A hybrid power drive system for an aircraft that comprises a rotor and a first power drive sub-system. The first power drive sub-system includes at least one engine in connection with the rotor and provides a first power to the rotor. The hybrid power drive system also includes a second power drive sub-system connected in parallel to the first power drive sub-system, which supplements with a second power the first power delivered to the rotor during operation of the aircraft. In addition, an electric power source provides a third power to the second power drive sub-system.