I've been covering with Ultracote for a lot of years and always have good sucess except for one thing. When I do a small patch over existing film, I always seem to get wrinkles on the ends. I've tried different techniques and temperatures always with the same results. I'm referring about an area say between wing ribs or another area where there isn't any solid frame to iron to. I'm sure someone out there has the answer.

I use a sock on my iron and when I'm doing a patch I run the iron just a little hotter than normal. I set my iron at 250 degrees with the sock.
I lay the patch on, lay the iron very gently on it, let it sit for a second, and then move slowly from center to end, pick up iron and go back to center and out the other end.

On this first pass I hold some of the weight of the iron off of the patch and move slowly. After the initial passes, I run the iron slowly over it again moving slowly and
let the weight of the iron do the work.

Slow and light, work from center out.

It depends on the plane, but lots of times I just patch a hole with shipping tape, especially if it is on the bottom of the wing.

Yeah! It does that. Once I have a patch stuck down I'll use my trim iron and lightly fan out a bit until the wrinkles are gone. Depending on how bad it is I might just hover the trim iron over the area without touching the covering.
Edwin

Better yet, just remove all the covering from the open bay and seam it at the ribs. This would work only if all a solid color though. Would look alot better. Make sure your patches have round corners. This will keep the corners from comming up while cleaning it.

Just use some trim solvent. No heat = no wrinkles. Works for me!

deadeye,
Thats one of those "Why didnt I think of that". So simple and obvious!
Edwin