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Aviation History
1955
1955 - 0207.PDF
POSITION TANK EDGE SLOTS- ""W0 FOLDING TAILRJfAj»NINC SPOILER POSITION ON UPPER SURFACE 207 ALL MOVINGTAIL FIN FOLD LINE FIRE CONTROL RADAR TWIN MOUNTED REMOTELY CONTROLLED 20 MM CANNON SELF-SEALING FUEL TANK 12 RAI.O.BOTTLES • TAIL BUMPER AFTER-FUSELAGE COMPARTMENT. AMMUNITION, ELECTRONICS, TURRET EQUIPMENT. to ensure that the aircraft could be flown without boost, even in the most adverse conditions, without stick and pedal pressures becoming excessive. On the other hand, it was not found possible to provide a low boost ratio in the aileron circuit, and dual aileron systems were therefore provided. These independent systems, when operating normally from the dual power source, give the equivalent of a 40 :1 boost ratio, although they are irreversible. Even with one system out of use the ratio power available is reduced by only SO per cent, providing a satisfactory control; in addition a manual system with a 2 :1 mechanical advantage was incorporated, and extensive testing and field landings proved that control was adequate for airfield operation. Nevertheless, for landing into the turbulent air behind a carrier it was considered that a higher rate of roll would be needed. A sketch on page 208 shows the enormous improvement in rate of roll, particularly at the upper end of the speed range, produced by fitting spoilers (these devices have long been standard on U.S. military aircraft, such as the Neptune and Stratofortress). The A3D spoilers are located above the outer ends of the inner wings, immediately forward of the flaps. They sense their required motion from the aileron controls; when aileron control force reaches a given value one spoiler flips open under hydraulic actua- tion and approximately doubles the rate of roll. The spoilers operate independently and, as they are not actually linked with the flying-control system, their operation causes no feed-back of load on the pilot's control column. The spoilers do not operate when the ailerons are on "manual." It may be noted that, owing to wing twist, the rate of roll on ailerons alone becomes zero at a speed Well within the limit for the aircraft (see sketch). The wings also carry very large high-lift flaps hinged from brackets projecting beneath the lower wing surface. Each flap is continuous from the fuselage to the wing-fold line. On each leading edge is attached a large slat extending in sections from the pylon to the tip. The slat-and-flap combination have been found remarkably effective in reducing the A3D minimum approach and landing speeds, in the face of high wing-loading. The necessity for rapid deceleration in the air is a fairly obvious requirement for all attack aircraft, and the A3D was provided with a pair of huge speed brakes, one on either side of the rear fuselage. Each takes the form of an unperforated panel hinged at its forward edge and opened against the airstream by a hydraulic jack. As the A3D is not intended to be flown in formation it was found unnecessary to provide for partial brake operation; accordingly, the panels can be selected "on" or "off" by a switch. As both brakes are either shut, fully open, or moving together, it was not necessary to provide any "cross-ship" connection. The fuel system of the A3D was made unusually simple for an aircraft of such a size. Fuselage fuel is carried in the two tanks already mentioned, which are of the self-sealing type. In addition, the whole wing forms an integral tank between the spars from the side of the fuselage to the wing fold. . As might be expected, a circuit is incorporated which main- tains the aircraft e.g. between the correct limits as fuel is burnt. This consists of an electrically controlled valve which either allows, or prevents, a flow of fuel from the forward fuselage tar* to the rear tank. It is governed by a predetermined scheduling of tank contents taking a signal from level-sensing probes located DOUGLAS A3D-1 SKYWARfMOR: LEADING DATA Three-seat carrier-based multi-purpose bomber powered by two Pratt and Whitney J57 turbojets of 10,000 Ib each. Span, 73ft; length, 74ft 6in; height, 26ft 6in; net wing area, approximately 680 sq ft; gross weight, 70,000 Ib; wing loading, up to 103 Ib/sq ft; maximum speed, over 600 m.p.h.; operating ceiling, over 40,000ft. First flight of prototype XA3D, October 28th, 1952; first flight of production aircraft, September 16th, 1953; deliveries now being made to U.S. Navy. The composite drawing below shows, superimposed upon each other, eight of the principal "shapes" assumed by the A3D project during its formative period in 1947-9. The final A3D-1 is shown in heavier outline, and is also the subject of the revealing drawing above.
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