Plywood leading edges on Center Section

Discussion in 'Starduster' started by Lotahp1, Jan 9, 2018.

  1. Jan 9, 2018 #1

    Lotahp1

    Lotahp1

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    I’m doing plywood (1/16 birch) leading edges on the Center section and will be doing on both lower wings also. (Hope to not have to uncover the uppers right now so they won’t get plywood leading edges now)

    I have the 1/16 plywood cut to size for the center section. (Figured I’d try small first!). My questions are

    1) I’ll use T-88. What thickener is preferred to add to it on the ribs?

    2) how long do i soak the plywood before I form to Center section? (In just warm water? Nothing added to water?) I’ll be doing this in a heated building.

    I think I have the rest figured out but was curious on a thickener to help keep the T-88 on the ribs as it’s pretty runny. I’ll squeegee T-88 on the inside of the plywood. Use straps and 1x2s to keep the plywood in shape while it dries.
     
  2. Jan 9, 2018 #2

    smizo

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    we form our leading edges out of 2 laminations of .8mm ply. this holds the shape. although I did my center section leading edge on the asiis years ago by the method you mention. soaked it in the bath tub then strapped it on for 2 days. use cabosil to thicken the t-88 for the spar and ribs. stick it in the microwave straight for 5-8 seconds to thin it to squeegee on the inside of the LE.
     
  3. Jan 9, 2018 #3

    Lotahp1

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    Thanks...cabosil is what I’ll use. I remember you saying to add something just couldn’t remember what. About how long did you soak before it was ready to strap it down ?
     
  4. Jan 9, 2018 #4

    garyg

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    water is not what really makes wood bend. The water holds the heat and the heat is what makes it bend. I am guessing that thinner wood helps the bend and that makes up for the lack of heat. Problem I had was trying to get some piece of thin wood to hold any heat at all because it cools rapidly once removed and worse than that is that the hot water in the tub isn't really hot enough.

    So I soaked the wood as much as possible to get it wet and then used a wall paper steamer to get the wood hot while I clamped it to dry. But then I used 1/16" wood on leading edges including the ailerons and I used a single upper and lower piece all the way to the tips. So I had a lot more bending and some were compounds.
     
    Last edited: Jan 9, 2018
  5. Jan 10, 2018 #5

    Lotahp1

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    Smizo...when you microwave the T-88 for 5-8 seconds is that after its mixed or when it’s still in its two bottles? (This is the T-88 that will be squeegeed on the inside of the leading edge)
     
  6. Jan 10, 2018 #6

    bigblackmastiff

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    I used 1/16 finnish birch for leading edges on one project. I put a beach towel on the floor and soaked it, then laid the ply on top, then another wet towel. I let it sit that way only a few hours then i placed the wood over a mock leading edge section i'd made which had an aluminum leading edge. I put the wet towel over the wood and wrapped a couple of bungees around it. The next day I took away the wet towel and let the wood dry in place. When i took the ply off the form, I used a loop of painters around the wooden LE until i was ready to glue it on. My point here is I moved very quickly and had no problem with the Birch taking shape or threatening to split.

    I too used straps and wood strips to hold the skin in place while the t88 set. This is one thing I'd do differently. I got a tip from a more experienced builder (too late) that he leaves the Leading Edge ply a little long in chord, an inch or so top and bottom. He drills a hole in the overhanging material and hooks the strap into it from behind, tightening and pulling the skin back onto the leading edge ribs. Later he removed the excess material with a router. I found it a battle to make sure i wasn't pressing a wrinkle into the single layer of 1/16 ply with the straps over strips method. Just a different approach that I'd prefer next time.
     
    Last edited: Jan 10, 2018
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  7. Jan 10, 2018 #7

    smizo

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    Kris, I cant remember how long I soaked the ply for, that was 7 years ago haha. microwave the 88 after mixing it.
     
  8. Jan 11, 2018 #8

    Lotahp1

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    Thanks guys. I got the Center section moved into the house tonight. Just to cold outside. I hope to get both sides formed tomorrow after work. I’ll leave on until this weekend or early next week. By then I should have the cabosil (thanks again Bob!) and new T-88. I’ll take some pics as I go. I think I’m going to try the hot water on towel method.
     
  9. Jan 11, 2018 #9

    NDTOO

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    I also did the towels soaked in hot water method for all my LE's. After they soaked for a few hours I strapped them on with 1" ratchet straps and let them dry for a few days.
     
  10. Jan 11, 2018 #10

    IanJ

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    I love this idea. I'm planning on two layers of 0.8mm like Chris mentioned, but I can definitely see the utility of leaving the ply "too long" to allow for strapping, then cutting the excess off later. This would also allow for a nice scalloped edge at the ribs by inserting a temporary corner block for the router bearing to run along.
     
  11. Jan 11, 2018 #11

    smizo

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    If you use the 2 layers you need to bond them together in a mold.
     
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  12. Jan 12, 2018 #12

    Lotahp1

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    Well it’s on. I am fairly happy. When I glue them I will make sure I go get several pieces of 1x2 instead of the mix I used for the forming. I had one try to crack a tiny bit but used a wallpaper steamer to correct that. (The first layer still looked cracked but it’s not bad and only about 1”) for my first go I think it went well. I do think it will produce the two pieces for the leading edge. I just will do it a tad different (use all the same size boards and have lot of those boards ready and pre cut, AND let the boards soak with the towels for 3-4 hours. I did one half about an hour after soaking...itsbthe one that had the one cracking issue. The second one i did after I took my son to his schools open house and to dinner. That leading edge piece bent much easier with no cracking tendency. View attachment IMG_5789.jpg View attachment IMG_5788.jpg View attachment IMG_5798.jpg View attachment IMG_5796.jpg View attachment IMG_5795.jpg
     
  13. Jan 12, 2018 #13

    garyg

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    You would think the wrap straps would work better than they do but it takes a lot sticks under them to keep even downward pressure. My wing kit has a center board so I only had to do one half at a time but even that took a lot of effort to keep constant downward pressure (and special angle cut wood).

    yeah the wood needs to be very wet and then very hot, depending on the bend. my wooden turtle deck had the tightest bends because of the wing design but the wing tips took compound bends. so the deck wanted to crack if not wet and hot and wing/aileron tips wanted to fight unless wet and hot.

    I have one piece leading edge all the way to tip on both the ailerons and wings. Ailerons are now covered but they look like the ailerons in Chris's wolf wing thread but they are also one piece of sheet from end to end (one on each side). with wet and heat you can do a lot more than you think is possible.

    IMG_1581.jpg

    IMG_1583.jpg
     
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  14. Jan 12, 2018 #14

    Lotahp1

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    That looks really good! After I get mine off and trimmed up I’ll reinstall with the boards I’m using for the glueing phase. (Should have bought and cut the 1x2s for the forming stage but thought I could get by with what I had laying around. I did...but more effort than needed i think) just to do a trial fit again all tightened up with the same boards I’m gluing with etc.

    The wallpaper Steamer seemed to really help. I have one corner piece that’s bent down about 45* I will steam into place after the glue has dried on the rest. (It’s a close out area by the spar)
     
  15. Jan 13, 2018 #15

    Lotahp1

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    Well I got both pieces back on the second time. I used the same hot water on a towel , lay the plywood on towel, add a second rolled up towel that’s wet with hot water. I used a piece of foil (hey I’m doing this on my kitchen island so might as well use kitchen supplies) in a effort to help keep heat in. I layed a dry towel over that. I let soak for about 5-6 hours. Then reinstalled on center section. This time I used more pieces of wood, and all 1x2s. It took shape very good and pulled into shape very nicely. I think this will be the ticket. I’ll take it off early next week. Should be installing for the last time with epoxy mid week. View attachment IMG_5827.jpg View attachment IMG_5826.jpg View attachment IMG_5825.jpg View attachment IMG_5822.jpg

    The wall paper steamer was used after it was basically on. I steamed the leading edge and made sure it was all nice and damp and hot. It’s hard because so much is covered by the 1x2s but I think the steam should help, or at least I see no harm. It will help on one small tab that has to be formed after it’s glued on....more on that later.
     
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  16. Jan 14, 2018 #16

    Dennis Flamini

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    Kris,
    You need to start another thread on the tank construction and anchors.
     
  17. Jan 15, 2018 #17

    Lotahp1

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    Dennis, what do you mean?
     
  18. Jan 17, 2018 #18

    Dana

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    Is your center section separate from the outer wing panels? Seems that would make a lot more sense than what I have on my SA100, which is a one piece wing from tip to tip.
     
  19. Jan 17, 2018 #19

    Lotahp1

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    Dana, the Starduster Too uses a three piece top wing just like a Stearman. Mine has the “optional” Center section fuel tank also. Seems 90% of the Starduster Toos I’ve seen have the Center section tank. Even if I didn’t want it...I’d build it to the fuel tank option specs. (There’s Aluminum ribs at each end inside the root rib that basically takes all the loads. That and being sheeted on the bottom completely...if you built it to the fuel tank option plans you could always install a tank in the future, have a place for a smoke tank, or have a place to make a extra baggage place. With my Ranger...and intentions of actually using the plane to go places, I’m very glad I have the extra 17 gallons.
     
  20. Jan 17, 2018 #20

    Dana

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    I'm just wondering why the Starduster One wasn't designed with a 3 piece top wing, or if anybody's built one that way. It would be a lot easier to work with. And if I have to replace my wing spars anyway...
     

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