I had downloaded these notes a couple years ago before I did my covering. Not sure where I got them from.
>>>>>>>>>>>> Shrinking the Fabric
Normally, you shrink the fabric in two separate passes. The first pass uses 200°F, and second and final pass is at 250°F. If you’re covering a light structure, like an ultralight, shrinking beyond 250°F can cause structural damage. Also, if you are using nitrate and butyrate dope, then you will only shrink to 250°F. If you used a fabric envelope with sewn seams or if you want straight seams, shrink the area immediately along the seam first.
As you begin the shrinking process, the fabric will shrink uniformly. If you’re doing a large surface, such as a wing, begin in the bay near the wing root. Shrink that at 250°F and then do the bay at the wingtip. You can then work your way toward the middle of the wing. This will help prevent warping.
Let the iron glide over the surface—no pressure is necessary. Don’t worry about leaving the iron in one place temporarily. It won’t scorch the fabric, nor will the fabric get any tighter. How much the fabric shrinks depends on the temperature, not pressure or time.
Don’t worry about removing all of the wrinkles on the first pass. They’ll come out at the higher temperature second pass. Be careful not to allow the tip of the iron to penetrate protrusions or rivets and cut the fabric. Also, and this is important, do not place the iron over cemented seams. A temperature of about 250°F will loosen fabric cement. After shrinking the fabric at 200°F, turn the heat up to the 250°F and iron everything. It’s important that you shrink every fiber of fabric.
[A 350°F setting will shrink the fabric to its maximum of 10 to 12 percent. Failure to shrink to this setting on most airplanes (other than ultra- lights) will cause the fabric to be loose forever.]
It’s a good idea to mark using a pencil each wing bay or area that has been shrunk to 250°F. That way if you are distracted, you will know which areas are completed.
If you are a beginning fabric coverer, I recommend learning the techniques on a small surface such as an elevator. Perfect your procedures before going to the wing or fuselage. |