Flap disc on fiberglass?

[Skymeat]

So I've used my skills to make the frame for a cowling for a bicycle. I covered the frame with fiberglass, and not need to do some sanding. Can I use a 120 grit flap disc on my grinder to do the basic sanding?

[Blacksmith]

Try it on a small area, but even at 120 grit it may be too agressive and hard to control. I've only ever used an orbital sander and hand blocks. I was an agressive snowmobile rider many years ago and got pretty good at fiberglass repairs. I say was because the last accident didn't damage the machine, but I had a cracked rib, cracked pelvic wing, and lacarated liver. Figured I'd quit before I got farther behind.