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Thread: Wing re-cover

  1. #1

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    Wing re-cover

    Recovering PA-18 wings -- Is there a wedge or jig to get correct twist during recovering or just set flat on table and put fabric on?

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    cubdriver2's Avatar
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    I've seen a pack of Marlboros used

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    55-PA18A's Avatar
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    Are you recovering or rebuilding? Seems like setting the twist would happen when assembling the wing.

    Jim

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    Hello, We just finished the cover of a PA-11, starting on a PA-12 after the Hollidays. What works well is a flat, long table and a block at the outboard end of the false spar at the rib with the correct twist. I recall is an inch and a 1/4 for the PA-11. A little different for a PA-18,

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    skywagon8a's Avatar
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    Quote Originally Posted by s48teve View Post
    Recovering PA-18 wings -- Is there a wedge or jig to get correct twist during recovering or just set flat on table and put fabric on?
    This is most important when assembling the component parts of the wing. IE: being certain the compression ribs are installed correctly and when screwing the new leading edge to the spar. The fabric alone is flexible enough not to be of a concern. When you hang the wing on the airplane you will find there is a lot of flexibility in the wing.
    N1PA
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    coxcub's Avatar
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    Have a look at this - Fig 5 shows it
    https://cdn.shopify.com/s/files/1/06...f?v=1656372917
    Frank

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    Marty57's Avatar
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    The only issue that covering might have on a wing twist is not properly shrinking the fabric. The twist is locked in when adding the leading edge to the wing during the wing build. When shrinking, I teach gradual vs three quick shrinks. I like to shrink in 4-5 increments to slowly shrink the fabric and give it time at each temp to actually allow the fabric to move. I start at 250 and end up about 340. 340 allows for any temp fluctuation and leaves a little shrink available in the fabric should a wrinkle or dent occur at some later point. I will do each temp twice; top then bottom and repeat. Center left, than right, than left, than right; a couple bays at a time will lessen uneven stress from the fabric. Shrinking slowly is much better all around.

    Marty57
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    Psalm 36:7 "High and low among men find refuge in the shadow of His wing"
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    I agree - I have never worried much about the twist when covering or painting, and once the wing is on the aircraft it can be adjusted without any wrinkling. Good thing, since there seem to be a lot of mis-matched ailerons out there.

    Early Cubs have less than rigid leading edges - they stop short of the spar. We just put the wing on sawhorses and pressed on. Even in the auto enamel days it didn't seem to be much of a problem.

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    Hardtailjohn's Avatar
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    I always put the twist in when I'm shrinking. It's in the rotisserie, so why not? I have seen them show up with a small wrinkle before, when they were set flat and then twisted on the airframe. I guess it's personal preference, and your mileage may vary.
    John
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    Quote Originally Posted by coxcub View Post
    Have a look at this - Fig 5 shows it
    https://cdn.shopify.com/s/files/1/06...f?v=1656372917
    Frank
    I see what is needed - I guess the false spar is already attached?

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    Charlie Longley's Avatar
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    I typically just cover on a couple of sawhorses or a big table. I’ve never had issues with the fabric wrinkling from the slight twist.

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    Quote Originally Posted by guanaco View Post
    Hello, We just finished the cover of a PA-11, starting on a PA-12 after the Hollidays. What works well is a flat, long table and a block at the outboard end of the false spar at the rib with the correct twist. I recall is an inch and a 1/4 for the PA-11. A little different for a PA-18,
    I am also in the process of rebuilding a set of wings for a PA11. During my research I have found recommendations for the block to be used to set the wash out at 3/8, 1/2 and 1 inch for a PA18. I have not found any information pertaining to the PA11. I was curious where the 1 1/4 inch recommendation came from?
    Thanks
    Dan

  13. #13

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    Soooooo. Some confuse rigging a plane with building a wing. If you want to build washout into a wing I believe it is the same for PA 22/20/12/14/18. Figure out what you want and start with the butt rib as zero. Once it is on a level plane the incidence will change and you will have to adjust for that with blocks or just use a smart level. Then go fly it and adjust to make it right. Do a search, a great few posts years ago explain it all.
    DENNY

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    Thanks Denny,
    The washout I'm referring to is done when building the wing. I did a search on this web site and read all I could find on the subject. The link to the Dakota Cub web site from this thread shows the process clearly. As you mentioned the measurements are the same for the PA22/20/12/14 and 18. As I'm working on a PA11 I was hoping someone might know what the measurement is for the block used under the rear spar at the outboard aileron rib for a PA11. Does anyone know what Piper instructed or did they just spell out the number of degrees between the butt rib and the outboard aileron rib? guanaco mentioned earlier that the PA 11 used a 1 1/4 inch block under the rear spar location and I was hoping there was a document that spells this out.
    Thanks
    Dan

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    This is from memory - so regard it with suspicion.

    Tandem Cubs have "wash" of two degrees from fuselage centerline to the outboard rib just outside the aileron cove.

    One can compute the size of a block from that information using a measuring tape and a small amount of trigonometry. Some of it depends on where you choose to anchor the block.

    Cubs are not adjusted by degrees - smart levels were unheard of - so the factory said "level the aircraft, go here and insert a block under a 30" level, and adjust until the bubble is centered." That procedure has almost nothing to do with what size block you would need at assembly, since with the aircraft level, the butt rib is up maybe a couple degrees to start.

    To avoid the trig, just get a Smart Level, and adjust the block until the bottom cap strips say roughly 1.8 degrees from butt to tip.

    Somebody double-check me on the two degree thing.

  16. #16

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    I don't recall seeing a specific piper instruction on how to build a PA 11 wing. If you plan on doing a stock washout when you rig I would just follow the Dakota cub instructions, or as Bob instructed. Even with a one inch block you should be able to get to a 0.5 degree washout if you want a slow flying wing. The aim is to get the wing into the ballpark. Worry about the home run hit when you are rigging it on the plane. Not a a&P stop take my advice with a grain or full shaker of salt as needed.
    DENNY

  17. #17
    courierguy's Avatar
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    I still use my 50 year old Starrett adjustable protractor for the most critical tasks. I trust gravity more then any digital thingie. I was an early adapter when the first ones appeared, my brother sent me one. I can't recall if it was setting washout or maybe when building a truck's flatbed, but when I came back out to the shop the next day the Smart thing didn't agree with the reading from the day before. Nothing had moved, I just never trusted them after that. Silly I know, but I'll keep the Starrett. Piper had them I'd bet.

  18. #18
    wireweinie's Avatar
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    Quote Originally Posted by courierguy View Post
    I still use my 50 year old Starrett adjustable protractor for the most critical tasks.
    Your grandchildren will be able to use that, when THEY grow up.

    Web
    Life's tough . . . wear a cup.
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    BC12D-4-85's Avatar
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    The digitals need to first be calibrated and then held in the same orientation when comparing surfaces. Using a long level base like square tubing to span surface irregularities helps.

    Gary

  20. #20
    courierguy's Avatar
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    Yes, just like a whiskey level, keep the left end on the left, etc., an old carpenter trick.

    The one digital level device I really like is made for pipe fitters, with a V shaped magnetic base. It has a built in spring center punch, you position where you want via it's readout, push a button to let the punch make a mark, and now you have a reference point for whatever degree of rotation you need. I used mine when I was in the sideline biz of fabbing large solar panel array mounting structures, designed of course to be lifted via crane, since I have one.

    Harbor Freight makes a laser/ whiskey level combo, and it's a good tool for setting blade pitch for the ground adjustable props: a simple jig that ensures it's in the same position on each blade, then you shine the red dot on the floor (with the plane firmly chocked, but it doesn't need to be level) and make a pencil mark on the floor, when subsequent marks for the other blade/blades all match, all are at the same pitch. Very small movements of a blade will mean large movements of the dot, making it a very precise way to set pitch.
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