Patent GB-1235141-A (GB)
Title: Helicopter rotor control system
Inventor: SPANGER HERBERT
IPC: B64C27/32
Filed: 1968-07-16
Abstract: 1,235,141. Helicopter rotor control system. VEREINIGTE FLUGTECHNISCHE WERKE-FOKKER G.m.b.H. 16 July, 1968, No. 33896/68. Headings B7G and B7W. [Also in Division G3] A control system for helicopters comprises a swashplate connected via a bridge linkage to a pilot's control column and to an automatic system responsive to deflections of the helicopter rotor, so that the angle of inclination of the rotor blade tip path plane to the axis of rotation of the rotor may be independently set either by the pilot or, in response to gusts or squalls, by the automatic system. When the rotor 1 is deflected through an angle a by a gust of wind, the deflection is transmitted via pivotally connected rods 2, 18, bellerank 17 and rod 16 to a double piston 15 in a control slide valve 10. Movement downwards of this piston allows hydraulic oil under pressure to pass from an hydraulic main 22 through a flexible conduit 12 to a servomotor 11, the oil displacing the servomotor piston 14 upwards and exiting from the servomotor via a flexible conduit 13 ; the motion of piston 14 is transmitted to a bridge 5 via a rod 4 pivotally connected to the bridge at 24. The point 9 on the bridge is connected to the pilot's control column 8 via a force amplifier 6, this force amplifier being unilaterally acting so that it transmits forces from the control column 8 to the bridge at 9 but does not transmit forces from 9 to the control column 8, and hence the upward motion of point 24 caused by the servomotor pivots the bridge 5 about point 9 and pivoted rod 4 moves the swashplate 3 so as to cancel out the initial rotor deflection α. When the pilot moves control column 8 to make inflight variations of α, such movement is transmitted to the swashplate via rod 7 and the force amplifier 6; to prevent the automatic mechanism described from cancelling out the value of α set by the pilot, the control column 8 is connected via pivoted rod 19, bellcrank 20 and rod 21 to the cylinder of the control slide valve 10, so that when the piston of valve 10 moves in response to angle α set by the pilot, the cylinder of valve 10 moves similarly, and there being thus no net motion in the valve 10 the servomotor 14 is not operated and point 24 may be regarded as fixed. Hence the pilot's control and the automatic control system are independent of one another. This system may be adapted to give a degree of overcontrol to minimize the effect of time lags in the system; the lower part of servopiston 14 is pivotally connected by a rod to one end of a bridge, the bridge being pivoted to the fuselage at its other end and pivotally connected to the lower part of the cylinder of the valve 10 at a point between the ends of the bridge, this arrangement transmitting a fraction of the motion of piston 14 to the cylinder 10, so that cylinder 10 moves in the opposite direction to its piston 15 thus increasing the opening of port 23 and providing overcontrol, Fig. 3 (not shown). To minimize the effects of rapid motion of the rotor caused by gusts; or rapid motions of the control mechanisms, thrcttle valves may be incorporated in the hydraulic conduits. An embodiment is described in which failure of hydraulic pressure causes a locking pin to pass through a hole in the wall of the servomotor cylinder and to mate with a groove in piston 14, the piston 14 being urged along the bore of the cylinder towards the hole by springs fitted between the piston and the cylinder ends, this motion of the piston being allowed by a valve which automatically connects conduits 12, 13 when pressure fails.