Patent GB-654089-A (GB)
Title: Improvements in adjusting and controlling means for the pitch of propellers, chieflyapplicable to helicopter rotors
IPC: B64C27/54
Filed: 1948-02-13
Abstract: 654,089. Controlling pitch of aircraft propellers and rotors. BREGUET, L. Feb. 13, 1948, No. 4332. Convention date, Feb. 18, 1947. [Classes 4 and 114] [Also in Group XXIX] A pitch-regulating device for an aircraft propeller or rotor comprises hydraulic means for varying the pitch through the agency of a main valve controlled by a centrifugal governor driven by a positive transmission from the propeller or rotor shaft, a fly-wheel driven from the shaft at a higher speed than the governor by a transmission allowing rotational lag of the fly-wheel in the event of acceleration or deceleration of the shaft, and further means responsive to such lag also acting on the main valve to vary the pitch to counteract the acceleration or deceleration. The invention is shown as applied to the pitch control mechanism of the blades 22 of a helicopter rotor. In the arrangement according to Figs. 2 and 4 the main valve 17 is subjected to the action of a compression spring 18 of the centrifugal governor 14 which is driven through gearing 15, 16 by a rotor-driven shaft 11, and the flywheel 23 is driven by planet pinions 2 carried by the governor casing 1. Rotational lag of the fly-wheel results in rotation of the normally fixed annulus 4, such rotation being transmitted by pinions 6, 7 to a rack 5 which, in the case of the arrangement shown in Fig. 2, is connected to a bell-crank 24 bearing against the base of the valve 17, which controls the supply of pressure liquid from a pump 12 to the pitchcontrolling piston and cylinder 40. In the arrangement according to Fig. 4 the pinions 6, 7 actuate an auxiliary valve 25 which with the valve 17 controls the liquid supply to the pitchcontrol cylinder 19, the piston of which is connected to the blade by a spring-loaded lever 41. In this arrangement the degree of compression of the governor spring 18 is controlled by the throttle lever 26 acting through a heart-shaped cam 27 and a lever 28, so that for small throttle openings the constant speed setting is first lowered and then held constant or increased so that the setting does not approach the autorotation value. In addition, a hand lever 30 is provided for direct manual pitch control, the governor spring being over-ridden and the valve 17 operated by links 59, 33 and a plunger 34. The link 33 is pivotally mounted at 35 on a lever 36, one end of which has a fixed pivot 37, the other being connected to the rod of the piston working in the cylinder 19. This construction prevents the blade pitch from being reduced below that determined by the governor setting. If desired the pitch setting of the rotor blades may be reversed on landing by a pneumatic jack 44 supplied with compressed air from a cylinder 47, by opening a valve 48 controlled by the throttle lever 26. In order to decrease the weight, and increase the speed of the flywheel 23, and thus increase the sensitivity of the auxiliary control, the fly-wheel may be driven by an electric motor energized by a generator driven by the rotor, Figs. 7, 8 and 9 (not shown).