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Thread: Ankle Saver mod.

  1. #1
    cubpilot2's Avatar
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    Ankle Saver mod.

    Ran across a couple of old photos of one example of why I started trying to promote this mod over the last several years.
    This was a wreck of a heavy loaded sprayer in 1974 which lost an engine on takeoff.

    See the following thread post #13 to see what it looks like.
    https://www.supercub.org/forum/showt...-something-new



    It is intended to reduce the collapse of the front bulkhead which can trap you inside. The consequences are obvious, especially if there is a fire.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Ed
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  2. #2

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    Has this mod ever been tested? I understand the reasoning but wonder where the force goes and what it does in a modified airframe.

  3. #3
    Cubus Maximus's Avatar
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    I think Jay at Javron adds this automatically to all his frames, it's not an option.

  4. #4
    www.SkupTech.com mike mcs repair's Avatar
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    thanks for the pictures, never seen one......

    you gotta crash just right to do this.... edge case...

    never have added that X....

  5. #5
    cubpilot2's Avatar
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    When I first brought this up about 15 years ago, several people contacted me or responded with their experiences.
    TJ (on this site, who later deleted all his activity) as I recall said that he had two separate friends killed in cubs by being trapped inside and fires started.

    One individual contacted me directly who was recovering from a bad wreck on a beach in SE Alaska. He had to be extracted by rescuers. He had a broken leg and hip. He was certain that this would have lessen the severity of his injury.

    Can it be tested? Don’t think so; but it is definitely in the direction of goodness!
    In my mind it is sort of like adding the box or X brace in the tail. Hard to say what tests would show; but we do know that longerons don’t bend like they did without it.

    I won’t rebuild one without it. Best part is that the Feds said that it is a minor change as it does not intersect the original tubing; therefore altering the original structure.
    Ed
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  6. #6
    skywagon8a's Avatar
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    Quote Originally Posted by cubpilot2 View Post
    Best part is that the Feds said that it is a minor change as it does not intersect the original tubing; therefore altering the original structure.
    Key point: Do not weld or add a small joining tube at the X as this will change the characteristics of the original tubing.
    N1PA
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  7. #7
    nanook's Avatar
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    Seems it would be stronger if it did intersect and form an ‘X’ brace, instead of a straight tube. So we design things to avoid involving the FAA’s scrutiny, instead of the best design. What size 4130 are you using on this diagonal tube?

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    skywagon8a's Avatar
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    Quote Originally Posted by nanook View Post
    Seems it would be stronger if it did intersect and form an ‘X’ brace, instead of a straight tube. So we design things to avoid involving the FAA’s scrutiny, instead of the best design. What size 4130 are you using on this diagonal tube?
    I tend to agree with you. However just imagine all the hoops you would have to go through in order to get an STC or other type of FAA approval to connect the two tubes. It likely would be many more $$$$$ than would be worth your while.
    N1PA
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    FWIW, this is what Backcountry does.

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  10. #10

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    Quote Originally Posted by skywagon8a View Post
    I tend to agree with you. However just imagine all the hoops you would have to go through in order to get an STC or other type of FAA approval to connect the two tubes. It likely would be many more $$$$$ than would be worth your while.
    Looks like a pretty easy DER approval. A couple hours writing it up tops.


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  11. #11
    skywagon8a's Avatar
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    Quote Originally Posted by stewartb View Post
    FWIW, this is what Backcountry does.
    On a noncertified experimental airplane. This is not applicable to the OP's airplane.
    N1PA

  12. #12
    cubpilot2's Avatar
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    Quote Originally Posted by nanook View Post
    Seems it would be stronger if it did intersect and form an ‘X’ brace, instead of a straight tube. So we design things to avoid involving the FAA’s scrutiny, instead of the best design. What size 4130 are you using on this diagonal tube?
    i used 7/8” x .035
    Ive considered the X bracing on this but looking at the geometry to bring them together with the existing diagonal puts about 1 1/2 in deflection into it. This tube is to work in direct compression so any offset would weaken it.

    Ive also thought that a clamping type device to the opposite diagonal would add stiffness. (Lessen deflection) This could be as simple as a hose clamp with a spacer between them.
    Ed
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  13. #13
    RVBottomly's Avatar
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    Quote Originally Posted by cubpilot2 View Post

    Ive also thought that a clamping type device to the opposite diagonal would add stiffness. (Lessen deflection) This could be as simple as a hose clamp with a spacer between them.
    I was going to suggest a heavy duty hose clamp and spacer, but didn't want sound foolish. It does sound like a good idea.

  14. #14
    wireweinie's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Key point: Do not weld or add a small joining tube at the X as this will change the characteristics of the original tubing.
    I agree that this could be a minor. But it shows the stupidity of semantics. We are in fact trying to change the characteristics of the original tubing; we don't want them to buckle where they do now.

    The games we play to keep 'them' happy.

    Web
    Life's tough . . . wear a cup.
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  15. #15
    cubpilot2's Avatar
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    I wish one of you creative types would figure out some sort of bolt or clamp in fixture for this. You could probably sell a bunch.

    Otherwise it will only get put in during a rebuild......
    Ed

  16. #16
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by cubpilot2 View Post
    I wish one of you creative types would figure out some sort of bolt or clamp in fixture for this. You could probably sell a bunch.Otherwise it will only get put in during a rebuild......
    very simple... but not worth the weight....but I'll take your money if you wish to hire me....

  17. #17
    www.SkupTech.com mike mcs repair's Avatar
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    if you actually look at the damage, the brace being installed is not as useful as a smaller lighter one in middle of lower side tubes to front top............

  18. #18
    Dave Calkins's Avatar
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    I had thought the same.

    Stabilizing the existing diagonal might be more useful.

    Eds picture above is worth a thousand words. Old Chinese saying.

  19. #19
    SuperCub MD's Avatar
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    The last time I had my boot cowl off I looked real hard at adding that tube. I figured I would x it through the original cross tube, but realized with the offset it may not do much good. I thought about adding it straight with a stub tube connecting the cross, but in a crash the stub tube would probably just break and it would collapse anyway. The only way I thought it would be worth while would be to combine the two ideas. Add the cross tube, and the stub tube at the cross. Then scarf two tubes on to the ends of the added tube that intersect the original tube.

    This would create a truss, not just a added tube which might stand a chance of holding the floor down in a a crash.

    After all this thinking, and looking at the added weight and work involved, I decided that for myself it would just be alot easier to just not land prop first. So far so good.

    Anything you add in that area will add strength, and not a bad idea, I just hope nobody ever puts it to the test
    Last edited by SuperCub MD; Yesterday at 04:47 PM.
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  20. #20
    Randy's Avatar
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    I thought I saw a photo of the tubes joined together here on the site, Bill Rusk's Javron Cub Build?

    EDIT:
    The photos are here, several down from the start/top of thread
    #154 - Modifications with Pictures and explanations - http://www.supercub.org/forum/showth...l=1#post525332
    Last edited by Randy; Yesterday at 07:54 PM. Reason: found pictures

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