Lockheed Martin plans to "back into" jet-borne flight tests of the short take-off and vertical landing (STOVL) F-35B Joint Strike Fighter, taking the approach used by Hawker with the original Harrier and Boeing with its X-32B JSF concept demonstrator.
Flight testing will start with conventional take-offs and landings, and transitions from wing-borne to jet-borne flight will begin at altitude and gradually "build down" to vertical landings, says Doug Pearson, vice-president, F-35 integrated test force.
The first F-35B, aircraft BF-1, is in ground testing at Lockheed's Fort Worth, Texas plant after roll-out on 18 December. The aircraft (pictured) is in the fuel barn, where the fuel system is being checked for leaks, tanks filled and flushed to remove debris, fuel quantity calibrated, and aircraft empty weight and unusable fuel measured.
Any manufacturing debris larger than 200µ must be removed before flight. On the first F-35, aircraft AA-1, this took one-third of the fills and flushes required for the first F-22, says Pearson, adding: "That's an indication of manufacturing quality." AA-1 also had no external leaks, he says.
After the fuel barn, flight test instrumentation will be checked out. BF-1 has the most complex instrumentation of all the development aircraft, says Pearson, because it will be the workhorse for propulsion, flying qualities and aerial refuelling testing.
This will be followed by structural coupling and ground vibration tests in various configurations, with doors open and closed. "We've got a lot of doors," says Pearson. Vehicle systems functionality will then be checked, including a taxi test of the F-35B's smaller and lighter brakes.
Early in the second quarter, BF-1 is scheduled on the hover pit at Fort Worth for the first of two periods of propulsion system ground testing. This will characterise the engine and check the functioning of doors and nozzles.
Lasting about a week, the tests will involve about 10h of engine runs with the aircraft strapped down, says Pearson. A second round of pit tests will follow, lasting about two weeks and looking at the STOVL propulsion system in more detail.
Lockheed then plans to change out "a very few of the subsystems", installing later versions, before beginning flight tests. BF-1 is planned to fly around mid-year, says Pearson, adding: "The window opens at the end of May." BAE Systems test pilot Graham Tomlinson is scheduled to make the first flight.
Testing will begin by flying BF-1 on the same conventional "up-and-away" profiles as AA-1 for comparison. "We will back into STOVL tests," says Pearson. "We could begin with 'press-ups', but the risk is higher. This way we make sure all the control and radios work."
Transition testing will begin at higher altitudes and speeds and work lower and slower, he adds. "We will begin the transitions up-and-away so if we have an issue there is altitude to recover. Then we will do slower and slower approaches and landings before we do a full-blown STOVL."
BF-1 is expected to fly at Fort Worth for several months before deploying to the US Navy test centre in Patuxent River, Maryland, "likely in the first quarter of 2009", says Pearson. In all, there will be 13 flight-test F-35s - four CTOL, five STOVL and three for the CV carrier variant, plus AA-1, which is not production-representative.