When I was a kid, there used to be this ad in the back of Popular Science (or maybe Boy's Life or Mechanic's Illustrated?) that offered plans for how to build your very own lawnmower powered UFO (i.e. hovercraft). Most of us lusted after getting them but never did. According to a story written many years later by somebody who had, it showed you how to make a 6-foot diameter pine wood frame and canvas disk with an engine in the middle, and a mast on the back to hang onto and "steer" with. The guy described its one and only trial run that ended with it flipping over - and fortunately throwing him a safe distance from the whirling fan blades under it.
No amount of Googling found either that ad or the story. So at first I wondered if I only imagined seeing it. Then I saw this article
showing what looks to be the exact same device (except it's metal) as was pictured in that old ad.
Although it's not the same story as the one I previously mentioned, the one that goes with the above picture is pretty amusing.