Help! broken wing dihedral
11-10-2003, 07:00 PM
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Help! broken wing dihedral
i broke the wing dihedral but both the wing sides are in perfect shape without any damage. I went to the local hobby shop and he wanted to sell me a new wing as he believes that this wing is now useless and it's impossible to take out the broken pieces. I would hate to throw it away like that. Just need a way to take the broken parts out so i can put in a new one.
11-10-2003, 09:26 PM
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RE: Help! broken wing dihedral
That's an odd place to break... did the pieces just snap apart? Were the root ribs damaged at all? What happened to the fiberglassed area around the wing joint (or wasn't there any fiberglass). Any repair would assume that all the wood inside (ribs, spars, dihedral brace, etc.) are properly glued in the first place with no gaps or cracks, etc. You are going to depend on the existing structure to make this repair work.
By the way, there is another 'condition'. I'm going to recommend that you cut away the center section sheeting to get at the brace. The sheeting provides a lot of strength, so you'd have to find a way to restore that strength by making the replacement sheeting as strong or stronger than the original piece was. Perhaps you could lay down some fiberglass over the removed (and replaced) sheeting.
I don't know your level of experience, so pardon me if I go into a little too much detail or restate the obvious.
I don't think that this is an 'easy' fix, but I think it could be fixed. And if it doesn't come out, you haven't lost anything, and you've gained a lot of experience.
Without looking at it, it's hard to say what to do... but you might start by cutting through the top sheeting until you could get clear through to the dihedral brace, and have some room to work. Save all the pieces. Only remove as much covering as you need to. You can always take more off. Also, perhaps you might make a tracing of the root rib. You may need to replace this later, so it would be nice to have a pattern to copy.
Once you can get a clear shot at the broken brace, you might want to make a template for a new brace, just to make sure that the fit and angle are right. That way, if you screw it up, you have only wasted cardboard, not wood and effort. Use a cut-up cereal box or something stiff like that.
Then, cut two new braces out of real ply (not lite ply). If this is a .40 or .60 sized trainer, then 1/8" (or better yet, 3/16") aircraft ply should do it.
Once the template is the way that you like it, make two new braces and trial fit the whole thing. If the fit is good, do a dry run of the glue-up to keep from getting any unpleasant surprises. This includes checking the whole wing for straightness, to be sure that you haven't introduced a twist or warp. If you need to tweak any pieces, you can do it before they have glue on them.
Dry-fit the clamp placement too. Get as many of those on there as you can, and make sure that they're strong. Make sure that the dihedral is correct. Also, make sure that both sides are equal length. This may sound dumb, but if you had to remove any material from the root rib area, you may have shortened one wing a bit more than the other.
Once you're happy with the whole thing, glue the new braces on either side of the broken brace and let this set up overnight. Re-check your work. If you don't like something, you can always take it apart.
If it's getting late and you're getting frustrated, just wipe all the glue off, put the pieces aside on a piece of waxed paper, and tackle it again the next day. Remember, anything that you do after 9:30PM will take twice as long to undo the next day... If epoxy has cured, you might have to roughen it up with sandpaper to give the next coat of glue a 'tooth' to grab on to.
You might also think about putting a couple of mini dihedral braces along the leading edge and trailing edge too, to help hold them together instead of having just a plain butt joint.
After the epoxy has cured for at least overnight, you can replace the balsa sheeting, reinforce the center section with Fiberglass tape (all around the joint, top and bottom) and re-cover.
And now a few words about gluing. Don't ask me how I learned this, but it was the hard way, OK? As I heard someone once say, you can never have too many clamps. Part of the dry fit process is to make sure that you don't have any surprised when you try put the clamps on. This clamp goes here, that clamp goes there. This way, you make sure that you don't have clamps getting in each others way or hitting some piece of the wing that you didn't notice before.
Use 30-minute epoxy, not 5-minute epoxy. There are reasons for this. The longer setting epoxy is less brittle, and stronger, and it soaks into the wood better for a stiffer joint. But you have to coat ALL mating surfaces, and 'work' the glue into the wood. Don't just spread it on. One of the mating surfaces can get by with just a 'skim coat' (but it has to cover the entire surface) but the mating piece has to be a little thicker to fill in voids in the wood. If you take the extra time to work the epoxy right into the surface of the wood, and clamp the daylights out of it, the wood will give long before the joint does.
Squeeze out all excess glue and wipe it away. Excess glue only adds weight, not strength.
So there you have it.
I'd be really careful about flying the airplane for the first few flights, to make sure that the wing will hold. Perhaps have a club test pilot look it over and fly it when there aren't other people on the field (in case the worst happens).
Does anyone else out there have any suggestions to do this more simply?
Hope this helps...
Bob
By the way, there is another 'condition'. I'm going to recommend that you cut away the center section sheeting to get at the brace. The sheeting provides a lot of strength, so you'd have to find a way to restore that strength by making the replacement sheeting as strong or stronger than the original piece was. Perhaps you could lay down some fiberglass over the removed (and replaced) sheeting.
I don't know your level of experience, so pardon me if I go into a little too much detail or restate the obvious.
I don't think that this is an 'easy' fix, but I think it could be fixed. And if it doesn't come out, you haven't lost anything, and you've gained a lot of experience.
Without looking at it, it's hard to say what to do... but you might start by cutting through the top sheeting until you could get clear through to the dihedral brace, and have some room to work. Save all the pieces. Only remove as much covering as you need to. You can always take more off. Also, perhaps you might make a tracing of the root rib. You may need to replace this later, so it would be nice to have a pattern to copy.
Once you can get a clear shot at the broken brace, you might want to make a template for a new brace, just to make sure that the fit and angle are right. That way, if you screw it up, you have only wasted cardboard, not wood and effort. Use a cut-up cereal box or something stiff like that.
Then, cut two new braces out of real ply (not lite ply). If this is a .40 or .60 sized trainer, then 1/8" (or better yet, 3/16") aircraft ply should do it.
Once the template is the way that you like it, make two new braces and trial fit the whole thing. If the fit is good, do a dry run of the glue-up to keep from getting any unpleasant surprises. This includes checking the whole wing for straightness, to be sure that you haven't introduced a twist or warp. If you need to tweak any pieces, you can do it before they have glue on them.
Dry-fit the clamp placement too. Get as many of those on there as you can, and make sure that they're strong. Make sure that the dihedral is correct. Also, make sure that both sides are equal length. This may sound dumb, but if you had to remove any material from the root rib area, you may have shortened one wing a bit more than the other.
Once you're happy with the whole thing, glue the new braces on either side of the broken brace and let this set up overnight. Re-check your work. If you don't like something, you can always take it apart.
If it's getting late and you're getting frustrated, just wipe all the glue off, put the pieces aside on a piece of waxed paper, and tackle it again the next day. Remember, anything that you do after 9:30PM will take twice as long to undo the next day... If epoxy has cured, you might have to roughen it up with sandpaper to give the next coat of glue a 'tooth' to grab on to.
You might also think about putting a couple of mini dihedral braces along the leading edge and trailing edge too, to help hold them together instead of having just a plain butt joint.
After the epoxy has cured for at least overnight, you can replace the balsa sheeting, reinforce the center section with Fiberglass tape (all around the joint, top and bottom) and re-cover.
And now a few words about gluing. Don't ask me how I learned this, but it was the hard way, OK? As I heard someone once say, you can never have too many clamps. Part of the dry fit process is to make sure that you don't have any surprised when you try put the clamps on. This clamp goes here, that clamp goes there. This way, you make sure that you don't have clamps getting in each others way or hitting some piece of the wing that you didn't notice before.
Use 30-minute epoxy, not 5-minute epoxy. There are reasons for this. The longer setting epoxy is less brittle, and stronger, and it soaks into the wood better for a stiffer joint. But you have to coat ALL mating surfaces, and 'work' the glue into the wood. Don't just spread it on. One of the mating surfaces can get by with just a 'skim coat' (but it has to cover the entire surface) but the mating piece has to be a little thicker to fill in voids in the wood. If you take the extra time to work the epoxy right into the surface of the wood, and clamp the daylights out of it, the wood will give long before the joint does.
Squeeze out all excess glue and wipe it away. Excess glue only adds weight, not strength.
So there you have it.
I'd be really careful about flying the airplane for the first few flights, to make sure that the wing will hold. Perhaps have a club test pilot look it over and fly it when there aren't other people on the field (in case the worst happens).
Does anyone else out there have any suggestions to do this more simply?
Hope this helps...
Bob
11-11-2003, 01:59 AM
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RE: Help! broken wing dihedral
Hello,
here's what i did. Drilled two 3 inch holes on each side in the broke brace. Took a metal wire (1/4 inch dia). Cut that into two 6 inch rods and sanded them so the epoxy holds. created an angel on them(exact same on both). Glued them back in the holes and joined the two pieces. The only problem is, Now, the dihedral is more than it was before and i might have to use some balsa to fill up the gap. the sides of the wing are parallel HOWEVER one is higher than the other. About 2 centimeters. But i think, as far as they are parallel, it wont matter. What do you think? took about 1 hour at a friend's shop where he had all the tools. All i need is a piece of balsa. Now that it's metal, i dont think i would need fiberglass.
Tell me about your opinion.
here's what i did. Drilled two 3 inch holes on each side in the broke brace. Took a metal wire (1/4 inch dia). Cut that into two 6 inch rods and sanded them so the epoxy holds. created an angel on them(exact same on both). Glued them back in the holes and joined the two pieces. The only problem is, Now, the dihedral is more than it was before and i might have to use some balsa to fill up the gap. the sides of the wing are parallel HOWEVER one is higher than the other. About 2 centimeters. But i think, as far as they are parallel, it wont matter. What do you think? took about 1 hour at a friend's shop where he had all the tools. All i need is a piece of balsa. Now that it's metal, i dont think i would need fiberglass.
Tell me about your opinion.
11-11-2003, 09:13 AM
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RE: Help! broken wing dihedral
May be to late now, but if it was me and your dealing with a flat bottom airfoil on a trainer, I would just glue the wings back together with no dihedral. I took all the dihedral out of my eagle II trainer several years ago. It still fly's great.
Regardless of how much dihedral you put in your wing, you will want to fiberglass the wing joint for strength.
Regardless of how much dihedral you put in your wing, you will want to fiberglass the wing joint for strength.
11-11-2003, 03:52 PM
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RE: Help! broken wing dihedral
For many wings, you can just butt-glue them together with 30-minute or longer epoxy, and then wrap the center section with 6"wide fiberglass cloth, using the 30-minute (or longer) epoxy. this gives you 3" of 'glass cloth on either side of the butt joint. This is very strong, and has been used on countless models, including all of the Bridi and Great Planes Kaos/Super Kaos kits and Trainer-series kits.
bax
bax
11-11-2003, 04:55 PM
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RE: Help! broken wing dihedral
What is the disadvantage of having an extra dihedral? I am just a beginner. The sides are parallel and i just measured them again and they seem to be the same height as well. However, the dihedral is about 3 inches more than it was before. That's a lot of dihedral. What would i notice when i fly it again? what would i be missing?
11-12-2003, 12:23 PM
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RE: Help! broken wing dihedral
3 extra inches is a LOT of dihedral. You will notice more sensitivity to rudder response. It might experience oscillations in yaw as it responds to your input. It will be extremely stable and will tend to correct itself each time you put it in a turn. Upside down flight will extremely hard if not impossible.
