# Highschooler who built a hovercraft

1. Dec 11, 2005

### aquaticlife

I am a highschooler who built a hovercraft that works pretty well. My question is how do I create a propulsoin system. I dont know any equations (if there are any) that would help me determine this, but if any of you do please tell me or I can possibly help.....It wieghs approximately 200 pounds with a person on it, 4' by 4' square with a 320 cfm leafblower.....if I am missing any information or there are any questions please tell me.
-Thank You

2. Dec 11, 2005

### Danger

There are lots of different options for what you want. One is simply to vent some of your lift air out the back for thrust. You can also install a second engine with a propellor or fan, or if it's not too difficult in the case of a leaf-blower, run a PTO shaft from it to your fan. You don't really need a formula, because any rearward airflow will get you moving. You just need enough to overcome any headwind that you're likely to encounter. There are fan formulae available though, and either they or the links to them are around here somewhere in another hovercraft thread.

3. Dec 11, 2005

### aquaticlife

thank you

4. Dec 11, 2005

### Danger

You're welcome. There'll probably be more detailed assistance from others.

5. Dec 12, 2005

### Ayrity

Danger pretty much has it covered, but if you wanted to calculate the amount of force (airflow) needed to make you go a certain speed, what you would need would be to find the coefficient of friction between your rubber skirt and the ground (this will probably be much much smaller than the average sliding friection because that is what a hovercraft is designed to do) multipy that by the normal force, or the weight of the craft while running, the amount of force pushing down on the ground. this will give you the amount of force you need to produce in order to get the craft to start movement, and that is a good basis for starting a calculation of force for a certain speed.

On a more physical note, I would advise against the bleeding of air from the skirt in your case, it is hard to control, and harder to steer the craft. Also (from my own experience) the amount of force downward is already hard enough to contain, and the answer is not to let some out! haha. I would agree with dangers suggestion of a second motor, or a leaf blower, it also gives an automatic steering and braking mechanism, which is very helpful when you are heading for a wall! good luck, let us know how it turns out.

6. Dec 12, 2005

### DaveC426913

And if you do use the secondary airflow idea, there's no need to overthink the mechanism. Your best bet might be to have the driver manipulate the airflow directly and intuitively by having it (the 2nd leaf-blower) in his hands and pointing it where he wants to go. Any additional mechanism is technically unnecessary (though it may look cooler to have a joystick/steering wheel).

7. Dec 12, 2005

### Danger

Good points, both of you. I might clarify that I didn't mean to bleed the air from the cushion itself (although that's the way it appeared); rather, some systems tap into the airstream before it enters the cushion. It seems in retrospect that it probably isn't possible in this case, and the concern about maintaining lift pressure is very real.
I agree with Dave also, that the KISS principle is probably the best approach in your case. My semi-compromise suggestion, which I think would be best overall for a combination of simplicity and driver convenience, would be to mount your second blower on an axle or turntable so that you can steer it as you would an outboard motor on a boat. Good luck with it, and keep us posted as to your results.