F-35B - Bulkhead
5:21 PM on Dec 09, 2011
This post is one in a series on the development of the F-35. Click here for a Flash graphic with system cutaways. Click on Read More to read the entire post on that system and check out next week's special coverage of the program in the Dec 12 edition of AW&ST.
Cracking in one of six forged-aluminum fuselage bulkheads was discovered about 1,500hr into 16,000hr of durability testing aimed at validating the F-35B's 8,000hr airframe life. The flight-test fleet was inspected and no cracks found, but none were near the 1,500hr mark.
Cracking of bulkead 496 was traced to a stress concentration where the main landing gear attaches to the fuselage. The initial fix for aircraft already produced was local blending of the affected area to relieve stress, with doublers to be added later to extend airframe life. The long-term solution is a redesigned, thicker bulkhead to be installed beginning with the 24th F-35B.
Subsequently, a crack appeared in the wing forward-root rib after more than 2,800hr of durability testing on the F-35A at BAE Systems in the UK. The forged-aluminum rib is common to both the CTOL and STOVL variants, and the crack was anticipated based on earlier structural analysis, the program office says. A redesigned root rib will be installed beginning with production lot 5, and earlier LRIP aircraft - 30 CTOL and 34 STOVL - will be retrofitted.
Mircrocracks have appeared in an actuator support beam inside the lift-fan bay on test aircraft BF-1, BF-2 and BF-4. The beam, which supports actuators for the upper and lower lift-fan doors, and which is under load in STOVL mode, was also a known "hot spot", says Lockheed Martin. A redesigned beam was installed beginning with aircraft BF-5 and the others are being retrofitted.
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