US Patent 9174741 Hybrid powertrain system

A hybrid powertrain for an aircraft may include a drive shaft, the drive shaft, an internal combustion engine to selectably drive the drive shaft, a propeller coupled to the drive shaft and an electric motor having a stator and a rotor and operable to selectably drive the drive shaft. The drive shaft may extend through the electric motor. The rotor may be coupled to the drive shaft to rotate with the drive shaft and the rotor is a flywheel for the internal combustion engine.