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ASH 26 E - an 18m self launcher with a difference
The popularity of self launching gliders continues to increase rapidly. This is really no surprise. More and more pilots appreciate the limitless opportunities, the total independence and, of course, the “retrieve avoidance” of auxiliary powered sailplanes. But self launching gliders offer more than just the elimination of inconvenience or constraints.
Gliding is greatly enhanced and frequently extended for hours because pilots can contact lift normally beyond reach and even explore wave with the ultimate “peace of mind”. On top of all that soaring safaris become a reality - even into and out of airstrips without any gliding infrastructure.
Schleicher responded to a strong demand for such a glider even before the official introduction of the 18m FAI class in 1997. However, instead of putting 18m wingtips on a racing class glider and installing a traditional 2-stroke engine, a totally new glider with new technology power plant was developed. The result is the ASH 26 E - a glider breaking new grounds in more ways than one.
For “purists” (or for customers who want to fit an engine at a later stage) the ASH 26 E is also available as a pure 18 meter sailplane. At speeds between 46kt and 60kt the best glide ratio is above 50:1 - a performance which has greatly contributed to the ongoing popularity of the aircraft. Thanks to a flat polar curve the performance degrades only marginally in the mid-speed range. For example, at a wing loading of 45 kg/m² and a speed of 80kt the best L/D remains at an impressive 46:1. It is no surprise that the ASH 26 E is holding the world open class speed record of 235km/h over a 100km triangle. The airfoil is identical to the ASW 27 B which took out first and second place at the world championship 2003 and is widely recognized as the world’s best performing 15m FAI glider.
With a laminar airflow over 95% on the underside of the wing the high speed performance is equal or even better than some open class aircraft. No wonder the ASH 26 E has created enthusiasm amongst pilots who dreamt about open class performance but wanted it in a smaller and more maneuverable 18 m aircraft.
But the ASH 26 E was not purely designed for performance. The design team led by Martin Heide (Designer of the open class ASH 25) recognized that a large number of glider pilots have no intention of breaking records but want to fly for long hours in a very comfortable and slightly larger than usual cockpit. For this reason the ASH 26 E cockpit was built to accommodate even the tallest of pilots with sufficient space for good pilot comfort plus luggage. It is therefore not surprising that the longest flight ever performed in a single seat glider was done in an ASH 26 E - a distance of 2311km in 14:25 hours at altitudes of 26000ft and ambient temperatures of -28°C. The pilot landed in driving rain at a remote airstrip in Argentina and was forced to spend the night in the cockpit of his ASH 26 E - simply unthinkable in a smaller and less comfortable cockpit.
The POWER PLANT of the ASH 26 E
It is remarkable that, for a variety of reasons most glider pilots would not even consider a 2-stroke engine for their lawnmower but have in the past reluctantly accepted such engines in self launching gliders? But Schleicher now offers a real alternative after embracing rotary engine technology. This is for good reason. Rotary engines have both simplicity and reliability in a compact design while having a very high power output for their weight and size. On top of all that there is a complete absence of vibration. The reliability of such rotary engines has been steadily improved to a point where they are now fitted to sports cars with a 3 year unlimited kilometer warranty. All these advantages make a rotary engine ideal for small aircraft and made Schleicher to selected the single disc, liquid cooled Diamond AE50R engine to power the ASH 26 E.
The engine not only comes with dual ignition and internal forced air cooling but is much more user friendly by not burning special fuel such as AVGAS or 2-stroke mixture. Engine lubrication is accomplished by an oil pump which injects oil where needed. The standard mechanical propeller stop makes the extension and retraction of the engine easy and avoids a dependence on sensitive electronics, sensors and switches. Another step forward is the tensioning of the drive belt by extending the propeller. This design avoids a permanent load on engine and belt and also allows the engine to remain stationary mounted in the noise shielding fuselage. This brilliantly simple and convincing concept also allows the engine to be permanently connected to a large volume silencer which further reduces noise emissions. In fact noise levels were measured to be well below the already stringent limits in Germany. Of course, the engine is equipped with starter motor and an 18 Amp. generator as well as a small lubrication oil reservoir.
The engine delivers a generous 50hp of power and together with a propeller especially developed for this aircraft the ASH 26 E features a quite impressive take off performance. For example, the ground run on a sealed runway is only 160m meter and the initial climb rate at maximum take off weight is as high as 3.4m/s - equal or perhaps even better than normal aerotow climb rates.
The engine’s vibration free running at all power settings and its ease of operation have made it a very popular choice for gliders of this size. Extended power cruising for ferry flights or even flying through controlled airspace at an assigned altitude presents no problem to aircraft or engine - another most welcome advantage over conventional two-stroke technology.
Fuel consumption might not be a decisive issue on a motor glider, but a fuel burn of only 16 l/h of standard unleaded fuel is very welcome news indeed. It makes the ASH 26 E by far the most economical self launching glider and gives it a range of 680km on the standard 16 liter fuselage tank using the saw tooth cruising method. If that is not enough, two additional 15 liter tanks for each wing are available on request.
No wonder there are numerous reports of ASH 26 E sailplanes being flown across continents into some of the most remote places on earth. Out and return gliding trips from Texas across Canada and Alaska to the border of Russia or expeditions from central Europe into Africa and back are only the tip of the “Iceberg of flights” accomplished so far by the ASH 26 E.
When required the entire drive unit can be easily removed from the fuselage in just a few minutes. Removal requires undoing three mounting bolts, unplugging the electrics and separating the fuel line. However, 10 years of operating experience with hundreds of such drive units all over the world has already earned this power plant an enviable reputation for reliability and dependability. Contrary to conventional 2-stroke technology it is not subject to a time limit and it is also not necessary to dismantle the engine for an inspection after 6 years. Instead, after 150 engine hours (1800 launches of 5 minutes each) only a detailed external inspection is necessary which includes a examination of the combustion chamber through the exhaust outlet. Provided no wear is found on the rotor seals the engine can be operated for another 150 hours up to its total design life of 1000 hours. All in all, the rotary engine and drive assembly are a huge step forward in terms of maintenance, power to weight ratio, reliability, fuel consumption, noise emission, power output, ease of operation and pilot comfort.
The airframe - just as advanced
But it is not only it’s rotary engine which ensures the ongoing popularity of the ASH 26 E. Pilots around the world also like its docile flying characteristics, its control responsiveness, its superb handling and its elegant appearance. The cockpit was designed for pilot loads of up to 110kg and includes the many award winning safety features, Gerhard Waibel developed for his W-designs. A maximum all up weight of 525kg allows wing loadings of up to 45 kg/m² and thanks to the use of the latest composite technology the maximum speed is as high as 146kt. The water ballast system is removable and comes with automatic control connections. Both drain outlets on the underside of the wing (used for filling and jettisoning of water ballast) are “concealed” to the airflow for minimum drag.
Assembling the ASH 26 E is made quick and easy by fully automatic control connections and the one piece wing weighing only approx. 72kg. This is similar in weight to the shorter two piece wings of our competitors. A two part wing does not reduce weight, but it does increase assembly and taping time.
Laminar airflow is maintained over 95% of the underside of the wing which means that blowholes for boundary layer control are not in the wing but on the underside of aileron and flaps. Such aerodynamic advances have so far only been accomplished in the ASW 27 and ASH 26 sailplanes. This achievement is in no small part due to our exacting manufacturing standards and a very high quality mylar seal installation. Pleasantly low control forces - due to the use of precision ball bearings in all control circuits - ensure fatigue free flying for long periods of time. Depending on the owner’s preferences newly developed 0.45m tall winglets can be fitted and even a steer able tail wheel is available as an optional extra. In combination with small wingtip wheels it now allows owners limited taxiing without a helping hand on the wingtip.
Landing the ASH 26 E is made very easy by a clever control mixer only found in Schleicher gliders sice the famous ASW 20. The 44 degree landing flap setting not only ensures pleasantly low landing speeds but also guarantees full aileron control until the aircraft has almost come to a complete stop. This control mixer has greatly contributed to the excellent safety record and the first class reputation of the glider. Take offs and landings on soft airstrips present no problem to an ASH 26 E pilot. A clever and very robust undercarriage design places the big 5.00-5 main wheel well forward of the aircraft’s center of gravity. The advantages are plentiful; first of all it means that ASH 26 E pilots don’t need to be concerned about scraping the nose on the ground on application of full take off power. Secondly, in conjunction with effective rubber shock absorbers it adds to pilot comfort on rough airfields and thirdly it ensures the highest possible degree of safety due to the most generous ground clearance of any 18m glider.
In flight adjustable rudder pedals, a hydraulic disc brake, a control column mounted quick trim device and a clear vision panel are standard features that Schleicher customers have come to expect. Also standard is an in flight adjustable back rest, a large air vent in the aircraft’s nose and an additional airliner style air-vent on the right fuselage wall. In combination with the comfortable cockpit these features ensure that the very last hour of a long flight is as enjoyable as the first.
Only the latest technology composite materials are used for the entire glider. All control surfaces including the vertical stabilizer are constructed in a modern low weight CRP sandwich design. Ailerons, elevator, flaps and airbrakes are actuated by maintenance free pushrods running in ball bearings for the lowest possible actuating forces and fatigue free flying. Even though the ASH 26 E is usually equipped with an engine a nose and a belly release are provided.
The removable fuel tank is located within the rear undercarriage compartment and does not form part of the fuselage structure. This is not only an important safety aspect but also offers real advantages for future maintenance and inspections.
Typical for all Schleicher sailplanes is the front hinged canopy with sliding window and tongue and groove seal. The ASH 26 E is no exception. The instrument panel hinges upwards with the canopy but fully encloses the instruments while the canopy is open. This “enclosed instrument area” greatly improves neatness in the cockpit. An integrated gas strut not only ensures low lifting forces but more importantly ensures that the canopy can not be blown shut by a wind gust and damaged in the process. When only the best will do, the ASH 26 E is the obvious choice!
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Photos: Manfred Münch