page_title: Lockheed Martin F-35 Lightning II
section_title: Engine
hierarchical_section_title: Lockheed Martin F-35 Lightning II / Design / Engine
caption_attribution_description: English: F-35B Joint Strike Fighter's thrust vectoring nozzle and lift fan
context_page_description: The Lockheed Martin F-35 Lightning II is an American family of single-seat, single-engine, all-weather stealth multirole combat aircraft that is intended to perform both air superiority and strike missions. It is also able to provide electronic warfare and intelligence, surveillance, and reconnaissance capabilities. Lockheed Martin is the prime F-35 contractor, with principal partners Northrop Grumman and BAE Systems. The aircraft has three main variants: the conventional takeoff and landing F-35A, the short take-off and vertical-landing F-35B, and the carrier-based F-35C.
  The aircraft descends from the Lockheed Martin X-35, which in 2001 beat the Boeing X-32 to win the Joint Strike Fighter program. Its development is principally funded by the United States, with additional funding from program partner countries from NATO and close U.S. allies, including the United Kingdom, Italy, Australia, Canada, Norway, Denmark, the Netherlands, and formerly Turkey. Several other countries have ordered, or are considering ordering, the aircraft. The program has drawn much scrutiny and criticism for its unprecedented size, complexity, ballooning costs, and much-delayed deliveries.
context_section_description: The single-engine aircraft is powered by the Pratt & Whitney F135 low-bypass augmented turbofan with rated thrust of 43,000 lbf (191 kN). Derived from the Pratt & Whitney F119 used by the F-22, the F135 has a larger fan and higher bypass ratio to increase subsonic fuel efficiency, and unlike the F119, is not optimized for supercruise. The engine contributes to the F-35's stealth by having a low-observable augmenter, or afterburner, that incorporates fuel injectors into thick curved vanes; these vanes are covered by ceramic radar-absorbent materials and mask the turbine. The stealthy augmenter had problems with pressure pulsations, or "screech", at low altitude and high speed early in its development. The low-observable axisymmetric nozzle consists of 15 partially overlapping flaps that create a sawtooth pattern at the trailing edge, which reduces radar signature and creates shed vortices that reduce the infrared signature of the exhaust plume. Due to the engine's large dimensions, the USN had to modify its underway replenishment system to facilitate at-sea logistics support.
  The F135-PW-600 variant for the F-35B incorporates the SDLF to allow STOVL operations. Designed by Lockheed Martin and developed by Rolls-Royce, the SDLF, also known as the Rolls-Royce LiftSystem, consists of the lift fan, drive shaft, two roll posts, and a "three-bearing swivel module" (3BSM). The thrust vectoring 3BSM nozzle allows the main engine exhaust to be deflected downward at the tail of the aircraft and is moved by a "fueldraulic" actuator that uses pressurized fuel as the working fluid. Unlike the Harrier's Rolls-Royce Pegasus engine that entirely uses direct engine thrust for lift, the F-35B's system augments the swivel nozzle's thrust with the lift fan; the fan is powered by the low-pressure turbine through a drive shaft when engaged with a clutch and placed near the front of the aircraft to provide a counterbalancing thrust. Roll control during slow flight is achieved by diverting unheated engine bypass air through wing-mounted thrust nozzles called roll posts.
  An alternative engine, the General Electric/Rolls-Royce F136, was being developed in the 2000s; originally, F-35 engines from Lot 6 onward were competitively tendered. Using technology from the General Electric YF120, The F136 was claimed to have a greater temperature margin than the F135. The F136 was canceled in December 2011 due to lack of funding.
  In 2016, the Adaptive Engine Transition Program (AETP) was launched to develop and test adaptive cycle engines, with one major potential application being the re-engining of the F-35. Both GE and P&W were awarded contracts to develop 45,000 lbf (200 kN) class demonstrators, with the designations XA100 and XA101 respectively. In 2017, P&W announced the F135 Growth Option 1.0 and 2.0; Growth Option 1.0, which had finished testing and was production ready in May 2017, was a power module upgrade that offered 6–10% thrust improvement and 5–6% fuel burn reduction. The power module could be retrofitted onto older engines and seamlessly added to future engines at low cost rise and no impact on delivery. Growth Option 2.0 would be the adaptive cycle XA101. In June 2018, Pratt & Whitney changed its development plan for the F135, and instead offered an adaptive three-stream fan as Growth Option 2.0 that's separate from the XA101, which would instead have a new engine core.
caption: Illustration of the STOVL swivel nozzle, lift fan, and roll-control posts
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