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Originally Posted by sperry
Actually, I don't know which one they selected (if they've even got that far). But my money's on the Boeing design that's sans the ducted fan and associated driveshaft/clutch... that's just too many bits to break. Stick w/ what works... the design similar to the Harrier w/ the forward nozzles.
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Sorry, Complexity won out, and the Lockheed lift fan won.
One of the primary reasons was it has better resistance to heat soak. (The engine injesting its's own hot exhaust and losing thrust) This is one of the Harrier's biggest problems. Losing thrust in close proximity to the ground in VTOL configuration.
From
http://www.jsf.mil
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Shaft Driven Lift Fan (SDLF)
Lockheed Martin developed the idea for a Short Take-Off Vertical Landing (STOVL) lift system that uses a vertically oriented Shaft Driven Lift Fan (SDLF). A two-stage low-pressure turbine on the engine provides the horsepower necessary to power the Rolls-Royce designed Lift Fan. The Lift Fan generates a column of cool air that provides 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 utilizes a clutch that engages the shaft drive system for STOVL operations. 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 concept, was developed and produced by Rolls-Royce Corp. in Indianapolis, Indiana and in Bristol, England.
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