Cracks found on Challengers

Discussion in 'Rules and Regulations / Flight Safety / Better Pil' started by Tiger Tim, Apr 12, 2019.

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  1. Jun 26, 2019 #21

    Mike W

    Mike W

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    A copy of my findings has been sent to the Canadian authorities by the LAA.
     
  2. Jun 27, 2019 #22

    Hephaestus

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    I have no more knowledge than the original picture gives - not sure if that's the one through the strut itself, but I'd tend to believe due to angles it must be the through the longeron one. As you'd never take off if you saw that kind of deformation on the one that connects to the strut, and I counted 6-8 posts dating back to the transport Canada release.
     
  3. Jun 27, 2019 #23

    Tiger Tim

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    I’m not an engineer. Would there be any compelling reason not to run a strap around the longeron to take the tensile (and bending apparently) load off that bolt?
     
  4. Jun 27, 2019 #24

    Hephaestus

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    High lift kit is what factory is recommending.
    Screenshot_20190626-182030.png
    Diy cable solution though is being argued could be worse but at least the wing won't fold on you. Twist may be an issue. Screenshot_20190626-181805.png
    LAA fix is discussed. Screenshot_20190626-182019-01.jpeg

    I should perhaps stop; noting that I'm now only a member of one Challenger group and the one I can see has had a purge of discussion about this topic.
     
    Last edited: Jun 27, 2019
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  5. Jun 27, 2019 #25

    bmcj

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    Since the longeron already carries that load under the current configuration, it shouldn’t make a difference as far as the longeron is concerned.

    I think a better solution is to find a way to rotate the bracket 90° so that the strut can pivot on the (strut attach) bolt so that it doesn’t create bending loads in the bracket or bracket attach bolt. Perhaps some sort of a universal joint might work?
     
  6. Jun 27, 2019 #26

    rollerball

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    Like in Weedhoppers/AX3s, X-Air's that have never suffered from this problem AFAIK. It's not rocket science - it only needs the manufacturer to have the will to change. If they don't, it'll bite their backside as it may well now do.
    And why have a bolt when, like the two aircraft I've mentioned, you can just have a pin with a safety ring.
    Why do US designers over-engineer? My pal had a Rans S12 that we broke up after an accident. I was amazed at the intricacy (and cost) of the design.
     
  7. Jun 27, 2019 #27

    BJC

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    What do you nominate as a non-USA designed HBA?

    What do you recommend to replace the S12 that is non over-engineered?

    Thanks,


    BJC
     
  8. Jun 27, 2019 #28

    rickofudall

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    When I was first looking at a two place "fat ultralight" I gravitated toward the Kolb series precisely because they have a welded space frame fuselage. After a week of climbing in and out of Challenger 2 I had in the shop I knew I made the right choice. Reading about QC's response to the bracket breaking only reconfirms it.
    What truly amazes me is that I don't hear QC or anyone talking about the simplest solution, make the bracket out 4130 steel. Adjust the thickness as required and MOVE ON.
    If you're still looking for your aircraft my recommendation, based upon over 20 years experience, is Kolb. They have a variety of aircraft, one of which should be yours. Give Bryan a call, you'll be happy you did, I'm sure.
     
  9. Jun 27, 2019 #29

    BJC

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    Is that a response to my question?


    BJC
     
  10. Jun 27, 2019 #30

    Hephaestus

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    I don't know if I'd lay all the blame like that.

    The original designers have all departed the surly bonds now. The current ownership doesn't seem to have engineering staff. And likely only has limited documentation on the original engineering.

    I can't blame them for trying to manage and perform damage control. I just don't like the way they're doing it. The years of corporate project Management I did tells me they're doing it wrong. But I'm not American and I don't have their lawyers and insurance companies lawyers to deal with on it.

    Curious these brackets appear to be "off the shelf" parts and are used on other aircraft. Anyone know which ones? Curious how the mounting differs.
     
  11. Jun 27, 2019 #31

    Mike W

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    The LAA reinforcing fix shown is my solution to the problem. See post 9. Looking through my calculations, I make the load in the front strut 3550 Lb at 6,0 g. To make the Rony bracket cope with this needs a 1/4" thick 7075-T6 reinforcing plate as shown and also rotate the fitting to cope with the strut vertical flexing as mentioned in post 25. The rear strut bracket requires a 3/16" thick spreader plate. This post says this is now the factory mod to cure the problem. It is a pity they didn't adopt it earlier instead of calling me an idiot for daring to suggest there was a problem . I might point out that I am a professional aircraft design engineer with more than 12 years experience in the stress office having worked on Concorde and many other projects.
     
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  12. Jun 27, 2019 #32

    Hephaestus

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    Don't forget there's a change in ownership, it's possible the current owners didn't even know of your report...

    I think where the rub exists - is the incident aircraft was equipped with the high lift mod. Was well known in the Challenger community, and was one of those OCD type AMEs with what a lot of people called an immaculate aircraft.

    I have no dogs in this fight, like I've said before, I probably will still be buying one as a play-toy, probably more so now since the used prices keep dropping likely because of the unresolved issue.

    Pretty sure it's resolvable issue. But some don't seem to agree.
     
  13. Jun 27, 2019 #33

    Riggerrob

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    A thick bar used to beat lawyers would be best.
    Seriously: do not feed lawyers!
     
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  14. Jun 27, 2019 #34

    BJC

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    Lawyers aren't the problem in the USA; juries that reject the concept of personal responsibility are.


    BJC
     
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  15. Jun 27, 2019 #35

    Victor Bravo

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    No matter what angle that fitting is rotated to, the tensile load from the strut is still trying to pop the head off of the longeron bolt. And the vertical component of the load is trying to bend the head of the bolt along with everything else. Some of you guys know a lot more than me, but I think this should be a shear load on all the bolts instead of tension.
     
  16. Jun 27, 2019 #36

    BJC

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    Shear often is preferred because it is easy to load the fitting / bolt in double sheer. But there is nothing wrong with loading a bolt in tension, if the attached parts are adequate.

    If your Cassutt was built per Tom's design, all lift loads were taken through four bolts in tension.


    BJC
     
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  17. Jun 27, 2019 #37

    Victor Bravo

    Victor Bravo

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    Yes, but it was four 6 inch long 3/8" NAS 1000 series bolts. And it still scared the s*** out of me :)
     
  18. Jun 27, 2019 #38

    BBerson

    BBerson

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    Quite a few wings are held by bolts in tension. (DC-3, Bonanza and my future design)
    Bolts are stronger in tension usually, just make em big. In tension the hole fit is a non-issue. So frequent bolt and wing removal is easier in sloppier holes.

    In tension, your 6" bolt is no different than another guys 2":D.
     
  19. Jun 27, 2019 #39

    Victor Bravo

    Victor Bravo

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    I always thought that allowing a little bolt stretch would delay a tensile failure for a short time, and a longer bolt would have a little more stretch before it let go? Whatever... I'm still here for better or worse
     
  20. Jun 27, 2019 #40

    BBerson

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    They will stretch (yield) when overloaded because that is good design. AN bolts are 125k tensile so they can stretch some unlike 220k bolts that can't stretch much. So if the bolts are say twice or more than needed, they won't be first part to fail. I might use four bolts where just one is enough on the wing attach. (for fatigue, etc.)
    Might want to replace them after a crash or hard landing or some time schedule.
    The eye bolts on a Cub strut are still bolts but very big.
     
    Last edited: Jun 27, 2019

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