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Aviation History
1943
1943 - 1229.PDF
MAY I3TH, I943 FLIGHT 497 tally opposed, horizontal H and acute X type engines have been specially developed for submerged installation. An essential feature of a flying wing is its relatively deep wing section. With modern knowledge this presents no insuper- able difficulty ; consequently the problem of housing the cabin and power units as well as providing accommodation for passengers and crew is greatly facilitated. In contemplating a large air liner for example, aero- dynamic efficiency, cleanness of design, plus the practic- ability of flight engineers gaining access to the engines by means of gangways formed in the wing section, all indicate the desirability of total enclosure of the motive units, whatever form they may take. Consideration of these facts lends emphasis to the view that the advent of the high-speed gas turbine with its smooth-running characteristics will revolutionise aircraft design, not merely from the angle of propulsive power but also accelerate a change in the aircraft structure basically and fundamentally. One foresees that instead of concen- trating thought on the possibility of adapting normal types of monoplanes to propulsion by turbine-compressor units, either driving airscrews or producing a propulsive jet, the perfection of prime movers of the type under discussion will bring about a complete transformation. That is, new aircraft will ultimately be designed around the power units rather than adapting and modifying orthodox types of air- craft to receive them. An Enveloping Wing From this train of thought the idea of the flying wing emerges as a logical, progressive development. The idea, as already suggested, is as old as the industry itself, but only in recent years have advances in aerodynamic and structural knowledge brought the thick section wing to the stage of practical realisation. High-powered turbine units would appear to offer great promise for the large aircraft of the future, particularly those designed for high-speed operation at high altitude. The views of Mr. F. W. Cald- well, Director of Research, United Aircraft Corporation, are of interest in this connection. He is reported to have stated recently that some form of jet propulsion, accom- panied by change in heat cycle, in the ratios of air to fuel, and increased cruising speeds (above 300 m.p.h.) offers hope, at least, for lowering the limit of fuel con- sumption set, at present, by the screw propeller. Further- more, that at 40,000ft. and 150 m.p.h. the propeller and engine combination is twice as good as the jet, that at 300 m.p.h. neither has the advantage over the other, whereas at 550 m.p.h. the jet is twice as good as the engine-propeller combination. Probably the latest conception of an aircraft designed to eliminate unnecessary drag is the Northrop flying wing, and a flying scale model with two "flat" type 65 h.p. four-cylinder Lycoming engines and later 120 h.p. six- cylinder air-cooled Franklin engines sub- merged in the wing has been tested in America, as recorded at the time. The model has a 38ft. span and is 17ft. long. After the tests in 1940 it was reported that adequate controllability and stability about all three axes had been achieved, obtained through the shape of the wing rather than through the use of external fins, rudders, stabilisers or other auxiliary surfaces. The wings are swept acutely backward and the tips dropped downward in a direction opposite to thfe dihedral of a normal wing. In this it follows the example of the designs by Dunne and Lippisch. These wing tips take the place of the conventional control surfaces and Mr. J. K. Northrop advances the claim that its use makes it possible to obtain almost any desired combination of lateral and directional stability without loss of "ft. The horizontal reciprocating engines are housed within the wings and drive Pusher-airscrews. Thus if it be accepted that progress with the " all-wing " design has been such that it is now as stable and manoeuvrable as conventional aircraft, the equally modern power plant of compact circular shape with few excrescences as represented by the turbine-compressor combination would suggest itself as an ideal form of power unit "for development with an aircraft of this character. It has been estimated that a flying wing has from 33J per cent, to 50 per cent. less total drag than a normal type, which implies that considerably less horse-power is needed to attain the same speed. Since a jet propulsion units is con- siderably lighter in weight than an equivalent reciprocating engine with its many auxiliaries, a double advantage is suggested on paper by marrying the flying wing to the gas turbine. It seems a logical development with attractive possibilities. The provision of a pressure cabin is a necessary con- sideration for future air liners of a type with motive power which excels at the higher altitudes. The extra weight entailed by pressurising the cabin would seem justified. A tricycle undercarriage is also a desirable part of the specification to enable a natural level for such a large multi-engined aircraft and ease of passengers in moving about when the aircraft is on the ground. As already stressed, a very low build is possible since little ground clearance is required with the comparatively small- diameter counter-rotating airscrews likely to be employed, and less still if propulsive jets are used exclusively. Inside the aircraft a small independent auxiliary engine or turbine driving a D.C. generator would be desirable to take care of the many electrically operated components and mechanisms such as starters, airscrews, undercarriage, flaps, lighting, and radio. "Mixed" Power Units By way of illustration I have roughly sketched for execution by R. E. Poulton an impression of a large flying wing transport embodying control surfaces of the Dunne, Lippisch or Northrop type. It is of approximately 120ft. span and powered by four submerged turbine units. The inboard pair drive counter-rotating airscrews, whilst the outboard units are of the jet propulsion type. A feature of this bare layout is that ducts for the respective air- streams are arranged in the leading-edge of the wing and the propulsion nozzles in the trailing-edge. Since the weight of the airscrews is considerable, it is suggested that they would be employed on the inner pair in order to concentrate weight near the central axis and permit lighter construction. In this arrangement the efflux of the turbines could be utilised as auxiliary pro- pulsive jets. By suitable ducting, as much of the heat as necessary could be diverted along the leading-edge of the wing and control surfaces to prevent ice formation Four suggested arrangements Of power units on flying-wing aircraft A. Four continuous combustion turbine and axialcompressor type jet propulsion units * C. Two reciprocating engines driving counter-rotating airscrews and two jet propulsion units. B. Two turbine-driven counter-rotating airscrews and two jet propulsion units.D. Two reciprocating engines driving counter-rota- ting pusher airscrews and two jet propulsion units.
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