remain sideways across the airflow, as with a conventional wing. Powered lift Convertiplane A convertiplane takes off under rotor lift like a helicopter, then transitions to fixed-wing lift in forward flight. Tiltrotor A tiltrotor or proprotor tilts its propellers or rotors vertically for VTOL and then tilts them forwards for horizontal wing-borne flight, while the main wing remains fixed in place. Tilting ducted fan Similar to tiltrotor concept, but with ducted fans. As it can be seen in the Bell X-22. Tiltwing A tiltwing has its propellers or rotors fixed to a conventional wing and tilts the whole assembly to transition between vertical and horizontal flight. Tail-sitter A tail-sitter sits vertically on its tail for takeoff and landing, then tilts the whole aircraft forward for horizontal flight. Vectored thrust Thrust vectoring is a technique used for jet and rocket engines, where the direction of the engine exhaust is varied. In VTOL, the exhaust can be varied between vertical and horizontal thrust. Tiltjet Similar to tiltrotor concept, but with turbojet or turbofan engines instead of ones with propellers. Lift jets A lift jet is an auxiliary jet engine used to provide lift for VTOL operation, but may be shut down for normal wing-borne flight. The Yak-38 is the only production aircraft to employ lift jets. Lift fans Lift fan is an aircraft configuration in which lifting fans are located in large holes in an otherwise conventional fixed wing or fuselage. It is used for V/STOL operation. The aircraft takes off using the fans to provide lift, then transitions to fixed-wing lift in forward flight. Several experimental craft have been flown, but only the F-35 Lightning II entered into production. Lift via Coandă effect Aircraft in which VTOL is achieved by exploiting the Coandă effect are capable of redirecting air much like thrust vectoring, but rather than routing airflow through a duct, the airflow is simply routed along an existing surface, which is usually the body of the craft allowing less material and weight. The Avro Canada VZ-9 Avrocar, or simply the VZ-9, was a Canadian VTOL aircraft developed by Avro Aircraft Ltd. which utilizes this phenomenon by blowing air into a central area, then it is directed down over the top surface, which is parabolic and resembles a bowed flying saucer. Due to the Coandă effect, the airflow is attracted to the nearest surface and continues to move along that surface