Pratt & Whitney F135

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F-35A Lightning II Joint Strike Fighter Powerplant on display at Centenary of Military Aviation 2014.jpg
An F135-PW-100 powerplant on display at Royal Australian Air Force Centenary of Military Aviation 2014
Type Turbofan
Manufacturer Pratt & Whitney
Major applications F-35 Lightning II
Developed from Pratt & Whitney F119

The Pratt & Whitney F135 is an afterburning turbofan developed for the F-35 Lightning II single-engine strike fighter. The F135 family has several distinct variants, including a conventional, forward thrust variant and a multi-cycle STOVL variant that includes a forward lift fan. The first production engines were scheduled to be delivered in 2009.[1]


The origins of the F135 lie with the Lockheed Corporation Skunk Works's efforts to develop a stealthy STOVL strike fighter for the U.S. Marine Corps under a 1986 DARPA program. Lockheed employee Paul Bevilaqua developed and patented[2] a concept aircraft and propulsion system, and then turned to Pratt & Whitney (P&W) to build a demonstrator engine. The demonstrator used the first stage fan from a F119 engine for the lift fan, the engine fan and core from the F100-220 for the core, and the larger low pressure turbine from the F100-229 for the low pressure turbine of the demonstrator engine. The larger turbine was used to provide the additional power required to operate the lift fan. Finally, a variable thrust deflecting nozzle was added to complete the "F100-229-Plus" demonstrator engine. This engine proved the lift-fan concept and led to the development of the current F135 engine.[3]

P&W developed the F135 from their F119 turbofan, which powers the F-22 Raptor, as the "F119-JSF". The F135 integrates the F119 core with new components optimized for the JSF.[4] The F135 is assembled at a plant in Middletown, Connecticut. Some parts of the engine are made in Longueuil, Quebec, Canada,[5] and in Poland.[6]

The F135-PW-600 engine with lift fan, roll posts, and rear vectoring nozzle, as designed for the F-35B V/STOL variant, at the Paris Air Show, 2007

The first production propulsion system for operational service was scheduled for delivery in 2007. The F-35 will serve the U.S., UK, and other international customers. The initial F-35s will be powered by the F135, but the GE/Rolls-Royce team was developing the F136 turbofan as an alternate engine for the F-35 as of July 2009. Initial Pentagon planning required that after 2010, for the Lot 6 aircraft, the engine contracts will be competitively tendered. However since 2006 the Defense Department has not requested funding for the alternate F136 engine program, but Congress has maintained program funding.[7]

The F135 team is made up of Pratt & Whitney, Rolls-Royce and Hamilton Sundstrand. Pratt & Whitney is the prime contractor for the main engine, and systems integration. Rolls-Royce is responsible for the vertical lift system for the STOVL aircraft. Hamilton Sundstrand is responsible for the electronic engine control system, actuation system, PMAG, gearbox, and health monitoring systems. Woodward, Inc. is responsible for the fuel system.

As of 2009, P&W was developing a more durable version of the F135 engine to increase the service life of key parts. These parts are primarily in the hot sections of the engine (combustor and high pressure turbine blades specifically) where current versions of the engine are running hotter than expected, reducing life expectancy. The test engine is designated XTE68/LF1, and testing is expected to begin in 2010.[8] This redesign has caused “substantial cost growth.”[9]

Pratt expects to deliver the F135 below the cost of the F119, even though it is a more powerful engine.[10]

In 2013, Pratt found that the latest F135 issue to ground the fleet was not a design problem but likely poor workmanship,[11][12] and was caused by using the afterburner during testing at four times the stress of normal operation.[13]

The 100th engine was delivered in 2013.[14] LRIP-6 was agreed in 2013 for $1.1 billion for 38 engines of various types, continuing the unit cost decreases.[15]

In 2013, a former Pratt employee was caught attempting to ship "numerous boxes" of sensitive information about the F135 to Iran.[16]

A blisk failure in December 2013 will require the part to be redesigned, which is expected to increase the weight of the engine by around 0.2%.[17]

F-35 program office executive officer Air Force Lt. Gen. Christopher C. Bogdan has called out Pratt for falling short on manufacturing quality of the engines and slow deliveries.[18] His deputy director Rear Admiral Randy Mahr said that Pratt stopped their cost cutting efforts after "they got the monopoly".[19] In 2013 the price of the F135 increased by $4.3 billion.[20] In 2014 an F135 exploded, grounding the F-35 fleet.[21] This was found to have been caused by excessive rubbing between the turbine blades and the engine casing during high-g maneuvering three weeks before the failure.[22][23] Five engines were pulled from aircraft for failing inspections ordered after the incident.[24] Pratt's Bennett Croswell said that the part in question had not been inspected because it had never failed on other models of jet engine.[25] The fix for the part in question is expected by the end of 2014.[23] As a short term fix, each aircraft is flow on a specific flight profile to burn a trench in the stator to prevent excessive rubbing.[26]

In May 2014, Pratt & Whitney discovered conflicting documentation about the origin of titanium material used in some of its engines, including the F135. The company assessed that the uncertainty did not pose a risk to safety of flight but suspended engine deliveries as a result in May 2014. Bogdan supported Pratt's actions and said the problem was now with A&P Alloys, the supplier. The US Defense Contract Management Agency wrote in June 2014 that Pratt & Whitney’s "continued poor management of suppliers is a primary driver for the increased potential problem notifications." A&P Alloys stated that it has not been given access to the parts to do its own testing but stood behind its product. Tracy Miner, an attorney with Boston-based Demeo LLP representing A&P Alloys said, "it is blatantly unfair to destroy A&P’s business without allowing A&P access to the materials in question".[27][28][29]


Thrust vectoring nozzle of the F135-PW-600 STOVL variant
Diagram of F-35B and smaller powered lift aircraft

The F135 is a two-shaft engine featuring a three-stage fan (low pressure) and a six-stage high pressure (HP) compressor. The hot section features an annular combustor with a single-stage HP turbine unit and a two-stage LP turbine. The afterburner features a variable converging-diverging nozzle.[30]

The conventional and carrier aviation engines, the F135-PW-100 and F135-PW-400, have a maximum (wet) thrust of approximately 43,000 lbf (191 kN) and a dry thrust of approximately 28,000 lbf (125 kN). The major difference between the -100 and -400 models is the use of salt-corrosion resistant materials.[30]

The STOVL variant, F135-PW-600, delivers the same 43,000 lbf (191 kN) of wet thrust as the other types in its conventional configuration. In STOVL configuration, the engine produces 18,000 lbf (80.1 kN) of lift thrust. Combined with thrust from the LiftFan (20,000 lbf or 89.0 kN) and two roll posts (1,950 lbf or 8.67 kN each), the Rolls-Royce LiftSystem produces a total of 41,900 lbf (186 kN) of thrust, almost the same vertical lifting force for slow speed flight as the same engine produces at maximum afterburner, without the extreme fuel use or exhaust heat as wet thrust.[31]

The STOVL variant engages a clutch to extract around 35,000 shp (26,000 kW)[citation needed] from the LP turbine to turn the forward lift fans, while switching power cycle from mixed (turbofan) to unmixed (turboshaft). Power is transferred forward through shaft to a bevel gearbox, to drive two vertically mounted contra-rotating fans. The uppermost fan is fitted with variable inlet guide vanes and the fan discharges efflux (low-velocity unheated air) through a nozzle on the underside of the aircraft. This cool air from the lift fan has the added benefit of preventing hot exhaust gases from the core section from being reingested into the engine while hovering. Finally, bypass duct air is sent to a pair of roll post nozzles and the core stream discharges downwards via a thrust vectoring nozzle at the rear of the engine.[3] Measured by lift thrust in full vertical lift mode, the engine operates as 43% turbojet, 48% turboshaft, and 9% turbofan.

Improving engine reliability and ease of maintenance is a major objective of the F135. The engine has fewer parts than similar engines which should help improve reliability. All line-replaceable components (LRCs) can be removed and replaced with a set of six common hand tools.[32] Additionally, the F135's health management system is designed to provide real time data to maintainers on the ground, allowing them to troubleshoot problems and prepare replacement parts before the aircraft returns to base. According to Pratt & Whitney, this data may help drastically reduce troubleshooting and replacement time, as much as 94% over legacy engines.[33]

The F-35 with F135/F136 engines are not designed to supercruise,[34] but the F-35 can achieve a limited supercruise of Mach 1.2 for 150 miles.[35]

Because the F135 is designed for a fifth generation jet fighter, it is the second afterburning jet engine to use special "low-observable coatings".[36]


  • F135-PW-100 : Used in the F-35A Conventional Take-Off and Landing variant
  • F135-PW-400 : Used in the F-35C carrier variant
  • F135-PW-600 : Used in the F-35B Short Take-Off Vertical Landing variant

Specifications (F135-PW-100)[edit]

Diagram of engine energy for LiftSystem prototype F100 with power output

Data from[37]

General characteristics

  • Type: Afterburning Turbofan. F-35B: also partially turboshaft
  • Length: 220 in (5.59 m)
  • Diameter: 51 in (1.29 m)
  • Dry weight: 1,701 kg / 3,750 lbs



See also[edit]

Related development
Comparable engines
Related lists


  1. ^ "F135 Engine Exceeds 12,000 Engine Test Hours as Pratt & Whitney Prepares to Deliver First Production Engines" (2009). Pratt & Whitney press release. July 28, 2009. PR Newswire Link
  2. ^ "Propulsion system for a vertical and short takeoff and landing aircraft", United States Patent 5209428. PDF of original :
  3. ^ a b Bevilaqua, Paul M. (2005). One-page preview of "Joint Strike Fighter Dual-Cycle Propulsion System." Journal of Propulsion and Power, Vol. 21, 5. pp. 778-783.
  4. ^ Connors, p. 171.
  5. ^
  6. ^
  7. ^ Trimble, Stephen. "US Senate axes F-35 alternate engine"., 23 July 2009.
  8. ^ Harrington, Caitlin. (2009) "Pratt & Whitney starts development of new F-35 test engine". Jane's Defence Weekly, March 27, 2009.
  9. ^ Donley: No JSF Alternatives Exist
  10. ^ Graham Warwick, Amy Butler "Pentagon Ramps Up Pressure On F-35 Price." Aviation Week, 3 December 2010.
  11. ^ "F-35 Grounded After New F-135 Engine Problems."
  12. ^ "Pratt rules out worst-case cause for F-35 blade crack: sources."
  13. ^ "F-35 Lightning II Resume Flying – ‘Blade Crack Caused By Stressful Testing’."
  14. ^ "Pratt & Whitney Delivers 100th F135 Engine for the F-35 Lightning II."
  15. ^ MEHTA, AARON (23 October 2013). "Pratt & Whitney, Pentagon Reach $1.1B Deal on F-35 Engines". Gannett Government Media Corporation. Retrieved 23 October 2013. 
  16. ^ DOWLING, BRIAN (13 January 2014). "Former Pratt Employee Arrested Trying To Ship F-35 Documents To Iran". The Hartford Courant. Retrieved 13 January 2014. 
  17. ^ Mehta, Aaron (7 March 2014). "F-35 engine part to be redesigned". Gannett Government Media. Retrieved 7 March 2014. 
  18. ^ Dowling, Brian (March 26, 2014). "Pentagon criticizes Pratt & Whitney for 'systemic' F-35 production issues". Hartford (Conn.) Courant. Retrieved March 26, 2014. 
  19. ^ Shalal, Andrea (7 April 2014). "Pratt must push harder to cut F-35 engine cost: Pentagon". Reuters. Retrieved 8 April 2014. 
  20. ^ Shalal, Andrea (17 April 2014). "Cost to buy F-35 up 2 percent; to operate down 9 percent: Pentagon". (Thomson Reuters). Retrieved 18 April 2014. 
  21. ^ Majumdar, Dave (7 July 2014). "Sources: Engine ‘Definitely’ To Blame in June F-35 Fire". (U.S. NAVAL INSTITUTE). Retrieved 7 July 2014. 
  22. ^ Butler, Amy (13 July 2014). "Blade 'Rubbing' At Root of F-35A Engine Fire". (Penton). Retrieved 13 July 2014. 
  23. ^ a b McGarry, Brendan (15 September 2014). "Bogdan: F-35 Engine Fix May be Ready by Year’s End". Retrieved 17 September 2014. 
  24. ^ Norris, Guy; Sweetman, Bill (5 September 2014). "F-35 Fire: In Search Of A Solution". (Aviation Week & Space Technology). Retrieved 5 September 2014. 
  25. ^ Mehta, Aaron (16 September 2014). "Pratt: F-35 fix could begin installation before end of year". (Gannett). Retrieved 16 September 2014. 
  26. ^ Osborn, Kris (31 October 2014). "Pentagon Implements F-35 Engine Fixes". (Monster). Retrieved 31 October 2014. 
  27. ^ Krauskopf, Lewis (29 August 2014). "Pratt halted F-35 engine shipments in May over titanium". (Reuters). Retrieved 29 August 2014. 
  28. ^ MEHTA, AARON (3 September 2014). "F-35 Head: Delays Coming if Test Planes Grounded Through September". (Gannett). Retrieved 4 September 2014. 
  29. ^ Capaccio, Tony (29 August 2014). "Pratt & Whitney Halted F-35 Engine Delivery Over Titanium". Bloomberg. Retrieved 5 September 2014. 
  30. ^ a b "The Pratt & Whitney F135". Jane's Aero Engines. Jane's Information Group, 2009 (subscription version, dated 10 July 2009).
  31. ^ LiftSystem. Rolls-Royce. Retrieved: 29 July 2009.
  32. ^ Pratt & Whitney F135 Press release[dead link]
  33. ^ Rajagopalan, R., Wood, B., Schryver, M. (2003). Evolution of Propulsion Controls and Health Monitoring at Pratt and Whitney. AIAA/ICAS International Air and Space Symposium and Exposition: The Next 100 Years. 14–17 July 2003, Dayton, Ohio. AIAA 2003-2645.
  34. ^ Frequently Asked Questions about JSF, JSF.MIL retrieved January 2010
  35. ^ Tirpak, John (November 2012). "The F-35’s Race Against Time". Air Force Association. Retrieved 4 November 2012. while not technically a "supercruising" aircraft, can maintain Mach 1.2 for a dash of 150 miles without using fuel-gulping afterburners 
  36. ^ Mecham, Michael. "Lower F-35 Output Challenges Engine Costs." Aviation Week, 9 July 2012.
  37. ^ F135 JSF engine characteristics Retrieved: 22 May 2010

External links[edit]