Calculating Air Flow and Pressure for a Hovercraft

[russ_watters]

Have you read the thread...? We've covered all of that except #3, which doesn't exist (it is propeller specific and you'll want to talk to the maker of the propeller).

 

[HoverLover]

My Apologies

Google dropped me in on page 2.

Nice tone. Maybe more fiber would help.

 

[Panda]

A hint for three, nip down your scrappy and find a bike wreck.

Racing crafts use big V-Twins. Norton Rotaries were very popular for a while as well.
The fastest craft use twin engines so you can accurate control the skirt flow and the thrust independently.
Its much cheaper though to use a single engine and put waste gates in the deck if your skirt is blowing out in turns.

 

[mcsnickel]

Im thinking of building a hovercraft. it would weigh around 200lbs with rider. According to the equation posted earlier (weight/area = pressure) I need .636638548 psi for it to lift of the ground. Would a 200-250 cfm fan be able to lift it off the ground?

Thank you very much!

 

[Loren Booda]

What does its skirt perimeter measure? Are you sure of that psi figure?

 

[russ_watters]

You'll need to look at the fan curve for the fan to see what pressure it generates at that airflow.

 

[mcsnickel]

the area inside the skirt will be approx. a 31 in diameter circle. i don't think that psi is correct. i was thinking of using at least one of http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100590976&N=10000003+90401+502756+4294965112&marketID=401&locStoreNum=8125...

 

[Normouse]

I didn't read all the posts, but in a hovercraft, the pressure needed is exactly equal to the weight of the hovercraft divided by the area of the skirt. It has to be. The catch, of course, is that if the fan isn't capable of generating that much pressure, it won't lift off.

Once the hovercraft lifts off, the height will be determined by what airflow the fan generates at that static pressure (the fan will ride its fan curve to that point as the hovercraft rises).

My guess would be that a bladed fan cannot produce enough pressure to lift a hovercraft. Bladed fans don't produce much pressure. A centrifugal fan/blower is what you would need.

If you want to measure flow/pressure, manometers and pitot-static tubes are pretty cheap or you can make them yourself.

Not to be a know it all but... That is not quite true about bladed fans. I have seen quite a few hovercraft with its lift provided by bladed fans. But I'm a new person about hovercraft myself however I've been able to pick up a few basic facts. The above mentioned is one.

 

[Normouse]

Not that deep.

Gentlemen (and of course, Ladies),
I agree with another "threader" in that curves for fans etc. is a little overkill. We after all are not designing a space shuttle but a hovercraft. The idea is to rise approx. 1 inch or so off the ground and pretty much remain there until you turn the machine off. The hovercraft, as far as I can figure, is in extreme "ground effects" and that's a good thing. Our requirements get more liberal, as far as weight per horsepower of the engine providing the lift, our physical dimensions also can vary more widely than if we wanted to travel to the moon, to provide an extreme example. Like " visitor from the Id" or something like that said, better to approximate and experiment around to get it flying and stable. I'm no expert but intuitively I feel that the powerful engines that are available today, I found a marvelous minibike engine on the trash pile( at least 3 hp), there is no worry ,really, about not having enough power to lift your craft off the ground 1 or 2 inches. Ditto, the fan and or certrifugal blower, the quality of "junk" out there, found in the salvage yard and even on the trash pile, is too good to worry about it"s self-destructing as you produce enough lift or push you craft along at a medium clip. Now racing is another matter which I'll steer clear of.
Basic info: the weaker the engine for lift the smaller the lift and the larger the bottom has to be in order to produce enough force to lift the weight of the craft and you. Those are the only limiting factors. Of course you see if the engine is very weak it might only lift the craft 1 mm which is tantamount to not lifting at all but actually it is lifting it. No good because you couldn't go anywhere unless you were on ice or extremely flat surface. Also we see that if the engine were too weak the bottom would have to be enormous to produce enough lift. So you really don't have to know too much more than that. Nevermind, the psi's, cfm's, densities, etc. that stuff will just prevent you from building your machine. The joke is once you calculate all that info and actually start to build the machine, 9 out of 10 times the calculations will be NA or just plain wrong. Not just for you but for everybody that's the case,( even engineers,or should I say especially).
Send us a picture of your craft when you finish.

 

[motomax99]

hey guys I am building a one engine hovercraft and i was wondering if 45lbs is too heavy for the deck?