Abstract: During flight, helicopter landing gears are suspended by a tuning spring m the helicopter airframe to provide limited relative movement between the landing gear masses and the airframe. As the aircraft vibrates due to vertical or in-plane forces at the rotor head, the landing gear masses react oppositely thereto, thus generating balancing forces which are applied to the airframe to balance the rotor excitations.

Abstract: An angle gear box for a helicopter main rotor drive has a more compact arrangement of the usual gear train elements of the input section as well as a freewheel unit. The input section gear train includes a power input shaft mounted on bearings and having a bevel pinion and a power output shaft mounted on bearings and having a bevel gear meshing with the pinion. The output shaft has an axial chamber in which the freewheel unit is housed and from which it can be readily removed without disturbing the mounting elements of the gear train and the critical relationship of the high speed bevel gears.