Hovercraft builder weighs in...
I've built dozens of hovercraft (models mind you, nothing you could sit in and ride).
First - As far as calculations go, forget 'em. Seriously.
Unless you have access to a lot of very delicate measuring equipment, AND can claim mastery of that equipment's proper use, AND quite a bit of expertise in compressible fluid flow, "calculations" really are a complete waste of time when it comes to building a model hovercraft you can make yourself and play with.
The problem is that "close approximations" JUST - WILL - NOT - CUT IT. Hovercraft, generally speaking, operate within a VERY thin band between just sitting there (because they lack the power to create a thin cushion of air to ride on), and flipping over (because they're so over powered that wind up trying to sit on top of a roaring torrent of air that's doing its dammedest to escape anyway it can from the confines of the hovercraft's airbox).
A much better approach is, frankly, to "tinker until it works".
My first hovercraft was made by mounting an "Oh-thirty-five" two stroke model airplane motor and prop, centered in the middle of an inverted Tupperware cake pan.
It's important to mount the motor and fuel tank as close to the center of gravity of your hovercraft as possible. It's also a good idea to mount the fuel tank directly under the motor to keep the center of gravity as low as possible. If you're going to use an electric motor and battery, both are going to require one HELL of a power to weight ratio. If you want to go that route I'd suggest using the motor and battery from a cheap electric airplane or helicopter, and making the airbox out of something VERY light, like Styrofoam.
When I first tried to "fly" my hovercraft it proved to be vastly over powered. It just jumped up off the ground and flipped over.
So I drilled a gazillion "vent" holes in the top of the Tupperware "airbox".
It then just sat there. Too many vents, allowed to much air to vent from the airbox.
But that was easy to fix. I just started covering some of the vent holes with duct tape from the inside. Once enough of the vent holes were covered the hovercraft hovered quite nicely.
Next I needed to get it to power itself forward. I did this by using a Dremmel tool (a "pencil grinder"), to grind away *just a bit* of the "skirt" formed by the Tupperware box at the rear end of the "hovercraft". This allowed more than enough air to escape from the rear edge of the "skirt", than from the front or sides, to push the hovercraft forward.
To control it, (mind you at this time radio controls were WELL beyond my budget), I just tied about 20 feet of string from the front left corner of the airbox to one end of a short handle, and 20 feet of string from the left rear corner of the airbox to the other end of the short handle.
We'd start that puppy up, someone would hold it until the "pilot" got hold of the control handle and stood with the strings held taught, and... you'd let 'er rip!
The bugger was quick too.
Lastly I added a few decorative things like fins, plastic missiles, radar dishes, and other sundry things from old model parts, a paint job, and some decals, and wound up with a homemade toy that looked like something out of an old Flash Gordon flick.
After crashing and rebuilding this thing dozens of times, it eventually acquired a pusher prop and rudder arrangement for radio control, which is where I learned a valuable lesson about toy hovercraft --
SLOWER IS BETTER! And a puller prop up front is a lot easier to control than a pusher prop in the back.
Hovercraft come about as close as you can get to exhibiting Newtonian motion, i.e., once they get moving in any particular direction they don't like to stop. So... the first thing you find is... NO BRAKES!
To stop one you have to turn it 180 degrees, and then POWER it to a stop. (Which is where a PULLER prop comes in handy, try it and you'll see why).
Turning one 90 degrees to the right and hitting the gas does NOT make it turn like a car or even a jet ski. Instead it keeps going in the direction it was originally headed while slipping sideways as if you had turned all four wheels of a car 45 degrees to the right.
To get a hovercraft to turn through an arc like a car you have to turn it more like 135 degrees to the right and hit the gas.
All in all piloting a hovercraft is especially NON-intuitive. It takes a lot of practice. Which is why slower is better, it gives you the chance to get used to things before cracking up.
Best of luck!
