An equation for the range of an aircraft stating that the range is equal to K(PE/SFC)(L /D ) ln (TOW/LW), where PE is propeller efficiency, SFC is specific fuel consumption, L /D is lift-to-drag ratio, TOW is takeoff weight, LW is landing weight, and K is a constant (equal to 375 if the range is expressed in miles and the specific fuel consumption is expressed in pounds per horsepower- hour).