There are a multitude of ways to accomplish the feat of dragging a hot wire through foam to make wings. It would be very interesting to see the bow and power supply setups that you all use. My few attempts at cutting a wing have not yielded a usable product, but I will keep at it. My templates shifted during the process and I think that I need more tension on the wire. There was a definite bow in the cutting wire as I pulled it through the foam.
Template shift: nail them down somehow! I'm not one to talk about the best way to do it, but for my efforts I've just glued them on with foam-safe CA, then broke them off carefully when I was done. I've seen articles where people did, literally, nail them down to the foam.
Bow: Wire, like just about everything else, expands when it gets hot. So you need a bow that will allow for expansion while retaining tension. I use a bow that, for a 30" long wire, has about 1 1/2" of spring in it when it's cold. You can see it relaxing a bit as the wire gets hot, but there's still plenty of tension.
Power supply: I'd like to know of good cheap ones, too. I use a 12V DC supply, which probably runs the wire a bit cooler than optimal. I need to pull the wire through the foam very slowly, which is a trial for me because I'm an impatient sort of fellow -- my first LE buck had the center bowed in, which I compensated for by sanding the ends to match, but had I pulled the wire more slowly I think it would have been just fine.