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Aviation History
1955
1955 - 0135.PDF
4 February 1955 The machine certainly appears to be entirely dependent uponengine thrust—as in fact it is—but failure of either engine has no effect upon the other, and the compressed-air control jetsare also capable of being supplied from one engine alone If one engine were to fail, therefore, the machine would descend,but control would not be lost. Finally, to descend and alight the pilot gradually reduces thrust until this is just less than theweight, and thus allows the machine to sink gently on to its wheels. The engines can then be cut. It should be stressed that the bedstead is not really a flyingmachine at all; more correctly, it should be thought of as a test bed which can rise from the ground. Rolls-Royce are, however,looking very far ahead, and it can be said that later vertical-lifting experimental craft are already being built. The remainder ofthe account describes how vertical lift might be applied in future aircraft. Jet-lift Possibilities The installation of vertical lifting jets makes possible the pro-vision of a lifting thrust greater than the weight, irrespective of forward speed. Thus, a future aircraft could be made to risevertically, while remaining in the horizontal position. Once well clear of the ground, it could be allowed to accelerate for-ward until the speed was sufficient for the wing to bear the weight of the aircraft. This would permit the employment of awing with an area much smaller than would otherwise be possible; the aerofoil section could also be tailored solely to therequirements of high-speed flight, no compromises being made to improve the behaviour of the wing at low airspeeds. Thesechanges would greatly increase the stalling speed of the wing (a matter of little consequence) and thus would also greatlyincrease the maximum speed. It should be noted that a wing stalls at an angle of attackwhich, for a given wing loading and atmospheric condition, is constant. Thus, the wing of a vertical-lift aircraft could beallowed to stall completely at low speeds with the lifting jets working, but would become unstalled as soon as the angle ofattack came within the forward-flight range. Aircraft of the future might have the following characteristics(in the drawings A and D might be transports, B a manned bomber and C a pilotless bomber). The wings of each of theprojects illustrated is seen to be small in comparison with those of present manned aircraft. The wing loading at take-off mightbe set at, say, 300 lb/sq ft. Each machine has a battery of lifting jets in the rear fuselage and another set mounted forward. Mainpropulsive engines—turbojets in the aircraft shown—are carried either on the wings or the tail, or wherever is convenient.It may be noted that a distinction is drawn between lifting jets and propulsive jets. In fact, both jobs could possibly bedone by the same units; certainly some aircraft designed for Mach numbers in excess of two will need propulsive thrustexceeding the all-up weight. The main engines could be used for vertical lift by so mounting them—in pods, or at the tipsof the wings—that they could be tilted upwards at take-off or at landing. The disadvantages, however, almost certainly outweighthe advantages. The unanswerable shortcoming of such an arrangement is the danger of losing an engine. The engine-out case of a vertical- lift machine supported by (for example) two large engines on one wing-tip and one engine on the other could scarcely be worse. Other drawbacks are the difficulty of putting the main propulsive engines in the right place for providing vertical lift without very great changes in trim, and the obvious mechanical difficulties involved. A much better arrangement, in spite of the fact that it wastesa lot of valuable space and adds to the dead weight, is to fit banks of special lifting jets. A large number of these engineswould be used, each with its own fuel system (probably dupli- cated) and accessories, so that failure of one or two would notcreate an emergency. Typical numbers might be 20 jets at the rear and a dozen at the front.The lifting motors could be rockets, since they would be needed for short periods only. Current Rolls-Royce thinking, however,presupposes the use of turbojets of a special form. Owing to the fact that they would be "one-purpose, one-condition units only—they would operate at full power, for a short period, and at low altitude—these low-compression lifting motors could be madevery light. Their fuel, accessory and control systems could be extremely simple, thus effecting, on this score alone, a saying ofperhaps 30 per cent in comparison with an orthodox installation; an even higher percentage of cost might be saved, and the struc-ture could also be radically simplified. Such a motor would, in fact, be "a distant cousin" to the Rolls-Royce Soar (7:1 approxi-mate power-to-weight-ratio) and should handsomely beat even that startling unit on specific performance.We calculated that a lifting turbojet for a total We of about 100 hours might have a thrust of 5,000 lb ^ *;^t ^ 600 1b,and achieve a specific consumption of 1.5 lb/hr/lb (fekte figure is high, but of little importance for such short duration). 135 The Rolls-Royce bed- stead thrust-rig roaring away at Hucknall in the hands of Capt. R. T. Shepherd. This photo- graph was taken some months ago — on the same occasion as the film recently released for general showing. Thirty of these couldeasily lift a 100- passenger airlinerdesigned to V.T.O. requirements. Theweight of these 30 lifting motors wouldbe less than that saved in the wing andundercarriage by de- signing for verticaltake-off and landing. Assuming a trans-port designed for Mach 1.5, a possiblemachine of 1970 (sooner for a militarycounterpart) might have a 70-deg deltawing with a span of about 80ft and anarea of about 1,000 sq ft. The all-up weight could be set at 300,000 lb, and the forward power mightbe four turbojets, each giving some 30,000 lb thrust at sea level. Such a machine could have 45 to 50 lifting jets of about 10,000lb thrust each (weighing a total of about 50,000 lb), rather more than half of these units being mounted at the rear. Some of the jetswould probably be arranged to tilt to provide stability at low airspeeds. The lift-jet bays would have simple fuselage-roofintakes which, like the outlets, would be covered by doors during forward flight. For take-off, all engines would be started, but the propulsiveunits would be allowed to idle. Opening up the lifting jets would raise the machine off the ground vertically. The apron itselfwould, of course, become very hot during take-off, and dehydrated concrete would need to be employed (normal concrete containsmoisture, which would boil and cause cracking). Vertical-jet lift is seen by Rolls-Royce up to limits of 300ftin height and about 200 knots in speed. At a safe height the main propulsion would start to be brought into play (the machinestill being supported by the lifting jets) and forward speed built up. At perhaps 150 knots an automatic system could begin tocut out the lifting jets until eventually the whole weight was being borne by the wing. Then the lift-jet doors could all beclosed for the climb (to perhaps 60,000ft, or according to range) and cruise at Mach 1.5. After a conventional let-down with weight now very muchreduced, some, or all, of the lifting jets would once again be brought into play. The final hundred feet of descent wouldprobably be almost vertical. The type of aircraft touched upon here may appear to be com-plicated and expensive, but it represents one reasonable solution to the problem of supersonic flight for large aircraft. To takejust one aspect of this overall problem, it is doubtful if this country could manufacture the wing for an orthodox-lift machinedesigned to carry 100 passengers at Mach 1.5; the type of con- struction required would be outside our present capabilities.With jet lift, however, the wing could be much smaller and much simpler, and could probably be made by the industrytoday. The jet-lift aircraft would not require a long runway; on theother hand, it would scarcely be able to operate from a city- centre. Jet lift is in no way competitive with the helicopter, noris it as efficient as a rotor for producing lift at low translational speeds. Both, however, are likely to present a noise problem. Thus, from the somewhat primitive but nevertheless portentousbeginning described on the opposite page, there may spring a new family of high-speed aircraft. At least one authority has statedthat the practical demonstration of jet lift marks as important a step forward as did the first flight of the aircraft gas turbine.Rolls-Royce have stressed that they are not aircraft manufacturers, even though they have now produced for the first time a completeflying machine. The next V.T.O. experiment with which this great company will be associated is likely to be the first flight ofthe American Ryan prototype, for which Avon;.—probably a pair —are to be used.
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