Anyone remember a movie from the 80's about 3 boys who build a spaceship?

I'm pretty sure it was in the eighties anyway. All I remember is that three boys build some sort of space ship from scrap parts, and the main body of the ship was an old "Tilt-a-Whirl". I know the thing actually flew because I remember them going into space.

I don't know why this movie popped into my head the other day. Anyone else remember it? What's the title? I think my kids would like it.