Unmanned aircraft with increased reliability and method for piloting such an unmanned aircraft

An aircraft includes an airframe including a fuselage, a wing, and a tail, a main propulsion unit, including a motor and a propeller, a flight control device, including electric actuators, movable surfaces and sensors, and an autopilot computer sending instructions to the main propulsion unit and to the flight control device. Such unmanned aircraft further includes a pair of auxiliary propulsion units, each auxiliary propulsion unit including an electric motor, a propeller driven by the electric motor, and means for orienting the plane of the propeller with respect to the airframe, the flight control computer being programmed for setting a steering angle and a propeller speed of each auxiliary propulsion unit so as to compensate for a malfunction of the flight control system and/or of the main propulsion unit, in order to control the trajectory along all axes, the unmanned aircraft thereby exhibiting increased reliability.