Richard, does it have a small a on the side of the outermost head fin? That stands for alpha (the trainer plane) and it would actually be a .455c.i. The latest ones are .40, .46 and .61...As to why they'd make a .455 and a .46, your guess is as good as mine. We (our club) bought the Xtra Easy 2 trainer, and it has the Alpha's .455 engine. I put a different prop (11x6 MAS) on 'er and it transformed the plane, it's bigger than the Alpha, and needed more thrust. Good running engine, but we're wondering how long it's gonna last...