 versions
• Short 'Super Stirling' versions

Further pictures:

Short Stirling Mk I in a rare colour snapshot


Short Stirling Mk III in full flight

Technical data on the Short Stirling B.Mk III

Powerplant	4 × Bristol Hercules XVI radial, rated at 1650 hp (1230.06 kW) each		Role during war	Heavy Bomber Transport
Length	87 ft 3 inch		Height	22 ft 9 inch
Empty weight	46900 lb		Operational weight	59400 lb typical, 70000 lb max
Wing Span	99 ft 1 inch		Wing Aspect ratio	6.72
Wing Area	1460 sq ft		Service ceiling	17000 ft
Maximum speed	270 mph at 14500 ft		Cruising speed	unknown
Initial climb rate	800 ft per minute		Range	590 miles minimum, 2010 miles typical
Fuel capacity internal	2,254 Imp gal (2,707 US gal), plus provision for 220 Imp gal (264 US gal) of auxiliary fuel in tanks installed in the wing bomb cells		Fuel capacity external	-
Machine guns	2 × 0.303 inch Browning trainable forward-firing in the power-operated Frazer-Nash F.N.5 nose turret 2 × 0.303 inch Browning trainable in the power-operated Frazer-Nash F.N.50 dorsal turret 4 × 0.303 inch Browning trainable rearward-firing in the power-operated Frazer-Nash F.N.20A tail turret		Cannons	-
Bomb load	Up to 14,000 lb of disposable stores carried in a lower-fuselage weapons bay rated at 11,000 lb and in 6 wing cells each rated at 500 lb. General disposables load consisted of: free-fall bombs up to 2,000 lb each		Torpedoes/rockets	-
Crew	7: pilot, co-pilot, navigator/bombardier, flight engineer, radio operator/gunner, two gunners.		Naval or ground based	Ground
First flight (prototype)	May 1938		Operational Service	August 1940 - 1946
Manufacturer	Short Brothers Ltd.		Number produced	2.370 total, 875 this version

Metric system

Length	26.59 m		Height	6.93 m
Empty weight	21274 kg		Operational weight	26944 kg typical, 31752 kg max
Wing Span	30.2 m		Wing Aspect ratio	6.72
Wing Area	135.63 m²		Service ceiling	5182 m
Maximum speed	435 km/h at 4420 m		Cruising speed	unknown
Initial climb rate	244 m per minute		Range	949 km minimum, 3235 km typical
Fuel capacity internal	10.246 liters, plus provision for 1.000 liters of auxiliary fuel in tanks installed in the wing bomb cells		Fuel capacity external	-
Machine guns	2 × 7,7 mm Browning trainable forward-firing in the power-operated Frazer-Nash F.N.5 nose turret 2 × 7,7 mm Browning trainable in the power-operated Frazer-Nash F.N.50 dorsal turret 4 × 7,7 mm Browning trainable rearward-firing in the power-operated Frazer-Nash F.N.20A tail turret		Cannons	-
Bomb load	Up to 6.350 kg of disposable stores carried in a lower-fuselage weapons bay rated at 4.990 kg and in 6 wing cells each rated at 227 kg. General disposables load consisted of: free-fall bombs up to 907 kg each		Torpedoes/rockets	-

Here is a quick overview of all different versions, without the full technical specifications:

Operational remarks:

Even though some performance numbers were unsatisfactory, the Stirling didn't fare that bad. Since it was a very sturdy, rugged aircraft most planes could return home even if hit very badly. Also, the maneuverability of the Stirling enabled the bombers often to escape a German nightfighter in the dark by executing voilent maneuvers.
The lack of operational height, however, made the Stirling more vulnerable and easier to intercept than it's contemporaries that could attain much higher altitudes. So when the Stirling was finally withdrawn from front-line service, other duties were waiting for it to carry on with. The Stirling was a good glider-tug, and could carry a good load. at a fair speed over a reasonable distance. Stirlings were widely in use as Airborne troop carriers during D-Day on 6 June 1944, the Operation Marketgarden landings at Arnhem, and the attack across the Rhine in March 1945. Also the Stirling was used for Special Duties operations, dropping supplies to the Resistance in occupied territory
In the end, the Stirling had flown 18.440 sorties in which 28.268 tons of bombs were dropped, and 20.000 mines were laid, for the loss of (only) 769 aircraft.

Strengths:

• Excellent structure, able to absorb massive damage
• Good handling during flight
• Excellent weapons load, but only for short ranges
• Adequate speed
• Excellent maneuverability, also called 'The fighter bomber'.

Weaknesses:

• Bad service ceiling
• Inadequate range when fully bombed up
• Unforgiving flight characteristics during take-off and landing

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