A few months back the F-35 test program was grounded due to a mid-air event that required a test aircraft to land right away,
Two generators attached to the aircraft’s jet engine failed. The cause as reported by Aviation Week was that there was an oiling procedure that was not to spec. Also reported was that this problem affected generators on newer test aircraft and not some of the old ones and that there was a design fix in the works.
The statement says: “Previous maintenance procedures could allow a small amount of extra oil to remain within the generator following servicing. Under some conditions, the extra oil that is churning inside a narrow air gap within the AES/G could cause internal temperatures to increase. It was assessed that high temperatures led to the generator failures.”
Soon after the incident it was determined that only those aircraft with the newer AES/G design were affected. Those with the earlier engine starter/generator (ES/G) — F-35A CTOL test jets AF-1/2/3 and F-35B STOVL test jets BF-1/2/3/4 — were returned to flight on March 14. This latest action clears those with the AES/G — AF-4, BF-5, F-35C CV test jet CF-1 and the first two low-rate initial production aircraft AF-6 and 7.
As for any effect on an already-delayed flight test program, the JPO says: “There was no significant impact to the System Development and Demonstration (SDD) program or production operations. Flight test schedules are built with a margin for precautionary safety stand-downs. The F-35 test programs at Edwards AFB, Calif. and Naval Air Station Patuxent River, MD remain ahead of their monthly flight test schedules.”
Bill Sweetman gives you an overview of the systems here and also mentions that DOD/Navair went out to small business last year to help find a more robust solution for electrical system problems.
There are efforts under way to improve the system. Navair issued a small business innovation research solicitation in August calling for more robust controls, and Graham Warwick has reported on the USAF’s Invent program, which is looking at a more thermally efficient hybrid architecture for stealthy aircraft.
So how will oiling be fixed? Well, here is another request from DOD asking small business for help with the oil system of the Pratt and Whitney F135 engine. (PDF file)
Something to think about when we hear more great platitudes about the F-35 program from the usual suspects. Yet more evidence that the aircraft’s design is not stable and there can be no great learning curve gained in production. Lots of engineering changes ahead. It may have a fresh coat of paint and make pretty pictures and videos, but there is still a lot of work to do. Buyer beware.
