A propfan, also called an open rotor engine, open fan engine or unducted fan, is a type of aircraft engine related in concept to both the turboprop and turbofan, but distinct from both. The design is intended to offer the speed and performance of a turbofan, with the fuel economy of a turboprop. A propfan is typically designed with a large number of short, highly twisted blades, similar to the (ducted) fan in a turbofan engine. For this reason, the propfan has been variously described as an "unducted fan" (UDF) or an "ultra-high-bypass (UHB) turbofan".
A mockup of the GE36 at the Musée aéronautique et spatial Safran
The GE36 on a McDonnell Douglas MD-80 demonstrator at the 1988 Farnborough Air Show. The gearless unducted fan engine had an overall diameter of 11.67 ft (3.56 m), with either eight or ten blades in front (depending on the particular configuration) and eight blades in back.
The Progress D-236 propfan engine on the Yak-42E-LL testbed aircraft at the Paris Air Show in 1991
Progress D27 Propfans fitted to an Antonov An-70
A turboprop is a turbine engine that drives an aircraft propeller.
GE T64 turboprop, with the propeller on the left, the gearbox with accessories in the middle, and the gas generator (turbine) on the right
A Rolls-Royce RB.50 Trent on a test rig at Hucknall, in March 1945
The Kuznetsov NK-12 is the most powerful turboprop to enter service
A military transport aircraft, over 2,500 Lockheed C-130 Hercules have been built
