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Thread: Lift strut dent

  1. #1
    jimboflying's Avatar
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    Lift strut dent

    I had a jack slip and wound up with a dent in the rear lift strut. Is it possible to remove the dent and if so what is the best technique or does a dent require a new strut? The picture is a little dark but the dent is below the 3 white dots.
    Click image for larger version. 

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  2. #2
    www.SkupTech.com mike mcs repair's Avatar
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    Before they were sealed, you would put air fitting in fork hole, air it up and soften dent with a torch, common... Be creative. Not going to finish the steps, but you get the idea.


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  3. #3
    skywagon8a's Avatar
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    Quote Originally Posted by mike mcs repair View Post
    Before they were sealed, you would put air fitting in fork hole, air it up and soften dent with a torch, common... Be creative. Not going to finish the steps, but you get the idea.
    mike, does just heating the strut with a torch harm the sealed struts? A welding rod could be welded to the center of the dent, then heat around the dent's edges while pulling on the welding rod. After the dent is out, cut off the rod and smooth the spot.
    N1PA
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  4. #4
    Steve Pierce's Avatar
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    They are mild steel.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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    Crash, Jr.'s Avatar
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    Quote Originally Posted by skywagon8a View Post
    mike, does just heating the strut with a torch harm the sealed struts? A welding rod could be welded to the center of the dent, then heat around the dent's edges while pulling on the welding rod. After the dent is out, cut off the rod and smooth the spot.
    Definitely not a good idea to heat a sealed strut. Being sealed there is a fixed amount of air in there and if you heat it that air will expand and possibly bulge the strut tube.

    Plus I don't think you can pop a dent in tubing out like you would pop a dent out of a car door.

    I don't have the data in front of me but allowable tolerance for strut dent depth is somewhere in the range of 1/2 the wall thickness of the strut tube which is about .035 for front struts and .049 for rear struts. Don't quote me on it though, that's from memory.

    Best bet is to replace the strut if it's out of tolerance. After all it's the thing holding your wings on....
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    Agree - although I flew for years with a slightly dented strut, probably not a great idea if you fly in heavy turbulence. A dent, or even a repaired dent, impairs the compressive strength. They are designed for limited compression anyway, and are really strong in tension.

    The only time you see real compression (other than flying inverted) is in heavy turbulence, or landing, or tied down in heavy wind.

  7. #7
    skywagon8a's Avatar
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    Quote Originally Posted by Crash, Jr. View Post
    Definitely not a good idea to heat a sealed strut. Being sealed there is a fixed amount of air in there and if you heat it that air will expand and possibly bulge the strut tube.
    That makes it sound like a viable solution for a small dent. It's unlikely that the expansion would cause a bulge unless you go overboard with the heat.
    N1PA
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  8. #8
    www.SkupTech.com mike mcs repair's Avatar
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    you guys realize the strut started out as a ROUND TUBE, and was rolled through a series of dies to make it into the streamlined shape...... fixing a dent is NOTHING compared to how they are made.....

  9. #9

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    I Once saw a cub with a belly tank which caught fire and burned. The heat made the lift struts round.
    Owned same cub for 36 years!!!
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  10. #10
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by skywagon8a View Post
    That makes it sound like a viable solution for a small dent. It's unlikely that the expansion would cause a bulge unless you go overboard with the heat.
    oil or air expands more????

    heat strut away from dent to pressurize, then heat dent perimeter to soften and remove dent...... carefully ....

    might want a hammer handy incase you over do it....

  11. #11

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    In the auto body world we use PDR (Paintless Dent Repair) techs to push hail and small dents out of damaged vehicles. In areas they cannot get behind such as the outer roof rails on your pickup or SUV they use a glue gun procedure. I have been amazed at how perfect the repairs have turned out. Each dent is unique and not all lend themselves to this procedure. Only an experienced tech would be able to determine if the repair has a chance to succeed. They typically approach the procedure from the standpoint they will make the dent disappear completely. They can sometimes be convinced to simply make it better which in my experience is amazingly good. And when they are done the paint is unscathed. No don’t go out and buy a glue gun. Ask around car dealers or autobody shops for a name of an experienced PDR tech. Hope this helps Good Luck. Rod

  12. #12

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    Is removing the dent for structural integrity or cosmetic
    If cosmetic...bondo
    I make a living sitting on tractors and horses


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  13. #13
    behindpropellers's Avatar
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    Quote Originally Posted by skywagon8a View Post
    That makes it sound like a viable solution for a small dent. It's unlikely that the expansion would cause a bulge unless you go overboard with the heat.
    I have read on this website about powdercoating and the oven caused the strut to look like a banana.

  14. #14
    www.SkupTech.com mike mcs repair's Avatar
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    Lift strut dent

    Quote Originally Posted by behindpropellers View Post
    I have read on this website about powdercoating and the oven caused the strut to look like a banana.
    No it makes them kinda round.

    Boodie (original airframes, they bought out) made bannnana shaped struts as they were originally getting rollers adjusted


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    Quote Originally Posted by Steve Pierce View Post
    They are mild steel.
    I thought some of the suppliers were using 4130 for the streamlined tubing and once it was roll formed it had to be NDI'd for micro cracks, am I way wrong here?
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  16. #16
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by astjp2 View Post
    I thought some of the suppliers were using 4130 for the streamlined tubing and once it was roll formed it had to be NDI'd for micro cracks, am I way wrong here?
    pretty sure boodie(Airframes) was 4130, at least heavy duty rear one....

    https://www.airframesalaska.com/PA-1...af89498-02.htm

  17. #17
    Crash, Jr.'s Avatar
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    Can confirm: Front struts are 1010 mild steel and rear struts (heavy duty) are 4130
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  18. #18
    mvivion's Avatar
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    It seems to me the question is: Is strength compromised by this dent? Since struts are stressed in extension, it seems to me that a small dent probably wouldn't effect strength.

    IF (note the big IF) that's the case, a little body putty and a rattle can spray job would seem to be the safest approach, rather than trying to re-form the strut.

    Maybe.

    MTV
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  19. #19

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    If the lives and safety of you and your passengers are in the slightest doubt, why would anyone ever consider not replacing the strut? Isn’t the constant worry about possible failure and the prospect of lifelong guilt and economic ruin enough motivation to spend the few dollars necessary to properly fix the issue?

    Taking little shortcuts in safety now leads to a mindset of taking greater and greater risks until disaster is inevitable. Flying is dangerous enough.

    Replace the strut.
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  20. #20

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    I flight wouldn't bother me but in parking? I've watched Cub wings fold under from aft strut failure. I wouldn't want a compromised strut on my airplane.
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