What is the best design for a miniature hovercraft for a race?

[Gambit]

Miniature Hovercraft Project !

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 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 the necessary items?

 

[ank_gl]

hey where do you have this competition? i might also give it a shot. some IIT is organizing it?
if you are interested, PM me, i may be of some help.pleasezzzzzzzzzzzzz
check this link https://www.physicsforums.com/showthread.php?t=54808&highlight=hovercraft
you will find the required help in there.

 

[Danger]

I think that it's a bit late for that link, Ank. The first post in this thread is a duplicate of the last one in the other, so he's seen it already.

 

[ank_gl]

oh yeah, i m bit late.
anyways Gambit, when is this competition??

 

[ank_gl]

maybe a stupid one this time around. since the hot air is lighter so can't we use hair drier for the purpose of filling up the under belly of the the the craft.
don't get mad on me for such a stupid suggestion !

 

[Gambit]

Well, to be precise. I think its in Guwahati or Madras. Not sure. My frnd only told that the event is abt hovercrafts. Can i know ur name? and where u stay? My name is Vignan. M frm Hyderabad.

 

[Gambit]

Hey ANK buddy...r u online?

 

[FredGarvin]

A word to all on this forum...Three suggestions to get the maximum amount of help from people here:

1) You have to post questions that are not broad in context. If you simply ask for someone to give you the best design for something, you're not going to get any help.

2) Show us some effort on your part. If you just show up with no post count and ask us to do your work for you, you won't get a lot of support.

3) DO NOT use text message grammar here. It is not appreciated by most of us. Take the time to make well thought out questions and posts. If you don't take the time to make your posts legible and somewhat professional, you are going to limit the number of people willing to assist you.

 

[Gambit]

A word to all on this forum...Three suggestions to get the maximum amount of help from people here:

1) You have to post questions that are not broad in context. If you simply ask for someone to give you the best design for something, you're not going to get any help.

2) Show us some effort on your part. If you just show up with no post count and ask us to do your work for you, you won't get a lot of support.

3) DO NOT use text message grammar here. It is not appreciated by most of us. Take the time to make well thought out questions and posts. If you don't take the time to make your posts legible and somewhat professional, you are going to limit the number of people willing to assist you.

@Fred,

Sorry about that. I should have been more specific about the help. Anyways, I will try from my part and ask for help only when stranded.

I am new to this forum. Hence it is understandable that i won't have many posts to my credit.

What I actually meant to ask was, with the given dimensions and the requirments, me using the equipments used on the usual Hover-crafts won't work right? Thats the reason, i asked for the help. Like I want to know more about Balsa wood and anyother substitute for that.

Also, for the given Dimensions, what motor or IC Engine would be sufficient? I don't want to go and buy a motor which won't be able to lift it. that's why i am asking for your help. Also, for the forward propulsion, which IC engine would suffice? I don't want it rocketting ahead without any control. So, I am trying to ascertain the optimum equipments for the Hovercrafts. I am not having any experience with making such things. Just a step Climber that's all.

Besides, I have observed that many of the forum members are not from India, the price and estimates could vary according to your country. Thats another problem I have.

Thank you.
Vignan a.k.a Gambit

 

[Danger]

Much better post, Gambit.
For a model of the size that you specified, material choice isn't terribly critical. Although lighter material is better, you could use thin-wall tubing and sheet aluminum without losing too much performance.
Balsa is strong, light, and fairly inexpensive, but it has limitations. For one thing, you pretty much have to glue it. In my experience, at least, it doesn't hold screws or nails very well. That makes design alterations almost impossible once you've started construction. (I guess that you could mock it up with pins or nails and then glue it when you're satisfied.)
You don't need to use 2 motors unless you want to. Thrust can be provided by simply building a diversion duct to capture some of the lift fan output. A moveable flap in the duct can serve as a 'throttle'.
Russ posted a link to a 'lift calculator' a while back. It's bookmarked on the computer at work, so I'll re-post it when I get there in a couple of hours.

 

[Aero Stud]

You can also use light plastic or wood beams and nylon, like some moden airplanes or.. don't know the english word - the white soft stuff that food containers and water jars for single use are made of (calcar - if that means something in English lol ). You also need a skirt. About the egnine - maybe a small vacuum cleaner engine could also do ? Like those small hand held table cleaners for the kitchen type on batteries.

 

[ank_gl]

Besides, I have observed that many of the forum members are not from India, the price and estimates could vary according to your country. Thats another problem I have.

thats the problem with me also. most of the time, you are not going to get things which seems to be easily accessible to people in europe and US. they are simply not here. but this lack of resources is the mother of inventions (hehe, or jugaad:tongue2: as you may understand it). i searched it all, but we don't have a single hobby shop in whole India(stupid place). i needed 2 OS .61 FX for my project and i ll get them in less than 2 months from now(record time) thanks to a friend. so you have to pretty much look for something from an old machine or go for electric motors.
anyways i m from new delhi

 

[Gambit]

Much better post, Gambit.
For a model of the size that you specified, material choice isn't terribly critical. Although lighter material is better, you could use thin-wall tubing and sheet aluminum without losing too much performance.
Balsa is strong, light, and fairly inexpensive, but it has limitations. For one thing, you pretty much have to glue it. In my experience, at least, it doesn't hold screws or nails very well. That makes design alterations almost impossible once you've started construction. (I guess that you could mock it up with pins or nails and then glue it when you're satisfied.)
You don't need to use 2 motors unless you want to. Thrust can be provided by simply building a diversion duct to capture some of the lift fan output. A moveable flap in the duct can serve as a 'throttle'.
Russ posted a link to a 'lift calculator' a while back. It's bookmarked on the computer at work, so I'll re-post it when I get there in a couple of hours.

What about the material for skirt? Would i find a motor or IC engine which could lift something like a balsa wood and also the weights of the motors/engines?

Also the center of weight plays a critical role i guess. Would it be better if I place the motor for lift in the dead centre with the propeller? I read a post by another member about Gunter propellers. Now I don't know where i can find them. Can I use another propeller instead? Or should I make a propeller with some material? The price of the propeller can be cheap according to your exchange rates. But it will become a costly affair once I try to order it from another country.

Another thing, sorry about sounding dumb. But I still can't believe that something like a hovercraft can ACTUALLY hover in air. I know the mechanism, I am not sure if it will work when I do it :shy:

 

[Gambit]

You can also use light plastic or wood beams and nylon, like some moden airplanes or.. don't know the english word - the white soft stuff that food containers and water jars for single use are made of (calcar - if that means something in English lol ). You also need a skirt. About the egnine - maybe a small vacuum cleaner engine could also do ? Like those small hand held table cleaners for the kitchen type on batteries.

Yes. Those stuff can be used. I am not planning about keeping it and using it for years. I want it to full-fill the purpose for only sometime. 1 month is more than enough. If you can suggest any cheaper alternatives, it would be better. I was thinking about alluminium rods with thin metal sheet around it.

I don't hav vacuum cleaner. The motor i can use is limited to 12 volts motor. and the IC engine I could use is limited to only 3.5 cc engine.

I hope I am a little clearer. would these suffice for the lift and propulsion? Also, suggest a propeller. Also about the skirt, what if I use polythene as skirt? Can it withstand the weight? How I get the necessary shape for the skirt? Can you provide any tips on shaping the skirt?

 

[ank_gl]

mythbusters made some hovering machines (a chair and a surfing board, yeah believe it) in season 2, episode 4. you can get a fair idea from there.
and why can't you believe that a hover craft can hover, i can't believe it.
forget about the custom made props and engines, you aint getting them even in next 5 years in India. think for a substitute, like a vacuum cleaner unit

 

[Gambit]

thats the problem with me also. most of the time, you are not going to get things which seems to be easily accessible to people in europe and US. they are simply not here. but this lack of resources is the mother of inventions (hehe, or jugaad:tongue2: as you may understand it). i searched it all, but we don't have a single hobby shop in whole India(stupid place). i needed 2 OS .61 FX for my project and i ll get them in less than 2 months from now(record time) thanks to a friend. so you have to pretty much look for something from an old machine or go for electric motors.
anyways i m from new delhi

Nice. Are you interested in participating in this event? I suppose its in IIT Guwahati. If you know about any place we can get our equipments, please suggest. You seem to be in Mechanical Dept. How much do you think a 3 or 3.5 cc IC Engine would cost me?

 

[Gambit]

mythbusters made some hovering machines (a chair and a surfing board, yeah believe it) in season 2, episode 4. you can get a fair idea from there.
and why can't you believe that a hover craft can hover, i can't believe it.
forget about the custom made props and engines, you aint getting them even in next 5 years in India. think for a substitute, like a vacuum cleaner unit

Buddy ! I just sent you a PM with my email id. hope we can get in touch

 

[Danger]

Hi again.
It's best to centre your majority of mass such as the motor, if it's simply a self-supporting machine, but the placement of the fan doesn't matter. If it's to be used to transport something, though, you should offset the motor/batteries to serve as a counterbalance for that load.
While on that same subject, a fan rather than a propellor is generally used for the lift air. If you're restricted to 12 volts, maybe the cooling fan from a car will work. Some of them are small enough to fit your design. You don't need a lot of power to get the thing off of the ground. (I'll find Russ' calculator link in a minute and paste it into this post.)
Since your model is kind of in limbo between being a toy and being a recreational vehicle, the skirt material might be a bit iffy. Something that would be used for a full-scale machine will be too rigid, and something for a toy won't be strong enough. Heavy gauge polyethylene, such as used for vapour barriers in houses, should work well. Just form it into a (+/- 4") tube as long as the perimeter of your deck with the valve from a beachball glued in, seal it with something like silicone, glue it to the deck, and blow it up.

edit: Here's that calculator. It's great. http://www.hoverhawk.com/lcalc.html"

 

[Gambit]

Hi again.
It's best to centre your majority of mass such as the motor, if it's simply a self-supporting machine, but the placement of the fan doesn't matter. If it's to be used to transport something, though, you should offset the motor/batteries to serve as a counterbalance for that load.
While on that same subject, a fan rather than a propellor is generally used for the lift air. If you're restricted to 12 volts, maybe the cooling fan from a car will work. Some of them are small enough to fit your design. You don't need a lot of power to get the thing off of the ground. (I'll find Russ' calculator link in a minute and paste it into this post.)
Since your model is kind of in limbo between being a toy and being a recreational vehicle, the skirt material might be a bit iffy. Something that would be used for a full-scale machine will be too rigid, and something for a toy won't be strong enough. Heavy gauge polyethylene, such as used for vapour barriers in houses, should work well. Just form it into a (+/- 4") tube as long as the perimeter of your deck with the valve from a beachball glued in, seal it with something like silicone, glue it to the deck, and blow it up.

edit: Here's that calculator. It's great. http://www.hoverhawk.com/lcalc.html"

Thanks for the link.

Now, You mentioned about using a beachball valve right? But such valves are used for restraining air from going out of the skirt i guess? But I suppose the hovercraft works on the principle of the rate of flow of air through the skirt using the fan. Then, why use a Valve?

Also, the maximum dimensions are 70X40 centimeters. So would a car's cooling fan work there? Shouldn't the fan be a little smaller? Something more common like the car's cooling fan which is easy to get.

I was suggested to use a small vacuum cleaner. Would that work?

 

[Danger]

There seems to be some misunderstanding of how the skirt works. In a toy, it's just some sort of soft edging that surrounds the plenum. A real hovercraft, however, has a large permanently inflated bag rather than a single layer of material (althought the preferred method is actually a series of smaller independent bags beside each other).
The air leakage is from the plenum under the skirt, not from the skirt itself.
As for the car fan, I didn't mean the single large fan that most cars have. Some have two small ones to either side of the radiator. I should have specified that. I don't think that any 12V vacuum cleaner will supply enough air. I can't even get mine to pull cat hair off of the couch. Remember that it has to not only pressurize the plenum in the first place, but also constantly replenish the amount that leaks out. While not a lot of power is required, you do need a substantial flow rate.

edit: I should have specified that the skirt on a large unit is permanently inflated while it's hovering. Part of the lift air is bled off to keep it that way. It collapses upon landing.

 

[Danger]

I screwed up big time. Sorry, guys.
Even while I was reading 'centimetres' in the specs, I was thinking 'inches'. None of my foregoing advice is applicable to the real scale of this thing.
For the skirt, I would still consider using 6-mil poly, but would implement it differently. My approach would be to cut four 10-cm strips (notice that I'm on the same scale as you now ) corresponding in length to the sides of your fusilage. Glue and/or staple them to the edges of the platform so they hang down like a curtain, then fold them up and attach the other edge in the same way to make the curtain double-layered. Seal the corners with silicone or tape.
A cordless vacuum cleaner motor and fan might indeed supply the required air, but I still have some doubts about that.
A thought just occurred to me now, but it might be more expensive than you want. As far as I know, this has never been done on either a model or a real hovercraft. I'm thinking of using 6 or 8 computer fans instead of 1 big one. You can evenly distribute them over the deck area. Mounting a couple more horizontally can provide your propulsion. Where I live, you can get them free by scavenging scrap computers, but I don't know about where you are.

 

[ank_gl]

yeah computer heat sink fans can be used and you can get them easily anywhere in local market for comp hardware, but i don't think its enough. try to put your hand against it and you don't feel anything(i mean any kind of thrust). i once used them for propulsion for a motor boat, it didnt even move(well actually i fail a lot of the times, when i try something this crazy ).
computer heat sink fans are pretty cheap over here if you(Gambit, i mean) want to give it a shot.

 

[Danger]

I have never, in fact, felt the output of a computer fan, so I'll take your word for that. They should still be sufficient for lift, though. A cordless blow-drier might be good for propulsion, and it's already ducted for increased directionality. (It can be hard-wired to the main battery to avoid conflict with the voltage rules.)

 

[Gambit]

Thanks Danger and Ankit. But the main problem here is the number of motors/engines to be used for lift and propulsion. According to the rules given by the event organisers, one 1 motor/engine EACH must be used for lift and propulsion.

So, I must use basically 2 motors/engines for lift and propulsion. I can use a motor and an engine combination. Like a motor for propulsion and/or engine for lift.

@Danger, I didnt quite get the idea about the skirt. Shouldn't the skirt envelope the air flowing beneath the set-up? Like totally surrounding the air in all directions? And the plenum should just support and monitor the air flow INSIDE the skirt.

Please, suggest a material for the skirt.

 

[Danger]

As I mentioned earlier, I would stick with 6-mil polyethylene for the skirt. It tough, but still flexible. You don't even need to make it double-layered; that's a redundancy in case of a tear, and also helps maintain the shape.
Sorry that I misunderstood the rules about the number of motors. All that I saw was the voltage/cc's restriction.
The plenum is the entire air-filled volume under the deck, which provides all of the lift. The skirt forms either the only walls of that space, or the lower part of the walls. Its purpose is to contain the air while still allowing the machine to pass over unyielding obstacles.
As the calculator shows, you don't need a lot of power for the lift fan, so I'd recommend using an electric motor for that. For thrust, you might want to go with the largest allowable gas motor with a propellor about 20-30 cm in diameter.
You mentioned earlier using a hair dryer for lift. That would work just fine, but the fact that the air is hot won't make a noticeable difference. Leave the heat element turned off so that all of your battery power goes to the motor. (For the record, I've never actually seen a battery-operated dryer, but I suppose that they exist.)

 

[Gambit]

As I mentioned earlier, I would stick with 6-mil polyethylene for the skirt. It tough, but still flexible. You don't even need to make it double-layered; that's a redundancy in case of a tear, and also helps maintain the shape.
Sorry that I misunderstood the rules about the number of motors. All that I saw was the voltage/cc's restriction.
The plenum is the entire air-filled volume under the deck, which provides all of the lift. The skirt forms either the only walls of that space, or the lower part of the walls. Its purpose is to contain the air while still allowing the machine to pass over unyielding obstacles.
As the calculator shows, you don't need a lot of power for the lift fan, so I'd recommend using an electric motor for that. For thrust, you might want to go with the largest allowable gas motor with a propellor about 20-30 cm in diameter.
You mentioned earlier using a hair dryer for lift. That would work just fine, but the fact that the air is hot won't make a noticeable difference. Leave the heat element turned off so that all of your battery power goes to the motor. (For the record, I've never actually seen a battery-operated dryer, but I suppose that they exist.)

Thanks Danger. Ill try using the 6mm platic. I have another question, what will support the craft before inflation? These should be a gap for the air to freely flow in the plenum right? If the craft is down, how can the fans send air into it? I was thinking there must be some structure to hold the craft atleast midway from touching the ground. Like, this structure will support the craft, while it creates space for the air to flow and fill up the plenum. Please help me with this...!

 

[ank_gl]

whats the problem with support. simply put support struts below the deck with enough height that they don't touch the ground when skirt is inflated and the craft rests on them when it is idle.
but that ll only add up to the weight, what's the problem in leaving the craft that way only

 

[Danger]

The strut idea is fine as long as the machine will only encounter flat surfaces. That would seem to be the case here. Alternatively, short sidewalls can be installed (so the thing looks like an upside-down cookie pan) with the curtain attached to the bottom of them.
For this particular project, though, I wouldn't bother with either method. The curtain won't completely collapse when at rest; there'll always be some airspace inside it. Even that isn't necessary, though. Just make sure that the fan doesn't protrude below the bottom surface of the deck so there's no chance of it hitting the floor.

 

[Gambit]

The strut idea is fine as long as the machine will only encounter flat surfaces. That would seem to be the case here. Alternatively, short sidewalls can be installed (so the thing looks like an upside-down cookie pan) with the curtain attached to the bottom of them.
For this particular project, though, I wouldn't bother with either method. The curtain won't completely collapse when at rest; there'll always be some airspace inside it. Even that isn't necessary, though. Just make sure that the fan doesn't protrude below the bottom surface of the deck so there's no chance of it hitting the floor.

But if the fan doesn't protrude below the bottom surface, how can air go inside the plenum? I was thinking that if the fan is a little inside, air can go in nicely and fully. Otherwise, the air might escape from the small air gap on the circumference of the fan set-up...please help out on this.

I still can't imagine that the skirt will be able to support the whole craft when not inflated. I just want a reconfirmation.

@Ank, I found the torrent file regarding the mythbusters episode. Is it the one named anti-gravity devices? But It seems that the torrent file has a problem. Its stopping the download process now and then and give a stupid error message. If i click on OK and resume the download, its continueing from that point again. Is this normal torrrent file download behaviour? I am using bittorrent application.

 

[Danger]

Just mount the fan face-down on top of the deck, with a hole cut out under it. The hole should be as close as possible to the fan diameter, with enough left around it for your mounting hardware. If it makes you feel better, you can make a shroud around the perimeter of the fan to capture all of the air.
When I get done here, I'll fire up the Mac and make a drawing. That might simplify things a bit.

 

[Gambit]

Just mount the fan face-down on top of the deck, with a hole cut out under it. The hole should be as close as possible to the fan diameter, with enough left around it for your mounting hardware. If it makes you feel better, you can make a shroud around the perimeter of the fan to capture all of the air.
When I get done here, I'll fire up the Mac and make a drawing. That might simplify things a bit.

Thanks about the picture. I guess a drawing might clear my doubts. I will also make a drawing of my design and ask for ur opinion.

 

[Danger]

Okay, here's what I've got. I'm at work, so I didn't have time to try making it properly. It's not to scale, and there's no detail shown. Fact is, I don't even know exactly what a model aeroplane engine looks like or how it's mounted. I hope that it conveys the idea, though.
"[IMG[/URL]

 

[Gambit]

Okay, here's what I've got. I'm at work, so I didn't have time to try making it properly. It's not to scale, and there's no detail shown. Fact is, I don't even know exactly what a model aeroplane engine looks like or how it's mounted. I hope that it conveys the idea, though.
"[IMG[/URL][/QUOTE]


Thank you for the image Danger. But I am more confused about the skirt. If we won't make an airtight skirt, won't the skirt go upskirt when we run the craft? like in this picture? That was my main doubt. I thought i the skirt would envelope the air under the deck rather than hang around the edge of the craft.

Besides wherever I googled about homemade hovercrafts, they enveloped the air under th deck and using holes underneath the dech, provided the levitation. But your model kinda contradicts that one.

 

[ank_gl]

for the torrent thing, i ll mail you the torrent file today.
and the drawing danger has put is absolutely correct.
for the upskirt problem, just make the base area(i mean the lower portion) a little less than the deck area, it won't go up.
and the hovercraft works on the principle of steady flow not some airtight thingy(i don't know much, but that's what i understand it to be)

 

[Gambit]

for the torrent thing, i ll mail you the torrent file today.
and the drawing danger has put is absolutely correct.
for the upskirt problem, just make the base area(i mean the lower portion) a little less than the deck area, it won't go up.
and the hovercraft works on the principle of steady flow not some airtight thingy(i don't know much, but that's what i understand it to be)

Ok. Now I get it. So then the lower part much be exactly even. Like there shouldn't be any curvy parts, then all the all will escape from that portion, won't it? How do we make sure that the air in the skirt escapes evenly around the craft? The skirt must be perfectly made I guess...