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Aviation History
1949
1949 - 1841.PDF
FLIGHT, 10 November 1949 605 student-fault is over-pitching. (This is a condition in which the rotor blades have too great a collective incidence, and no matter how wide one opens the throttle there is not sufficient power in the engine, which becomes overloaded while the machine loses lift and sinks rapidly with rotor revs falling off alarmingly.) Correction on the Hiller is simple: the drill is to reduce pitch very rapidly, at the same time giving the engine full throttle; then, just when it appears too late to avoid sharp contact with the ground, one increases the pitch again. As this condition usually arises when the student is hovering at about 30ft above the ground, it can easily be realized that the manoeuvre must be a quick one. It was during this first flight in the 360 that I had my first introduction to the stability imparted by the Hiller Rotor-Matic control. The outstanding difference between the control system of the Hiller and that of other heli- copters is these Rotor-Matic '' paddles,'' which take the form of two aerofoil surfaces set on a small-diameter bar at right angles to, but revolving in the same plane as, the main rotor blades. The cyclic-control stick is connected, through a swashplate with these paddles, so that movement of the stick results in a cyclic increase or decrease in the pitch of the aerofoils. The resulting aerodynamic forces are transmitted to the main rotor and have the effect of tilting the rotor disc in the required direction. Effect of the Control The effect of the control is one of great stability. Watch- ing carefully on the take-off, I followed through the motions with Bristow. The starting procedure seemed straight- forward, and I noticed that almost as soon as the engine fired and began running smoothly the centrifugal clutch started to engage the blades. A brief warming-up at 2,000 engine r.p.m., and we were ready to take off. Speed was brought up to 2,500 r.p.m. and slight left rudder was applied; pitch and throttle were then increased simul- taneously with a slight backward pressure on the control stick, pressure on the left rudder being increased to coun- teract the increasing engine torque. As soon as the machine became airborne at approximately 3,000 engine r.p.m., 310 rotor r.p.m., and 27-28in of manifold pressure, Bristow let go of the collective pitch and throttle ; then, with a slight adjustment to the longitudinal trimming device on the cyclic control stick, he released his hold on that too. There we were, hovering hands-ofi with no tendency to stray or "fall away." Admittedly it was a very still day and we were directly into what little wind there was. Even so, the demonstra- tion was most convincing, and later I learned, when trying to maintain a stationary hovering position, that if I made a mistake it was far better to let go of the controls and allow the machine to adjust itself, rather than to fight it back to normal. Naturally, as one gains experience this probability becomes less true, but with most students there is a tendency to over-control in the early stages. After this familiarization we flew across the airfield at four feet altitude with an air speed of about 70 m.p.h. ; trimmed for forward flight, we remained at this altitude for well over a mile, still hands-off. Then Bristow intimated that he was going to try a new experiment. Using only the collective-pitch and rudder controls, he climbed the machine to 500 feet, made a right-hand circuit and descended again to within ten feet of the ground. The complete circuit had been made without touching the cyclic control at all. A landing was not made, however, as we were still trimmed for forward flight. On trying the same thing with a left- hand circuit the machine was found to fall away badly as a result of the extra power neces- isary to tarn against the torque of the engine. A spectacular impression of a Hiller 360 heli-copter crop spraying in America. •» 5 The Hiller cockpit, showing bench-type seat-ior-three anddual control column. Nevertheless, from that day I have been completely sold on Rotor-Matic control. Without a doubt, this method of control greatly simpli- fies pilot training, though it may lead to over-confidence. For myself, I had had very little previous flying experi- ence—some 25 hours twelve months before—and yet, after only 2% hours in the Hiller, I was quite capable of solo flight. In all, I had a little over 6\ hours flying at the Paris school and now feel confident to fly the machine any- where under normal conditions. During this time I flew with Bristow 300 km across country and it may be said that neither of us had anything to do other than eat grapes and argue about our position. It is to be hoped that, despite this country's present position with regard to dollar purchases, it will be per- mitted to bring one Hiller into England, if only to be tested at our research establishments. To my mind this new method of control deserves very serious consideration. By sub-contracting the construction of this machine, and Concluded at foot of page 612)
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