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Aviation History
1955
1955 - 0134.PDF
134 FLIGHT JET LIFT First Experiments in Control and Stability: Future Possibilities ACCORDING to Newton, every action has an equal andopposite reaction, and this is a postulate that lies behindL every form of heavier-than-air flight. In the fixed-wing aeroplane, the action of deflecting a relative airflow in adownward direction results in a pressure distribution over the wing sufficient to sustain the aircraft. In a helicopter thesame condition applies, although in this case the wing, or rotor blade, can move relative to the air even when the air-craft as a whole is stationary. The same can be said of most types of convertiplane. Jet lift, on the other hand, does not involve any deflection ofthe surrounding atmosphere per se and, therefore, is completely independent of aerofoils, control surfaces and forward speed.What it amounts to is that, if a vehicle—in fact, any sort of rigid structure—is given an up-thrust slightly greater than its weight,then it can be made into a flying machine. Thus, neglecting the added weight of the lifting motors, 7,000 downward-pointingRolls-Royce Avons could fly H.M.S. Eagle. Rolls-Royce—and, in particular, Dr. A. A. Griffith, their chiefresearch engineer—have for long appreciated this principle, and have sought means whereby it might actually be applied topracticable flying machines. One of the first, and certainly the most grotesque, of the tangible results of this work is the vehiclecolloquially known as the Rolls-Royce Flying Bedstead, and more accurately styled a controllable flying thrust measuring rig. This apparatus consists largely of a pair of conventional turbo-jets—Nenes were used, owing to ready availability and, to a high degree, suitability—mounted horizontally and opposing eachother to produce the thrust at a convenient position and to cancel out gyroscopic torque. The jet from each Nene is turned through90 deg to issue from downward-facing propelling nozzles (Nenes are not normally equipped to operate in the vertical position. A"vertical" Avon is now being developed.) Actually, there appear to be three nozzles; possibly one engine "fires" through the largercentral hole while the other jet is bifurcated to exhaust on either side. Then, if either engine were to fail, no out-of-balance forcewould be created. The basic structure of the contraption could hardly be moresimple, and it is doubtful if there is much "airframe" that cannot be seen in the photograph. Welded tube is prevalent, and thedevice is supported on the ground upon four long shock-absorb- ing legs carrying small castoring wheels. A fuel tank can beseen beneath each engine, and the pilot's seat is perched above the centre of the machine, facing one of the engines. The whole device is inherently unstable for, although theresultant thrust acts directly through the e.g., the latter lies above the "centre of buoyancy" (to use a nautical term), so that the bed-stead has a natural tendency to topple over. This lack of stability has been overcome by a comparatively simple, and very effective,control system developed largely by the R.A.E. at Farnborough. A collector pipe can be seen around the diffuser case of eachengine. This bleeds off compressed air, which can be passed along braced horizontal pipes leading outwards from each sideof the machine (to the front and rear, left and right) to exhaust from a downward-pointing nozzle. In perfectly level flight all fournozzles are shut off by valves. If the bedstead were to begin a "topple" to the left, an automatic control system, obviously basedon a vertical-gyro reference, would open the valve leading to the left-hand stabilizing nozzle and the thrust of the jet of compressedair would then right the aircraft. In normal flight, all four valves are continuously being individually opened and closed to main-tain the machine on an even keel. The stabilizing jets are also under the control of the pilot. Ifhe wishes the bedstead to move forward, he has only to move his control column forward in the normal manner. This causesthe rear pitch-jet to open and so tilt the whole machine forward, i.e. the nose (denoted by the small horizon index carried on thefront air-pipe) drops below the horizon. The resultant horizontal thrust component then produces a slight acceleration in a for-ward direction, in exactly the same way that a conventional heli- copter starts to move over the ground—nose-down. To stop the machine, the column is pulled back, so openingdie front jet, raising the nose and causing the Nene-thrust to have a horizontal component in the opposite direction. The bedsteadcan also be flown sideways or backwards; furthermore, the fore- and-aft stabilizing jets are fitted with swivelling nozzles so that,by applying a pressure on either rudder pedal, the machine can be yawed about a vertical axis.The control and stabilizing system works very well indeed. The pilots who have flown the machine praise its handling andsteadiness, and have found no difficulty in "converting" to it. The controls act in the normal sense, and rather resemble those ofa helicopter in their effect. The present Rolls-Royce bedstead weighs about 8,000 lb (and,presumably, can call upon some 10,000 lb thrust). It is not intended to fly fast or high, and consequently manages withoutmany of the refinements needed on conventional aircraft. It has, however, flown in a 15-knot wind, and has also developedforward speeds of the order of 20 knots. All the flying to date has been done at the Rolls-Royce airfield at Hucknall, Notts, byCapt. R. T. Shepherd, A. J. Heyworth and H. N. D. Bailey. About 15 free flights have been made, each of about eight minutes' dura-tion. The endurance is about 9\ minutes. The bedstead may be started up by the ground crew in thenormal manner, and the Nenes can be idled with their jets beating down upon the concrete apron. In order to avoid theturbulent efflux the pilot enters by means of a stairway reminis- cent of those used on large airliners. He is then strapped in andall the servicing equipment surrounding the vehicle is cleared away. The Nenes are next opened up until, at something very nearto full thrust, the contrivance leaves the ground. Climb appears to be quite rapid, although flying has generally been restricted toheights below about 30ft. Handling is positive, and the control system makes it possible for the pilot to be completely relaxed. • -A Some possible future types of high-speed aircraft employing vertical jet lift. In each case the characteristics of the wing would virtually preclude operation from any normal present-day airfield. The projects are discussed in the text opposite.
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