This is my first attempt at building a hovrcraft. It all came from the tip and given time, it all went back there too!!!! The squirrel cage fan is the type that is used in air conditioning a big building. They are mostly made of pressed steel. The fins are just a tight fit and pressed into the main frame. I asked around to find out what sort of a rev limit these things had and couldn't get a real answer. Orignally I'd put an 8Hp Briggs & Stratton motor on it but I couldn't it get out past half throttle. So I fitted a 250cc motorbike engine on it thinking I could use the gears and get higher revs in a higher gear but not over load the engine. It hovered well but when I split the air for thrust it wouldn't go foward so I changed into top gear and gave it some more throttle. That's when I found this fan has a rev limit. The little fins all came out of their press fit groves and landed in the bottom of the barrel. I still don't know what the rev limit is, but it's less than the output of the 250cc engine. And it was lots of fun.