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F-35 Joint Strike Fighter (JSF) Propulsion

The F-35 Propulsion Systems are the most powerful fighter/attack turbofans in the world. There are two manufacturers with propulsion systems currently being tested. The propulsion systems are interchangeable and both will power the F-35. There are two major engine variants for the F-35. One engine will power the CTOL and CV versions of the aircraft, while the other will power the STOVL version. The F135 engine is made by Pratt & Whitney, the F136 by a team, known as the Fighter Engine Team comprised of General Electric and Rolls-Royce. Both the F135 and the F136 STOVL engines will utilize common exhaust and Lift System systems.

Engine testing was well along when in 2004 F-35 Propulsion team members identified a new requirement: find ways to increase installed propulsion efficiency as part of the SWAT effort to improve STOVL variant short-takeoff distance and vertical-lift bring-back capability. Ultimately, the Propulsion team succeeded through a number of improvements, including optimization of the STOVL nozzle design to generate more STOVL mode thrust. As a product of this activity, the installed vertical hover thrust was increased by almost 700 pounds and the short-takeoff roll axial thrust was increased by 2,800 pounds.

Overall, the Propulsion Integration Team has had a very successful and busy year during 2004, starting with the completion of the F-35 Propulsion Integration Critical Design Review in January. Other propulsion integration testing successfully completed included: full-scale inlet/engine compatibility testing in March, STOVL low-speed wind tunnel inlet testing in May, core nozzle testing in June, up-and-away jet effects testing and static inlet testing in August, hot gas ingestion testing in September, STOVL inlet and force moment testing in October, and a full-scale plume survey testing in December. The Propulsion Integration Team fi nished 2004 by successfully completing the F-35 Propulsion Integration Technical Interchange Meeting, which reviewed progress made since the Propulsion Integration Critical Design Review in January 2004 and set the team objectives and priorities for 2005.

Moving into 2005, Propulsion engineers were working toward timely qualification of the CTOL and STOVL propulsion systems. Challenges remained, but the success in solving weight/propulsion issues early demonstrates confidence in a replan that called for CTOL engine installation in the first F-35 flight test aircraft in January 2006 and flight test initiation in the third quarter of 2006.

F135
The Pratt & Whitney F135 family of advanced propulsion systems utilize cutting edge technology to provide the F-35 with higher performance than conventional fighter aircraft. The engine consists of a 3-stage fan, a 6-stage compressor, an annular combustor, a single stage high-pressure turbine, and a 2 stage low-pressure turbine.

The F135 is using the lessons learned from the F119 engine core and the JSF119 during the CDA stage to reduce risk in SDD. During SDD the F135 test engines will undergo a range of ground and flight tests to simulate various mission profiles. In these tests the system demonstration engines will be run for hours throughout various flight envelopes to ensure they meet performance requirements. One of the vital milestone tests occured at the end of 2003 with the first F135 engine to test.

The first CTOL F135 engine test occurred on 11 October 2003. The first STOVL F135 engine test occurred on 14 April 2004.

F136
The GE Rolls-Royce Fighter Engine Team (FET) F136 engine Pre-SDD phase objective was to reduce risk prior to entering SDD. The FET is utilizing technology developed from previous aircraft engine programs to design this engine. The F136 engine consists of a 3-stage fan, 5-stage compressor, a 3-stage low-pressure turbine section and a single stage high-pressure turbine.

The F136 team transitioned into the SDD phase of their program later in 2005. The F135 and F136 teams are working closely to develop common propulsion system components.

The first CTOL F136 engine to test occurred on 22 July 2004. The first STOVL F136 engine to test occurred on 10 February 2005.

Rolls-Royce Lift System
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. The Lift System is comprised of the Lift Fan, Clutch, Drive Shaft, Roll Posts and the Three Bearing Swivel Module (3BSM).

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 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. 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.