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Thread: J-3 strutsn

  1. #1

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    J-3 strutsn

    Folks: I’m new here and just bought a wrecked J-3. Will probably go experimental so am looking at options. The five metal struts are all about a quarter inch short and I’d rather not work that way. Rebuilding the struts is certainly an option but I wonder about compression ribs. Having built an Eagle, it features a number of 1/2” ribs, a 3/4”x 1/2” horizontal member between the spars and faced on each side with 1/16” mahogany ply which serve as compression ribs. Is there any reason I can’t duplicate that in the J-3 wing?

    Thanks for any input I might receive,

    Sarpy Sam

  2. #2
    www.SkupTech.com mike mcs repair's Avatar
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    Pictures and a better explanation would help


    Sent from my iPhone using SuperCub.Org

  3. #3

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    There are 5 metal compression struts in each wing. 4 are internal and one spans between the lift strut mounts on the bottom of each wing. They assist the ribs in maintaining the space between the spars. I’d send a pic but have already disassembled the wings. Hope this clarifies the topic.

    Thanks for the interest.
    Sarpy Sam
    Likes mike mcs repair liked this post

  4. #4

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    How do you know they are short? Were the ribs all buckled up before you loosened the bolts? Metal spar or wood spar?

    if you are going experimental you can put Starduster wings on - or DC3 wings if you want. you just need to build 51% from scratch.

  5. #5
    RVBottomly's Avatar
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    Quote Originally Posted by bob turner View Post
    How do you know they are short? Were the ribs all buckled up before you loosened the bolts? Metal spar or wood spar?

    if you are going experimental you can put Starduster wings on - or DC3 wings if you want. you just need to build 51% from scratch.
    I was wondering the same thing. But now I want to see the DC3 wing installation!

    But I'm trying to figure out how the compression struts could be 1/4 inch short. Were they compressed in some way?

  6. #6

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    It’s a wood spar and they’re all broke at the butt rib. My measurements are based on the Wag Aero plans but that brings up a good point Bob. Does W/A use Piper’s measurements? I don’t know. I just assumed they did. If I use the W/A rib jigs, I hate to start out different than the certified.

    Anyone know?

    Sarpy Sam

  7. #7
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Sarpy View Post
    ... and they’re all broke at the butt rib. ...

    Sarpy Sam
    ????????

  8. #8
    RVBottomly's Avatar
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    Which Wag Aero plans? The Sport Cub? As far as I know, the spacing between the spars is the same for the wood sparred J-3 and the Wag design. Aluminum spars required spacers for the ribs.

    The ribs for the Wag Sport Cub, Wagabond, and 2+2 all look pretty much the same--but I only have drawings for the Wagabond and the 2+2.
    Vic

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    That’s where they attach to the fuselage. Most of the ribs are dinged and dented that make most of them unusable but the wing is fairly well intact.

    Sarpy Sam

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    Vic: It’s the Sport Cub plans that I’m working from. It’s obvious that the wing has been worked on many times since 1939 and it wouldn’t surprise me if the compression struts have been tinkered with at some time in the last 80 years give or take!

    Thanks for the interest,

    Sarpy Sam

  11. #11
    skywagon8a's Avatar
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    Your initial statement indicates that you should review the regulations which are related to "Experimental" certification. This part of your question indicates that you have experience with "Experimental-Amateur Built"
    Quote Originally Posted by Sarpy View Post
    Having built an Eagle,
    This part is suggesting that you intend to convert a certified Piper J-3 to "Experimental-Amateur Built". It doesn't work that way. If you just go ahead as you seem to have indicated, you will just end up with a pile of parts which may resemble an airplane but is legally just stuff. There are many "Experimental" certifications which in themselves have various restrictions. None as liberal as "Experimental-Amateur Built". Yet you can not just convert from certified to "Experimental-Amateur Built" because it makes your life easier. This has been extensively discussed here in the past. Also you can get the straight scoop from the EAA.

    Quote Originally Posted by Sarpy View Post
    Folks: I’m new here and just bought a wrecked J-3. Will probably go experimental so am looking at options.

    Thanks for any input I might receive,

    Sarpy Sam
    N1PA

  12. #12
    S2D's Avatar
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    Quote Originally Posted by Sarpy View Post
    Vic: It’s the Sport Cub plans that I’m working from. It’s obvious that the wing has been worked on many times since 1939 and it wouldn’t surprise me if the compression struts have been tinkered with at some time in the last 80 years give or take!

    Thanks for the interest,

    Sarpy Sam
    Lee
    I've got a couple wood wings where I'm working right now,
    I can get the measurement on a couple of my struts and call you.
    Brian
    I may be wrong but that probably won't stop me from arguing about it.

  13. #13
    Cub junkie's Avatar
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    Wag Aero uses 31" spar centers same as Piper. Wag Aero Sport Trainer wings if built to their plans use wood ribs and spars with aluminum spars as an option. All the metal components in their plans are J3 wood spar fittings. You can use use Piper parts, aftermarket parts or fabricate your own. Pretty simple stuff.

  14. #14

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    What I have now is just a pile of stuff. With a set of plans, I can go buy a fuselage and build an experimental airplane. The pieces I purchased includes mostly junk and a very nice fuselage. I’ll have no problem complying with the 51% rule. This isn’t my first rodeo, just the first Cub I’ve built.

    Sam
    Thanks skywagon8a thanked for this post

  15. #15

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    Thanks a bunch Brian. I appreciate that.

  16. #16

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    Suggest you start here to document the 51%. Your DAR will likely want that when you are done, might as well start with it? https://www.faa.gov/aircraft/gen_av/...syCklistFW.pdf


    Sent from my iPhone using Tapatalk

  17. #17

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    Good idea. I’ve recently completed a Hatz that had been badly ground looped and destroyed everything but the fuselage and tailfeathers and it came in at 70 some odd%. I suspect this one will be near that. The fuselage and tailfeathers of the Cub are nice. Included in the purchase is a new gear so that will reduce the percentage but I have no doubt that I’ll be able to comply. I’ll take their work sheet and go through it early. Sure gives a guy a good idea of where he’s at.

  18. #18

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    Be careful taking credit for anything that was used even on an Experimental Amateur Built. I had a guy that purchased a home Built that the builder removed the data plate and turned in the registration and airworthiness as aircraft destroyed. New owner went to register it and had lots off issues that filtered through the FSDO. Final ruling was he put a new data plate on with his name as the builder, but wouldn’t qualify as amateur built. I ended up issuing an Experimental Exhibition Certificate.


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