Common components could reduce development costs. Shared manufacturing processes could simplify production. A common supply chain could reduce logistical complexity. Training, maintenance, upgrades, and spare parts could also benefit from similarities between the variants.

However, commonality also created a major engineering problem.

The aircraft had to accommodate requirements that were sometimes fundamentally incompatible.

The F-35A needed neither carrier landing equipment nor a vertical-lift system. The F-35C needed a larger wing, stronger landing gear, and structures capable of surviving carrier operations. The F-35B needed perhaps the most unusual modification of all: an integrated STOVL propulsion system.

The challenge was therefore not simply to build a fighter and then create two modified versions. The basic architecture had to be sufficiently flexible from the beginning to accommodate the three configurations.

That requirement had profound consequences for propulsion.

Why One Engine?

The decision to use one common engine across the three variants was closely connected to the larger goal of commonality.

If the F-35A, F-35B, and F-35C had required three completely different propulsion systems, many of the economic and logistical advantages of a common aircraft family would have been reduced.

An engine is one of the most complex and expensive systems in a modern fighter. It affects the aircraft’s weight, internal volume, fuel system, cooling requirements, maintenance procedures, structural design, and overall performance.

Using a different engine for each variant could therefore have created substantial differences between the aircraft.