Horrible warp in planked T/E!

I just put together my first planking trailing edge on a Flight Streak, and despite carefully bulk cutting and sanding my ribs and building on a flat board I got a bad warp on one part of my trailing edge.

If it's just the TE that's warped will it be okay? If not, what's the best remedy? I'm not sure the ribs will survive being seperated from the planking.

My building method was to pin the lower spar to the board, add all the ribs, add the upper spar, tack the L/E 3/16" piece in, then move on to the T/E planking.

I'm most disheartened, I thought I was doing really well up to that point

When you say warpped do you mean both planking on the top and bottom have a twist that is causing the whole wing not be straight? Or are you saying that one side of the planking is flat and straight and the other side is drooping or sagging between the ribs?

If it is the later of the two you can simply place a piece of 1/16 balsa in there as a sheer web. Make it attach to the ribs and carefully cut it to shap so that it slide right inbetween the top and bottom planking. This will prop the planking that is drooping up and hold it staright and flat. I sheer web my trailing edges on most of my planes now. It is an easy way to get some strength and add no weight.

If it is the whole thing twisted dont worry about it. Get it all together and then weight in down on your FLAT building board so that the TE is flat and straight. Then wet it down with water that has amonia in it. Let it dry out for a day dont move it then wet it again and let dry for a day or so. It must be dry before you move it. The part on the table will take twice as long to dry out as the part on top that is exposed. So be sure it is dry. If you are building on an actual board you will want to cover it with saran wrap or wax paper just something to keep the water off of you rbuilding board so it doesnt absorb water and become warped also. Site down the TE as see if it is straight. If not set it up again and this time set it up so that you have twisted or warping a little more than is needed and it will end up really close. This is a guessing game that you will get good at over time. I have straightned out many wings at this way and it will hold. Once you get it straight go ahead and sheer web the trailing edge and it should stay straight.

I hope this helps.

Please describe your warp a little more.

LAST EDITED ON Jun-13-02 AT 11:34 AM (CST)

It sounds as though you didn't have the TE supported when the planking was added. That's an almost sure way to get a warp as you found out. You're probably going to have to go in with a new X-Acto blade and slice the ribs away from the TE on the offending part of the wing, pin the bottom TE plank firmly in place on the board and re-glue the ribs to the bottom. After that, using something besides CA, glue the ribs to the top plank and then evenly weight down the TE until it's completely cured. Make sure you support the bottom spar and/or the LE with identically sized pieces of balsa so that the TE can lay flat on the board while the assembly dries. With the LE or the spar properly and evenly supported if you have to press the rear of the rib down to make contact with the TE plank then it's probably going to re-warp when it comes off the board. Thin slices at the spar and LE locations may be necessary. The idea is that before glue-up begins try to have the ribs resting on the various spars and TEs without forcing them into contact. Easy in principle but sometimes very hard in practice.---Mark

P.S. Forgot about the ammonia thing...way easier to try that first for sure.

I am also having the same problem with a Brodak Jr. Lightning Streak. But mine is bowed in the middle - both TE and LE.

Bob from Shalimar, Florida

Mine has a couple of dips in the trailing edge.
We (kids in airplane club) ignored it and
the plane flies fine.

As long as there isn't a gross twist in the wing
I would say it could stand it.

Rex

Mine has a couple of dips in the trailing edge.
We (kids in airplane club) ignored it and
the plane flies fine.

As long as there isn't a gross twist in the wing
I would say it could stand it.

Rex

Hmmm, Xain,

You could cover the wing with heat shrink polyspan and then pull the warp out of the wing when doing the heat shrinking, but you must be careful not to overshirnk the polyspan because it will split open and cause problems. Just though I would put that idea out there, but if I were doing it I would do it the way Doug said to do it. You could still cover it with the polyspan and if it ever did come back then use some light heat on it possibly straighten it out again.

Hi DMoon,

I looked again this evening and it isn't as bad as I thought. Basically about 1/2 way out on one side of the wing, the T/E dips, top and bottom together but about 1/8" max. The wing looks fairly straight.

I think what happened was the although I had the bottom spar pinned down, the L/E "spar" didn't fit as well as I'd liked, and I gently teased the ribs to make it line up. So the LE is straight.

Howewer, when I came to the TE, it seemed one rib was rotated nose-down slightly, giving the warp. I had to force the rib up by about 1/16" to meet the planking. In fact once it was together I could see that the main spars were bent *slightly* forward around that rib.

Seems like I didn't get this rib quite right and relied too heavily on the LE spar fit for my "true". I'm a bit annoyed because I worked really hard to get those ribs perfect, but now I'm not so sure about the TE part of them. Maybe there was too much margin for error.

Anyway, I'm probably going to stick with it, since the wing itself looks pretty straight, and the warp is really just a dip in the T/E

Thanks, and I'll remember the Ammonia and polyspan tricks for later.

You're right, it was a bit ad-hoc. I thought that pinning the bottom spar would be okay, but as I glued I *knew* it was a bodge. I just don't have the jig that I should have. Maybe I'll built one (bent, probably!)

Boil a large pot of water, and hold the TE over the pot. Put pressure on the TE in the opposite direction of the warp. Try to apply the pressure over the entire warp, which means you'll be moving your hands some. In a couple of minutes, you will feel some give. Go a little bit past neutral, because the wing will have some memory. Reglue the TE.

If all fails, just use a tab.

Cheer up, because this is not the End of the World! It is quite fixable.

Thanks Currell. I've got over the worst of the crushing despair

This is very good that this early in your building you are recognizing why you got a warp.(I am prett sure I remember you saying somewhere that your are new to CL right?) You cant push the ribs into place. They have to rest in place. The ribs determine the shape of the wing. The sheeting and spars are the strength. If it was straight on the front but having a little whoopty doo in the rear then the edges on the front of the ribs where they met the LE spar where not uniform and the same all the way down the span. Having caught this early on you wont be building like me for several years and trying to figure out why this keeps happning until someone shows you why. Now your next one will be straight.

The small warp you described should have very little if any on the Plane. Flight Streak right? You still have to glue up the aft portion of the wing to the back of the TE. Make sure this is straight. After it is glued on there will be a dip on one side and a bump on the other. On the dip side fill it 1/16 balsa until it bumps up a little then sand flat with your long flat sanding block. Then on the bump up side put balsa inside the wing under the bump. Then sand away using your long flat sanding block. You want to put that little balsa inside the wing under the TE planking in case you sand through there will be wood there. Whoooolllla you now have a flat TE.

Or you could glue it up make sure it(aft portion of fixed flap) is straight and go fly. The warp you described was small and probably wont do anything at all. You could try the above just to see how it works out.

Hope this helps.

You talked about a jig for support. My brother went to the local hardware store and bought some Angle IRON(not aluminum) 2 at 36" long and 1 60 or 72" cant remeber which. He then places them on the table and glues a piece of balsa wood onto the long one(72") The iron is straight and if the table is warped it wont follow the table. The iron is 1.5"x1.5" and heavy and wont flex like aluminum might. The peice of wood on the iron is straight because the iron is straight. He glues it up with thin CA it sticks good. This peice of wood supports the TE.

He uses the two 36" ones to support the LE spar. In the same manner. It works out real well and cost about 7$ dollars total. You just have to make wure that the front pieces where they come together are the exact same height as the pieces are at the outboard edges of the wing. This way the wings LE is straight as well as the TE. If they are lower or higher you will build in a warp that wont come out no matter what you do. It is easy to get it right(just shim it with balsa, or if your table is flat then it doesnt matter, it will be flat) and the front can be lower or higher than the back it doesnt matter. They just have to be straight across from end to end like the one for the TE.

Just an idea. There are many ways to jig stuff. Another good way is (dont laugh) to use LEGOS. the Duplo blocks for ittle kids work great. All of the pieces are exactly the same size and thinkness. If your table is flat then you can glue them down in a straight line with abroid so you can get them off later. They will support your TE and LE at the same height all the way across. It really works well. The cool thing is they are perfect for supporting 1/4" spars in the LE.

Just ideas about different JIGs. There is 100s of ways to do it. It just has to have good even support. Since it is such a light material you dont have to go overboard with whatever you use.

It sounds like you have one rib that is causing the warp. How about cutting it loose from the spars, taking the warp out and then regluing it with the TE straight? Might work. Do something about it, if nothing else to demonstrate that you, not the structure, is in charge.

I'm with JimT!
I read all the way through the posts to see if anyone else would suggest fixing the problem instead of treating the symptom, especially since you already know where it lies. Cut loose whatever you need to cut loose, get the wing straight however you need to (weight it down or whatever), re-fit wood as needed & re-glue.
When you recognize you have a problem, fix it right then, don't compound it by adding more structure. I've been fixing bent cars for a living for nearly 34 years & the same rule holds true. For instance, if one frame rail is 1/2" higher than the other on a Honda car after a crash, by the time you build your way up to the top of the core support the grille won't fit right, the headlights won't fit right & the hood ain't gunna fit by a large margin!

LAST EDITED ON Jun-14-02 AT 00:45 AM (CST)

I'm with Nils and Jim T. Slice & dice to make it straight right now. As a metalworker ("Machinist" here = "Turner & Fitter" to y'all), I promise you that metal stock is very often NOT straight and it doesn't matter too much what type it is, extrusion, plate, black iron, cold rolled, round, etc. Don't trust anything to be straight without giving it a good look. Your eye is probably more accurate than anything else in your workshop. Count on your ribs not being identical. Did you stack sand them between templates that were stack sanded together? Then you need to match mark them and keep all the marks on top or bottom. The typical way to build a wing like that is to lay the TE on a flat workbench, shim the spars off the bench (I think Brodak uses a strip of balsa under the ribs, not spars), then gently pull the LE into position. Any piece of bowed wood needs to be used with care or avoided. Steve

>The typical
>way to build a wing
>like that is to lay
>the TE on a flat
>workbench, shim the spars off
>the bench (I think Brodak
>uses a strip of balsa
>under the ribs, not spars),
>then gently pull the LE
>into position. Any piece of
>bowed wood needs to be
>used with care or avoided.

I used this method for my Flitestreak wing and it's as straight as a die. It's a bit fiddly but it does the job. I am too tight-fisted to buy a jig. I dis find that using a stripof balsa can lead to warps especially if the edge used to shim the ribs is not pind down in an exact straight line.

Have a go at cutting out the rib or perhaps cutting around the spars to allow the rib to be manipulated in to a more sutable position.

TTFN

Vernon
with a straight but still unflown Flitestreak.

>I am too tight-fisted to
>buy a jig. I

You and me both Vernon!

I think it's probable that after all my careful sanding of the ribs all together in one block, I may have installed one of them upside down. It's going to be a pain to remove it, but I can probably re-jig (no pun) the spar cutouts so that it sits back again.

I'll take a look tonight.

Thanks guys
Jon

Hi Steve,

they were all cut into blanks seperately, then stacked in wing halves (which are still together) and then cut and sanded in those "gangs". I may have put one rib in upside down. That sould probably be enough, despite the fact they're symetrical.

I thought about the construction method, but my enthusiasm to just get on with it, and not keep putting it off like my last plane got the better of me.

So you should pin the T/E plank to the bench, shim up the bottom spar so that the rib is at the right angle, then start installing the ribs? It sounds like it would be hard to get the angle of the spar right, hard to get the T/E of the ribs lined up correctly, and easy to get ribs not pointing forwards. I guess I'm missing something.

Now if I hadn't glued all my 36" spars together like a prat, only to realise that I only needed them to be 36" anyway, I'd be tempted to build a second wing alongside the first, using a better method. As it is I'll have to go the LHS now, which isn't so local. So inertia being what it is...

Jon

Pat Johnston told me to close off the space between the TE sheets as Doug mentioned to really stiffen the wing up and Tony Eifflander uses diagonal braces just in front of the TE for similar effect. When you get the TE straight, put is the shear webs as Doug suggested and it should stay straight.

Jon,

A couple of suggestions:
1. When you have finished sanding the stacked ribs, make a mark on one side only (with a magic marker, etc.) in a place that will later be covered, such as under the TE planking. Use this mark for orientation (all up or all down) so that all ribs will be oriented the same way. That way, any minute differences made by sanding will not show.
2. Use the spars for holding the ribs in position while installing the TE and LE, but do not glue them until the LE and TE glue is dry. Then remove the top spar and glue it. When the glue dries, turn the wing over and glue the bottom spar in place.
Hope this helps.

If all else fails and you are unable to get the warp out by any of these methods, don't despair. Just go ahead, finish the bird and when it's done grab your wife (or mistress) to come over and help "unwarp" the wing. This is easier if you covered the wing with Monokote, Fascal or some other mylar material. Just bend the TE a little past the straight position, and then heat the wrinkled skin(loose slack side) to tighten it up. Repeat as required until it's straight throughout. If you covered the wing with dope and silk try steaming it with a kettle or poring boiling water over it. If none of this works (it should) an unsightly trim tab hung on the outboard wing is your last option.

Well I cut the offending rib loose, adjusted the points that were off and re-glued everything with the TE pegged flat. It's now *much* better.

Thanks guys, I'm glad I did it now.

Hi Jonathan!

Look at this:

http://www.clstunt.com/htdocs/dcforum/DCForumID1/2012.html