It's got big motors with classy wood mounts . . . it's got props . . . it's got a skirt . . . it's even got a Batman seat. It just doesn't got it when it comes to hovering.
Those are Radio Shack 9-18v motors there. They look like nice motors, and they aren't bad motors after all, except that they only draw about 9 watts at 9 volts. That's not enough power to lift that 1+ pound slab of plywood. At 12 volts the motors draw about 17 watts each, which just gets it off the ground and moving. I suppose that at 15 volts, each motor would draw about 26 watts and you'd get some real action. But model airplane motors are more efficient, providing more thrust per watt. For an efficient hovercraft, I figure each watt of lift should be able to hover 2 oz of craft.
At this time I also didn't know that the propeller is supposed to fit tightly in the lift duct. It would be obvious to someone who thought about it, I suppose. Maybe I should think before I carve. In any case, it's an inefficient duct. 1/16 inch gap around the propeller would be good, with a nice smooth duct wall, but the propeller tips are actually more like 3/16 inch from the (rough) edge.
The skirt is made from a strip of plastic trash bag, taped into
a tube, and glued onto the styrofoam. (Did you know that some
kinds of glue melt styrofoam? I didn't. Use epoxy or Sears'
"Sealant/ Adhesive" that comes in a toothpaste tube.) In the photo to
the right, you can see that the hovercraft is hovering (at 11.8v), but
that's quite a gap in the skirt, isn't it?
Efficiency calculations. The hovercraft is about 10" by 16", and at 11.8 volts there is an air gap averaging maybe 0.1 inches beneath the skirt. Let's see, that's a 52" circumference, or 0.036 ft2 air gap. With air escaping at an estimated 40 ft/sec that's 1.1 ft3/sec. The craft's weight of 1 lb on an area of 1.1 ft2 is 0.9 lbs/ft2. Total hover power: 1.0 ft lbs or 1.4 watts. The motor is actually drawing 16 watts, so overall efficiency of the lift system, converting electricity to torque, torque to air power, air power to lift, is 9%. Compare to about 15% on zippy. Differences included a poor lift duct, a poor skirt, possibly a a non-optimal propeller, and a less efficient motor.