The preliminary design phase of an aircraft requires quick calculation methods to assess its performance. This note develops an analytical method to obtain the optimum range and associated flight parameters for a piston-prop aircraft. The aircraft is flying so that the altitude and airspeed are kept constant.

Such a flight is called “constant altitude-constant airspeed” flight or simply “constant h-V flight”. Transport aircraft generally utilise this type of flight profile. Such a profile has been analysed by Bert for turbojet aircraft, and Hale has discussed it for both turbojet and piston-prop aircraft. This note further improves the analysis of constant h-V flight by optimising it independently and without using the known values from any other flight profile.