GB635017A - Improvements in or relating to pitch control for helicopter rotors - Google Patents

Abstract

635,017. Helicopters. DOMAN-FRASIER HELICOPTERS, Inc. July 2, 1947, No. 17440. Convention date, July 18, 1946. [Class 4] The pitch changing mechanism of a helicopter rotor is connected to a gyroscopic control member mounted on a vertical axis and incorporating liquid or friction dampers rendering the control member fully responsive to long term changes of fuselage attitude, but insensitive to short term changes, such as pendular oscillations of the fuselage. In the form shown the gyroscopic control member consists of the engine cooling fan 35 mounted on a vertical shaft 36 by a homokinetic universal joint 37, and connected to the piston rods of two hydraulic cylinders 30, 32 disposed perpendicular to each other. These cylinders are connected by pipe lines 23, 24 and 25, 26 to a second pair of cylinders 20, 21, the piston rods 17, 22 of which are connected to the azimuth control plate 16 at points spaced 90 degrees apart. The fan 35 is connected to the vertical shaft 36 by dashpots 38, 39 having light damping characteristics, whereby the fan 35 remains substantially horizontal when the fuselage executes pendular oscillations, but changes its plane of rotation into one perpendicular to the shaft 36 in response to gradual changes of attitude. The hydraulic connections ensure that the azimuth control plate 16 remains parallel to the gyroscopic member 35. Instead of dashpots, frictional dampers may be employed, and in either case the degree of damping may be adjustable. Manual control of the azimuth plate 16 may be effected by a pair of hand levers 46, 52, or a single universally mounted lever, connected to hydraulic pistons and cylinders 49, 54 in communication with the cylinders 19, 21 by pipelines 50, 51 and 56, 57 respectively, the latter being fitted with equalizing valves 58.