Williams International F-121 Fanjet By Note: This item is currently in storage. The advent of small jet-propelled aircraft challenged engine manufacturers to provide propulsion systems for them. When an engine was required to propel unmanned aircraft, such as the AGM-136A Tacit Rainbow, on a one-way trip to a target, they faced the added challenge of designing a "throwaway" engine. It had to have a long "shelf-life" but a short life expectancy -- once started -- of about three hours. Williams International responded with the F-121, one of the smallest engines of its type ever built and flown in an aircraft. The F-121 first flew in an AGM-136A on July 30, 1984. Since the engine could not be started until after the vehicle left its parent aircraft, it had a pyrotechnic (cartridge) starter. Flight test experience proved it to be a relatively trouble-free engine. Out of 32 free-flight test missions, not one was impaired by an F-121 engine problem. While the display engine obviously never flew a Tacit Rainbow test mission, it was used in many "bench" tests before being retired to the museum in February 1993. TECHNICAL NOTES: Model: F-121 Length: 40 in. Diameter: 8 1/2 in. Weight: 49 lbs. Compressor: 6-stage axial Turbine: 2-stage axial Fan by-pass ratio: 1.7:1 Thrust: Approx. 70 lbs. at 45,000 rpm Click here to return to the Featured Accessions index. Find Out More Related Fact Sheets Northrop AGM-136A Tacit Rainbow Note: The appearance of hyperlinks does not constitute endorsement by the National Museum of the USAF, the U.S. Air Force, or the Department of Defense, of the external website, or the information, products or services contained therein.