Pratt & Whitney F135

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The F135 afterburning turbofan is the primary powerplant for the advanced, single-engine tactical F-35 Lightning II, being developed by Lockheed Martin. The F-35 has unique capabilities for land-based conventional takeoff and landing (CTOL), carrier-variant takeoff and landing (CV) and short takeoff and vertical landing (STOVL). The F135 propulsion system already proved that it can meet these diverse requirements, during preliminary flight testing of the X-35 and X-32 aircraft in 2000. As planned, new F-35 aircraft will replace the F-16 Fighting Falcon, A-10 Thunderbolt II, AV-8B Harrier, and F/A-18 Hornet.

Pratt & Whitney, a United Technologies company, developed the engine from their most technologically advanced F119 turbofan which powers the F-22 Raptor. The F135 integrates the proven F119 core, a high-performance six-stage HP compressor and single-stage HP turbine unit, with a new low-pressure spool, featuring a very high pressure ratio fan driven by a single-stage LP turbine. In addition, the propulsion system features advanced prognostic and on-condition management systems that provide maintenance awareness, autonomic logistic support, and automatic field data and test systems.

Propulsion system support and maintainability are further enhanced by the F135's maintenance-focused design. It has approximately 40 percent fewer parts, which also improves reliability. All line-replaceable components (LRCs) can be removed and replaced with a set of six common hand tools. And, the F135 has a 50 percent lower infrastructure support requirement compared to current engines.

The first production propulsion system for operational service is scheduled for delivery in 2007. The F-35 will serve the U.S. Air Force, Navy and Marines, the United Kingdom's Royal Air Force and Royal Navy as well as other international customers.

All initial F-35s will be powered by the F135. Plan is that from 2009 to 2010 engine contracts will be split between P&W and the F136. The General Electric/Rolls-Royce F136 turbofan is also being developed specifically for the F-35. Initial Pentagon planning also requires that after 2010, the Lot 6 aircraft, the engine contracts will be competitively tendered. However, recent Defense Industry reports seems to indicate that the Pentagon is poised to cancel the alternate F136 engine program, and recoup $1.8 billion in the coming years for other Air Force and Navy priorities. Canceling this initiative would leave Pratt & Whitney, maker of the F135 engine, as the sole provider of engines for the fighters.

Whatever powerplant is selected for STOVL variants they will both employ the Rolls-Royce LiftSystem ® which incorporates:

Rolls Royce LiftFan ®
Engine to fan driveshaft
Three-bearing swivel module (thrust vectoring)
Roll posts

The F135 STOVL engine delivers 17,600 lb_f (78.3 kN), the LiftFan 18,500 lb_f (82.3 kN) cold thrust and the roll posts 3,700 lb_f (16.5 kN) for a sum of 39,800 lb_f (177 kN) for the entire system. This compares with the a maximum thrust of 23,800 lb_f (106 kN) for the Harrier's Rolls-Royce Pegasus engine.

A major feature of the F135 STOVL engine is flow multiplication, which enhances the lift thrust available. Flow multiplication is obtained by the addition of airflow from a remote shaft-driven fan, in the lift mode. A clutch is engaged, to extract around 35000shp extra power from the LP turbine. Power is transferred through a bevel gearbox, to drive a vertically mounted contra-rotating fan. The uppermost fan is fitted with variable inlet guide vanes, whilst the fan efflux discharges through a thrust vectoring nozzle, on the underside of the aircraft. Owing to the significant increase in LP turbine expansion ratio, implied by the large power off-take, the exhaust of the basic turbofan is switched from a mixed to unmixed configuration. Bypass duct air is ducted to a pair of roll post nozzles, whilst the core stream discharges through a thrust vectoring nozzle at the rear of the engine.