Using hydraulic transmission to drive a helicopter is a good idea, when we use one-rotor design or use a many-rotors design.
One type of the Hydraulic Motors, applicable to driving rotors of a Helicopter, reminds a car motor, with pistons moved by the fluid pressure produced by a pump and passed through Hydraulic Transmission. The other type is a hydraulic turbine, which could achieve high speed of rotation. Helicopters do not need high speed of rotation of their rotors, but motors should be reliable, and, if possible, quiet. Hydraulic Motors deliver that.
Speed of rotation of a Hydraulic Motor is controlled by controlling speed of fluid passing through it. It could be reduced by diverting some fluid of the Hydraulic Transmission to other devices or by reducing speed of pumping of transmission’s fluid by the Engine.
The Engine and the Pump pumping hydraulic fluid could be placed practically in any place in Helicopter, which is convenient.
With Hydraulic Transmission, using multiple rotors is about the same as having one rotor. Speed of rotors’ rotation is controlled by valves controlling speed of transmission fluid through the motors.
Having two rotors with synchronized rotation as in a heavy lift helicopter, would require mechanical synchronization of their motors, which should reduce efficiency.
When rotors are attached to the cabin with some supporting structure, this structure could be light, because motors of rotors are fed through the hydraulic transmission.
It is easy to add a compressor, when there is hydraulic transmission in place. With it, it is easy to add four “legs” to the body of the Helicopter, with some associated support structure. Each leg should have a pneumatic cylinder, which cushions landing.
When a Helicopter is not powered and dissents, its rotor rotates automatically and this slows down dissent. This is a useful safety feature. It could be easily reproduced in case of the Hydraulic Transmission.
A controllable “shunt” could be introduced in the transmission, which allows hydraulic fluid bypassing of the Pump(s) of Hydraulic Transmission. When Pumps are not working and it is open, the rotor operates as a pump and moves hydraulic fluid (in opposite direction).
Alexander Liss 7/29/2019