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Aviation History
1953
1953 - 1464.PDF
"Flight" photograph C-ALIK gives a winch demonstration—one of the first to be seen in this country. Winching is one of the final items in the helicopter pupil's syllabus. 3-D AVIATION . . . ward—advancing blade (starboard side) decreases pitch. Control column rearward—advancing blade (starboard side) increases pitch. Control column to right—blade over cabin increases pitch. Control column to left—blade over cabin decreases pitch.) The collective-pitch lever has a friction control on its slide. All being clear outside, the fuel tank is selected (front, rear or both), the fuel and oil cut-out levers are pulled up, a row of six switches are swept on(booster pumps, booster coil, battery and ignition) and then, with rotor brake off, the starter button can be pressed. The twist grip is opened as far as it can be (this is, in fact, very little) without bringing the starter cut-out into opera tion. This device over-rides the starter button to prevent a sudden burst of r.p.m. on firing, which might damage the automatic clutch or rotor blades. A primer, button operated, may be used spar ingly. To blow out if over rich, fuel cut-out and all the switches' except that for the battery, are put off, die throttle is opened wide, and then the engine is turned a few times with the starter. As soon a;, the engine is running evenly it should be opened-up gently to 1,800-2,000 r.p.m. when the clutch will engage and the rotors start to turn. Warming-up then continues at about 2,000 r.p.m. Rotor and engine r.p.m. needles are on one dial. Controls and instruments of the W.S.5f. They are identified as follows : Top row of dials: altimeter, compass and A.S.I.; middle row: fuel pressure, rate of climb, r.p.m., boost, oil pressure and temperature; lower row: fuel gauges, ammeter, clock, cylinder-head temperature. Dial at top of pedestal: transmission- oil temperature. Push-pull controls: rotor brake and wheel brake; between them: primer, starter button and fire button. Switches on pedestal (upper row): magnetos, battery master, booster coil, fuel pumps; (lower row) pitot heater, riav. lights, five circuit-breakers. Levers at foot of pedestal: fuel cut-off, oil cut-off, air shutters. Also shown are the fuel selector cock and, on the left of the cabin, trimmer and radio controls. 618 FLIGHT Meticulous attention was paid to the warming-up and running-up procedures on every occasion. Oil at a minimum of 35 deg C and cylinder-head temperatures at 100 deg C was the order before each flight. Mag drops, checked at 2,800 r.p.m (rotor speed 188 r.p.m.) were so slight as to be almost undetectable. The sudden closing of the throttle at 3,000 r.p.m.—a part of the run-up i procedure designed to show that the automatic rotor free wheel is working properly and the engine idling without stopping—seemed a rather drastic check, but a worthwhile one all the same. For those interested in the details, the Wesdand schedule of flying instruction is listed at the end of this account. Several of the exercises were new to me, or felt sufficiently different in the W.S.51 to call for a remark or two. I noticed very early on that the likelihood of overpitching on the W.S.51 is very much less than on the Bell. Again, the twist-grip throttle control is, with advantage, less sensitive. The linkage of power to collective pitch seems to be better also, and thus there is less to be done in the way of power adjustment when changing attitude. It would not be misleading to a pilot to remark that for normal flying the twist-grip serves to adjust engine r.p.m. almost like a v.p. airscrew control and the collective-pitch lever, in addition to its primary function, acts as a boost-control lever as well (assum ing constant r.pjn.). There are, of course, no other power controls for the Alvis Leonides. To give an example of their use, the change from climb to level flight may be instanced. The stick is eased forward to start increasing speed from the 50 m.p.h. climb to about 75 m.p.h. cruising. Immediately following this action the twist-grip on the lever is turned a little, reducing r.pjn. from 2,900 with 38in boost (1 hr climb) to 2,800 r.p.m. A reduction in boost follows this first adjustment, and only a small up-movement of the lever is then required to bring the boost to the correct figure of about 30in for cruising. In theory the linkage of collective pitch with engine throttle should make manual adjustment of the r.p.m. unnecessary. The result in practice is a fair approximation to this. Lowering of the lever fines-off the blades. The r.p.m. may build up a little even though the engine power is reduced by the same action, but this is at least a change on the safe side. Low rotor r.p.m. are to a helicopter as the approach of stalling speed is to a fixed-wing type. For hovering and slow-speed flying one should always have the full 3,000 r.p.m. engine speed and 202 rotor r.p.m. Transitions One of the things diat impressed me during early exercises was the rate at which the W.S.51 can accelerate. Helicopters are on the whole rather lumbering beasts, but if when hovering the stick is put forward and the lever kept well up, the machine puts its nose down, gathers itself up, then fairly bounds forward to 60 or 70 m.pJi. in a hundred yards or so. The acceleration effect is exaggerated by the needle of the A.S.I., which, being virtually inoperative below 40 m.pJi. usually jumps from 0 to 50 m.p.h. An accurate and reliable slow-speed A.S.I, is some thing which has yet to be produced and will certainly be called for when helicopters are regularly operated at night and on instruments. I may add that to slow down as quickly as one can accelerate is not an easy matter. The nose has to be pulled well up and the pitch and power lever lowered to prevent the machine zooming. It will be noted that "quick stops" appear in die instructional syllabus; they are regarded as an emergency procedure. Accelera tions and slow-downs are practised under the heading of "transi tions." Quite apart from the need to be able to start and finish a flight neatly, this exercise gives good practice in co-ordination. It is easy to over-speed both engine and rotor when slowing-down, and when you come to the hover, the smooth change to full power with lever well up and plenty of torque correction calls for a good deal of practice. But perhaps the best co-ordination exercise of all—and one which really makes the beginner perspire—is 360-deg turns. It might be supposed that these would merely entail taking off, hovering at, say, 10ft, and then putting on or taking off rudder as required and according to direction. I will not try to analyse in detail what really happens, but the results during early attempts are as often as not reminiscent of an Irish jig, and the stronger the wind, up to the safe maximum for practice of 15 m.p.h., the more energetic the jig. Briefly, the difficulties as I found them were as follows. A beginner can control his machine safely but not very precisely nor is his anticipation as good as it could be. Thus, having started by hovering nose into wind, he first uses rudder to start to turn. This calls for a little more or a little less power from die tail rotor according to direction, and if the correct engine and pitch-lever adjustment is not made, height may not remain steady. As the helicopter reaches the cross-wind position the full weather- cocking action has to be countered (more power to the tail rotor) and because the wind is now blowing the machine sideways, some opposite stick is called for. And, for this same reason, the stick must come back a bit to centre. Alterations of power or
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