Armstrong Whitworth AW52
| Armstrong Whitworth AW52 | |
|---|---|
 Second prototype of the AW52 |
|
| Type: | Flying wing - test aircraft |
| Design country: | |
| Manufacturer: | |
| First flight: |
March 2, 1945 (AW52G) |
Armstrong Whitworth Aw52 was the name given to two different blended wing - experimental aircraft , which in the 1940s in the UK have been developed. First a driveless concept model (AW52G) was built, which was followed by a twin-engine, scaled-up model (AW52).
history
The flying wing design has some advantages compared to a conventional aircraft, so theoretically the total resistance of the airframe is only half as high. One of the fundamental disadvantages is the difficulty of steering around the transverse axis , which takes place via elevons that combine elevator and ailerons . As a result of the small lever arm , the control surfaces must be made relatively large.
Another approach to reducing the aerodynamic drag is the influence of the boundary layer . The aim here is to keep the flow around the wing profile laminar as long as possible and thus to move the transition point from laminar to turbulent flow conditions as far back as possible along the profile depth, as the turbulent Proportion of the flow is responsible for the majority of the profile resistance.
The boundary layer is usually influenced by providing suction slots or holes on the surface through which the boundary layer is sucked in before it can become turbulent. The control surfaces primarily benefit from the smooth flow. Investigations carried out on a Hawker Hurricane with laminar wing during the war showed the sensitivity to contamination by e.g. B. Insects known. A newly developed wing was able to maintain the laminar flow over 60% of the profile depth; the reduction in resistance compared to a normal wing was up to 50%. After a relatively short time, however, the rough surface destroyed the laminar flow.
If a flying wing is combined with a boundary layer control, particularly significant improvements in aerodynamic drag can be expected. In the years after the Second World War, the possibilities of such constructions were also the subject of studies in Great Britain. The activities were coordinated by the Tailless Advisory Committee set up by the Ministry of Supply . One of the companies included was Armstrong-Whitworth Ltd. in Coventry .
A study of a jet-propelled flying wing airliner with a laminar profile was started under the direction of John Lloyd. This design meant that passengers and engines had to be accommodated in the wing and, accordingly, the height of the passenger cabin determines the wing thickness and thus the size of the aircraft. The span would therefore have to be at least 49 m and the total weight 80 to 90 t.
Armstrong-Whitworth's first draft was for a swept wing with a normal vertical stabilizer, but without a horizontal stabilizer. Designated as the AW50 , it should have a wingspan of 36.6 m and a total weight of around 23 t. The drive was to consist of four Metropolitan Vickers F.3 turbofan engines. Since neither the Ministry of Supply nor the company itself wanted to tackle such a project without preliminary investigations, a scaled-down version as a glider was suggested. This construction, known as the AW51 , with a span of just 12.20 m, was just as unsuccessful as the AW50.
Constructive further developments of these abandoned proposals finally led to the AW52. But here too, a scaled-down glider should help clarify the basic problems of control, stability and handling. Construction work on this machine, called the AW52G, began in May 1943 and construction began in March 1944. The first flight took place on March 2, 1945 from the Baginton Aerodrome (now Coventry Airport ) towing an Armstrong Whitworth Whitley . The next half-hour flights from a release height of 6100 m confirmed the results of the wind tunnel tests and also the expectations with regard to stability and controllability.
The test flights of the machine with the RAF serial number RG324 extended over two years, after which it was set up at the entrance of the Baginton Aerodrome and finally scrapped in 1950.
However, the development work in the high-speed range could only be carried out with a powered aircraft. Therefore, at the end of 1944, the Ministry of Supply placed an order to build two test aircraft in accordance with the Air Ministry Specification E9 / 44 . This required a twin-engine, all-metal aircraft with a flying wing design and twice the size of the previous glider. For the first time, the wings were to use a National Physical Laboratory laminar profile that could theoretically maintain laminar flow up to half the depth of the surface. The angle of incidence changed from 1 ° 2 'at the root to -2 ° at the wing tip. To get the necessary smooth surface, the wing should be made in two horizontally divided halves. The paneling made of a relatively thick Alclad sheet was clamped into a jig and then the wing structure was built up from the outside in. The two halves were then screwed together and the wing nose and trailing edge attached separately. The deviation from the ideal rounding should only be 2/1000 inches .
A bigger problem that the design team around John Lloyd was confronted with was the tendency to premature flow stall at the wing tips with the swept wing layout used. The remedy through slots in this area was forbidden, as this would have lost the desired laminar flow properties of the wing. Instead, a boundary layer control procedure, starting from the wing tips, should also include the entire span of the elevons . This was achieved through suction slots on the top of the wing, which were located in front of the trim surfaces . Theoretically, removing the boundary layer before its turbulent transition point should delay the stall. The slots were inside the wing and connected to flaps in the engine inlet. When the engine power was reduced and the control stick pulled back, the flaps opened automatically and generated suction. In the case of the AW52G, the suction power was provided by wind-powered propellers on the landing gear legs.
The first AW52 (RAF registration: TS363) made its maiden flight at the Airplane and Armament Experimental Establishment from Boscombe Down Airfield on November 13, 1947. The second aircraft (TS368) flew for the first time nine months later on September 1, 1948. Both aircraft were demonstrated together at the Farnborough International Airshow in 1948. The flight performance of the draft, however, fell short of expectations; Lloyd concluded that laminar flow could not be sustained in a swept wing. Together with the low lift coefficient of around 1.6 with the flaps extended, the performance was far too low for the engine power used. The Nene version reached 800 km / h, while the machine with Derwent drive was 80 km / h slower.
On May 30, 1949, John Lancaster was flying the TS363 at high speed when wing flutter from the ends spread over the entire wing. This resulted in uncontrollable vibrations around the transverse axis, so that the pilot had to get out of the ejection seat. The second prototype continued testing, but with a speed limit of 250 kn . In 1950 the machine was transferred to Farnborough, where further experiments on wing sweep and laminar flow were carried out. Due to the two-year test load, the wing was only able to achieve a laminar flow over 20% of the profile depth again after extensive treatment. However, it was finally determined that the necessary quality of the surface cannot be maintained permanently in daily flight operations, whereupon the further tests with the AW52 were discontinued. The plane was scrapped in 1954.
construction
AW52G
The tailless glider was mostly made of wood. The wing used the NACA-653220 profile and was manufactured in three parts: a central part with a swept front wing and straight trailing edge and two outer parts with a more pronounced swept and trapezoidal outline. The parts had a spar made of pine and plywood. The planking consisted of Plymax , in which plywood was glued to duralumin panels with a thickness of 0.711 mm or 22 swg ( standard wire gauge ).
The rudder disks were located at the extreme ends of the wings. The control system already corresponded to that of the planned larger machine. The two crew members sat one behind the other in the middle section under a streamlined hood. The nose wheel landing gear was not retractable.
AW52
Because of the relatively small dimensions, the crew members could not be accommodated in the fuselage, but sat in a pressurized fuselage gondola that protruded over the flying wing at the front. The cockpit canopy was offset slightly to the right (in the direction of flight). The two jet engines were housed in gondolas largely integrated into the wing on both sides of the crew compartment. Like the AW52G, the AW52 also had a slotted Fowler flap along the entire rear edge of the wing center section. The nose wheel chassis was retractable.
The first AW52 with the RAF serial number TS363 was powered by two Rolls-Royce Nene with 22.2 kN thrust each, while the second model (TS368) had two Rolls-Royce-Derwent jet engines (15.5 kN each) . The fuel supply of 7728 l was in eight tanks.
It was controlled via elevons on the outer wing tips. Normal elevons function as elevators when they are moved in the same direction, or as ailerons when operated in opposite directions. The variant used here was modified in such a way that trimming surfaces were attached to the rear edge of the movable control surfaces, which were referred to as "correctors". The purpose of the hydraulically operated “correctors” was to enable trimming without impairing the ease of movement of the manually operated elevons. The correctors were connected to the Fowler flap control ; if the flap deflected downwards and thus changed the trim towards the nose , the corrector moved upwards in the opposite direction to compensate. Rudder and fins were provided as end disks on the outside of the wings, and an anti-spin parachute was housed in a fairing at the tail unit root.
Technical specifications
| Parameter | AW52G | AW52 |
|---|---|---|
| crew | 2 | 1 |
| length | 7.63 m | 11.4 m |
| span | 19.02 m | 29.5 m |
| Wing area | 41.2 m² | 122.1 m² |
| Empty mass | 8,900 kg | |
| Takeoff mass | 14,000 kg | |
| Top speed | 770 km / h at 11,000 m | |
| Summit height | 15,000 m | |
| Engine | - | 2 × Rolls Royce Nene with 22.2 kN thrust each |
literature
- Oliver Tapper: Armstrong Whitworth's Flying Wing Experiments , Airplane Monthly, December 1974, pp. 998-1004
- Fliegerrevue 5/90, p. 159
- Fliegerrevue list of types 1970–2000 on CD
