How the F-35B Works – STOVL Technology Explained
- The lift‑fan and swivel nozzle give the F‑35B vertical lift.
- A single Pratt & Whitney F135 engine powers both cruise and STOVL modes.
- Advanced avionics fuse sensor data for autonomous landing.
- STOVL capability adds weight and cost compared with the F‑35A.
How does the F-35B lift fan mechanism function?
The F‑35B combines a conventional jet engine with a vertical lift‑fan to take off from short decks and land vertically. A Pratt & Whitney F135 engine pushes air through a swiveling rear nozzle for forward thrust, while a shaft‑driven lift‑fan sits behind the cockpit and pushes air downward for lift. Sensors and flight‑control software constantly balance the two thrust sources, letting the pilot transition smoothly from cruise to hover. In essence, the aircraft uses two coordinated thrust streams—one for forward motion, one for upward lift—to achieve its unique STOVL capability.
What is the role of the Pratt & Whitney F135 engine?
Lockheed Martin describes the lift‑fan as a “quiet, high‑flow fan” that delivers about 19,000 pounds of thrust when the F‑35B is in vertical mode. The fan is driven by a shaft linked to the main F135 engine, so no separate power source is needed. When the pilot selects vertical lift, a clutch engages, spinning the fan at roughly 13,000 RPM. The fan’s airflow is directed through a series of ducts that exit just behind the cockpit, creating a cushion of air that lifts the aircraft. Because the fan is internal, the aircraft retains a sleek shape and can still cruise at supersonic speeds.
How does the F-35B hover and land vertically?
During a short take‑off, the rear nozzle points slightly downward (about 30 degrees) while the lift‑fan runs at reduced power, adding extra lift without a full vertical thrust. This lets the plane leave a 300‑foot deck with a payload of up to 12,000 lb. For a full vertical landing, the nozzle swivels to 90 degrees and the lift‑fan operates at full thrust, cancelling forward momentum. The flight‑control computer monitors airspeed, weight, and wind, adjusting nozzle angle and fan speed in real time. The result is a smooth, controlled hover that can be performed on ships without catapults.
What engines power the F‑35B?
The heart of the F‑35B is the Pratt & Whitney F135‑P turbofan, rated at about 43,000 lb of thrust in afterburner. This single engine drives both the rear thrust nozzle and the lift‑fan via a shaft and clutch system. According to the U.S. Navy’s 2025 fact sheet, the F135’s dry thrust (no afterburner) is roughly 28,000 lb, enough for high‑speed cruise, while the combined lift‑fan and nozzle output can reach 30,000 lb for vertical operations. The engine’s modular design allows for easier maintenance, but the added lift‑fan hardware increases overall weight by roughly 4,000 lb compared with the F‑35A.
How does the avionics suite manage flight?
The F‑35B’s sensor‑fusion system, known as the Distributed Aperture System (DAS) and the AN/APG‑81 radar, feeds data into a single cockpit display. The flight‑control computer uses this information to automatically balance lift‑fan thrust, nozzle angle, and wing‑control surfaces. During vertical hover, the system can keep the aircraft steady within a 2‑meter radius without pilot input, as noted in a 2024 Lockheed briefing. This level of automation reduces pilot workload and improves safety, especially on moving ship decks where wind and sea motion are unpredictable.
What are the trade‑offs of the F‑35B design?
The STOVL capability adds about 4,000 lb of weight and reduces internal fuel capacity by roughly 10 percent, limiting range to about 900 nautical miles compared with the F‑35A’s 1,200‑nm range. Maintenance costs are higher too; the U.S. Department of Defense reported an average unit cost of $115 million in 2025, about 15 percent more than the conventional variant. Operators also note that the vertical thrust system requires more frequent inspections of the lift‑fan clutch and nozzle bearings. So while the F‑35B offers unmatched flexibility, it comes at the price of extra weight, reduced endurance, and higher upkeep.
How much does an F‑35B cost?
Official procurement data released in early 2025 lists the flyaway price of an F‑35B at roughly $115 million per aircraft. That figure includes the lift‑fan, swivel nozzle, and the full suite of avionics. By comparison, the F‑35A’s price is about $95 million, making the B‑model roughly 20 percent more expensive. Nations that have bought the B‑variant, such as the United Kingdom, often negotiate support contracts that add another $30 million per plane over a 20‑year service life. Potential buyers should weigh this premium against the operational advantage of operating from ships without catapults.
Frequently asked questions
The F‑35B uses a shaft‑driven lift‑fan located behind the cockpit. Power from the Pratt & Whitney F135 engine is transferred via a driveshaft, spinning the fan to produce vertical thrust that, together with the rear nozzle, enables short takeoff and vertical landing.
During vertical landing, the lift‑fan provides upward thrust while the rear nozzle pivots to direct engine exhaust downward. The aircraft’s flight‑control system balances lift‑fan thrust, nozzle vectoring, and control surfaces to maintain a stable hover and a smooth descent.
The F‑35A is a conventional takeoff and landing (CTOL) variant for the Air Force. The F‑35B adds a lift‑fan and swiveling nozzle for STOVL operations, used by the Marines and the UK. The F‑35C features larger wings and reinforced landing gear for carrier‑based catapult launches and arrested recoveries.
As of the latest procurement round, the flyaway cost of an F‑35B is roughly US$115 million per aircraft, though total program costs including sustainment are higher.
The integrated avionics combine sensor fusion, flight‑control computers, and a digital flight‑control system that automatically manages lift‑fan speed, nozzle angle, and control‑surface deflection, allowing pilots to focus on mission tasks while the system handles the complex STOVL dynamics.
