F-35 Shaft Driven Lift Fan (SDLF)
Lockheed Martin has developed a STOVL lift system that uses a vertically oriented Lift Fan. A two-stage low-pressure turbine on the engine delivers the horsepower to drive the STOVL Lift Fan. The Lift Fan generates a column of cool air that produces nearly 20,000 pounds of lifting power using variable inlet guide vanes to modulate the airflow, along with an equivalent amount of thrust from the downward vectored rear exhaust to lift the aircraft. The Lift Fan has a clutch that engages for STOVL operations and a telescoping "D"-shaped hood to provide thrust deflection. Because the lift fan extracts power from the engine, exhaust temperatures are reduced by about 200 degrees compared to traditional STOVL systems.
The SDLF concept was successfully demonstrated through a Large Scale Powered Model (LSPM) in 1995-96 and during the flight-testing of the X-35B during the summer of 2001. The Lift Fan, a patented Lockheed Martin design, was developed and produced by Rolls-Royce Corp. at its North American facility in Indianapolis, Indiana. During the summer of 1997, Allison conducted testing of a model of the Lift Fan nozzle at the NASA-Lewis Powered Lift Facility in Ohio. The test results validated the computational fluid dynamics predictions of exhaust nozzle performance. B.F. Goodrich conducted testing of the Lift Fan clutch that is being developed under a subcontract to Allison. Testing demonstrated high-speed clutch engagements that were representative of the X-35 STOVL operating conditions.
The Lift System is comprised of the Lift Fan, Clutch, Drive Shaft, Roll Posts and the Three Bearing Swivel Module (3BSM). The exhaust from the engine flows through the 3 Bearing Swivel Nozzle (3BSN). The 3BSN nozzle, developed by Rolls-Royce, was patterned along the lines of the exhaust system on the Yakovlev Yak-141 STOVL prototype that flew at the 1992 Farnborough air show. While Rolls-Royce is a member of the Fighter Engine Team with GE on the F136, they are also subcontracted to Pratt & Whitney on the F135 to provide the Lift System for the F-35. A U.S. Navy program also developed swivel nozzles in the late 1960's and was proposed for a supersonic STOVL design by Convair (one of the Lockheed Martin heritage companies) in the early 1970's.
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