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Aviation History
1964
1964 - 0946.PDF
FUGHT International, 2 April 1964 pitch director which, if followed, results in a smooth levelling-off at the desired height. In practice, these facilities will normally be used in conjunction with the autopilot. One big advantage of this presentation in comparison with its predecessor is the fact that by reference to the beam compass one always flies up the face of the instrument to a fixed lubber. With the drift index coincident with the lubber line, and the desired track set up by pushing in the setting knob and rotating it until the required track is showing on the 360° counter and the track pointer, a signal proportional to the heading error will be fed into the flight director. It is then only necessary to roll the aircraft up to a max- imum of 20° or 30° (according to which has been selected on the azimuth master switch), until the bank director wire moves to the centre of the instrument. This bank angle is then held until the bank director starts to lay off in the other direction. This choice of a 30: bank angle has been introduced to take account of the very high cruising speed of the aircraft. At 600 m.p.h., 20° of bank results in something very much less than a Rate 1 turn, and the spatial displacement is such that where a turn on an airway is involved it could mean that the aircraft would leave the confines of the air- way altogether. Levelling off at 30,000ft, the Machmeter settled at 0.86 at 11,600 r.p.m. with an outside air temperature of — 52°C (corrected). In this condition the q-feel resulted in a heavier elevator control and the rudders were very heavy indeed. This, of course, is of no consequence; the rudders are never normally used in cruising flight, for the yaw dampers take care of slip and skid in response to aileron displacement and transitory sideslip terms which are fed to them. The yaw dampers were then switched out, and a dutch roll pro- duced by rudder deflection. It was of a medium-high frequency with a greater yaw than roll element. There was no difficulty in damping it out with a little aileron control, which was still pleasantly light. When the yaw dampers were switched in they immediately collected the aeroplane, and the heading was constant from then on. The nose was then depressed until the critical Mach number of 0.93 was reached and the powerful tailplane trim employed to take out the stick load. The nose was then depressed still further and the loads held manually until Mach 0.96 was indicated. In this condi- tion the only indication that the critical Mach number had been exceeded by an appreciable margin was a mere suggestion of buffet, and a marked nose-up trim change. On releasing pressure on the control column the nose came up smoothly and the speed fell away rationally. The aircraft was then put into a dive again, and at Mach 0.94 the dive brakes were extended. Considerable buffet was experienced, accompanied by a powerful nose-up trim-change. Lower End of the Scale A descent was now made to 20,000ft, during which the speed was held at the Vmo of 380kt IAS. The elevator loads were comfortable, and the ailerons still pleasantly light. The speed was then reduced to 300kt, and both the outer engines put into reverse thrust. With 10.000 r.p.m. indicating, the VSI reading went from l,500ft/min to 4,000ft/min at the same speed. Some buffet was present, but the longitudinal control was quite positive and there were no oscillations in pitch. Forward thrust was then restored, and MAIN GEAR AS AIR BRAKE selected. In this condition only the mainwheels extend, resulting in two red and two green lights showing on the under- carriage indicator, and an amber warning lighting up next to the switch. Despite the aerodynamic cleanliness of the aeroplane, there should be no difficulty in complying with an air traffic control request to expedite descent. It would be interesting to know the rate of descent achievable when using this expedient coupled with air brakes and reverse thrust. The speed was then further reduced to 250kt, the mainwheels retracted and the leading edge droop lowered. At 220kt, 10° of flap was extended, 60° of bank applied and the turn tightened until the g meter registered 1.75. Stick loads were not abnormal and there was no trace of a dynamic stall threshold. Aileron self-centering is adequate, and control forces are never high. The rate of roll is very considerable, and the spiral stability appears to be slightly on the positive side of neutral. The aircraft was rolled out and the speed further reduced by lowering the gear and extending full flap. There were negligible trim changes throughout, though some buffet accompanied flap extension beyond the 20° mark. Stick forces were trimmed out at 135kt, and the power reduced FLYING THE TRIDENT . . . The centrally positioned third pilot sits within easy reach of the systems panel mounted on the starboard side behind the second pilot's seat to approach the stall at lkt/sec. Our weight was now 42,400kg, and the e.g. slightly aft of the mid position. At 115kt the incidence meter showed 13°, and the stick shaker came in, causing a very-high-frequency vibration of the control column. At 106kt and 17° incidence, the stick pusher sent the control column quickly forward, the nose dropping squarely. The point where the stick pusher takes over is just beyond CL max and is considered to be the point of the stall. The nose drop at this juncture is not considered sufficiently positive, hence the require- ment for a stick pusher. During a subsequent stall I tried to over- power the pusher, and in fact succeeded in restraining it, keeping the aircraft in an incipient stall by the use of some force. Both the shaker and the pusher are activated by probes situated just aft of the main entrance doors, and there are a number of safe- guards against possible malfunction. The pusher will operate only when both the control valves activated by separate probes are open. Should only one valve operate, then a warning light on each instru- ment panel glows, and the system can be inhibited by pushing it. The system depends on air pressure supplied from the two out- board engines and, should this supply fail, an amber caution light shows. There is a further push button on the pedestal by which air pressure can be released from the system in an emergency. The stick pusher and shaker were then isolated, and the stall approached again. Longitudinal control by the powerful tailplane was excellent throughout and the speed could be accurately con- trolled. Lateral control was good, and at an incidence of 18° at just over lOOkt a little buffet was followed by a nose-drop without roll. With the elevator fully effective only a slight depression of the nose was required to regain speed, but in the subsequent pull-out during other attempts the stick shaker came in again. Flap setting was next reduced to 20° and the shaker and pusher re-armed. This time the stick shaker came in at 129kt, and the pusher at 114kt and 17° incidence, but the aircraft remained laterally level. Flap was then extended fully, and the aircraft put into a 30° bank. By tightening the turn with falling speed the pusher was encouraged to act at 112kt, the interesting point being that, as the nose was swiftly depressed, the lateral level was naturally regained. For an aircraft of this configuration, the stalling characteristics are remarkably innocuous. Angles of incidence well in excess of those quoted have been achieved during the testing programme; in fact, each new aircraft is tested without the stick pusher and to angles of incidence in excess of 17° to check its particular behaviour in this area. The stalling tests complete, the aircraft was then turned back towards Hatfield. The flying controls are hydraulically operated by three indepen- dent systems pressurized by pumps on each of the engines, each system operating a separate jack on every control surface. Addi- tionally, two electrically driven stand-by pumps are available, and in extreme emergency a ram-air turbine can be lowered into the airflow to provide hydraulic pressure. There is no manual reversion. One of the basic design concepts on which the Trident's specifica- tion was based involved the use of fully automatic control to facilitate approaches and landings under conditions of lower
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