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Aviation History
1955
1955 - 0355.PDF
18 March 1955 355 FOLLAND GNAT (Bristol Orpheus Turbojet) These drawings are from a foreign source. The side view purports to show the Fo.143 (Gnat 2) intercepter with a wing of 6 per cent thickness. Also in evidence is the Aden gun installation, which makes provision tor retaining the belt-links aboard and for discharging the cases. The plan view shows the installation of wing-tip tanks, a 1,000 Ib bomb under the port wing, and six rocket projectiles under the starboard wing. The first prototypes will have a span of 22ft 2in. JET DEFLECTION IT is now possible to amplify the brief description of the West-land jet-deflection Meteor published in our issue of February18th last. The programme is not foreseen as direct-lift V.T.O. research; rather is it intended to facilitate the design and operationof very fast aircraft of conventional type. It is, of course, relatively simple to increase the maximum speed of an aircraft at the expenseof poorer behaviour at the low-speed end. Merely by deflecting some, or all, of the jet thrust downwards, it is possible to reducethe effective weight on the wing by a corresponding amount, and thereby reduce the stalling speed. At present, jet deflection is not foreseen as a take-off aid, al-though there is no doubt that a fully developed installation (in which the jet angle could be varied) might offer prospects for eithera shorter ground run or, more probably, a steeper climb-away. As an aid to the landing of high-speed aircraft, however, jet deflec-tion is most promising and can produce excellent results in applica- tions where orthodox high-lift devices would be inadequate. Inparticular, the additional lift obtained from deflected jets is sub- stantially independent of forward speed. This enables the designerto produce a high-speed aircraft, the plan-form of which is not compromised by the requirements of the lower part of the speedrange. Other advantages of jet deflection are that vertical accelera- tion can be applied immediately merely by moving the enginepower lever forward and that the geometry of the installation can be so arranged that no change of trim results. Jet deflection needinvolve no induced-drag penalty. Clearly, such a development is of a long-term nature, and thefirst thing to do is to prove a suitable deflection mechanism and then test it in flight. The first task was accomplished by theNational Gas Turbine Establishment. When the deflection valve- box was ready for flight, the P.D.S.R. (M.o.S.) asked WestlandAircraft, Ltd., to undertake exploratory flight trials. For this purpose the company were provided with MeteorRA 490, originally a Mk 4 used to flight-test the Beryl turbojet, and later modified up to Mk 8 standard. In order to align thedownward-directing jet orifices with the centre of gravity, it was apparent that the engines would have to be moved further forward;in view of this the aircraft was fitted with more powerful Rolls- Indicative of the sort of performance which can be realized with a jet at 63 deg, these curves refer to half- power (top) and full power, for a hypotheti- cal machine.JET AT Royce Nenes. In the event, 90-deg deflection was not considered,since it was desired to retain some forward dirust component, and the eventual angle selected was 63 deg from the horizontal.Conversion was done at Yeovil. The aircraft was then mounted in a fully equipped test-bed built at the company's airfield atMerryfield, where pre-flight ground-running was carried out. Apart from a slight problem of heat-transfer, no particular diffi-culties were encountered. On May 15th last year the aircraft took the air in the hands of Westland test pilot S/L. Leo de Vigne,D.S.O., D.F.C., A.F.C. He flew the aircraft for over 15 hours at Merryfield and Boscombe Down before handing over to R.A.E.pilots. Additional fins were fitted to increase the directional stability.Nevertheless, conventional aerodynamic controls naturally become less effective at low speeds and definite limits were establishedwith the Meteor. While the aircraft was in Westland hands, all take-offs and landings were made conventionally and deflectionwas not employed at altitudes below 3,000ft (at which point the Nenes were, at full power, giving 88 per cent of s-1 thrust). Thejets were arranged to be either "all horizontal" or "all deflected"; control of the deflection boxes was effected electro-hydraulicallyby actuating a small switch in the cockpit. S/L. de Vigne stated that without consulting cockpit instruments it was impossible todetermine whether the jets were deflected, so successful were the Westland engineers in eliminating trim changes. The Westland Company were given strict terms of referenceforbidding exploration of the ultimate potentialities of the aircraft. In the event, the following were some of the results achieved:stalling speed, clean, without deflection, 110 kt; stalling speed with flaps up, undercarriage down, jets deflected and 60 per centpower, 95 kt; and, during later testing at the R.A.E. with 100 per cent deflected thrust at low altitude, the aircraft has been flownunder full control at speeds below 70 kt. From assymetric flying at about 9,000ft results were: at 150 kt I.A.S. with full deflectedpower on the port engine and the starboard unit dirottled back, the aircraft could be held with three-quarters port aileron; at120 kt, with almost full power on the port engine (j.p.t. limit) it could be held with full aileron and a touch of rudder with eitherflaps up or down; at 105 kt and with full aileron and some rudder, it slowly rolled to starboard. Naturally enough, RA 490 was not subjected to any particu-larly hazardous flying during its early trials, but it has certainly accomplished its task of proving the complete practicability ofthe system. To the designer, jet deflection is valuable in that it enables a heavy load to be carried by a small aircraft with ahigh wing-loading and thus permits the attainment of a very high maximum speed; to die pilot, jet deflection means a steep approachand landing, with the engine power lever available as a sensitive control of vertical acceleration, without having to wait for theaircraft to build up or lose forward speed. OS 0 6 THRUST/WEIGHT RATIO 07 08
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