Forum: F-35 Lightning II

F-35 Replan Adds Time, Resources For Testing

Feb 4, 2011 By Graham Warwick, Amy Butler
Washington, Washington

Details of the revamped F-35 Joint Strike Fighter program are emerging and showing that, despite more than nine years of work, almost six years of challenging development and testing still lie ahead for the Lockheed Martin-led project.

Both flight testing and software development have been replanned using industry-standard productivity rates rather than the aggressive—and unachievable—assumptions on which the original program was built. This means many more sorties to refly flight-sciences test points and for regression testing of mission-system software changes.

The replan adds 2,000 flights to the program—for a total of 7,800, just 600 of which have been completed—and extends development testing to October 2016. In addition to more refly and regression flights, the new plan adds sorties for test-pilot training and builds in a 500-flight margin for unexpected flight-sciences and mission-system issues.

For the mission system, the replan means more software development engineers, more integration laboratory capacity—and more time. The final software standard, Block 3C, is scheduled to be released to flight test in June 2015. Of the 8 million lines of code on the aircraft, “we have 4 million to do, but we still have four years of development,” says Eric Branyan, deputy general manager of the F-35 program.

Software development has undergone a significant change with the decision to “sunset” the Block 0.5 standard originally planned to be released for training. Numerous issues with the software led to the decision to move early to the Block 1 standard, which includes new processing hardware, says Branyan.

In F-35 parlance, Block 0.5 provides basic “aviate and navigate” capabilities, Block 1 introduces onboard sensor fusion, Block 2 integrates weapons and data links, and Block 3 provides the full capability planned for development.

Block 1 hardware began flight tests on mission-system development aircraft in April 2010, and is now the baseline through low-rate initial production (LRIP) Lot 4. While LRIP 1 and 2 aircraft will still be delivered with Block 0.5 functionality to begin training, this is now part of Block 1A running on the new hardware.

Regression testing of the Block 0.5 capabilities in Block 1A was completed in December, including collection of the first synthetic-aperture radar maps. Branyan says the Block 0.5 issues have been cured and the software is “solid.” As a next step, LRIP 1 aircraft AF-6 and -7 will test the maturity and suitability for training of the initial functionality.

AF-6 and -7 have been instrumented and will be delivered to the Air Force Test Pilots School at Edwards AFB, Calif., in March/April for independent testing of the initial mission-system and flight-envelope capabilities. This testing is intended to clear the LRIP 2 aircraft, beginning with AF-8, for delivery to Eglin AFB, Fla., where training is now expected to begin in September.

Flight testing of the additional capabilities in Block 1A is under way on development aircraft BF-4 at NAS Patuxent River, Md., and AF-3 at Edwards. Block 1B, which adds the multi-level security required for multinational operations, is planned to be loaded in June and released to production aircraft at the end of the year. Block 1B requires one hardware change, says Branyan: adding a crypto module for data security.

Block 2 will be a “major improvement,” he says, involving weapons certification and integration of the Multifunction Advanced Data Link and Link 16. Development will be in two phases: Block 2A is to be released to flight test in November, followed by Block 2B in September 2012. Flight trials will continue through 2014, then the final block will be released in three spirals: 3A, B and C.

Software development has been replanned around conservative industry-standard rates for defects per line of code, requiring additional resources. Lockheed is adding 110 software developers to the 300 already in place, and an extra integration test line will be ready by late 2012. “We have much higher confidence in the schedule,” says Branyan.

Mission-system flight testing is slated to pick up pace in 2012 following the release of Block 2A. While some of the development aircraft previously assigned to mission-systems testing will move over to flight-sciences work under the replan, production aircraft beyond AF-6 and -7 will be added to the program for mission-system work.

“The replan puts more aircraft into the program,” says Branyan, but “through 2011 we will have only three mission-system jets.” BF-4, which has been the workhorse, is moving to flight sciences, AF-3 has to complete signatures trials, AF-4 just arrived at Edwards, and CF-3 will not join testing until the summer.

In addition to increasing the re*sources for flight tests, the replan essentially decouples flight-sciences work on the three variants, he says. This is intended to overcome the impact of delays in testing the short-takeoff-and-vertical-landing (Stovl) F-35B on the smoother-running conventional-takeoff-and-landing F-35A and F-35C carrier variant.

The Joint Program Office (JPO), meanwhile, says each of the known problems with the Stovl F-35B are “readily solvable through engineering adjustments.” Among the issues being worked on are lift-fan clutch heating, thermal expansion of the lift-fan driveshaft and roll-post heating. Additionally, “selective redesign” of the lift-system doors is needed to “increase durability,” the JPO says.

The Pentagon will seek an additional $4.6 billion in its fiscal 2012 budget for the replanned program. This includes funds “to address known discrete improvements to include propulsion lift system, durability and structuring testing shortfalls, training systems, pilot-vehicle interface upgrades and others.”

Branyan says clutch heating is being addressed with a cooling modification that will be in the first Stovl production aircraft, along with an improved driveshaft. Clutch and roll-post temperature sensors are being installed.

VERY few people have any idea of the complexity of writing real time embedded programming. Add to that the fact that programming languages and computer capability are constantly changing and the concept of "flow down" for reuse of the software becomes unworkable.
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