March 28, 2024

F-35C Testing Lags Thanks to Software

F-35C JSF catapult launch

By Jay Friess
Editor

F-35C JSF catapult launchAccording to the annual Director of Operational Test and Evaluation report released by the Pentagon this month, the Joint Strike Fighter Integrated Test Team at Naval Air Station Patuxent River stayed very busy, but, thanks to delayed software deliveries, the team didn’t complete its testing goals for the year.

The F-35C test team focused on verification of the basic flight envelope for the first production F-35C aircraft; expansion of the flight envelope with external weapons loaded on the aircraft (AIM-9X short-range missile in subsonic flight); testing of arresting hook system modifications; preparing for executing carrier landings in the simulated carrier environment; surveying handling qualities in the transonic flight regimes; and regression testing of new air vehicle systems software.

As of November, the test team executed a sortie rate of 7.1 sorties per aircraft per month compared to the goal of 6.4. The program completed 22 more sorties than planned. However the team was held back from completing their goal of 1,327 test points, completing only 1,060 because software delays created flight restrictions that blocked a portion of the planned baseline test points. The test team flew an additional 253 test points from flight test requests and pulled 896 test points forward from work planned for 2013 in order to keep ahead of the pace of the cumulative test point objectives scheduled for the program.

Testing has resulted in lowered expectations for the aircraft. The Pentagon has reduced the requirement for turn performance from 5.1 to 5.0 sustained g’s and increased the time for acceleration from 0.8 Mach to 1.2 Mach by at least 43 seconds.

Due to the F-35C’s larger wing design, the DOT&E reports notes that transonic buffet becomes more severe in the F-35C than the other variants.

“The program is making plans for investigating how to reduce the impact of transonic roll off in the F-35C with the use of wing spoilers; however, detailed test plans are not complete,” the report notes.

As with the other variants, horizontal tail surfaces are getting hotter than expected during sustained high-speed/high-altitude flight, resulting in scorching of the surface coatings and structure. A new coating designed to prevent this ended up coming loose in flight.

The report notes that the test team has consistently received late delivers of software upgrades for the aircraft.

“Deferrals of mission systems capabilities to later blocks and delays for corrections to test instrumentation and data recording have removed the schedule margins,” the report states. “The impact of these delays will potentially require an additional 18 months added to the schedule for weapons integration events.”

The F-35C received a redesigned tail hook in 2012 to compensate for its inability to catch a carrier-style arresting cable in early tests. The new hook had a new point shape, was one inch longer and included a damper to reduce bounce. The team tested this new design in Lakehurst, New Jersey in August, but the plane only caught the cable five of the eight times it attempted.

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