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Aviation History
1946
1946 - 1154.PDF
592 FLIGHT JUNE I 3TH, 1946 Counteracting Single-rotor Torque, and an Intermediate Stage Between Qyroplane and Helicopter THE relative simplicity of thesingle-rotor helicopter is attrac-tive, but the problem of torque reaction is somewhat troublesome. Igor Sikorsky has shown that it can be controlled by a small airscrew at the tail, set with its axis at right angles to the line of flight. Other arrangements are possible, and two projects which were stopped by the war are of more than passing interest. One was provisionally patented by the Cierva Autogiro Co., Ltd., and the other by its licensees, G. and J. Weir, Ltd. The patents were not completed, but it is interesting to recall that the firms applied to their 1938-39 schemes the name "Gyrodyne." The Weir Gyrodyne was a heli- copter, while the Cierva project was more ambitious in that it could oper- ate either as a helicopter or as an Autogiro, while in the cruising condi- tion it was intermediate between the two. ferential. For starting, the primary clutch was engaged, and the airscrew, driven through the differential, began to turn until it experienced an ap- preciable resistance from the air. As this resistance grew, torque would be smoothly and progressively applied to the rotor, which would speed-up until rotor and airscrew were taking the same amount of torque. Jump-starts would be achieved without any ap- preciable overspeeding of the engine. In the Cierva project two airscrews were to be used for forward pro^ul- The Weir project in which the offset airscrew gives pro- pulsion and a very "cushy" clutch effect for starting the rotor. hind the rotor. In other words, the mean axial flow through the rotor disc was substantially zero. In that atti- tude the torque required is approxi- mately equal to the torque needed to overcome the profile drag of the blades. Minimum Drag In addition, the slight backward in-/ ' clination of the thrust vector of the rotor required a propulsive thrust, to be supplied by the airscrew, which also had to overcome the drag of the Known as the Type W.7, the Weir project had as its most unusual fea- ture an offset airscrew with its axis in the fore-and-aft direction, the thrust of this airscrew counterbalanc- ing the torque-reaction of the rotor. There was, however, more in it than that. The engine was to drive, through a primary clutch, a mechanical dif- ferential gear which divided the torque evenly between the rotor and the airscrew. Yawing control was by brakes or clutches on the differential shafts. An "Air" Clutch In addition to this, however, the airscrew provided a secondary fluid (air) clutch effect by the difference of the moment of inertia between rotor and airscrew and the mechanical dif- CIRCULAR HONEYCOMB RADIATOR WITH AUXUARY FAN COOLING IN AIR DUCT sion, that on the side where the rotor blades were advancing being perma- nently geared to the rotor, while that on the "retreating " side had a clutch mechanism so arranged that when the rotor clutch was engaged, the airscrew was disengaged, or vice versa. The idea was that if it was desired to fly the machine as a gyroplane, both air- screws would provide propulsion, the rotor autorotating as in the Autogiro. Rudder control was by pedal, pitch being increased on one airscrew and decreased on the other. It was, however, in the stage inter- mediate between Autogiro and heli- copter that the Cierva Gyrodyne dis- played its greatest advantage. Things were so arranged that, at the cruising (Speed of the machine, the angle of in- cidence of the rotor disc to the air ahead of the rotor was positive and smaller than the downwash angle be- J AR ENTRANCE RDR CABIN HEATING J In the Cierva project two airscrews were to be us d, one perman- ently coupled to the transmission and the other having a clutch. rotor in the plane of the rotor disc and, of course, the parasite drag of the whole aircraft. The torque in- put to the rotor would be lower than if it were operating in the pure heli- copter condition, and a further ad- vantage was that the pitch angle was within, or only just beyond, the maxi- mum limit of the autorotative range. This meant that little or no change of pitch angle was required for passing from power-driven flight to motorless gliding in autorotation. Trimming in yaw could be attained by varying the airscrew pitch or by the adjustable tail fin situated in the slipstream of the permanently con-jt nected airscrew. w Of other refinements visualized for the Cierva Gyrodyne, mention may be • made of a governor for controlling the mean pitch angle of the rotor blades and keeping rotor speed constant. This was to operate very much as does the hydraulic mechanism of the de Havilland constant-speed airscrew. Interesting as these two projects are, they add still more mechanical com- plication to the helicopter and, as we pointed out in a leading article recently, it seems rather a pity that the gyroplane has been dropped en tirely. Jump-start versions gave nearly all the advantages of the heli- copter and were relatively simple.
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