An air vehicle, such as a manned or unmanned air vehicle, has a fuselage, a rotor/scissors wing, and a scissors wing. At helicopter mode, the rotor/scissors wing rotates to make the air vehicle fly like a helicopter to achieve vertical and/or short take-off and landing, hovering, and low speed flying. At airplane mode, the rotor/scissors wing and scissors wing form a scissors wings configuration to maximize the air vehicle's flying efficiency at a wide range of speed and flying conditions by adjusting the yaw angle of the rotor/scissors wing and scissors wing. During the conversion from helicopter mode to airplane mode, the scissors wing generates lift to offload the rotating rotor/scissors wing and eventually the offloaded rotor/scissors wing's rotating speed is slowed and stopped so that the rotor/scissors wing can be locked at a specific position and the conversion can be achieved. In a reverse order, the air vehicle can convert from airplane mode to helicopter mode. Either turbofan or turbojet engine, or turboshaft/turbofan convertible engine can be used to power the air vehicle.