There was good news for the F-35 program when U.S. Secretary of Defense Leon Panetta ended the two-year “probation” for the STOVL version a year early. Lockheed Martin F-35B executive v-p Larry Lawson said that “critical engineering challenges” had been solved.
The F-35B’s specific problems have included a crack in the wing carry-through bulkhead, auxiliary air inlet doors that needed strengthening, thermal expansion of the engine driveshaft and overheating of the roll-control nozzle actuators and lift-fan clutch.
Lockheed Martin vice president for F-35 business development Steve O’Bryan said that fixes are in hand for all these issues. But the recent annual report from the Pentagon’s Director of Test & Engineering (DOT&E) lists a total of nine F-35B door and propulsion problems and says that “significant work and flight tests remain to verify and incorporate” the modifications.
Weight growth affects all variants but has been a particular problem for the F-35B, and according to the report it remains “a significant challenge.” O’Bryan said that weight margin has improved by more than 290 pounds.
Two F-35Bs successfully completed a 19-day trial on board a Marine Corps amphibious assault ship last October, and 330 short takeoffs and 268 vertical landings were logged last year. In addition, the first two production F-35Bs were delivered to the training base at Eglin AFB on January 11.
More generally on the F-35, the DOT&E report notes that “limited mission systems software flight testing took place in 2011,” and that concurrency between F-35 missions systems development and testing is growing. This report also reveals that a redesign of the fuel tank inerting system is under way.
In additon, the DOT&E report gives perspective on the relative progress of the F-35 flight-test program: by the end of November last year a total of 1,371 flights had covered 11,612 test points. These totals are 24.5 percent and 19.5 percent, respectively, of the totals anticipated to complete development.
However, the report cautions that some “traditionally difficult” test regimes are still to come for the F-35, including high-angle-of attack testing, elevated g-load testing and weapons integration.