Hello,

I was covering my Sig Somethin Extra with ultracote, and i covered one side in silver. Then I went to cover the bottom of it in silver, and when I took the gun to it, it looked like it was like bubbling up or something. I'm thinking it was the hot air maybe was trapped, and couldn't escape, so it just bubbled. Not sure. Any hints, tips, or ideas and how to resolve this problem would be great!!!

Thanks</p>

The Sig Something Extra has a built up tail structure. These are hard to cover because when you seal up each open area in the structure the air has no place to go. So when you heat the covering over that area it expands and bubbles up the covering. Then when you take the heat away it sags.

Here's the trick to prevent this from happening. Provide each bay with a "vent" so the air and equalize as you heat it. Take a straight pin and push it through the wood between each bay in the structure. Then at the trailing edge of the stabilizer push a pin through the trailing edge into one bay. Now make sure there is a "path" between each bay and the one that vents out the trailing edge. Now when you cover the structure the air will be able to escape as it expands and you won't have the covering bubbling up. Once you are done you can seal over the hole in the trailing edge, or you can leave it open, it won't hurt either way.

Hope this helps

Ken

I would say its hot air trapped inside, sometimes I take a needle and poke it through the trailing edge and into the open spaces in the middle of the elevator which will create holes to help the hot air escape.

These guys are right on with their process for eliminating air bubbles. I do it the way Ken described and have had excellent results with many different kinds of covering, I.E. Monokote, 21st Century Fabric and Ultrcote.

Regards,
Brian

Do what RCKen says and your problems will be solved. Another thing I do on built up structures like this is to only go over the edges with my iron and then shrink it down with my heat gun.....that will reduce any tendencies to trap air as well.

Ok thanks RCKen. I wasted about 1/3 roll of expensive!!! ultracote cause it looked very ugly. Would this be the same for the wings? Or are they bigger areas for the air to move around?

Thanks Much!!!

Nope, it's exactly the same with wing structures. Just make sure you have a path for air to escape out of the open structures in the wing

Ken

Wings should not be a problem as there are holes in each rib and the wing tube provides an exit for the air.

The elevator, however, will need the same needle holes. Rather than TE, you can also make a hole in the CA hinge cut; you should have a small hole in the center anyway to help CA flow so just push it all the way through to help air flow too.

The ailerons are the worst because making a hole it a little harder given how thick the sections are; again use the CA hinge locations to help.

Also start out with the lowest heat needed to do the job, you can always go hotter later if needed -