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Thread: Cub/Super-Cub tail feather repair

  1. #1

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    Cub/Super-Cub tail feather repair

    Hi all,

    I have a general question for anyone doing repair of certificated PA-18 (or J3, etc) aircraft: What material thickness are you guys using for ribs on the tail feathers?

    I have an old J3 rudder that is pretty much a basket case, and I'm going to rebuild it to basically hang it on a wall. While reviewing the Northland drawings, I see they call out 0.020" thickness ribs--but that thickness material seems pretty hard to find. My local metal supplier doesn't stock it in mild steel (1020) for instance. They stock 26-gauge (0.018") and 24-gauge (0.024"), but nothing in 0.020". So do you guys tend to go a bit lighter than the original drawings, or to the heavier 24-gauage thickness...which is what I would tend to do. For a typical rib the difference between 0.024" and the 0.020" thickness called out on the drawings is less than half an ounce (edit: Per Solidworks)--so you're talking a minimal amount of added weight.

    Thus I really do not see an issue using the 24-gauge stuff--and that's what I'm going to use to rebuild this rudder that I have. I was just curious though, and thought I'd ask to see what other folks are doing?

    Thanks in advance.

    TB
    Last edited by tcbetka; 09-23-2020 at 08:02 PM.

  2. #2

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    That's what I would do. Mine would be counterbalanced, though; I used .032 on the cowl, instead of factory .025.
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  3. #3
    skywagon8a's Avatar
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    Since this rudder is just going to be hung on a wall as an art piece, it would make no difference which thickness is used. If you were planning to make it airworthy, you would use the thicker materiel. Using the thinner materiel would reduce the original strength thus rendering the rudder not airworthy.
    N1PA
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  4. #4
    Steve Pierce's Avatar
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    I use 4130 sheet. Seem to remember a recent post that the ribs were available from Univair or maybe another vendor.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
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    Quote Originally Posted by skywagon8a View Post
    Since this rudder is just going to be hung on a wall as an art piece, it would make no difference which thickness is used. If you were planning to make it airworthy, you would use the thicker materiel. Using the thinner materiel would reduce the original strength thus rendering the rudder not airworthy.
    Exactly right regarding the original strength comment. I guess I was more just wondering if others had found a source for the exact materials called out in the original drawings. Anytime I've done an airworthy repair on such a component, I always used something heavier to meet the whole "same materials or stronger" guideline set out by the FAA. The thicker material is more forgiving to weld as well, so that's an added bonus...

    TB

  6. #6

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    Quote Originally Posted by Steve Pierce View Post
    I use 4130 sheet. Seem to remember a recent post that the ribs were available from Univair or maybe another vendor.
    Wow--I bet that's on the pricey side! 4130 sheet isn't cheap. My local metals supplier has 1020 cold-rolled sheet in stock, in 24-gauge and thicker. So that's a piece of cake. I see Piper called out 1025 alloy in at least some places, but I don't know whether or not that alloy is even available any longer. I've always just used 1020 cold-rolled. Pretty economically-priced, and very easy to work with. I'm going to call my local metals supplier today just for kicks, and ask about the alloys they have available.

    TB

  7. #7
    Steve Pierce's Avatar
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    Doesn't seem to expensive to me but all depends on your perspective I guess.
    https://www.aircraftspruce.com/catal.../4130sheet.php
    Steve Pierce

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    Will Rogers

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    On the ribs that are under 18" in length, then no...it's not terribly pricey. But go over 18" in length, and the price jumps considerably. An 18x36" sheet of 0.025" is $22.50, but it would make 2-3 ribs. In contrast, a full 48x96" sheet of 240gauge (0.024") 1020 cold-rolled steel was about $75 when I bought it last fall (2019). I haven't checked lately though--it might be higher now. But my point is that you can build the ribs for an entire set of tail feathers for well under $100, whereas it would cost a fair bit more than that if you wanted to do it using 4130.

    TB

  9. #9
    Steve Pierce's Avatar
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    What do you use to brake the ribs?
    Steve Pierce

    Everybody is ignorant, only on different subjects.
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  10. #10

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    I have a 24" brake now, but when I was making more of them in the 1990s I was using a 48" Tennsmith brake. Is that what you were asking? Sorry if I didn't understand your question Steve.

    TB

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    jay at javron im sure will sell you ribs ready to go.
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  12. #12

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    Steve Furjesi also sells tailfeather rib kits. Super-12.com
    Last edited by 1934A; 09-24-2020 at 10:04 AM.
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  13. #13

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    Quote Originally Posted by tempdoug View Post
    jay at javron im sure will sell you ribs ready to go.
    I'm sure he would. I'm made a BUNCH of them though, over the years. They're not difficult to make--I was just wondering (when I created this thread) how folks were reconciling the specs Piper called out in their drawing(s), against the materials that are now commonly available. I'm an A&P, so I'll just make whatever I need in that sense, and reference the applicable FARs and AC43.13.

    TB

  14. #14

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    Quote Originally Posted by 1934A View Post
    Steve Furjesi also sells tailfeather rib kits. Super-12.com
    Wow--looks like they make some NICE stuff out there! All those engine mounts in that one shot...incredible!

    TB
    Tom Betka, CFII, A&P
    Green Bay, WI

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    Gordon Misch's Avatar
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    Yeah, about 12 minutes from here by Cub. FIRST CLASS operation.
    Gordon

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    RVBottomly's Avatar
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    Quote Originally Posted by tcbetka View Post
    Wow--looks like they make some NICE stuff out there! All those engine mounts in that one shot...incredible!

    TB
    I agree. Now I know where to go when I give up on making my own engine mounts. LOL. Just a day trip for me on a good day.

  17. #17
    Steve Pierce's Avatar
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    Quote Originally Posted by tcbetka View Post
    I have a 24" brake now, but when I was making more of them in the 1990s I was using a 48" Tennsmith brake. Is that what you were asking? Sorry if I didn't understand your question Steve.

    TB
    The foot on my brake is to tall at the trailing edge. I have another tool like they use to make 3/8" u-channel on. Have to take a picture.
    Steve Pierce

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    Click image for larger version. 

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    Quote Originally Posted by Steve Pierce View Post
    The foot on my brake is to tall at the trailing edge. I have another tool like they use to make 3/8" u-channel on. Have to take a picture.

    Ah, I see what you're getting at...

    I tell you what--I have this el-cheapo Shop Fox 24" finger brake that I paid about $250 for on Amazon a few years back. The bend radius is about 1/16" or so (I'm sure it's metric), but for mild steel it's fine. But the fingers are just "thin" enough to allow me to bend a rib of 18-20" (at least), and not get interference. Sometimes if I'm not careful enough I might have to tweak (sharpen) the seam with a hand seamer, but it only takes a minute or so to do. I had to do the same thing with the Tennsmith brake too though, back when I was doing a lot of it in the 90s.

    Last winter I made three miniature tail feathers for a demo I was doing, and I used the little Shop Fox brake. Here are a few pictures of how they turned out, including some (fairly) close-up shots of the ribs. You'll see in the last picture that sometimes the end of the rib gets straightened a bit when you finalize the bend--so all I do is hit it with the hand seamer and it's fixed.


    EDIT: For some reason it's not taking images for upload now, so they didn't upload. I'm still working on it...
    Last edited by tcbetka; 09-24-2020 at 05:38 PM.
    Tom Betka, CFII, A&P
    Green Bay, WI

  19. #19

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    I figured out the issue--it was related to me using the Chrome browser on the first post. It seems to work perfectly with the MS Edge browser.

    Click image for larger version. 

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    Last edited by tcbetka; 09-24-2020 at 05:59 PM.
    Tom Betka, CFII, A&P
    Green Bay, WI

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