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Aviation History
1951
1951 - 0642.PDF
The Fairey P.14 engine (below) comprised two 1,000 h.p. units. On the left, in the Fairey Battle, used as a flying-test bed, only one of the co-axial airscrews is rotating. NAVAL-AIRCRAFT DESIGN . . . •attention on landing and not have to "jockey" his aircraft. In recent years a continually increasing standard of control and stability had been demanded. The nosewheel played some part in contributing to the improvement of stability through its influence. on e.g. range, lending itself to a forward range giving greatc margins. In some cases control was reinforced by power boosting but the question of manual reversion which permitted noJowestog of the standard for slow-speed approach, had to be considlSed, If an aircraft had a natural buffet as it approached the stall, this was considered a good feature, but it was extraordinarily difficult to design it into the aircraft in the first place, and Still more difficult to reproduce on a production series. *>i*" * The piston engine was very satisfactory for deck landing: on the "cut" the response to closing the throttle was immediate, and the loss of slipstream velocity over the wing promoted the right conditions for the sink on to the deck. Turbines had introduced different circumstances, and there was a tendency for thrust to persist after the "cut". The glide-path after the "cut" could be flat or steep, depending on aerodynamic variations. To achieve a flare-out just before con- tact excess lift was required, which meant that the glide-in speed must have a margin over the engine-off stalling speed. The steeper the glide the greater the excess lift, and, consequently, the faster the glide speed. If the flare-out was not made accurately, then the undercarriage shock-absorber system was called into play and if the gliding-angle was sufficiently steep to load-up the shock-absorbing mechanism unduly, trouble must be expected. For the designer, the flat glide was the more attractive as it per- mitted the slowest approach and the easiest conditions for the flare-out, without too much demand on the shock-absorbing capacity if judgment erred. But it meant that the "cut" must be given at a point some distance aft of the stern, and this was more difficult for the batsman to judge, and made a wave-off more likely under rough-sea conditions. For both pilot and batsman it was preferable to have a steep glide-path after the "cut", so that the "cut" could be given close up to the stern, when the pitching of the deck would be less likely to interfere with the landing. The great thing, said Mr. Hollis Williams, was to build plenty of con- trollable drag into the flap system, and then this could be balanced during development by adjustments to residual thrust. The tailwheel undercarriage had many natural advantages. This was realized only after the problems of the nosewheel aircraft had been solved. The stability of a tailwheel aircraft in a rolling ship, especially with backward wing-folding, was excellent. Towing ahead or astern was simple and controllable. There was no need to worry about the dynamic motion of the aircraft on its shock- absorber system, and because of the long wheelbase there were no important magnifications of movement. The attitude on the catapult was naturally correct, and the folded height was less of a problem. The tailwheel aircraft was reasonably good directionally for take-off; it was only the landing that required a certain accuracy of speed and altitude. In a misjudged landing, leading to bounce and float over the wires, the aircraft was usually gathered up safely by the crash-barrier. , The theory underlying the change from tailwheel to nosewheel, so that a first contact with the deck, ahead of the aircraft e.g., promoted an increased wing incidence, with tendency to bounce and float, whereas the first contact aft of the e.g., promoted a decrease in incidence, reduced lift and so lessened the tendency to bounce and float. The nosewheel undercarriage was primarily a device for reducing lift at the moment of contact, but it had other advantages, and some disadvantages. Some aerodynamic device for destroying the lift on a tailwheel undercarriage might eventu- ally prove to be the right way of retaining the advantages and avoiding the disadvantages. A naval aircraft might be stowed athwartships or in a tight park on deck, with its tail projecting over the side. It was essential that the aircraft should have stability on its nosewheel undercarriage up to the ship's maximum angle of roll, which might be as much as 20 deg. The stability on the undercarriage was mainly important in the folded condition, as the aircraft was never likely to be athwartships with wings spread. The e.g. could be moved forward in the folded condition either by a forward component on the fold or, on jet aircraft, by a sort of "kneeling" position of the nosewheel. Because the base of the nosewheel undercarriage was relatively shoit, there were magni- fications of movement at the tail. If the nosewheel oleo had spongey characteristics, a sudden check by brakes or chocks when moving the aircraft might increase the height of the tail by an amount proportional to the compression of the nose oleo. A four-wheel undercarriage might be the right answer provided that the aircraft was stabilized positively one way or the other in the folded condition. An aircraft which just rocked about its main wheels on to its nosewheel or tailwheel in sympathy with the motion of the ship would impose an unacceptable limitation on parking arrangements. The nosewheel undercarriage introduced problems on the catapult. It was desirable to cater for the catapult condition under normal static attitude of the aircraft. The machine should sit naturally on the deck with its wings at a positive angle of inci- dence and its tail low down—in fact, almost in landing attitude. If it had a zero-incidence attitude, then a forced attitude would be required on the catapult. This might require ancillary equipment and would, in any case, mean the loss of valuable seconds in loading and firing. It was possible for a nosewheel aircraft to come clear off the deck under sheer recoil of the undercarriage and, according- ly, the arrester gear must be sufficiently long to retain contact with the deck. Mr. Hollis Williams described the development of arrester gear as "mainly a case of hammering on the test bench." The damping gear must be completely reliable to ensure that the hook was pressed down on the deck without bounce; it must follow the deck, whatever the motion of the aircraft, until it had picked up a wire. At present sting-type arresters were in favour, but perhaps at times the pilot would prefer his arrester hook not to be quite so far behind his sight-line, as on a large aircraft he progressed well towards the crash-barrier before feeling the satisfying drag of the arrester cable. Concerning wing folding, the lecturer said that
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