Just last week, I used a sharpened brass tube (1/2") to cut a hole about 10" into foam wing halves. It worked great using the shucks to keep the wing aligned with a jig. The jig is simply a block of wood with a V groov cut along its length. I rolled the tube in the V as I pushed it into the foam. Just clean the foam from the tube every couple of inches and it cuts fine. I even pushed a rocket body tube into the opening to help prevent collapsing from the vacuum.