Maximum range for battery-powered aircraft

The interest in electrically-driven propeller airplanes has been steadily increasing over the last 15 years with applications ranging from small electric remotely piloted vehicles up to large high-altitude/long-endurance aircraft, passing through general aviation size airplanes powered by means of hydrogen fuel cells. Unfortunately, the extension of the results valid for conventional configurations to electrically powered aircraft is not always straightforward. As a matter of fact, the determination of the best range flight condition for piston props as the minimum drag airspeed is carried out by maximizing the specific range, taking into account weight variations induced by fuel consumption. On the converse, the weight of electrically powered aircraft is constant during cruise. This is especially true for battery operated aircraft, but an approximation of constant weight also holds when hydrogen fuel cells are employed, inasmuch as only negligible variations of aircraft weight are expected, since the mass fraction of hydrogen being negligibly small