Minimalist Hovercrafting


Last fall, I spent a few weeks in limbo, staying at friends' vacated apartment, waiting for my current apartment to be ready. I didn't want to unpack everything for just a few weeks, so I often found myself sitting around without amusing ammenities like books, stereo, or television. One evening I felt like building a model hovercraft. This didn't seem practical -- all of my tools were packed away. But I had a sheet of white styrafoam left over from the moving, and once you've got a sheet of styrafoam, you're most of the way to a hovercraft! I needed props and power, so I went to the toy store and bought several rubber-band powered airplane kits. When I came home, I cut a rough hole in the sheet foam for lift -- I didn't bother with tiny prop clearances -- this was a bare-bones finish-it-now kind of operation). I used a smaller piece of foam to mount a lift prop and a thrust prop, and ripped up a plastic sleave that the day's newspaper had come in to make a skirt. A balsa wing from the airplane kit became the rudder and a balsa sliver from the other wing became the divider bar on the lift duct. Duct tape left over from the move did the rest. In no time I had an ugly but functional hovercraft. It couldn't hover for long, of course (and I thought run times for electric models were bad!), but in the time it took for the lift prop to unwind, the thrust prop could make it flutter across my livingroom and into the next room -- with a little shove to get it started, the craft could regularly be made to travel well over 15 feet. And you'll never find a quieter hovercraft!

Winding up a prop while holding an already wound prop was kind of tricky, and as it turned out, the craft didn't work so bad even if the thrust prop was removed and the lift prop was tilted 45 degrees from vertical -- white styrafoam can be a lot lighter than the stronger pink or blue foam modelers use on gas or electric models, and without motors, the whole contraption was light enough that it didn't take much air underneath the styrafoam board to lift it. Actually, the lightness allowed me to get it away with putting it together in such a sloppy way, for instance I didn't bother about cutting out perfect skirt templates -- I just ripped up strips of plastic and taped them into a rough tube that ran around the craft. I sure didn't worry about the shape of the skirt corners the way I have with heavier electric crafts, and it just didn't matter. This high degree of tolerance for a lack of precision might make a rubber-band powered craft a good project for kids. Even with the skirt removed, the craft would hover and kind of skitter along but that excercise sure drove home how much even a rough skirt can help. The exercise also showed how fun andeasy it is to make a model hovercraft.

Modeling tip: Use as large a prop as you can. On my first visit to the toy store, I bought a pair of the cheapest kits I could -- balsa kits made by Guillows (shown standing in the picture). These kits had 5 inch diameter props, and their performance was marginal. The next day I went out and got the slightly more expensive Estes kits which comes with 6 inch diameter props, and it allowed for much improved performance. The Estes kits come in a blue and white box and are shown lying sideways in the picture. The Estes kits also came with longer rubber bands, and that helped too, but experiments showed that the prop size makes the biggest difference.

Have fun!


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