I've built several Predators. No pics right this second but I'll work on that. Like Jimbo said it depends on what you're using the Predator for. If it's just for club stuff with relaxed rules a 40fp or 32f would make great engine choices. If you're gonna fly RCCA rules than the Irvine, OS 25fx or OS 28heli (if you can find one) would all make good engine choices with some form of tuned exhaust. I've pretty much built mine per instructions with a tweak here and there. Probably the biggest deviation that I've made is to install 1/8" fiberglass spars top and bottom doubling the thinner middle spar. This simply allows me to pull more horsepower without fear of it snapping (into pieces that is). Try not to place to much gear right in the center near that thin spar as the removal of too much of the foam will weaken the plane. Outside of that mine have pretty much been stock. They're a great plane for club combat and they are nearly indestructible. If I can scrounge together some pics I'll post them here in the future. If you have any questions let me know........
