Hovercraft calculations

Hi Tlewis3348.

How big do you want it to be?

As a general rule, bigger is better when it comes to hovercraft. The limiting factor is when the volumetric leakage of air between the skirt and the ground equals the volumetric input of air to the skirt. This will determine the maximum size you can use.

As the size increases, so does the perimeter, but the area enclosed by the skirt increases much faster, making a larger vehicle more volumetrically efficient.

The weight that can be lifted is calculated my multiplying the pressure in the skirt by the area enclosed by the skirt.

When I was a kid (a few years ago now!) I built hovercraft to race.

My first vehicle was 4'x8' with a 12 HP engine and could barely move, and only then on a flat surface. Using the exact same engine and fan, I then built one that was 10'x6'. This could do 30 mph on reasonably long grass and could carry two people.

A quick bit of mental arithmetic will show the second one had twice the enclosed volume of the first, so required half of the pressure to lift the same weight, which left way more airflow for thrust (all of my hovercraft have been of the 'intergrated' or single fan design).

I could go on for hours about this, but then I would get fired, so instead I will direct you to the hoverclub of Great Britain www.hovercraft.org.uk I had great fun with these guys when I used to live in that country, and have always found them very helpful.

They were also nice enough to give me a trophy for winning the Formula 3 Championship in 1990!

Hope this helps

IPG

I like the idea of making a hovercraft. Seems a great project for the boys and I. Having no experience, I immediately think of a means to evenly displace load weight/mass over entire surface of craft.

As long as the centre of mass is more or less in the middle of the vehicle, the load does not need to be evenly distributed. Moving your weight around inside the vehicle is often used in racing to assit with the steering, similar to motorcycle racing (though those guys are CRAZY).

The hoverclub of Great Britrain should be able to put you in contact with people who have plans for simple hovercraft, some that will work with lawnmower engines.

I strongly recommend it as a good family sport, very freindly, at least when I was doing it.

Cheers

IPG

Isn't a drawback of the larger machine that it couldn't cover such undulating ground as the smaller?

That depends. The bigger the vehicle the larger the 'hover height' which is the hard obstacle clearance.

At Hoverclub meetings we used to run over a marshal to entertain the crowds, having a hoverheight of 8 - 12 inches. The big SRN4's that used to cross the channel had a hoverheight of around 10 feet I think. They could certainly go out in weather that I would not with my little racing machine!

You may also wish to check out the Hoverclub of America (www.hoverclubofamerica.org), and forums like HoverLovers@yahoogroups.com. Folks on the latter are usually willing to offer advice pretty freely - you may want to lurk a bit to get the feel of the site first, or check archives for suitable threads.

I love this thread!! (see my avatar) I actually got paid to fly one of these for about 5 years. Best time of my life. I don't have much experience on these smaller machines, but building one is on my list of things to do. Here are some links.

Neat little hovercraft calculator:

http://www.olshove.com/HoverHome/hovcalc.html

Some basic guidelines for building a hovercraft:

http://links999.net/hovercraft/mem_hov/hovercraft_construction.html