GB871267A - Helicopter rotor correction mechanism - Google Patents

Abstract

871,267. Helicopters. KAMAN AIRCRAFT CORPORATION. June 19, 1959, No. 21198/59. Class 4. A helicopter comprises at least two blades each connected to a rotor drive shaft for movement about a substantially horizontal transverse axis, means for controlling the pitch of all the blades during flight, means carried by the rotor for adjusting the lift of a selected blade relatively to that of the other blade(s), and means in the fuselage for controlling the adjusting means in flight. Fig. 12 shows part of a three bladed rotor hub 152, each blade such as 160 being mounted through a pitch change bearing on a fork 166 pivoted on a flapping axis to a gimball member 164 pivoted on a drag axis 162 to an arm 158 of the hub. A pitch change arm 172 extends from the blade root, and has a cranked portion 174 which is forked at its free end, and a cylindrical member 180 extends across and is journalled in the fork. The member is recessed at 182, Fig. 14, and a rod 178 has one end pivoted within the recess on a pin 184 eccentric to the cylindrical member 180, and has the other end pivoted to a conventional swash plate 176. A crank arm 186 on member 180 is operable through link 188 by the output arm 190 of an electrical repeater unit 86 mounted on arm 172. This unit is controlled through slip rings on the rotor drive shaft, by an electrical transmitter unit under the control of the pilot. Conventional cyclic and collective pitch changes are applied to the blade through the swash plate 176, rod 178, and arm 172, pin 184 being held stationary relative to crank 174 by the output arm 190 of unit 86. If the pilot detects mismatching of the blades, by the resultant vibration or by observing the tip paths of the blades, which may have their tips painted different colours, the pilot may rotate a wheel on the transmitter unit corresponding to the mis-matched blade, producing a proportional rotation of arm 190. This sets pin 184 in a different position relative to crank 174, and thus alters the pitch of the blade for a given position of the swash plate, to correct the mis-matching. A limit switch operates a warning light visible to the pilot. All, or all but one of the blades, have such individual lift correcting means. An application is also described to a two bladed rotor as in Specification 676,398, in which the blades are connected to a hub through drag pivots associated with frictional damping means, the hub being pivoted to the drive shaft about a horizontal axis transverse but not perpendicular to the longitudinal axis of the blades. All pitch changes are effected by servo tabs on the blades causing torsional twisting of the blades about their longitudinal axes. A pair of intermeshing counter-rotating rotors is employed.