The first flight test of the F-35's Short Takeoff Vertical Landing (STOVL) variant in that mode is now expected to take place in September, a further delay of about six months beyond that already expected, due to problems with the jet's engine built by Pratt & Whitney, Reuters reported from the Navy League Sea Air Space conference.
The first flight in STOVL mode was initially scheduled for March.
Quoting US Navy Captain Wade Knudson, the F-35 program’s acting program manager, Reuters reported that the STOVL variant had completed hover pit tests that simulated missions in short takeoff and vertical landing mode, and would resume testing of conventional takeoffs and landing this summer, followed by the STOVL mode flight.
The STOVL aircraft has already flown in conventional mode.
The reasons for the new delay are the need to fix the engine that failed, to “tweak” the software controlling the leading edges, and to ensure that the nine doors that open during STOVL all operated correctly, according to another report by the DoD Buzz website from Navy League.
Noting that the F-35 STOVL version was facing a serious excess weight problem – it is some 3,000 pounds overweight-- DoD Buzz said that this is no longer seen as a problem because STOVL pit tests indicate that the engine now generates more power than planned, possessing what Knudson said was an “excess” 300 to 500 pounds of thrust.