Can a new structural crack suggest F-35 is healthier?

alcoa bulkead spar forgings.jpgIllustration courtesy of Alcoa



When an aluminium alloy bulkhead inside the Lockheed Martin F-35B cracked last year after just 1,600h of durability tests, the programme was caught by surprise. Lockheed’s analysis had not predicted the 496 bulkhead would buckle before the end of the 16,000h-long durability exam.

A year later, the programme claims to have made some progress.

Unfortunately the airframe structure is still not immune from early cracking, but this time Lockheed was not caught by surprise.

Lockheed’s analysis predicted root rib forgings in each wing for the F-35A and F-35B also would fail, and they actually survived slightly longer than expected, the programme office says. The root rib actually succumbed after about 2,800h of the 16,000h durability test.  Lockheed had already designed a fix to install in the next lot of low-rate initial production (LRIP).

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16 Responses to Can a new structural crack suggest F-35 is healthier?

  1. NORGCO 6 September, 2011 at 3:39 pm #

    So the forgings are SUPPOSED to last 16,000 hours and instead last 2800, ie 17% of expected life.

    Lockheed is celebrating because that is up from the 1600 hours – 10% of expected life – it used to be.

    Do I have that right?

    Are they going to be sued if they try selling aircraft that will need major work – replacing the wing forgings – nearly six times as often as it is supposed to?

    Is the program going to be held up until the problem is fixed, thereby grounding the F-35 fleet again, or are they going to send pilots up in planes whose wings are known to not be held on as securely as they are supposed to be?

    How did the western world get stuck depending on this plane to secure the skies for the next half century or so?

  2. K 6 September, 2011 at 4:40 pm #

    This is usually the point where some wisenheimer says “They should have gone with Boeing”, since paper airplanes never have any problems.

    That being said, Lockmart isn’t exactly covering themselves in glory on this one, are they?

  3. Soviet 6 September, 2011 at 5:31 pm #

    NORGCO,

    Guess reading comprehension is not your strong suite. They are celebrating because improved computer models predicted this early crack and they have a redesign already in the pipeline.

    Are you going to be sued for mindlessly attacking a program that has demonstrated better, not worse, performance than current comparable defense projects?

  4. Weaponhead 6 September, 2011 at 6:56 pm #

    On what date did the fatigue test failure actually occur? How much will the production fix cost? How much will the retrofit to the aircraft already built cost? How much aircraft down-time will be involved in the retrofits? What other “expected failures” are expected that have not been announced yet? Why do we only find these things out from the IOT&E community?

  5. Uwe 6 September, 2011 at 8:11 pm #

    Do you have some examples for that?
    i.e. core structure failing at 1/5th
    the expected lifetime on non fatique testframes?

    However much Jingoism you apply the F35 is
    a dud. It is a ressource hog that is designed
    to siphon off money from unsuspecting partners.

  6. catalin 6 September, 2011 at 8:35 pm #

    maybe i am wrong, but i believe that 16000 hours is much more than an aircraft is really flying “in real life”
    in order to fly that much you need to be in the air 2 hours a day, 365 a year, for exactly… 21,97 years :)

  7. jetcal1 6 September, 2011 at 10:17 pm #

    16K hours?
    If I remember correctly, the -14/-18 were designed for 4K life. (And they still cracked.) Mighty long reach that 16K.

  8. Stephen Trimble 6 September, 2011 at 10:29 pm #

    F-35 lifespan is planned at 8,000 hours. Durability testing is 2X projected lifespan, so 16,000 hours. That’s an industry standard for durability testing.

  9. alloycowboy 7 September, 2011 at 2:53 am #

    Hey Stephen,

    Everyone needs to chillax a little bit here. Designing a light weight fighter is an iterative process. When you design an aircraft there is always some educated guess work in what the actual structural loads the aircraft is going to see. So when the structural designers lay out the structure of the aircraft they are going to have too much material in some areas and not enough in some other areas. The optimum solution sees the vehicle fail exactly as planned when planned in the computer models which are for the most part highly educated guesses of how the structure is going to fatigue. Of course that never ever happens because complications arise and manufacturing flaw get introduced in the structure during the manufacturing process and the computer models are never 100% accurate. This is the reason why aircraft go through fatigue testing and real world flight tests. This is also the historical reason why famed Lockheed Skunk Works designer Kelly Johnson liked to get to a new design flying aircraft as quickly as possible and then tweak and perfect the aircraft as it went through testing. Kelly in his genus recognized early on that it was easier and much more cost effective to “ball park” an aircraft design and deal with problems as they came up rather then trying to engineer an aircraft to with in an inch of its life and hope that every thing works exactly as planned. This iterative process of aircraft design always works the best and every time manufactures break from it they pay, and they pay, and they pay. The Boeing 787 and Airbus A380 are recent examples of where the manufactures broke from the iterative design process and tried to out source the design and engineering process as much as possible. Inevitably both programs end up biting the manufactures in the ass as they came in significantly over budget and really late.

    So going back to the F-35 air frame, Lockheed Martin is likely going to be finding induced manufacturing structural flaws all the way through the fatigue test program and will beef up the structure where required. In fact if your aiming to build the lightest most structurally efficient air frame possible it is better to be on the light side and beefing up the structure where needed as you go through fatigue testing rather then having to much material and being over weight and not know where to remove material from the air frame.

  10. cc 7 September, 2011 at 8:11 pm #

    alloycowboy,

    I don’t think ‘beef’ is going to help in this. It’s damage tolerance sucks, too.

    The problem here is the that bulkheads were originally slated to be titanium. At the last minute, LM, faced with an overweight airplane, switched to a proprietary Alcoa aluminum alloy in a panic move, without fully understanding the issues.

    Typical Do-Act-Plan-Check cycle for LM.

  11. Amicus Curiae 8 September, 2011 at 4:04 pm #

    @Soviet: Get hold of yourself. This problem may be years old (analytically)and months old(by test confirmation) and is only breaking into media now. No one is celebrating. Doesn’t it trouble you that they entered into an important test knowing there was an analytical deficiency? They were “winging it”? Why was that risk taken? Are there more known trouble spots at risk? There are also unknowns to be discovered too. Oh well. Time and money will fix it. Now, what other project do we kill to get the money, and how do we convince potential adversaries to delay their aggression until we are ready? Problems…problems.

  12. Atomic Walrus 9 September, 2011 at 9:15 pm #

    Amicus Curiae,

    “Doesn’t it trouble you that they entered into an important test knowing there was an analytical deficiency?” No. It’s called model validation. My guess is that the hardware and facilities were ready for the test anyway, so the cost of proceeding was not excessive. Validation of the improved model mitigates risk regarding the revised design. I realize you’ve got an axe to grind regarding the F-35 program, but you’ve got quite a bit to learn regarding engineering development.

  13. Aussie Digger 11 September, 2011 at 2:03 am #

    Amicus, “how do we convince potential adversaries to delay their aggression until we are ready?”

    LOL. Implying that the West is somehow “deficient” in air power right now compared to potential adversaries?

    Yeah right. Of course. Who’s got LO platforms in-service for more than 30 years and who doesn’t?

    Who’s got AESA radars in-service and who is struggling to buy, let alone build one of them?

    Who’s airforces demonstrated terrible performance against such a lightweight threat as Georgia and whose has completely obliterated every single opponent since the 1960′s?

    Wake up and smell your own BS buddy. The West is NOT behind. Everyone else is struggling to catch up…

  14. Uwe 11 September, 2011 at 8:42 am #

    Reagan expressly wanted to beggar the USSR by way of “StarWars”.

    The US has spent better than $ 4 trillion to, in the final culmination, kill a single person.

    Today the US is broke and has massive problems in being competitive in consumables and with fast growing social disparity.

    Riddle me that ;-)

  15. Objective 21 September, 2011 at 3:14 am #

    Aussie Digger once again demonstrates his bias, lack of knowledge and the mentality typical of the drones of the US that Australia is. The under-estimation of others capabilities is moronic as is the negative exaggeration of other countries capabilities.
    AESA – they are available. You forget who were the first to have PESA?
    LO is not the be-all, end-all benchmark, and the Soviets would have been able to make one had they not run out of money. Also remember it was on the back of Soviet theory that LO saw the light of day.
    Obliterate every opponent? Vietnam was not all one sided, and the US has never taken on anything other than Third World air forces.
    As for Georgia, go do some research. The Russian Airforce was up against capable SAM systems that had been modernized and lost some of their aircraft to friendly fire. The vast majority of their losses were CAS, which is, by nature, very dangerous. And they still achieved air sup very quickly.

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