I have three planes covered in Monokote, and in the dry winter months in Michigan the Monokote sags and gets big unsightly bubbles all over the planes. They are all kept inside, heated basement, temp about 70F. In the summer, it lays back down nicely without having to reshrink it with an iron or heat gun. Does anyone know what causes this? Is it just the lack of humidity in the air? I was going to take a couple of the planes to show off at our club meetings, but would be embarassed to show such a saggy covering job, so I'll wait 'til spring to unveil them. I don't want to have to re-shrink the covering since it took so long to get it to lay down without sags/bubbles in the first place!

Is it just the lack of humidity in the air? Yup thats it, it's realy one Tip/trick is to cover without wrinkles Low Humidity!
Balsa is like a sponge it soaks up moisture from the air and swells
thats why it tightens up during the warmer months/

TIP > if you can wait to cover a plane with film till cold dry winter months you almost never get wrinkles in the summer.
You can however go ahead and shrink "carefully" now and it will look even better later on for the next season.
Always with all film type heat shrink materials leave a little shrink left in the covering the Ultra and Mono coats have a point of no return.



Den

Den,
Thanks. That makes sense. I have another kit I'm ready to cover and will make sure to do so before it gets "moist" again in the spring. I had humidity play another trick on me once when I laminated balsa fuse sides to a plywood doubler. I glued the pieces together- nice and flat, but when I went to assemble the fuse, the sides had bowed terribly due to the balsa and ply swelling at different rates. I had to clamp, push, and prod in order to get the pieces to go flat while the epoxy cured. (I am a slow builder, and sometimes seasons pass before I complete a plane).

It is definitely the humidity. I moved into a new house in January.
My old house had a humidifier on the furnace and the new one did not. After one week I noticed all my planes had terrible wrinkles and everyone in the house was complaining of dryness and itching.
I had a humidifier installed right away on furnace and it was set to 35%.
One week later everyone was happy including me as my planes were nice and tight again.

My planes did the same thing. I moved them from my chilly basement to my gargage that I converted to a shop and I noticed the same wrinkles in the covering. The humidity in the new shop is only about 30% and 68 degrees. The basement was about 55-60 degrees and about 45 humidity at all times due to laundry room.