Posted by Ryan on April 14, 2002 at 21:14:50:
In Reply to: RE:HOVER CRAFTS posted by Ryan Sullivan on April 26, 1999 at 18:02:12:
ULTRA-SIMPLE HOVERCRAFT
can lift several adults!
NEEDED:
• PLYWOOD, 3ft or 4ft square, 3/8in or 1/2in thick
(or buy a 48in precut round tabletop)
• PLASTIC SHEET, 1ft larger than the above wood
(use a heavy 10mil plastic dropcloth 'Visqueen,' or a shower curtain)
• LEAF BLOWER (battery powered, gasoline), or 'ShopVac' vacuum cleaner
• SMALL PLASTIC DISK, coffee can lid, or 6" Lexan disk 1/8in thick
• BOLT, 2in, 1/4-20
• NUT, 1/4-20
• FENDER WASHERS (TWO)
• SMOOTH FLOOR (linoleum, ball court, or smooth concrete)
• electric saber saw, drill, razor knife, staplegun, duct tape
• Optional: lawn chair and clamps/screws to hold it down.
• Optional: some sort of rubber bumper for the edge. Nail on some old bike tires? Just cover it with duct tape?
INSTRUCTIONS:
Cut out your plywood disk. Drill a 5/16in hole in the exact center, and make sure that the 2in bolt easily passes through it.
Make a hole in the plywood which exactly fits the end of your leaf blower or shopvac hose. This hole must be placed half way between the center of the disk and the edge, as shown below. It's a good idea to trace the hole in pencil on the wood (place the mouth of the leaf blower on the wood and trace around it.) It DOES NOT have to fit perfectly. Later you can seal any leaks with duct tape. Or just let it leak.
Next, lay your plywood disk on the center of your large plastic sheet. Fold the edges of the sheet up over the plywood, then use the staplegun to staple it to the top of the plywood disk. Put a staple about every 4 inches. Don't pull it too tight or the plastic will tear loose when inflated. When finished, use a razor knife to cut off the excess plastic. If you wish, tape the edge of the plastic down to make it look nice.
Poke a hole in the center of the coffee can lid. Attach it to the bottom of the hovercraft as shown below. It goes over the plastic sheet. It pins the plastic sheet firmly against the plywood. (The coffee can lid forms the "donut hole" when the leaf blower inflates the plastic into a "donut" shape.)
Use your razor knife to cut six vent holes in the plastic as shown below. They should be about 2in diameter. They must be placed within a few inches of the coffee can lid. Space them out so that there is plenty of plastic between each of them. But if they are too far away from the center, they will become plugged when the plastic sheet lays flat against the floor. If the plastic between the holes is too narrow, it will tear. If you wish, reinforce the thin necks of plastic between the holes using a couple of layers of duct tape.
DONE!
Flip your hovercraft over so the plastic sheet is on the bottom. Place it on a smooth floor. Stick the leaf blower into the hole and turn it on. The plastic on the bottom should inflate. If it does not, lift the plywood up a bit to let the air get in and inflate the "skirt." The hovercraft will lift up and start gliding around.
HOW IT WORKS
The air inflates the plastic which pushes upon the floor and provides a ground-hugging "skirt." This lifts the entire hovercraft. The coffee-can lid provides "strain relief" so that the inflated plastic doesn't tear loose from the center. It also lifts up the vent holes so air can escape into the center donut-hole. The air leaks along the floor and out from the edges of the hovercraft. This creates an "Air Film Bearing" which has very low friction. Climb aboard! This hovercraft can support many hundreds of pounds. It works best on very smooth surfaces (linoleum, or school gym floor.)
Lift it up at the start, otherwise the bag might not inflate.
SAFETY ISSUES
ADULT SUPERVISION REQUIRED! Don't let little kids play alone with this device.
• To be safest, operate the hovercraft in a small classroom. (In the school gym adults must control it, since it can get going too fast!)
• Climb aboard carefully, since the thing is darned slippery. Or climb aboard BEFORE turning on the blower
• Bystanders should watch their feet, since the edge of the moving board can give stubbed toes. (WEAR SHOES!!)
• Don't push it too fast, and remember how to stop it quickly: yank the leaf blower out of its hole.
• Don't jump off it while it's moving, or you'll launch it at high speed in an unexpected direction (it could crash into somebodies feet.)
• Don't remove the leaf blower suddenly while it's moving fast, because the hovercraft will stop, but the passengers will keep going, fast!
• SUGGESTION: attach a long rope to the hovercraft, and let it trail behind. That way it can be grabbed if it starts going too fast in the wrong direction. Even better: use an AC-powered leaf blower or shopvac, and have an adult remain near the wall outlet. If the hovercraft moves too fast, yank the power plug to put on the "brakes."
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