In today’s Sydney Flyer article we are delighted to welcome back author Anthony Coleiro and the most recent instalment of his X-Files series. This is Anthony’s 135th article under the ‘X-Files’ banner for the club magazine. What a record!
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FILE X135: ARMSTRONG WHITWORTH AW.52
In the last instalment of the X-Files series, we had a look at the initial concept design of the Avro Vulcan, a design that was devoid of a fuselage and tail. Avro were not the only ones toying with that planform, Armstrong Whitworth (AW) also had their eye on such an aircraft.
The actual concept of a flying wing is almost as old as the story of flight itself. In a report released in the United Kingdom in 1943 by the Tailless Aircraft Committee, it was noted that at almost every stage of the development of flight, this sort of aircraft had been considered. In fact, at the time the report was being released, the Americans too were working on flying wing aircraft with Northrop taking the lead. That company’s work resulted in the XB-35 which was piston powered and as jet engines developed further, this was later converted to the jet powered YB-49.
The concept of a flying wing to date was not really able to hold its own against conventional types. The reason was simple enough, and that was the reduction in drag did not outweigh the technical difficulties that such an aircraft posed and so had always tended to lose out, but that did not deter researchers. They continually stuck at it because that reduction in drag was so attractive and also with the design’s clean field of fire to the rear of the aircraft. It was not unusual for rear firing gunners to shoot off parts of their own aircraft in the heat of battle! Additionally, the type lent itself nicely to the fitting of jet engines and the construction of laminar flow wings. A laminar flow wing is a wing of low curvature that allows the airflow to remain streamlined where air in different layers passing around the wing do not twist or mix thus reducing drag which means less thrust is required to generate the same amount of lift. Studies during WWII showed that this sort of wing was a requirement for high speed flight.
Just as the initial concept of the Vulcan was studied to see if it could have commercial applications, so too did AW with their AW.52 as back then as is the case nowadays, if you want funding there needs to be a commercial application for the design. While paper drawings, mathematical calculations and wind tunnel models are all critical in the development of new aircraft so to was the construction of an actual aircraft back then; these days computer modelling has mostly done away with expensive construction.
The physical building of a full-size aircraft to test a concept is an expensive undertaking so to ensure that researchers are not wasting their time and money running up blind alleys, test models are made and put through their paces in wind tunnels. Following successful tests with these, in 1943 a 3/5th scale concept aircraft of their concept aircraft was built. It was a non-powered version of the intended planform built mainly from wood with a cockpit for two seated in tandem, the front seat for the pilot, the rear for the engineer with his test equipment and instrumentation. The wing had to be quite torsionally stiff to prevent control reversal and flutter at high speeds. It was dubbed, AW.52G, G for glider. It was towed to altitude by a converted AW Whitley bomber and first took to the air in March 1945. The glider was designed to operate to an altitude of 16,000 ft. with a speed range of 80 to 402 km/h. On one occasion it was taken up to 20,000 feet where 35 minutes of flight time was available.
Testing with the glider proved successful enough for the construction of the full size jet powered version that was to also carry a crew of two but this time, provision was also made for mail carrying capacity to test its utility and also to have the ability to describe the development of this aircraft as ‘mail plane’ so that this feature can be used as cover to justify the expense of its development. The reality was that the AW.52 was meant to be a scaled version of a much larger aircraft, an aircraft that can be used as a long range bomber and ultimately a six engine jet airliner.
A specification was drawn up to cover its design and construction, E.9/44 to study the characteristics and problems associated with such an aircraft. The specification called for two aircraft to be constructed of a 27.5 metre wingspan, they were to be made of metal and powered by a pair of Metro-Vick F.2 Mk4 turbojets but these were unavailable so 5,000 lb thrust Rolls-Royce RB.41 Nene 2 jet engines were substituted. The aircraft was to have a pressurised fuselage but it had to be kept as small as possible to take the maximum advantage of the laminar flow wing. The undercarriage was to be the retracting tri-cycle type. It had to have a range of at least 2400 km when flying at 290 km/h and be able to climb to 45,000 feet.
Not only was the fuselage small, but also the engine nacelles, they were almost completely buried in the wing. Vertical surfaces and rudders were fitted to the wingtips to aid stability and were of a size sufficient to deal with the engine out case.
Control in flight was provided by the use of elevons, these are flight controls that combine the functions of elevators and ailerons, and it had the same control system as was tested on the glider. Due to the sweepback of the wings the aircraft had a tendency to tip stall early at low speeds and so boundary layer suction was provided to prevent this. Large Fowler-type flaps were fitted to the straight trailing edge portion of the wing that could be lowered to 40°.
The two aircraft were issued with serial numbers TS363 and TS368, their construction was undertaken simultaneously at Baginton and putting them together proved to be a challenge as the aircraft surfaces had to be as smooth as possible and free from wrinkles to preserve the laminar flow. During the construction, a decision was made to fit the second aircraft with lower powered 3,500 lb thrust Rolls-Royce Derwent 5 engines this meant that the engine intakes were correspondingly smaller and the fuel system needed to be revised. A push was made to have these aircraft ready in 1946, but this proved optimistic for the difficulties encountered and it was only in April 1947 that the aircraft were ready to commence taxi trials. TS363 started off with these trials. No intention was made to fly the aircraft at this stage but during high-speed taxi trials, it was found to be impossible to hold the nose of the aircraft down and a consequent short hop was made before the pilot regained control of the situation.
Some problems were found with the control system and it took a while to sort them out. Once this was done, the aircraft was partially dismantled and sent by road to Boscombe Down for flight testing. Once put together, more taxi trials took place on October 1947 and the following month, TS363 took to the air proper on 13 November of that year with a flight lasting 20 minutes. By December 2, the aircraft had completed six flights but not at a speed above 467 km/h because it was found that at that speed, the retractable gear doors would suck open causing vibration. Two weeks later, it made its first public appearance at Bitteswell airfield and it was noted by all those observing from the ground how quiet the aircraft was when compared to other jet aircraft when it flew overhead.
As flight testing progressed with TS363, the flight controls came into criticism due to their lack of harmony and approaching 463 km/h, the aircraft felt tail heavy and full elevator trim was needed to keep the aircraft from descending requiring the pilot to maintain constant back pressure on the stick. At this speed, the aircraft also developed a vibration which in gusty conditions would turn into a short period oscillation. The aircraft was then partly dismantled and then major modification was made to try and sort out the problem. The aircraft resumed flying in March 1949, some of the problems were corrected but the oscillations remained if the aircraft encountered turbulence. Two months later during stability testing, on descent through 5000 ft., the aircraft encountered some rough air which started the oscillations off again, this time however, the pilot was unable to regain control of the aircraft due to the violence of the oscillations which meant that he could not even see his instruments and he was almost at the point of blacking out, he had to eject from the stricken aircraft. This was the first time ever in the UK that an emergency evacuation from an aircraft was made using a Martin-Baker ejection seat under real conditions. The pilot was fine from his ordeal but the aircraft broke up on impact with the ground. By the time TS363 had crashed, it had clocked up 65 flights. Overall, the performance of the aircraft proved to be lack lustre and there was disappointment that the laminar flow wing did not live up to expectations with regards to drag reduction.
After the loss of the first aircraft, it was decided that testing of the second aircraft would only occur with the pilot aboard as had been the case on the ill-fated flight of TS363 and that was because the second seat did not have ejection capabilities and could not be made to have so. If the performance of the first AW.52 was a disappointment, it was even more so with the lower-powered Derwent engine version of the aircraft. Tests continued until May 1954, it was then scrapped. It was taken to the Proof and Experimental Establishment at Shoeburyness and ended its days as a weapons firing target. The project came to a dead end. The problems of stability and control were not completely overcome, the concept was ahead of its time, these days we have fly-by-wire and laminar flow did not turn out to be practical as even dead bugs on the leading edge caused drag rise. The concept of the flying wing had to wait; now of course we have the B-2 Spirit stealth bomber in the US aerial inventory, a design concept that had a gestational period almost as long as the history of modern aviation itself.
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