Balsa wing warp (when applying mylar?)

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CMS AC
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Balsa wing warp (when applying mylar?)

Post by CMS AC » April 8th, 2018, 2:38 pm

How would I correct for wing warp as a result of applying mylar? Do I apply a little bit of water to curve it, or do I use a rear strut to level it?

coachchuckaahs
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Re: Balsa wing warp (when applying mylar?)

Post by coachchuckaahs » April 8th, 2018, 5:07 pm

Did you wrinkle the covering before applying? That usually prevents it from adding a warp, as it makes it more compliant.

If you are stuck with a warp, you can try some water, then fixture it to slightly warp in reverse and hope for the best. Problem is it will then keep changing with humidity.

Alternatively, you can make a diagonal slit in the warped edge (LE or TE), reposition, and glue the slit. It should be a very long slit, say 1cm long in a 3/16" wide LE. That gives plenty of gluing area. We sometimes do this to add washout. However, it is likely the warp is progressive along the entire length.

My choice would be to re-cover it with wrinkled covering. Make a "box" our of scrap balsa or foam core, hot melt glue it together. It should be about an inch larger than your wing in all directions, and perhaps an inch deep. This assumes a flat wing. Some people will cover the entire wing flat and then add dihedral. Others may cover ins sections. You could make your covering fixture follow the dihedral as well.

Cut covering slightly larger than the fixture. Maybe another inch all the way around. Cut with a soldering iron to avoid tears. Ball it up as small as possible. Really mash it. Now unball it and CAREFULLY straighten it out. Massage it form the center outward, rather than pulling on edges. Once nearly flat, ball it up a second time and unball it a final time. Now it will be filled with micro wrinkles. Perfect.

Run some chapstick along the edges of your fixture. Stretch the covering over the fixture, just enough to get it to lay flat. Rub along the chapstick to pull out any small wrinkles.

Now spray your frame with a light mist of 3m77, turn it over, and drop it onto the covering in the fixture. Lightly push down to ensure good contact. Let it dry, preferably overnight.

Cut around the edges with a soldering iron.

This will provide a covering the follows the airfoil, and even compound curves, but is "Stretchy" and should not give you warps.

Coach Chuck
Albuquerque Area Home Schoolers
Coach, Albuquerque Area Home Schoolers Flying Events
Nationals Results:
2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records

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Re: Balsa wing warp (when applying mylar?)

Post by drcubbin » April 8th, 2018, 5:24 pm

coachchuckaahs wrote:Did you wrinkle the covering before applying? That usually prevents it from adding a warp, as it makes it more compliant.

If you are stuck with a warp, you can try some water, then fixture it to slightly warp in reverse and hope for the best. Problem is it will then keep changing with humidity.

Alternatively, you can make a diagonal slit in the warped edge (LE or TE), reposition, and glue the slit. It should be a very long slit, say 1cm long in a 3/16" wide LE. That gives plenty of gluing area. We sometimes do this to add washout. However, it is likely the warp is progressive along the entire length.

My choice would be to re-cover it with wrinkled covering. Make a "box" our of scrap balsa or foam core, hot melt glue it together. It should be about an inch larger than your wing in all directions, and perhaps an inch deep. This assumes a flat wing. Some people will cover the entire wing flat and then add dihedral. Others may cover ins sections. You could make your covering fixture follow the dihedral as well.

Cut covering slightly larger than the fixture. Maybe another inch all the way around. Cut with a soldering iron to avoid tears. Ball it up as small as possible. Really mash it. Now unball it and CAREFULLY straighten it out. Massage it form the center outward, rather than pulling on edges. Once nearly flat, ball it up a second time and unball it a final time. Now it will be filled with micro wrinkles. Perfect.

Run some chapstick along the edges of your fixture. Stretch the covering over the fixture, just enough to get it to lay flat. Rub along the chapstick to pull out any small wrinkles.

Now spray your frame with a light mist of 3m77, turn it over, and drop it onto the covering in the fixture. Lightly push down to ensure good contact. Let it dry, preferably overnight.

Cut around the edges with a soldering iron.

This will provide a covering the follows the airfoil, and even compound curves, but is "Stretchy" and should not give you warps.

Coach Chuck
Albuquerque Area Home Schoolers
Thanks Coach! I just build my first Freedom Flyer this past weekend, and If I hadn't I would have had to take out my Greek dictionary to understand what you were talking about :D ;)

coachchuckaahs
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Re: Balsa wing warp (when applying mylar?)

Post by coachchuckaahs » April 8th, 2018, 6:36 pm

We all learn one way or another! Hope your FF flies nice, it should!

Coach Chuck
Coach, Albuquerque Area Home Schoolers Flying Events
Nationals Results:
2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records

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