Hey Bootlegger! , i fly several 1/2a coroplast planes. They can take a beating. The largest one i have done is with an .09 torpedo and was a riot. The problem with bigger on coroplast is they become floppy. I use different diameter wooden kabob sticks to stiffen the wings and around the engine mounting area. We have a trainer we call the Trooper that has gotten about 8 people their wings, at least 50 crashes and still flies! I believe it would take some serious design thinking to get a .25 mounted and be rigid, also vibration starts to be a factor. I can send some pics of mine if you like. Good luck and would like to hear of your sucess! Ray