General Electric GE36 Unducted Fan (UDF) Turboprop Engine

General Electric designed this proof-of-concept turboprop “unducted fan” engine as part of NASA’s Advanced Turboprop Project, which was aimed at overcoming the three-fold increase in fuel prices resulting from the 1973 Middle East oil embargo. GE modified a standard F404 engine with advanced “propfan” blades in a unique gearless counter-rotation configuration, which reduced fuel consumption at flight speeds by 32 percent.

NASA successfully flight tested the engine in 1986–87 on modified Boeing 727s and McDonnell Douglas MD-80s. The engine earned the NASA and industry team the prestigious Collier Trophy for 1987. While the engine met its efficiency and overall performance goals, fuel prices fell when the embargo ended, and further development costs could not be justified.