Miniature hovercraft

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  • #51
Danger
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Ararat77 said:
I want to test how high it can go depending on the temperature it is in.
The temperature is irrelevant to a hovercraft, unless it's cold enough for air to freeze. Unlike an aeroplane, which is sensitive to air density, a hovercraft traps the air cushion under itself. Low-density (warm) air might take a wee bit longer to inflate the cushion, but after that nothing will change. How high it will go is just slightly higher than the cushion depth (unless, as ceptimus pointed out, you make it so tall that it falls over).
 
  • #52
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Okay, well, I've changed my project so that it doesn't involve temperature. I've created a hovercraft with a ground-hugging skirt thats 4 feet by 4 feet. I now need a thrust fan but don't know where to get one. Do you have any suggestions for cheap new or used hovercraft fans? I'm hoping to find something $50 or less. I need it as soon as possible. I don't need a very powerful one, just one that will take me at 5 or 10 mph.
 
  • #53
Danger
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Somewhere along the line, I've lost track of what voltage you're running. If you have 12 available, I'd think about getting a heater fan motor from a junked car and replacing the impeller with the blades from a 12-14" household cooling fan. It won't have a lot of thrust, but probably enough for a few mph.
 
  • #54
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If all you want is a simple demonstration of the air lift effect, tis easy. A circular flat plate of iron about 1/4 to 3/8 thick, 1/4" tapped hole with nipple, valve and quick disconnect in the center. Connect to an air hose and open the valve. Won't lift very high, but it does lift.

Ever hear of the Avrocar? Check out some of the old films on it and you'll see the problems with stability.
 
  • #55
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Sorry to dig up old threads, but I'm curious to see how these projects turned out...
 
  • #56
Danger
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Don't be sorry. I lost track of this sucker myself, and I'm still interested in what's going on.
 
  • #57
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For those who find R/C hovercrafts interesting, I recommend you check out this video entitled "R/C Boat+Plane+Hovercraft" ...

http://video.google.com/videoplay?docid=9219568793902200741&q=hovercraft [Broken]

I must say, the seemingly simplicity of the design baffles the mind. Can somebody please explain the logistics behind its design?
 
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  • #58
Danger
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They look like neat toys, for sure, but they're definitely not hovercraft. I surmise that they're hydroplanes with built-in ground effect capability. From the way that they fly, I'm also pretty sure that they have close to 1:1 thrust to weight ratio. The title should give you a hint; they're made out of foam plastic. A hovercraft can't do any of the things shown in that video other than straight line travel. You certainly can't make one manoeuvre like that or become airborne.
 
  • #59
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Ground effect

THats little R/C is cool! You said it's not a hovercraft, but ground effect. What is ground effect, and can you make a machine that uses ground effect for personal use instead of a Hovercraft? And be cann, I mean is it possible for someone with little experience to make it, like a HC?
 
  • #60
russ_watters
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http://www.se-technology.com/wig/index.php [Broken]

Ground-effect is an aerodynamic phenomena where, essentially, the wing squeezes air between itself and the ground, allowing the craft to lift a small distance off the ground at relatively low speed (yeah, it is actually more complicated than that). There has been talk of making massive craft for transoceanic transport. They'd be faster than boats, but more efficient than planes. Trouble is, at 50 feet altitude, a big wave (not to mention a mast) could still knock one down.

I first heard about them in a Popular Mechanics article a decade ago - it was a one-seater.
 
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  • #61
FredGarvin
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http://www.se-technology.com/wig/html/main.php?open=showpic&code=&pic=21 [Broken]

http://www.se-technology.com/wig/html/main.php?open=showpic&code=&pic=14 [Broken]
 
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  • #62
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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 gonna 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 gonna 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 gonna 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.
 
  • #63
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I want to know how changing the area of the base is gonna 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?
 
  • #64
Danger
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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.
 
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  • #65
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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 : )
 
  • #66
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Also, ya 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 hight is gonna change with a given base area increase/discrease?
 
  • #67
Danger
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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.
 
  • #68
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russ_watters said:
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.:rofl:

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).
 
  • #69
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Hmm, I've just figured out that all my calculations were wrong. Perhaps I should be working with m^3 instead of m/s? :confused:
 
  • #70
Danger
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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.
 
  • #71
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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 gonna 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 gonna 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
 
  • #72
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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?
 
  • #74
51
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70 and 40 cms respectively.

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

Good luck.
 
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  • #75
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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
 
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