Mini Hovercraft DIY: Build an 8''x3'' Craft with 9-Volt Batteries

[FredGarvin]

http://www.se-technology.com/wig/html/main.php?open=showpic&code=&pic=21

http://www.se-technology.com/wig/html/main.php?open=showpic&code=&pic=14

 

[arthuritus]

Hummm, I'm doing a hovercraft for my science fair project too. The idea is to make a self-contained hovercraft capable of lifting a person. I'm going to be using an electric leaf blower, electric because they are MUCH cheaper than petrol ones of the same power to weight ratio. The only thing is, I'm not sure if the leaf blower is going to be able to lift it up. Sure, it's powerful, but it has a small fan and goes for airspeed rather than volume. Is this going to affect my pressure in the skirt? Is my goal realistic? I'm also trying to figure out what deck area would be the most efficient BEFORE I start hacking into my precious plywood. I understand how to work out how much pressure is needed to lift a given weight, but I have no idea how to figure out what the pressure is.

 

[arthuritus]

I want to know how changing the area of the base is going to affect how much weight it can lift.Would I be right in saying that to calculate velocity pressure in N/m squared you use the formula VP=0.6xV^2? In my case, VP = 0.6x77.7^2 = 3622.37 N/m^2 Is this the right formula to be using for what I'm after?

 

[Danger]

I don't know from formulae, but I have a personal relationship with hovercraft. How the curtain area affects the lift potential is direct; the more area you have, the more lift. Whatever pressure your source can obtain is evenly spread over the entire area. If your leaf blower can put out, say... 20 psi, then it will lift 20 x [area] lbs., but the larger the area is, the longer it will take to pressurize it. Your source must be able to keep up to the curtain leakage to maintain that pressure.

Great link, Fred.

 

[arthuritus]

Yep, that seems to figure. I was amazed; I made a rough prototype today with a .75m^2 circlular base, and it could comfortably lift my 80 kg brother. I think my leafblower was churning out about .3629 N/cm^2, which means with a 1m^2 base it should be able to lift about 360 kg?, provided there's no unwanted leakage etc. I though that was ridiculous, maybe it was meant to be 35 kg? But it could lift 80 kg plus it's own weight, so... It shall be interesting to see how much it can lift with a decent skirt and stuff. Amazing. Bring on the big beasties : )

 

[arthuritus]

Also, you know how that if you make the base bigger it'll be able to lift more, but won't float as high off the ground? Is the amount of floatiness measured from the bottom of the skirt or is it the total air cushion? Is there any way of calculating how much your float height is going to change with a given base area increase/discrease?

 

[Danger]

I'm not quite sure where that came from. The lift height shouldn't be in any way reliant upon the cushion area, unless the attendant weight gain from the extra material overcomes the lift pressure. Adding weight, such as passengers, will initially raise the pressure, but the excess will almost immediate bleed out. That is dependent upon the skirt design, though. Something rigid, such as a single long strip of rubber, will hold more pressure than the preferred multiple 'mini-skirt' type. Regardless, the pressure will always equalize automatically. Too much will leak out; not enough just won't lift. The lift height is typically measured from the lowest 'solid' part of the machine, since the skirt is always in contact with the ground. That solid part can be the bottom of the frame, or the upper part of the skirt that isn't flexible enough to move easily. The measurement is essentially an indicator of how large an object the craft can pass over without hanging up, like the ground clearance of a car.

 

[kach22i]

Trouble is, at 50 feet altitude, a big wave (not to mention a mast) could still knock one down.

WIG's ......like airplanes, never fly higher than you are willing to fall.

My hovercraft flies only six inches off the ground/water, plow-in or grounding out can still get nasty.

Overall hovercraft are the safest form of transportation ever invented (WIG's excluded).

 

[arthuritus]

Hmm, I've just figured out that all my calculations were wrong. Perhaps I should be working with m^3 instead of m/s?

 

[Danger]

I'm not sure which calculations you're referring to. M^2 is how you figure out your lifting capacity, because it's area x pressure. To know the volume of air that needs to be initially supplied, then M^3 is appropriate. For figuring out curtain leakage, you use the perimeter, so that's just M. Your sustained airflow is based upon the leakage.
And before you ask, I don't have the formulae at hand. They're around somewhere, but I can't remember where.

 

[arthuritus]

Well, instead of mucking around with calculations I've decided to approach it the other way. I built a manometer, and used it to measure the maximum pressure that my leafblower can produce, which is in turn the maximum pressure there is going to be inside my skirt. It worked out to be around 3900 Pa, which divided by 9.8 (N to kg) then multiplied by 1.13 (area of my base) turns out to be about 450 kg! Of course, this is only theoretical, as by then my skirt would probably have blown up, among other things. It works out too, as with only 40 kg on the hovercraft (including it's own weight), the water in the manometer moves about 1/11 of the distance it did with just the leafblower attached. It also means I can work out the rider's weight to within about 5 kg.
I found this project very interesting. Next time round I'm going to try fiddling with different skirt designs. At the moment I've got a simple wall skirt with a lead string at the bottom (200g/m), but I'm curious to try out the type at http://www.amasci.com/amateur/hovercft.html. I'm thinking perhaps that one would be more stable, but you'd have to muck about replacing the skirt more. Any comments? Cheers

 

[Gambit]

Hovercraft race !

Hi everyone,

M supposed to build a hovercraft for a race. I want your help. I understood the basic concept of a hovercraft. This hovercraft need not have anyone to align it. It shud go alone, without a load.

length and breadth limits are 70 and 40 cms respectively. IC engine of less than 3.5 cc must be used OR motor or less than 12volts supply must be used.

the race track is completely straight. Pls help me out wid the best design possible. I am from India, so anyone who has already done it, pls help me out. Where do I get Balsa wood?

 

[aychihuahua99]

You can get balsa wood from http://www.specializedbalsa.com/products/index.php

 

[kach22i]

70 and 40 cms respectively.

Look up examples here:
http://rc-hovercrafts.com/phpBB2/index.php?sid=1eb821416eb3b0486fc5a7a26c6c225a

Good luck.

 

[UUallace]

Balsa (Ochroma pyramidale) is native to the tropical Americas.

Kapok (Ceiba pentandra) grows in the rainforests of Africa and the Americas (except the Canadian rainforest). It is lighter and standard in life preservers. You could cut open a worn out life praserver.

Indian Kapok (Bombax, 3 species) is darker and heavier than the life preservers.

We flew to Denver for a few days. This was my seven-year olds first flight. On the fourth of July, in the childrens' activities room he built a hovercraft.
styrene foam plate (Solid thin plastic would be more durable, but many have fancy edges.)
plastic cup 12 ounce (bottom cut out)
propeller
motor (Looks likes something Radio Shack would sell.)
9 volt battery
2 popsicle sticks
rubber band

Since we have been to an air show. Then he built paper airplanes, lots and lots, both from the Internet and on his own. I could add a paper clip or trim them some, to get them to fly.

Then he discovered origami. He did some decorative, then a face, followed by a bird. Its maiden voyage was Sunday.

Larry Wallace
Cincinnati

 

[UUallace]

Two nine volt batteries will get if off the ground a fraction of an inch. The air has to escape.
A full size helicopter can carry 4 times its rated capacity, but won't get more than 10 feet high.