This paper proposes a method to derive the torque and speed of an airplane propeller out of a given altitude and velocity profile. The method includes an efficiency optimization for the variable pitch propeller at every single time step and therefore, utilizes the advantage that an electric drive system can dynamically follow the resulting variable speed reference. The determined torque-speed-characteristic forms the basis for designing a suitable electrical motor. Additionally, the influence of the blade angle to the required power of the drive is discussed. Finally, the derived method is applied in order to compare the proposed variable speed strategy to a conventional strategy with constant rotational speed, which reveals only small improvements.