The F135 originated with
Lockheed Corporation Skunk Works, with efforts to develop a stealthy STOVL strike fighter for the
U.S. Marine Corps under a 1986
DARPA project under the auspices of the Advanced STOVL (ASTOVL) program, an early progenitor of the
Joint Strike Fighter (JSF) that resulted in the F-35. Lockheed engineer
Paul Bevilaqua developed and eventually patented a concept aircraft and a propulsion system called the Shaft-Driven
Lift Fan (SDLF), and then turned to Pratt & Whitney (P&W) to build a demonstrator engine. The ground test demonstrator used the first stage fan from a F119 engine for the lift fan. The engine fan and core from the
F100-PW-220 were used for the core of the demonstrator engine, and the larger low-pressure turbine from the F100-PW-229 was used 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 through the low-pressure spool shaft, which would be engaged by a clutch in STOVL mode. Finally, a variable thrust deflecting nozzle was added to complete the "F100-229-
Plus" demonstrator engine. This ground demonstrator engine proved the shaft-driven lift fan concept and led to the development of the eventual JSF engine. ASTOVL continued under the
Common Affordable Lightweight Fighter (CALF) program in 1993 before eventually being merged into the Joint Advanced Strike Technology (JAST), which was renamed JSF in 1995; under the JSF program, contracts for flightworthy concept demonstrator aircraft were awarded in 1996 to Lockheed Martin and Boeing for the air vehicle designs and P&W for the initial propulsion system. P&W developed the JSF engine from their
F119 turbofan, which powers the
F-22 Raptor, as the "F119-JSF". A flightworthy prototype system that incorporated the shaft-driven lift fan, designated "YF119-PW-611", was tested on the
Lockheed Martin X-35 concept demonstrator aircraft and first flew in 2000. P&W also made another prototype, the "YF119-PW-614", for the competing
Boeing X-32 which had direct lift system. In flight tests, the X-35B was able to demonstrate STOVL by taking off in , then flew supersonic before landing vertically. The X-35 concept beat the X-32 for the JSF competition and the YF119-611 would form the basis for the F135, which integrates the F119 core with new components optimized for the JSF. , roll posts, and rear vectoring nozzle, as designed for the
F-35B V/STOL variant, at the Paris Air Show, 2007 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. The F135 is assembled at a plant in
Middletown, Connecticut. Some parts of the engine are made in
Longueuil, Quebec, Canada, and in Poland. The first production propulsion system for operational service was scheduled for delivery in 2007 with the purpose of serving the U.S., UK, and other international customers. The initial F-35s went into production with the F135 engines, but the
GE/
Rolls-Royce team planned to develop a replacement
F136 engine in July 2009. In 2010, the Pentagon planned for the two propulsion systems to 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. (AEDC) As of 2009, P&W developed a more durable version of the F135 engine to increase the service life of key parts. The life expectancy of the parts was reduced because the hot sections of the engine (combustor and high-pressure turbine blades specifically) ran hotter than expected. The test engine is designated
XTE68/LF1, and testing is expected to begin in 2010. This redesign has caused "substantial cost growth". P&W expected to deliver the F135 below the cost of the F119, even though it was a more powerful engine. However, in February 2013 a cracked turbine blade was found during a scheduled inspection. The crack was caused by operating at high turbine temperatures for longer periods than usual. In December 2013 the hollow first stage fan
blisk failed at 77% of its expected life during a ground test. It was to be replaced by a solid part adding in weight. In 2013, a former P&W employee was caught attempting to ship "numerous boxes" of sensitive information about the F135 to Iran. Despite the troubles, the 100th engine was delivered in 2013. LRIP-6 was agreed in 2013 for $1.1 billion for 38 engines of various types, which helped to decrease the unit cost. Air Force Lt. Gen. Christopher C. Bogdan, the executive officer of the F-35 program, has called out P&W for falling short on manufacturing quality of the engines and slow deliveries. His deputy director Rear Admiral Randy Mahr said that P&W stopped their cost-cutting efforts after "they got the monopoly". In 2013 the price of the F135 increased by $4.3 billion. 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. Bogdan supported P&W'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 they stood behind their product even though they were not given access to the parts to do their own testing. 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" In July 2014 there was an uncontained failure of a fan rotor while the aircraft was preparing for take-off. The parts passed through a fuel tank and caused a fire, grounding the F-35 fleet. During
high g-force maneuvering three weeks before the flight, flexing of the engine caused excessive rubbing at the seal between the fan blisk and the fan stator initiating the impending failure. The rub caused a temperature of over 1,000 °C (1,900 °F), well beyond the material limit of 540 °C (1,000 °F). Micro cracks appeared in third-stage fan blades, according to program manager Christopher Bogdan, causing blades to separate from the disk. The failed blades punctured a fuel tank and hot air mixing with fuel caused the fire. As a short term fix, each aircraft is flown on a specific flight profile to allow the rotor seal to wear a mating groove in the stator to prevent excessive rubbing. Pratt & Whitney managed to meet their 2015 production goals, but "recurring manufacturing quality issues" in turbine blades and electronic control systems required engines to be pulled from the fleet. ==Design==