Warped wings

[strongeagle]

Does anyone have a sure-fire way to prevent wings from warping after covering? I just finished covering a 100 series SE-5 and both the upper and lower wings warped like a potato chip.

The wings were reasonably straight and true before I covered them. I did note that the wings were quite flimsy and fragile while in the uncovered state and that they could be easily twisted by hand. Does anyone else have this problem?

I painted the wings with a lacquer based nitrocelluose sanding sealer (similar to clear dope) before I covered them and applied the kit paper dry using thinned white glue. I then shrank the paper with water, misted on with a spray bottle.

I'm thinking that a stiffer wing would help, perhaps adding an upper 1/16th spar or two and a heavier trailing edge. I don't have a lot of confidence in the kit supplied thin trailing edge. I had this problem when I built the 100 series Spad also.

Suggestions?

Tom S.

[SteveM]

The flying surfaces must be held flat while drying. Also, don't use any more water than you have to.

Check out Mike's flying scale model pages where he shows how this is also done. Interestingly, he uses steam on the tissue of the weaker tail feathers. I forgot he does that and may have to try it as I often fight tail feather warping.

[supercruiser]

Steve is right. Pin it flat while drying or weigh it down. I still get some warps when I cover. Next set of tail feathers I do, I think I will pre-shrink the tissue and then apply. I have found that to prevent some pesky warps, adding diagonal braces inside the wing helped greatly. a 1/16th sq. stick from the trailing edge of the wing, where it meets the tail end of the rib going diagonally inboard to the Leading Edge where the L.E. and rib nose meet. Worked on my Spitfire to hold about 4 degrees washout and on the Javelin to keep out a warp I couldn't fix otherwise. But, I think beefing up the structure is more like a last resort.

[strongeagle]

Sounds like a plan. I stripped the old covering off and am going to try it again. This time I'm going to pin the wing down to the workbench as it dries. I don't want to have to rebuild or reengineer the wing if I don't have to.

Thanks for the ideas.

Tom

[kittyfritters]

Tom,

Here's an example of the rig I use to pin down wings while drying. The model is a Guillow's 500 series Hellcat.

I use a stiff. straight piece of plywood for the base and some pine strips to brace under the dihedral of this one piece wing. The wing is not pinned directly but with pieces of card stock that are pinned to the wood, off the edges of the structure with push pins. This is the method illustrated in the Don Ross book and it works very well for me.

I wet the tissue with rubbing alcolhol, not water. The rubbing alcohol is 70% water and shrinks more slowly without putting as much stress on the structure as straight water. There will still be a little shrink left in the tissue, even when quite tight, so if there are small areas with wrinkles left after shrinking you can put some water on them to make them tighter. Hellcat Wing

Another example of the pin down rig with a Rufe wing Rufe Wing

I like to put small wedges, about 1/16 inch, behing the trailing edges at the wing tips to shrink in some wash out. This will stay after the tissue is dry and sprayed with Krylon of doped.

Here's what the model looked like after the tissue had tightened. Hellcat Tight (Yes, I did poke a hole in the fuselage behind the wing opening and put a patch on it.)

Hope this helps,

Howard

[strongeagle]

Ahoy Howard,

I've been practicing my covering technique today on a dime scale Comet Spad. The wing is much smaller than the SE-5's wing, but I've had extraordinary success covering it using the dope/thinner method per Mike's flying scale pages. I like your technique for pinning the wing down as it dries because it doesn't leave holes in the balsa. My current practice of shoving a pin through the leading and trailing edges makes me uneasy because of the damage it does to the structure. I'll be back to work on the SE-5 this coming week and I'll give your non-destructive method a try.

In the past, I've used thinned white glue to stick the paper to the frame. However, the dope/thinner method that I used today impressed me very much. I've never had the guts to try it, nor did I understand the technique enough to execute it properly. Mike's site was excellent instruction. The technique made me work slower but more carefully.

I've always considered covering to be a chore, and consequently, I rushed my work and achieved my usual less-than-ideal results. The light bulb came on today as I was covering the Spad. I decided to put the same effort into covering the airplane as I previously put into building the model in the first place and it made a difference.

I may go back to using the white glue method again after the novelty (and the lingering odor) of the dope/thinner method wears off. The next challenge will be getting a warp-free set of wings for the SE-5.

Thanks for your suggestions and for the photos. I will put them to good use.

Tom

[Xanadu]

Some builders even pre-shrink the tissue, then apply it to the frame.

Hang the tissue sheet on a wire hanger, pinned in place. Give it a misting spray, and let it hang dry.

[strongeagle]

I finished recovering my pair of SE-5 wings this morning using many of the suggestions provided by this forum and am exceptionally pleased with the results.

I have two flat and true wings ready for mounting!

Thanks for the good ideas.

I'm going to attach a photo below, If I can figure out how to do it.
[/img]http://www.virtualaerodrome.com/image_detail.html?p_aircraft_id=37&p_image_id=7642&offset=