Pratt & Whitney F135
Pratt & Whitney F135-PW-600
The origins of the F135 afterburning turbofan 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 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.
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. 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 for the F-35 Lightning II single-engine strike fighter. 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.
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 is responsible for the fuel system.
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 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.
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.
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.
The STOVL variant engages a clutch to extract around 35,000 shp (26,000 kW) 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. 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. 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.
The F-35 with F135/F136 engines are not designed to supercruise, but the F-35 can achieve a limited supercruise of Mach 1.2 for 150 miles.
Because the F135 is designed for a fifth generation jet fighter, it is the second afterburning jet engine to use special "low-observable coatings".
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 (the 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. This redesign has caused “substantial cost growth.”
In 2013, Pratt found that the latest F135 issue to ground the fleet was not a design problem but likely poor workmanship, and was caused by using the afterburner during testing at four times the stress of normal operation.
The 100th engine was delivered in 2013. LRIP-6 was agreed in 2013 for $1.1 billion for 38 engines of various types, continuing the unit cost decreases.
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
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
Compressor: Axial 3 stage low-pressure compressor, 6 stage high-pressure compressor
Combustors: Short, annular combustor
Turbine: Single stage high pressure turbine, two stage low pressure turbine
Maximum thrust: 43,000 lbf (191.35 kN) max, 28,000 lbf (124.6 kN) intermediate
Specific fuel consumption: 0.886 lb/(hr·lbf) or 25,0 g/kN·s (w/o afterburner)
Thrust-to-weight ratio: 11.467