Rotax sell their certified engines for aircraft use. What do you think they sell their same spec uncertified engines for?I have yet to have a problem. The local hardware store owner jokes about how I'm shopping in his "aviation section", and the guys at the auto parts store think it's cool that I'm shopping for aircraft supplies, too. Online, one rarely talks to a human. The only weird one is Zerkel, who sells Cuyuna engine parts... he has to know they're all used on ultralights, but the website says that "nothing sold here is designed or intended for aircraft use."