Lift fan

A lift fan is a type of powered lift system utilized primarily in vertical takeoff and landing (VTOL) aircraft. It consists of a fan, usually ducted, installed within the fuselage or wing of the aircraft, oriented to produce a downward thrust for vertical lift. Lift fans differ from propellers in that they are typically smaller in diameter and operate at higher rotational speeds, generating lift by accelerating a larger volume of air through a smaller area.

Lift fans are typically powered by a separate engine or by diverting power from the main propulsion engines. During vertical takeoff and landing, the lift fan provides the primary lift force, while during forward flight, the lift fan is either shut down or its inlet and outlet are covered to reduce drag. In some designs, the lift fan may continue to operate during forward flight to provide additional lift augmentation.

Advantages of lift fan systems include a relatively compact design and the ability to generate significant thrust for vertical lift. Disadvantages include complexity in design and operation, potential for increased weight and drag, and noise generation. Lift fan technology has been explored and utilized in a variety of experimental and operational VTOL aircraft.