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Aviation History
1949
1949 - 0588.PDF
FLIGHT April jth, 1949 Detail of rotor head showing mounting, control transmission and blade articulation. The drag hinges and snubber units are evident. damping media for pitching oscillation, whilst the vertical surfaces can be moved a few degrees to give rudder effect compensation for torque reaction unbalance.^ In addition to this function they provide additional keel surface area aft of the e.g. as an aid to directional stability. One aspect of the three rotor configuration which renders it so valuable is that e.g. position is relatively uncritical, the movement range being 01 the order of 3% to 4 ft fore, and aft, whilst laterally it is quite uncritical within the practical loading limits of the aircraft. The drive transmission from engine to rotors is not com- plex, although it embraces a large number of bits and pieces. (An excellent survey of the design considerations ROTATING SWASH-PLATt HEAD involved was given by Mr. K. Watson, the chief mechanical engineer, in a paper rea.d before the Helicopter, Association —Flight, March 3rd, 19*49.) The normal I^erlin reduction gear of 0.42:1 is retained, the engine's airscrew sbdit giving drive into the distribution gearbox carried direct on the front of the engine. Torque reaction is fed back into the engine casing through a serrated coupling between distri- bution gearbox and engine reduction gearbox, whilst for- ward extensions of the fore and aft engine mounting beams take the weight of the distribution gearbox. To the airscrew shatt is splined an input drive carrier with a twin-walled scalloped skirt, carrying 15 Silentbloc- bushed couplings to the bell housing of the clutch assembly. The clutch itself is used only during running up; at above 100 rotor r.p.m., the drive path changes and the clutch becomes inoperative. Pressure is applied to the 5 Ferodo and 4 steel clutch-discs AIR HORSE .... by means of 18 G.E.C. heavy-alloy bobweights which, under centrifugal force, bear against the pressure plate and so squeeze up the disc sandwich. The steel discs are keyed to the clutch hub which, through a wedging roller assembly, transmits drive to the clutch driving-hub splined to the primary drive shaft. The plate clutch is designed to slip at power flows above that necessary for approximately 100 rotor r.p.m., and when this occurs, the drive is taken up through a second, larger, wedging-roller assembly between the clutch bell housing and the clutch driving-hub. Should the rotors tend to overspeed, the wedging rollers will act as freewheels. The advantage of this scheme is that, even if the engine is rapidly • """""^^k SPROCKET PLANET T^ CARRIER ORIVINC CONE COLLECTIVE PITCH. SCREW-JACK TRANSMISSION SHAFT Detail of hub gearbox and blade anicvkition, showing secondary bevel and epicyclic sub-stages of gear reduction, and head ele- ments of pitch-change mechanism. The inset at top right shows the interior of the swash-tolate assembly for cyclic pitch change.
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