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Thread: Rock Damage- horizontal stabilizer

  1. #1

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    Rock Damage- horizontal stabilizer

    Put my first ding on my pristine cub. Woops.

    Must have thrown up a rock on landing or maybe taxi/takeoff. Mike on my field thought landing as it was in line w the mains.

    Whatever hit it must have been moving pretty good to ding that metal. Any potential for structural issues here? I gave it a good tug up/down and felt solid.

    Just want to make sure its not a safety thing, or something that needs addressed immediatley. Anything i need to do?


  2. #2
    supercrow's Avatar
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    How far out from the fuselage side? That's a pretty good hit. A lot of leverage going on there too if it's very far out. The dent itself wouldn't bother me if it didn't actually make a break in the tubing, but look things over carefully. I can see a little distortion top and bottom from the impact. That is an interesting one.

  3. #3
    skywagon8a's Avatar
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    Check the condition of the front bolts (both sides) which hold the stabilizer to the cross tube. The loads from the impact would concentrate there. The dent appears to be mostly cosmetic in that location.

    ps. I'm surprised Mr. FAA hasn't said something about the N number being hidden behind the stabilizer.
    N1PA
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  4. #4

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    Seems to be a gravel bar thing saw a Pa-12 with one that looked similar not long ago.

  5. #5
    cubdrvr's Avatar
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    Quote Originally Posted by skywagon8a View Post
    ps. I'm surprised Mr. FAA hasn't said something about the N number being hidden behind the stabilizer.
    That is precisely where mine is..........and legal. Only hidden if you look up at any angle..........otherwise very readable within 50' or so
    "Sometimes a Cigar is just a Cigar"
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  6. #6
    spinner2's Avatar
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    Same issue discussed here exactly 10 years ago.
    https://www.supercub.org/forum/showt...p-tailfeathers
    "Fast is fine, but accuracy is everything." Wyatt Earp
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  7. #7
    RaisedByWolves's Avatar
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    Mine had a dent bigger than that when I got it. I sandblasted the tail feathers when I recovered it looked fine. Still there now.


    Sent from my iPhone using Tapatalk

  8. #8
    RaisedByWolves's Avatar
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    Quote Originally Posted by cubdrvr View Post
    That is precisely where mine is..........and legal. Only hidden if you look up at any angle..........otherwise very readable within 50' or so
    Hypothetically if you flew by someone taking your picture and you lifted your wing it also lifts the tail too.


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    Quote Originally Posted by supercrow View Post
    How far out from the fuselage side?
    I will look. Couple feet. Its directly back from mains.

  10. #10

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    Quote Originally Posted by skywagon8a View Post
    Check the condition of the front bolts (both sides) which hold the stabilizer to the cross tube. The loads from the impact would concentrate there.
    The cross tube is where it connects to the jack screw?

  11. #11

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    Quote Originally Posted by Douten View Post
    Seems to be a gravel bar thing
    I actually picked this up on a pretty benign strip of dirt. Must have gotten unlucky.

  12. #12
    mvivion's Avatar
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    One of the advantages of treadles (smooth) tires is that they don’t pick up AS MUCH junk and throw it at the tail.

    But, sometimes the most benign looking places can result in this stuff. I was taking off from Allakaket in a 185 and actually SAW the rock come off the back of the tire, go forward and come back through the prop, with a loud “ding”.

    Shut down, and huge ding in one blade. Called maintenance and they said wait right there. Prop blade turned out to be junk. It was a frosty morning, and those tires picked up lots of rocks.

    MTV

  13. #13

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    If it's a certificated aircraft, allowable dents in tubes would need to be published by Piper. If Piper provides no guidance, AC43.13 has tube inspectiin and repair data.

    Reasonably certain what you have is not within limits for acceptable damage to primary structure.
    S
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  14. #14
    skywagon8a's Avatar
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    Quote Originally Posted by Cardiff Kook View Post
    The cross tube is where it connects to the jack screw?
    Yes, the bolts in question are outside the fuselage in the leading edge of the stabilizer. Easy to pull and inspect.
    N1PA

  15. #15
    BC12D-4-85's Avatar
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    From AC 43.13-1B CHG 1. Just a reader here not an A&P,

    4-94. WELDED-PATCH REPAIR. Dents or holes in tubing may be repaired by using a patch of the same material, one gauge thicker. (See figure 4-36.)
    a. Dented Tubing.
    (1) Dents are not deeper than 1/10 of tube diameter, do not involve more than 1/4 of the tube circumference, and are not longer than tube diameter.
    (2) Dents are free from cracks, abrasions, and sharp corners.
    (3) The dented tubing can be substantially reformed, without cracking, before application of the patch.
    b. Punctured Tubing. Holes are not longer than tube diameter and involve not more than 1/4 of tube circumference.

    Gary
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  16. #16
    RaisedByWolves's Avatar
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    Bushwheels will throw rocks.
    Sucks when you have a brand newly rebuilt 180 and land on a gravel bar for the first time Click image for larger version. 

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  17. #17
    skywagon8a's Avatar
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    Quote Originally Posted by RaisedByWolves View Post
    Bushwheels will throw rocks.
    Sucks when you have a brand newly rebuilt 180 and land on a gravel bar for the first time Click image for larger version. 

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    That's what the glued on rubber abrasion boots are supposed to protect against.
    N1PA

  18. #18
    BC12D-4-85's Avatar
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    Here's a boot installation instruction: https://support.cessna.com/custsupt/...df?as_id=34171

    I recall them on Cessna's having a raised center to help absorb impact. What takes a hit are the exposed elevator counterweights outboard of the stabilizers. They get shotgunned. I never had a LE dent on a C-185 thanks to the boots but did manage to crease the lower stab surface a few times. The bigger the rock the bigger the damage.

    Gary

  19. #19
    wireweinie's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    From AC 43.13-1B CHG 1. Just a reader here not an A&P,

    4-94. WELDED-PATCH REPAIR. Dents or holes in tubing may be repaired by using a patch of the same material, one gauge thicker. (See figure 4-36.)
    a. Dented Tubing.
    (1) Dents are not deeper than 1/10 of tube diameter, do not involve more than 1/4 of the tube circumference, and are not longer than tube diameter.
    (2) Dents are free from cracks, abrasions, and sharp corners.
    (3) The dented tubing can be substantially reformed, without cracking, before application of the patch.
    b. Punctured Tubing. Holes are not longer than tube diameter and involve not more than 1/4 of tube circumference.

    Gary
    Correct criteria for repairs but I think the OP is looking to asses whether he can continue to fly safely or ground it for repairs.

    Web
    Life's tough . . . wear a cup.

  20. #20
    BC12D-4-85's Avatar
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    I'd let an experienced A&P inspect and advise.

    Gary

  21. #21
    skywagon8a's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    Here's a boot installation instruction: https://support.cessna.com/custsupt/...df?as_id=34171

    I recall them on Cessna's having a raised center to help absorb impact. What takes a hit are the exposed elevator counterweights outboard of the stabilizers. They get shotgunned. I never had a LE dent on a C-185 thanks to the boots but did manage to crease the lower stab surface a few times. The bigger the rock the bigger the damage.

    Gary
    1/4"-5/16" at the center, tapering back to almost nothing at the trailing edge, top and bottom. The 185s also have a sheet metal leading edge doubler as part of the increased gross weight for extra strength.
    N1PA
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  22. #22
    stewartb's Avatar
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    All later model Skywagons have a LE doubler. Most I lnow have the thick nosed abrasion boot, too. My LE dents tend to be below the equator of the LE. Maybe a design feature or maybe because I keep the tail up as much as possible.

    With the milled tubes that insert in the front and back tubes of Cub stabiliazers I can’t imagine the bolts at either place take much stress from rock hits. With through tubes fore and aft the overall stab is hell for stout on the lateral plane. Not dent-proof but that’s a different thing. Cardiff needs to get in the habit of inspecting tail brace wires and tabs to make sure those aren’t getting rock damage. The rock that dented his tube could have easily damaged a brace wire or end.
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  23. #23
    mvivion's Avatar
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    Quote Originally Posted by RaisedByWolves View Post
    Bushwheels will throw rocks.
    Sucks when you have a brand newly rebuilt 180 and land on a gravel bar for the first time Click image for larger version. 

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    Yep, ANY tire will throw rocks. Treaded tires just do so a little more enthusiastically....

    MTV
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  24. #24
    stewartb's Avatar
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    Tanalian Air’s website says their removable leading edges are designed to hold up better to rocks thrown when landing. If that’s the case, tire shape has more to do with it than anything. The round profile of a Bushwheel throws fewer rocks than an Air Hawk. I’m certain of that. Exactly when the rocks are thrown is less certain. In my ownership my Skywagons’ tail tips have seen more damage than leading edges.

  25. #25
    Charlie Longley's Avatar
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    Pull the stabilizer and repair it is the safest thing.
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  26. #26

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    Id take Kookies hail dent over this one any day….

    Click image for larger version. 

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    35s picked up this big flat rock and it got the leading edge, tail brace wire and bent the internal structure before exiting out the top. I could see the rock kick up from a 1/4 mile away.

  27. #27
    G44's Avatar
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    That dent will compromise the strength and integrity of the tube. In my opinion that is NOT airworthy. Pull it and replace.
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  28. #28
    BC12D-4-85's Avatar
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    Find a tubing fixer and go on a trip. Fly when you return.

    Gary

  29. #29
    courierguy's Avatar
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    Quote Originally Posted by KevinJ View Post
    Id take Kookies hail dent over this one any day….

    Click image for larger version. 

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    35s picked up this big flat rock and it got the leading edge, tail brace wire and bent the internal structure before exiting out the top. I could see the rock kick up from a 1/4 mile away.
    I had similar on this mountain LZ, clear thru, taped it up with pipe wrap tape, used by well drillers for securing cabling to the drop pipe, great stuff and doesn't leave the gunk behind that duct tape does, even if left on long term. I also put a bend in the lower brace strut/wire, mid span, gently straightened with no end fitting stress, so I thought....but a few hundred hours later that fitting failed.

    That was a few years ago, this year I rode my new electric Sur Ron motorcycle up to the exact same spot, and right after I took this picture dropped my phone and busted the screen on a rock. Later I thought..., it was probably the same darn rock!
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  30. #30

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    Quote Originally Posted by courierguy View Post
    I had similar on this mountain LZ, clear thru, taped it up with pipe wrap tape, used by well drillers for securing cabling to the drop pipe, great stuff and doesn't leave the gunk behind that duct tape does, even if left on long term. I also put a bend in the lower brace strut/wire, mid span, gently straightened with no end fitting stress, so I thought....but a few hundred hours later that fitting failed.

    That was a few years ago, this year I rode my new electric Sur Ron motorcycle up to the exact same spot, and right after I took this picture dropped my phone and busted the screen on a rock. Later I thought..., it was probably the same darn rock!
    Hijacking my own thread- but that Never heard of the Sur Ron so looked it up.

    That thing looks fun!

  31. #31
    courierguy's Avatar
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    It's amazingly practical, and a lot of fun. A great way to scout out new LZ's, and the plane of course is a great way to scout out new trails to ride, on a blown out day for flying. they compliment each other. Not a dirt bike, not a ebike, somewhere in between, real torquey (especially with the large 64T rear sprocket I have on mine), while still fast enough to hurt you/keep your attention. Now I need to get a pic of the Sur Ron on this same site I landed this weekend.
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