The F-35 program instead centered on the Pratt & Whitney F135 after Pratt & Whitney’s propulsion concept was selected for production. The same basic engine family powers all three F-35 variants, although the F-35B incorporates the additional hardware required for STOVL operations.

This distinction is important.

The F-35B does not simply use a normal F135 engine and somehow point its exhaust downward. Its propulsion system includes an interconnected arrangement of mechanical and aerodynamic components that transform the engine’s power into both conventional thrust and vertical lift.

The critical component is the lift fan.

The Origin of the Lift-Fan Concept

The idea behind the F-35B’s propulsion system can be traced to Lockheed Martin’s earlier experimental work on STOVL aircraft.

During the Joint Advanced Strike Technology and subsequent Joint Strike Fighter development process, Lockheed Martin investigated concepts that could achieve vertical lift without requiring a separate lift engine.