I have both Dave Patrick's Extra and Edge ... They are both beautifully built and excellent airplanes. I had a YS 140DZ on the Extra and I didn't like it so I just swapped with a 40cc last week. I did not have the chance to fly with the new power yet. My Edge is still new and I'm planning to put a light 50cc gas in there. Both airplanes were built very light that was the main reason Dave Patrick did not recommend any gas engine installed but if you beef up the structure around the engine compartment and manage your throttle carefully then I don't think it would be a problem. The Edge was built a little stronger so is the use of my 50cc.
Dave Patrick Model was no longer around but I heart that another manufacturer took over and is producing his famous Yellow Cub and still keeping his name. They are going to release the new Cub soon!
tdang