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Aviation History
1964
1964 - 1651.PDF
904 FLIGHT International. 28 May (964 This sketch has been prepared by a "Flight International" artist to indicate the general configuration of the neat R&.I62 lift pod evolved by the Hawker Siddeley de Havilland Division, with engines "lying down" DORNIER DO31 ... in a reduction of the critical Mach number. It must be borne in mind that higher flying speeds no longer entail better transport performance on the short flying distances planned. If the wing is taken by itself, i.e., without lift-engine pods, optimum correlation of sweep-back and profile thickness for 20°-25° sweep of the quarter-chord line gives the least wing weight. Assuming a cruise Mach number of 0.7, the appropriate profile thickness is 14 to 15 per cent. But since the arrangement of the lift engines in the pods, and hence the pod length, also depend on the sweep-back, the weight of the pods must be taken into account in determining optimum wing design. The best overall weight of wing and pod is provided by less sweep-back. The foregoing considerations made Dornier decide on an engine arrangement consisting of two jet engines and ten additional lift engines. The aircraft is designed as a high-wing monoplane with pressurized fuselage and rear loading ramp. The wing is swept back 10°, and intended for a cruise Mach number of 0.7. It is equipped with double-slotted flaps, ailerons and spoilers. Fuel is carried in integral wing tanks with a capacity of about 1,540 Imp gal. The horizontal tailplane is affixed atop the vertical fin in the form of a T. The retractable tandem undercarriage with low-pressure tyres is accommodated in the fuselage. Without the two lift-engine pods—which can be removed and, if applicable, r^naced by auxiliary tanks—this largely conventional jet transport can also be operated economically from normal airports over long distances. At present the RB.153, a very advanced turbofan, is a long way from being cleared for use in aircraft. Two Do31E experimental prototype aircraft are under development at Dornier. For reasons of availability both will employ two Bristol Siddeley Pegasus vectored-thrust turbofans as the main propulsion units. To complement the Pegasus engines in the wing nacelles, it is planned to install 2x4 Rolls-Royce RB.162 lift engines in separate wing-mounted lift engine pods. The arrangement of the main engines with symmetrically located cold and hot nozzles is deter- mined by the required distance of the jet of hot gases from the fuselage. On the two prototypes the lift engines are installed m wingtip pods, so as to compensate effectively the roll moment in case of failure of an inboard engine in the vertical take-off phase. This engine layout entails a relatively simple jet control system, which responds quickly in hover and transition flight. For pitch control, high-pressure bleed air from the Pegasus engines is ducted to nozzles in the tail, two pointing up and two down. Roll control is effected by thrust modulation of the lift engines, and yaw control by swivelling the lift-engine nozzles in opposite directions. This system, in which the controls mentioned work practically inde- pendently, meets or surpasses AGARD controllability recom- mendations. The rates of climb and descent are set with the throttle of the Pegasus engines. For attitude control in hover flight a unit developed by the Bodenseewerk Perkin-Elmer is used. Design (far advanced) and construction (already under way) of the Do31E experimental aircraft are being carried out in co-opera- tion with the North German aircraft manufacturers, grouped into Entwicklungsring Nord (ERNO). In allocating the [work, account was taken of the specialized experience gained by each company in the Transall programme: the fuselage centre-section and empen- nage are being built by the Vereinigte Flugtechnische Werke GmbH, and the rear fuselage by Hamburger Flugzeugbau GmbH. Design was preceded by extensive tests on models. Various com- plete and part models were thoroughly tested in wind tunnels at Stuttgart, Gottingen and Brunswick, as well as in the Dornier research facility at Immenstaad. At the NASA Langley Research Center free-flight tests were carried out using a scale model of the Do31 with compressed-air propulsion. The NASA engineers, who have a wide experience of these testing techniques and their applica- tions, gave a very favourable evaluation of the Do31's flying characteristics in the VTOL and STOL phases. To supplement the studies on hover flight stabilization on an electronic simulator, preliminary free-flight trials are already being carried out in a control test rig which is dynamically similar; the required lift is produced by four RB.108 lift engines. Into this programme have now come the de Havilland Division engineers assigned by the Ministry of Aviation to assist in evolving the optimum joint design. Details of how this will be achieved have not been disclosed, but it is generally assumed that the basis will be the Do31 and that this will be modified in the light of British experience. In particular, Dornier will be able to use the very neat lift-jet nacelle evolved at Hatfield in which the engines lie on their sides. Although this requires 90' cascade deflectors in the nozzles, it makes the pod smaller and better streamlined and also allows lift jets to be installed directly under the wing box. To contribute to the Do31 programme may appear a poor reward for the design team at Hatfield, whose original D.H.129 was an outstanding and completely uncompromised aircraft—and technically the winner of the NBMR-4 contest. But in the absence of a British military "requirement"—and, therefore, of any money—it is the best solution that can be devised. This "Flight International" drawing outlines the basic characteristics of the original Do3l production version, with twelve vertical lift engines. Current data: propulsion engines, two 8,8O0lb-thrust Ro/Zs-Royce/MAN RB./53/72 vectored turbofans: lift units, ten S.SOOIb-thrust Rolls-Royce RB./62/3/; span, 64ft; length, 70ft bin; height, 25ft 3#n; wing area, 602 sq ft; aspect ratio, 6.8; gross weight, 51,8001b; wing loading, 86lbjsq ft; cruising speed, 465 m.p.h. O oo
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