F135 Engine: Specs & Variants

What is the F135 engine?

The Pratt & Whitney F135 is a two-spool after burning turbofan and the sole propulsion system for the Lockheed Martin F-35 Lightning II, derived directly from the F119 engine lineage.

F135 engine technical specifications

The F135 has a 43-inch inlet diameter and uses advanced turbine materials to handle extreme temperatures, supported by a thermal management system that keeps it running efficiently under heavy loads.

The engine is rated in the intermediate thrust class at 28,000 pounds and can accommodate additional mechanical systems depending on the variant. The F-35B, for example, integrates a shaft-driven lift fan for vertical flight.

How much thrust does the F135 produce?

Without afterburner, the engine produces roughly 28,000 pounds-force (125 kn) of thrust, giving the aircraft strong acceleration and maneuverability.

With afterburner engaged, output climbs to a maximum of 43,000 pounds-force (191 kn).

That’s a notable step up from the F119, which generates around 35,000 pounds of thrust.

F135 engine variants explained

The F135 comes in three variants, each matched to a specific role. The F135-PW-100 powers the conventional takeoff and landing F-35A, while the F135-PW-400 is configured for the carrier-based F-35C.

The short takeoff and vertical landing version, the F135-PW-600, adds a shaft-driven lift-fan system for operations from ships or shorter runways.

F135-PW-600 and vertical lift

The F135-PW-600 introduces a shaft/drive coupling and a 3-bearing swivel duct nozzle to enable vertical lift. Rolls-Royce provides the lift components for the F-35B as a key partner in the propulsion system team.

During a vertical landing or short takeoff, lift is distributed across three points: the forward lift fan contributes 46 percent, the vectoring exhaust nozzle another 46 percent, and the bypass-duct nozzles handle the remaining 8 percent. This distribution is what allows the aircraft to hover and land in confined spaces.

Why the F135 matters for stealth

Stealth is central to the F-35, and the engine’s design contributes directly to it. The F135 supports the aircraft’s low-observable signature through 5th-generation stealth features built into its architecture, including RAM-coated curved vanes. The larger fans also move more mass flow, which helps manage internal temperatures and exhaust profiles.

The engine also has a stealth-optimized nozzle that reduces radar cross-section and heat emissions. As with the F119, shaping the exhaust plume lowers the infrared signature, making the aircraft harder for sensors to detect.

How the F135 engine is controlled

Pilots control the engine through a Full Authority Digital Engine Control (FADE) system combined with integrated prognostic health management. The system automates fuel flow, thermal management, and variable geometry components, so the pilot doesn’t need to intervene constantly across different altitudes and speeds.

Maintenance is also simplified by the design. All line-replaceable components are accessible, and technicians can remove and replace them using just 6 common hand tools, which cuts downtime and keeps more aircraft ready to fly.

F135 engine history and lineage

The F135 traces its origins to the Pratt & Whitney F119, the engine that powers the F-22 Raptor. Engineers took the F119’s core and adapted it to handle the greater airflow and mission requirements of the F-35.

During the Joint Strike Fighter program, General Electric and Rolls-Royce developed an alternative called the GE/RR F136. The Department of Defense ultimately chose the Pratt & Whitney engine as the sole power plant for the global fleet.

F135 fleet service and users

The F135 is in active service with military operators around the world. Unlike its predecessor, which was built around super cruise and air-to-air performance, the F135 was designed from the start to cover a wider range of missions, including carrier operations and vertical landings.

Running a common engine across three aircraft variants simplifies training and logistics for every allied nation operating the F-35.

What is changing in the F135 upgrade?

Rather than switching to entirely new engines from the Adaptive Engine Transition Program, the Air Force has opted for the Engine Core Upgrade (ECU), a fleet-wide F135 Block IV improvement that builds on the existing architecture. Around 400 engineers are currently working on it, with the goal of increasing thrust and thermal capacity.

The current engine already shows an 89 percent reduction in unscheduled removals compared to 4th-generation fighter engines. The ECU will use the engine’s built-in growth margins to support future electronics, cooling demands, and weapons systems, keeping the platform viable for decades ahead.