March 28, 2024

F-35B Testing Runs Behind Schedule in 2012

Attack Aircraft

By Jay Friess
Editor

F-35B JSF 200th flightThe F-35B has always been the most complex and thus most problematic of the three variants of the Joint Strike Fighter.

This year, the Integrated Test Team of Lockheed Martin contractors and Navy testers at Naval Air Station Patuxent River worked to iron out the nagging problems in the short takeoff and vertical landing aircraft with mixed results, according to an annual Pentagon report by the Director of Operational Test and Evaluation.

The report notes that the test team stayed busy this year. By the end of November, the team accomplished 6.8 test sorties per month, exceeding the goal of 4.4. At this pace, they completed 374 sorties, 130 more than planned.

However, the team only completed 1,075 of the 1,939 test points planned for the year. The report notes, “This was primarily a result of higher-than expected loads on weapon bay doors, which prevented planned envelope expansion test points and required
additional unplanned testing.”

This year, the F-35B test team focused on expanding the vertical-lift operations envelope testing of the newly designed auxiliary air inlet door; engine air-start testing; expansion of the flight envelope with weapons loaded on the aircraft; fuel dump operations; and regression testing of new vehicle systems software. The test team also accomplished radar signature testing and accomplished a successful safe separation of an inert GBU-32 JDAM bomb using the BF-5 test aircraft.

Since they were unable to complete their planned envelope expansion test points, the report says the team pulled an additional 992 points from testing planned for 2013 back into 2012 and added 292 points for regression testing of new software. This allowed the team to keep close to their overall multi-year testing schedule.

Lots of Moving Parts

In order to accomplish short takeoffs and hover landings, the F-35B has been equipped with several hatches and nozzles to bring air into the engine and spew exhaust out of it at precise, computer-controlled angles. With more moving parts has come more problems.

During testing this year, the team found that the upper lift fan inlet doors continue to fail to operate correctly. Newly designed actuators will not be available for production until Lot 6 airplanes in 2014. All existing aircraft and those currently being manufactured will have to be retrofitted.

The roll control nozzle actuator will also need a redesign as it keeps overheating. Testing for that part will begin early this year.

Designers have also decided to reduce the size of the F-35B’s clutch to reduce drag and overheating. Currently, in order to cool the overheating clutch, pilots must descend below 11,000 feet and cruise below 280 knots.

“…Such a procedure during combat missions would likely increase the vulnerability to threats and cause the pilot to abort the mission,” the report states. “Further, a vertical landing under high clutch temperature conditions needs to be avoided if possible, making return to forward basing or ship-borne operations in the combat zone, where a vertical landing would be required, not practical.”

The driveshaft will also require a redesign to account for an unanticipated amount of stretching that happens during flight. Currently, the program has added spacers to the shaft to compensate.

Still Too Hefty

Pentagon specifications require the F-35B to be able to fly a mission and come back to the ship loaded with fuel and weapons and still conduct a vertical landing. In order to accomplish this, the jet can’t weigh more that 32,577 pounds.

The JSF program has been trying to find ways to reduce the F-35B’s weight to have more leeway in changing the design in the future, but isn’t having any luck. The DOT&E report states that the jet actually gained 14 pounds this year. It is now a mere 231 pounds underweight.

“Managing weight growth with such small margins will continue to be a significant program challenge,” the report notes.

New Wrinkles

The DOT&E report noted that the JSF program has lowered its expectation for the F-35B, reducing turn performance from 5.0 to 4.5 sustained g’s and extending the time for acceleration from 0.8 Mach to 1.2 Mach by 16 seconds. “These changes were due to the results of air vehicle performance and flying qualities evaluations,” the report states.

And the performance issues keep coming.

The test team found this year that the aircraft is literally scorching the paint off its tail during sustained high speed, high altitude flight. The program changed the tail surfaces on one aircraft in September 2012, but the aircraft still burned the coating off. The team has suspended further high-speed flight testing until the issue is resolved.

The team also found that fuel was collecting behind the wing flaps during fuel dumps, creating a potential fire hazard. The test was still testing a solution to this problem in November 2012.

Finally, pilots training to fly the F-35B at Eglin Air Force Base in Florida can’t fly during or after a rainstorm. The aircraft’s new braking system has not yet been tested on a wet runways because of “the inability to create the properly degraded friction conditions at the Patuxent River Naval Air Station.”

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