While Rolls-Royce was lukewarm on propfan technology in the 1980s (although it had the rear (pusher) configured RB.509-11 and front (tractor) configured RB.509-14 geared propfan designs, which produced using the gas generator from its XG-40 engine with of shaft power), it had now developed an open rotor engine design that was thought to be a finalist for the new Irkut MS-21 narrowbody aircraft.