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Aviation History
1971
1971 - 1783.PDF
The simplicity of construction and the excellent visibility afforded to the pilot are evident in these views of the Land Development Aeroplane. The picture at top was taken before the installation of a centre fin for early trials. The rear-engine installation keeps the noise and vibra tion in the cockpit to a minimum position it forms part of the 60 cu ft available for cargo. The fins and rudders are made similarly of welded tubular steel and are fabric covered. The three wings, of constant chord and section (NACA 23012), are constructed conventionally of light alloy, stressed-skin riveted with J ain pop rivets with parallel main and rear spars. There are four strong-points in the centre of each wing panel; these act as attachment points to the fuselage when posi tioned as a foreplane, as fin-post attachments, or as lift- strut and picketing points when positioned as a port or starboard mainplane. They are also employed to locate on a "luggage rack" which enables the aircraft to carry its own spare wings as it has been designed to be capable of carrying all its own spares. The four-wheel undercarriage has hydraulic brakes (a motor-car system) on the rear wheels and Ackerman steering on the front, so that the pilot may accurately position the aircraft on the ground to straddle a new pack to speed the turn-round time. The engine is a Continental C-85-12 driving a fixed-pitch 5ft 3in-dia propeller of 38in pitch. The control system bears more similarity to the Saab Viggen than any other contemporary aircraft, as in fact does the lift distribution. The foreplane is fitted with a screwjack-operated flap which doubles as a pitch trimmer and works in the con ventional sense. The mainplane has flaps on the two inboard sections and ailerons outboard in the normal way. Superimposed on these mainplane controls is the elevator which they combine in unison to form. The reasoning behind this system of control (as opposed to having an elevator on the foreplane) is the need for safety at the stall. The foreplane, which is adjustable on the ground, is mounted at +212° to the mainplane aerofoil datum and is designed to stall first. It is fitted with leading-edge breaker strips for this purpose, since its low aspect-ratio com pared with that of the wing would otherwise cause it to stall after the wing, causing undesirable pitch-up. Wind-tunnel tests showed that a vortex from the fore plane wing-tips disturbs the flow over the centre semi-span of the mainplane at a 15° angle of attack; the fin and wing fences are designed to contain this disturbance. By this means, therefore, safe slow-speed handling will be assured, since the foreplane will lose its lift before the mainplane, with its roll and pitch controls. The aircraft is very stable on the ground, the front wheels are visible to the seated pilot and manoeuvrability is good. Initial test flights in cross-winds showed, as may be expected from the bluff fuselage shape, rather high side- forces with sideslip, and also a discrepancy between the calculated and actual directional stability. This is the reason for the additional central fin but it has always been the intention to fit a shroud round the propeller to increase propeller efficiency, protect the ground crew and make a contribution to the weathercock stability. In the air the excellent view combined with low noise and vibration level, compared with that of old-fashioned front-engined aircraft, is dramatic. At the time of writing only three flights have been made, all at a take-off weight of just under 1,3001b and these not in sufficiently calm air for an accurate handling assessment. Generally, how ever, the aeroplane behaves well, with a roll/yaw relation ship not dissimilar with other light aircraft. With only 85 h.p. the aircraft is underpowered, but as it is stressed to 5 • 5g proof it is quite able to accept a larger engine which, if of sufficient power, would enable this size of aircraft to carry 1,0001b or lOOgal of spray liquid. Position error checks with a chase aircraft showed a sensitivity to inci dence and repositioning of the static vent will probably be necessary; a level flight speed of 83 m.p.h. was recorded. '^m>pA ******., ««§ NM 1 «... 8®)
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