How do I stop getting ripples and small dings in vacuumed bagged wings?

I am bagging carbon fibre over white foam,using the usual carbon, glass and mylar sandwich technique.

From : Joe Hahn

Dave,
A couple of possibilities come to mind. Excess resin in the layup can get trapped and basically "puddle" under the mylar creating ridges or wavy areas. Also, any compound curve that the mylar may have to negotiate, such as a fairly highly tapered tip panel, or a radiused wing tip shape, will create the same effect. Mylar will conform to fairly subtle contour changes, but it will only do so to a point. Are you bagging any dihedral into your panels? A dihedral break can do the same thing, just too much flexing required of the mylar---ripples, usually chord wise.

The "dings" may be another problem. If you are bagging over low density white foam the vacuum. pressure may be too high. It is possible to pull the layup down into the soft "beads" and give you a pitted surface. We use quite a bit of white foam called "pattern" foam which has a little higher density with smaller beads, and run about 15 inches of vacuum with good results. Bagging can be a trial and error process at first, depending on the shape of the parts you are bagging.

If you are referring to very tiny "voids" in the surface finish, that may be a result of the squeegeeing methods or the epoxy. Use thin laminating resin for layup work that will penetrate fully through the laminates to the mylar so as to displace all the tiny air bubbles. Too much pressure used when squeegeeing can effectively remove too much resin and draw air down into the laminate causing the same thing. This is a "dry" layup which can be structurally dangerous.

Hope this helps, and good luck with your projects!!!

Joe Hahn