The AL-41F is a designation for two different Russian military turbofan engine variants. A single Rolls-Royce Spey turbofan engine serves as the AMX's powerplant. A fan disk is the central hub of a fan in a turbofan engine. The X-50A was powered by a single conventional turbofan engine. Development of the WS-15 afterburning turbofan engine began in the early 1990s. . The powerplant used is the Lotarev D-36 turbofan engine. It features a single Rolls-Royce Pegasus turbofan engine with two intakes and four vectorable nozzles. The propulsion unit is a turbofan engine. During development, Saab had opted to power the type using a single large turbofan engine. Boeing and Saab offered a new-technology design powered by the General Electric F404 turbofan engine. The Harrier is powered by a single Pegasus turbofan engine mounted in the fuselage. In 1971, the first Model 25 powered by a Garrett TFE731-2 turbofan engine was flown. It would be a stealthy flying-wing concept aircraft with internal weapons and a turbofan engine. The U-2S and TU-2S variants incorporated the more powerful General Electric F118 turbofan engine. It has a low-mounted cantilever wing and is powered by a single turbofan engine.