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.
Presidential Budget 10 cancelled the F136 alternate engine program for the Joint Strike Fighter, and removed all further funding for the development and procurement of this second engine. The Air Force and Navy are executing the funding appropriated by Congress in the 2009 budget to continue the F136 program. The cost to continue F136 engine development was approximately $1.8B through FY15. In addition, the Department of Defense will have to fund the production of GE engines to get the suppliers on equal footing in the amount of approximately $2.8B. Continued funding for the F136 engine carried cost penalties to both F135 and F136 engines for reduced production line, learning curves and inefficient economic order quantities. The Department concluded that maintaining a single engine supplier provided the best balance of cost and risk. DOD's belief was the risks associated with a single source engine supplier were manageable due to improvements in engine technology and do not outweigh the investment required to fund a competitive alternate engine.
The FY2010 budget request contained no funds for development of a competitive F–35 propulsion system. The budget request also contained no funds for either procurement of competitive F–35 propulsion systems or for advance procurement of competitive F–35 propulsion system long-lead components. The competitive F–35 propulsion system program is developing the F136 engine, which would provide a competitive alternative to the currently-planned F135 engine. For three years, in the committee report (H. Rept. 109–452) accompanying the John Warner National Defense Authorization Act for Fiscal Year 2007, in the committee report (H. Rept. 110–146) accompanying the National Defense Authorization Act for Fiscal Year 2008, and in the committee report (H. Rept. 110–652) accompanying the Duncan Hunter National Defense Authorization Act for Fiscal Year 2009, the House Armed Services Committee recommended increases for the F–35 competitive propulsion system, and in all cases, the other three congressional defense committees also recommended increases for this purpose. Despite section 213 of the National Defense Authorization Act for Fiscal Year 2008 (Public Law 110–181), which required the Secretary of Defense to obligate and expend sufficient annual amounts for the continued development and procurement of a competitive propulsion system for the F–35, the Department of Defense (DOD) has, for the third consecutive year, chosen not to comply with both the spirit and intent of this provision by opting not to include funds for this purpose in the budget request.
The F135 engine development program has experienced cost growth since the engineering and manufacturing development (EMD) program began in fiscal year 2002. At the beginning of EMD in fiscal year 2002, the F135 engine development program was expected to cost $4.828 billion in then-year dollars. The F–35 program manager reported that as of the end of 2008, development costs have grown to $6.7 billion in then-year dollars, an increase of $1.872 billion, or 38 percent. Additionally, the committee notes that the F–35 program manager has reported an increase of approximately 38 to 43 percent in F135 engine procurement cost estimates between December 2005 and December 2008, in the annual selected acquisition reports for the F–35C and F–35A variants. Between December 2005 and December 2008, engine procurement cost estimates for the F–35B have grown approximately 47 percent, but the F–35B engine procurement cost growth is attributable to both the F135 engine and the F–35B’s lift fan.
Conversely, the F136 engine program has not experienced any cost growth since its inception. The F136 pre-EMD contract, which began in 2002 and was completed in 2004, was for $411.0 million and did not experience cost growth. The F136 EMD contract was awarded in 2005, and the cost estimate, at $2.486 billion, has been stable since contract award. Given the F135 development and procurement cost increases, the House Armed Services Committee stated in Juned 2009 that it was "perplexed" by the Department’s decisions over the past three years to not include an F–35 competitive propulsion system program in its budget requests.
Based on the F135 cost growth, F135 test failures noted in the committee report (H. Rept. 110–652) accompanying the Duncan Hunter National Defense Authorization Act for Fiscal Year 2009, and resultant schedule delays due to F135 engine test failures, the committee remained steadfast in its belief that the non-financial factors of a two-engine competitive program such as better engine performance, improved contractor responsiveness, a more robust industrial base, increased engine reliability and improved operational readiness, strongly favor continuing the F–35 competitive propulsion system program.
