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Author Topic: Help in removing warp on mylar wing  (Read 298 times)
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randoloid
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« on: February 13, 2019, 07:26:16 AM »

Have a lovely wing that is now half covered in mylar. During the covering I've developed a warp in the right main that has taken away the wash-in and replaced it with 1/16 washout.  Since Mylar is impervious to moisture should I steam the wing prior to finishing?  if it were tissue I'd simply wait til it was complete, steam, pin and let it dry, but not sure how to handle.

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edhardin
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« Reply #1 on: February 13, 2019, 08:45:07 AM »

completely cover the wing. Shrink the mylar with heat gun or iron. Twist wing to desired warps and
heat mylar with iron to hold warps in place. This may require three hands. I usually try for 1/16 washin
on right panel and 1/16 washout at each tip
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Crabby
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« Reply #2 on: February 13, 2019, 09:22:20 AM »

What was your adhesive? is this a common occurrence? I am doing my first mylar job this week.
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randoloid
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« Reply #3 on: February 13, 2019, 12:56:07 PM »

Hey Crabby,  This was my first time using mylar too.  Glad to share what and how I was using.

Adhesive was thinned contact cement by Goop thinned with nitrate dope.  The mylar was the aluminized .05mil (if I recall correctly).  I also tried using a UUH glue stick as I'd watched a youtube video saying they had great results with it but my results were underwhelming at best.

I'm sure that there were several factors to my warpage.
  • Wing was built very light- without covering was 10.8g 5lb I used: 1/16 ribs that are capped with carbon, 8lb C-grain leading and trailing edges and finished it off with 5lb 1/32 sheeting for the front of the wing
  • I'd been warned that the shiny mylar doesn't shrink as much as clear so I was stretching it as much as I dared.
  • My mylar was really wrinkled when it arrived- not sure if this is the case for all
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randoloid
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« Reply #4 on: February 13, 2019, 12:57:34 PM »

completely cover the wing. Shrink the mylar with heat gun or iron. Twist wing to desired warps and
heat mylar with iron to hold warps in place. This may require three hands. I usually try for 1/16 washin
on right panel and 1/16 washout at each tip


Thanks for the direction- your specs are exactly what I was building to.  Right main 1/16 in, both tips 1/16 out.

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randoloid
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« Reply #5 on: February 14, 2019, 09:33:48 AM »

What was your adhesive? is this a common occurrence? I am doing my first mylar job this week.

Crabby,

Wanted to share a little update on my mylar education-  I noticed when I tried using the glue stick that mine seemed a little funky- unlike the usual problem of being dried up, it was really soft so I purchased a fresh one and I was really impressed with the results-  it was really easy to work with and there was no smell. 

Another thing I learned was to only work one panel at a time.  While I've read that it's possible to cover an entire wing, my skills aren't there yet.  I attempted to cover the the under side of my wing in two pieces and both sides had wrinkles just after the dihedral break.- Might have been easier with clear mylar that shrinks a little better, but in the future, I'll be playing it safe and only covering one panel at a time.

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Crabby
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« Reply #6 on: February 14, 2019, 10:06:37 AM »

I assume you are not using a tack iron?
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Red Buzzard
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« Reply #7 on: February 14, 2019, 05:18:07 PM »

Perhaps I can help a little. My experience has been with both .25 mil and .5 mil clear mylar. Unless you are covering something that is fairly large .25 mil is probably more in keeping with light construction. BUT it is also not easy to handle and sometimes needs three hands to keep it away from itself. A trick I learned here is to always keep it in contact with some backer as you unroll it. Unroll it onto another sheet of paper until you cut it. Even then keep it on paper until you are really ready to place it.

I used Velcro adhesive thinned 50/50 with acetone. You will have to really mix it to get it to dissolve, but once you do that you can store it in a sealed container and re-use it. The glue eventually turns and interesting purple which I am not sure indicates anything. Use two coats on any wood you want the mylar to stick to. When you put it on, put it on fast as it dries very fast. A slow brush just brings the drying goo up and makes bumps under the covering. Once the glue is dry (it is heat activated) you are ready to place the mylar. Just lay it on the surface, tease out any really annoying wrinkles until the surface approaches smooth. Don't pull or tug except to move the film around. The mylar should NOT stick to the glue, if it does your moving too fast. When you have the mylar placed, touch your iron around the perimeter to begin the to fix the mylar. Once the mylar is stuck down around the perimeter, use the tip of your iron to stick it down in the interior. Keep the major part of your iron as far from the mylar as possible or you begin the shrink process.

As you now know, don't shrink the mylar until you have both sides covered, then you move from top to bottom and back. I suggest you NOT use a heat gun as it will loosen the mylar from all the places you previously stuck it to. But rather use an iron to shrink on the lowest setting it takes to move the wrinkles around. And, as much as possible, do not touch the iron to the surface of the mylar in the shrinking stage, just wave it over the mylar surface. When viewed from the side you will see the wrinkles flee as the heat moves over them. Move slow, use lowest hear. When you have finished this, if you have warps, then you use the 3-hand method to neutralize them, two hands holding in opposition and one hand waving the iron. The heat gun may unstick your perimeter giving you just another headache.

If all else fails, the glue comes unstuck with acetone and you peel off the offending piece and take another run at it. If you are taking out one panel you will need to put glue all around it to get the mylar patch to stick. I don't know a thing about silvered mylar so someone else may be able to help.

Still a mylar novice,

Bill
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randoloid
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« Reply #8 on: February 14, 2019, 06:16:37 PM »

As you now know, don't shrink the mylar until you have both sides covered, then you move from top to bottom and back. I suggest you NOT use a heat gun as it will loosen the mylar from all the places you previously stuck it to. But rather use an iron to shrink on the lowest setting it takes to move the wrinkles around. And, as much as possible, do not touch the iron to the surface of the mylar in the shrinking stage, just wave it over the mylar surface. When viewed from the side you will see the wrinkles flee as the heat moves over them. Move slow, use lowest hear. When you have finished this, if you have warps, then you use the 3-hand method to neutralize them, two hands holding in opposition and one hand waving the iron. The heat gun may unstick your perimeter giving you just another headache.


I actually didn't know- and probably why I got the warp in the first place
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Red Buzzard
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« Reply #9 on: February 15, 2019, 12:14:51 AM »

Yep, Randoloid, we went to the same experience school. And, of course, I did not know when I made the identical mistake. As a good and philosophical friend once said,"there is no free education, just some less expensive and some more so".

B.
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