Wikipedia
Proprotor
A proprotor is a spinning airfoil that is used as both an airplane-style propeller and a helicopter-style rotor during the same flight. Proprotors are typically used on vertical takeoff and landing (VTOL) aircraft.
The dual-role airfoil is accomplished by one of several design approaches:
:*changing the angle of attack of the wing that the proprotor is attached to, from approximately zero degrees to around ninety degrees: a tiltwing aircraft,
:*changing the angle of attack of only the rotor hub, and possibly the engine that drives it, as on a tiltrotor,
:*changing the angle of attack of the entire aircraft, as on a tailsitter, which launches and lands on its tail.