Helicopter rotor speed changing transmission

A helicopter having two power sources for driving a main sustaining rotor and auxiliary propulsion means, and a transmission system selectively operable to vary the speed of rotation of the sustaining rotor and the auxiliary propulsion means, the transmission system including, for each power source, a layshaft, a first output pinion on each said layshaft connected through a freewheel device to a rotor output gear for driving said main sustaining rotor, a second output pinion on each said layshaft connected through a freewheel device to an auxiliary propulsion output gear for driving said auxiliary propulsion means, and a third output gear on each said layshaft drivingly connected to a common differential gear having a central output shaft connected through an actuatable freewheel clutch to said auxiliary propulsion output gear.

A helicopter having two engines arranged to drive a main sustaining rotor and auxiliary propulsion means through a transmission system, the transmission system including layshafts driven by the respective engines, each layshaft having a first output pinion drivingly connected through a freewheel device to a rotor output gear for driving the sustaining rotor, a second output pinion drivingly connected through a freewheel device to an auxiliary propulsion means output gear for driving said auxiliary propulsion means, and a third output pinion drivingly connected to a common in-line differential gear having a central output shaft connected through actuatable freewheel clutches at its ends to the rotor output gear and the auxiliary propulsion means output gear, the gear ratio between the third output pinions and the differential gear being lower than that between the first and second output pinions and the rotor output gear and auxiliary propulsion means output gear respectively.