PARIS --- The F-35 Joint Strike Fighter has encountered a new, serious problem as a bulkhead on an F-35B fatigue test airframe developed cracks after only 1,500 hours of tests that are due to last 16,000 hours.
“The aft bulkhead of the F-35B BH-1 fatigue-test specimen has developed cracks after 1,500 hours of durability testing,” Aviation Week’s Ares blog reported yesterday. “This is less than one-tenth of the planned fatigue test program, which is designed to prove an 8,000-hour airframe life with a safety factor of two.”
This incident again raises questions about the technical viability of Lockheed Martin’s redesign of the aircraft, especially for the F-35B STOVL version, and about the company’s claims that its simulation systems are so good that flight testing can safely and drastically be cut back to lower costs.
Lockheed Martin issued the following statement on the issue:
"During a recent durability ground test, fatigue cracks were discovered in the aft bulkhead of BH-1, an F-35B ground test aircraft. The cracks were discovered during a special inspection when a test engineer discovered an anomaly; the aircraft has logged approximately 1500 hours of durability testing. Precautionary inspections were conducted on all flight test aircraft and the CTOL ground test aircraft. No additional cracks were found and flight testing has not been impacted.
“The root cause investigation is underway and will determine if the cracks were caused by a test anomaly that is not indicative of flight conditions, an engineering issue or a material failure. Durability testing is conducted early in the development of a new aircraft program to avoid costly sustainment issues later in the life of the aircraft."
A knowledgeable source confirmed to defense-aerospace.com that the frame in question is the STA 496 bulkhead, and added that “by all accounts, so far, the undercarriage loads are in the mix, which brings into focus a debate that was had some time ago about whether or not the full spectrum of the [Conventional Take-Off and Landing] loads should be used as well as those for the STOVL scenarios ([Vertical Landing] and, possibly, Ski-Jump)” for the fatigue test program.
Click here to read the Ares report on the Aviation Week website.