The F-35B Lightning II is the short takeoff and vertical landing (STOVL) variant of the F-35 family. It is designed to operate from short runways, amphibious assault ships, and locations where conventional fighter aircraft may be unable to operate. At its heart is the Pratt & Whitney F135-PW-600, an advanced afterburning turbofan engine integrated with the Rolls-Royce LiftSystem, which redirects engine power to produce vertical lift.
The F135 is a fifth-generation fighter engine developed by Pratt & Whitney and derived partly from technology used in the F119 engine of the F-22 Raptor. Pratt & Whitney describes the F135 as producing more than 40,000 pounds of thrust. It also includes digital controls, thermal-management systems, and health-monitoring technology.
Different versions of the F135 power the three F-35 variants. The F-35A and F-35C use configurations for conventional operation, while the F-35B uses the specially modified F135-PW-600 with the equipment needed for STOVL flight.
Like other modern fighter engines, the F135 compresses incoming air, mixes it with fuel, burns the mixture, and uses the hot gases to generate thrust. An afterburner increases thrust when maximum performance is needed. What sets the F-35B apart is how part of the engine's power is redirected before it becomes rearward jet thrust.
The Rolls-Royce LiftSystem
The F-35B's STOVL capability comes from the Rolls-Royce LiftSystem, which includes a LiftFan, driveshaft and clutch, three-bearing swivel module, and roll posts. Together with the F135 engine, these components produce and control vertical thrust. Rolls-Royce states that the LiftFan produces about 20,000 pounds of cold thrust and is driven by the main engine through a driveshaft and clutch.
The LiftFan sits behind the cockpit and ahead of the main engine. In normal forward flight, the aircraft operates much like a conventional jet fighter. During STOVL operations, engine power is transferred through the driveshaft to the LiftFan, which pushes a large volume of cool air downward to create vertical lift.
This system is different from simply pointing the whole engine downward. The F-35B divides lift and control among several thrust sources, allowing it to hover and land vertically while still retaining the performance of a supersonic fighter.
The Three-Bearing Swivel Module
At the rear of the aircraft is the three-bearing swivel module (3BSM), a swiveling exhaust nozzle that redirects hot exhaust from the F135 downward. Rolls-Royce states that the nozzle can rotate about 95 degrees in roughly 2.5 seconds.
In conventional flight, the exhaust points rearward to propel the aircraft forward. During short takeoff or vertical landing, the nozzle rotates downward to provide another major source of lift.
The LiftFan and 3BSM work together: the LiftFan provides forward vertical lift, while the rear exhaust supplies additional downward thrust. Pratt & Whitney's F135-PW-600 specifications place the STOVL propulsion system in the 41,000-pound thrust class.
Roll Control
Producing vertical thrust is only part of the problem. A hovering aircraft must also be able to control its movement and remain stable. The F-35B accomplishes this with roll posts located in the wings.
The roll posts use engine-derived air to produce downward thrust near the wingtips. By controlling this thrust, the aircraft maintains lateral stability and roll control while hovering. Rolls-Royce identifies each roll post as producing about 1,950 pounds of thrust.
Together, the LiftFan, swivel nozzle, and roll posts allow the flight-control system to coordinate multiple thrust sources, one of the most technically demanding aspects of the F-35B.
Digital Engine Control
The F135 also relies on digital control technology. Its Full Authority Digital Engine Control, or FADEC, manages key engine functions automatically. During STOVL operation, precise control is essential because small thrust changes can affect the aircraft's position while hovering.
The propulsion system coordinates engine power, LiftFan operation, exhaust-nozzle position, and roll control, allowing the pilot to command STOVL manoeuvres without managing each component manually.
Why the Engine Is Important
The F135-PW-600 is important because it solves two competing requirements. A fighter needs a powerful engine for high-speed flight, while a vertical-landing aircraft needs large amounts of lift at low forward speed. The F-35B combines both in one integrated propulsion system.
The aircraft can make a short takeoff instead of using a long runway, then slow down and transition into a hover for vertical landing. This is valuable for naval forces operating from amphibious assault ships and for missions from austere or damaged airfields.
The technology has trade-offs. The LiftSystem adds weight, occupies space, and increases mechanical complexity compared with a conventional fighter engine. The aircraft's design had to fit the LiftFan and related equipment while preserving stealth characteristics.
The F-35B uses the Pratt & Whitney F135-PW-600, but this engine is best understood as the core of a sophisticated STOVL propulsion system that combines the F135 with the Rolls-Royce LiftSystem.
The engine supplies the power for high-performance flight, while the LiftFan converts part of that power into vertical lift. The three-bearing swivel module redirects rear exhaust downward, and the wing-mounted roll posts provide control during hovering. Digital controls coordinate these systems so the aircraft can shift between conventional and STOVL flight.
The result is one of the most distinctive propulsion systems ever fitted to a fighter aircraft. The F135-PW-600 allows the F-35B to combine supersonic, stealthy performance with short takeoff and vertical landing capability, enabling operations from places inaccessible to conventional fighters.
