X to F: F-35 Lightning II And Its Predecessors

By Eric Hehs
Illustrations by Boyd Pryor

from CodeOne Magazine

F-35 First FlightA side-by-side comparison of the X-35 Joint Strike Fighter prototype with the F-35 Lightning II production aircraft underscores the huge strides the JSF program has made transitioning from demonstration to development. The X-35 demonstrators, built and flown during the concept development phase of the program in 2000-2001, validated specific propulsion and design features incorporated on today’s F-35 Lightning II.

The most important part of the demonstration for the X-35B (the short takeoff/vertical landing, or STOVL, variant shown in the illustrations here) was the integration and operation of the STOVL propulsion system. The X-35B proved the viability of the shaft-driven lift fan and the performance available in STOVL. It also proved the viability of up-and-away flight. The demonstration culminated in the successful completion of “Mission X” on 20 July 2001. This mission combined a short takeoff, acceleration to supersonic flight, and a vertical landing in a single flight. Mission X demonstrated the integration of a STOVL lift system into a high-performance fighter.

The X-35 demonstrators, by any standard, were much simpler than the F-35 Lightning IIs that will be rolling out of the Lockheed Martin factory in Fort Worth, Texas. The demonstrators, for example, used a number of off-the-shelf components to speed design and fabrication. The fast pace of the program meant that only essential functions and capabilities were provided and tested. For instance, the X aircraft did not carry or drop weapons or include mission avionics. The demonstrators also did not carry signature treatments.

Still, the production versions maintain a strong family resemblance to their predecessors. The basic shape and layout are the same. The wing sweep angles for the leading and trailing edges are identical. (The F-35C has a much larger wing to improve low-speed handling characteristics for carrier landings, but the sweep angle is the same. The X-35C also had larger wings and tails than the X-35A/B.) The fundamentals of the shaft-driven lift fan system for the STOVL variant remain unchanged as well, which includes keeping the original three-bearing swivel nozzle. However, at a more detailed level, the production versions are different in every respect