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Aviation History
1957
1957 - 1393.PDF
PLIGHT, 20 September 1957 483 ,,c ne the wo independent hydraulic systems. Again unlimited nneration on either system alone is possible, except at supersonic cf^ed where the available rate of roll is reduced. The actuator valves' are operated by push-pull rods and cables via a small actuator The two hydraulic systems also feed this actuator which is used for overcoming the circuit friction so as to give very low break-out forces at the stick. Feel is provided by a simple spring that does not vary with speed. The electric trim actuator provides a bias to this spring. The rudder is little used at high speed and one hydraulic system orovides actuation and q feel. Reversion to direct pedal control is used if this one system fails. Engine failure and landing with one engine on pedal control causes no headaches. The flaps are operated by a link in the tailplane control system, in order to move also the tailplane and maintain the aircraft in trim. As the trailing edge flaps go down, the nose flaps and "blow" come into operation. For landing the flaps come full down and bring in the fuselage flaps. For take-off or overshooting, drag is reduced without any noticeable change in lift by partially raising the flaps. Handling, (a) Catapulting. The aircraft is pulled hard down on to its tailskid for launching at an attitude of 12 degrees which, surprisingly, feels quite comfortable and normal. Flap blowing is used for the catapult take-off because the extra lift available more than outweighs the loss of engine thrust; the minimum launching speed is about 10 knots less with blow on than off. A further reason for using blow is a marked improvement in fore- and-aft controllability. So far the aircraft has not been catapulted with external stores. (b) Climb: high-altitude handling. When climbing at the best climbing speed the aircraft is difficult to control accurately in pitch. The reason for this is that it suffers a nose-down trim change corresponding to a degree of tailplane angle in going from M = .85 to .95. The position is aggravated by inadequacies of the tail actuator system which are manifest to the pilot in the form of a slight lag from stick movement to aircraft response. A similar problem exists on the aileron control, making it difficult to fly the aircraft level with the degree or precision one would like. As a result both die tail and the aileron controls have been subjected to a "five-star" flight test programme. The departures from straight and level flight referred to are extremely small and in no way limit the aircraft—in fact the problem does not exist at higher speeds. Most noticeable is the disappearance of the buffet boundary when pulling g at transonic speeds. The buffet boundary is low at subsonic speeds up to .95 but at supersonic speeds quite high g can be pulled without a sign of buffet. The pitch-up problem—the bete noire of modern aircraft—has been transformed by the anhedral tailplane which is now fitted to all Scimitars. [Cmtd. overleaf "The control system has remained basically unchanged since the first flight . . ."
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