Rolls-Royce Merlin exhaust flow and waste-gates, meant that this option was rejected in favour of the two-stage supercharger. Fitted with the two-stage two-speed supercharger, the Merlin 60 series gained 300 horsepower (224 kW) at over the Merlin 45 series, at which altitude a Spitfire IX was nearly faster than a Spitfire V. The two-stage Merlin family was extended in 1943 with the Merlin 66 which had its supercharger geared for increased power ratings at low altitudes, and the Merlin 70 series that were designed to deliver increased power at high altitudes. While the design of the two-stage supercharger forged ahead, Rolls-Royce also
Rolls-Royce RB3011 Rolls-Royce RB3011 The Rolls-Royce RB3011 (previously designated RB2011) is a prototype propfan engine in development by Rolls-Royce plc. The design is also known as an "open rotor" engine. The RB3011 is designed for the 180-300 passenger aircraft (e.g. Boeing 737 or Airbus A320). Rolls-Royce bought the Allison Engine Company in 1995, and has studied the Pratt & Whitney/Allison 578-DX propfan engine built in the 1980s. The engine has two contra-rotating rotors (fans) on the outside of the engine nacelle, either at the front of the assembly ("tractor") or at the rear ("pusher"). Both pusher and tractor open rotor designs form