IMAA states 1/4 scale, if it's not a scale then it must have an 80 inch wing span. Bipes must have a 60 inch span. The funny thing is to see something like a Shoe String 1/4 scale, about the size of most 40 size planes but they are legal. When people started building Giant Scale planes we thought anything bigger then a 60 was huge but these days at an IMAA meet a 1/4 scale Extra is small sitting next to a 42% Extra. Weight is 50 pounds but you can get a waver for up to 100 pounds, however you, the pilot and the planes must be inspected for both safety and ability to fly by an AMA certified inspector every year to keep the waver. When I was involved with the Castle IMAA meet in Calif. we had several people show up every year for there inspection so they could hold there waver. It was really something to see!!!