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James (Magnets)
Member
Username: Magnets

Post Number: 13
Registered: 6-2006
Posted on Wednesday, July 5, 2006 - 3:18 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

This is a question that iv'e tried to find on google but i can't seem to figure it out. I know the equation to figure out how much pressure is needed to lift a hovercraft off the ground (weight in pounds / area in inches=pounds per square inch) but how can i determine how much pressure underneath the hovercraft i'm creating with my fan?

Thanks for the help
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Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1356
Registered: 12-2004
Posted on Wednesday, July 5, 2006 - 6:38 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Work backwards.

You know the weight of the craft, and the area under the craft.
If the craft is hovering, the pressure of the air under it will
exactly equal the mass divided by the area.
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James (Magnets)
Member
Username: Magnets

Post Number: 14
Registered: 6-2006
Posted on Wednesday, July 5, 2006 - 10:35 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

ya i know that if it "is" hovering, but isn't it possible to crank out numbers before the real thing is built? What i'm saying is can i get some equations so i know what the air pressure is under the craft before i waste time trying to build it? I've built too many unsuccessful hovercrafts and can't figure where i'm going wrong (these are just toy hovercrafts).
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scott (Ichyc)
Intermediate Member
Username: Ichyc

Post Number: 24
Registered: 6-2006
Posted on Wednesday, July 5, 2006 - 10:40 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

First you should make a good design and then you should know how wide it is going to be and how heave it is going to be.
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James (Magnets)
Member
Username: Magnets

Post Number: 15
Registered: 6-2006
Posted on Thursday, July 6, 2006 - 1:06 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

ya i know how heavy it is and its size but what i want to know is, is there an equation to determine the pressure inside a hovercraft caused from the fan/proprellor?
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Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1358
Registered: 12-2004
Posted on Thursday, July 6, 2006 - 11:04 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

You have an inlet and an outlet. You know the pressure you need.

You need to do two things.
1. Calculate the rate that the air is leaving the outlet.
2. Calculate how you can replace that air through the inlet.

The outlet can be considered a nozzle. A good treatment of how to calculate
flow through a nozzle is here. Another one is here. General flow equations
are covered here. NASA has a nice description here.

For your purposes, it comes down to the dynamic pressure, which is the density
of the air, times the square of the velocity, divided by two.
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Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1359
Registered: 12-2004
Posted on Thursday, July 6, 2006 - 11:27 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

You might also like this link, and this one, and this one.
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James (Magnets)
Member
Username: Magnets

Post Number: 18
Registered: 6-2006
Posted on Saturday, July 8, 2006 - 7:24 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Thanks Simon
I just recently bought a small motor (http://www.radioshack.com/product/index.jsp?productId=2102822&cp=&origkw=motor&kw=motor&parentPage=search) from radio shack. I'm telling you that this thing can spin crazy just from 2 AA batteries (1.2 volts each). The package says that at no load it can spin 11,600RPM with no load. I put a small, light, Styrofoam propeller on the motor wich has a diameter of 4.25 inches. The hull of the craft is a paper plate with a diameter of 9 inches (the plate is circle...). I'm going to hope that when i put the fan motor and the 2 AA batteries on the craft that it will still hover.
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vignola (Unregistered Guest)
Unregistered guest
Posted From: 136.242.156.58
Posted on Friday, December 1, 2006 - 2:57 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I would like to know how to calculate the thrust force that and fan / engine combination can produce. I know that the force is equal to the change of the momentum. But as a practical thing, from the limited information you get on a manufactures web page (may all they tell you is x cfm and the diameter of the fan) how can I calculate the thrust force? And then, given the same limited information how I size the engine to the fan if they donít give you a fan performance curve?

Joe Vignola
vignola@cua.edu
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Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1591
Registered: 12-2004
Posted on Friday, December 1, 2006 - 5:33 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

You know the area of the fan.
You know the depth of the fan blades.
You know how many times the fan rotates per minute.
You can look up the weight of air.

Now you know how much weight you are throwing, and how fast you are
throwing it. That is thrust.
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Innes Poopface (Princess_mellow)
New member
Username: Princess_mellow

Post Number: 2
Registered: 2-2008
Posted on Thursday, February 21, 2008 - 2:14 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Also for best results the hover height should be 20% of the diameter, e.g. 20ft diameter has to have 2ft hover height.
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Kasper Emil Feld (Magnetfeld)
Advanced Member
Username: Magnetfeld

Post Number: 57
Registered: 11-2007
Posted on Thursday, February 21, 2008 - 7:31 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Thats ten percent...
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Patrick (Firewire)
Junior Member
Username: Firewire

Post Number: 5
Registered: 12-2007
Posted on Friday, February 22, 2008 - 5:32 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Try using a small computer fan, an old CD, and some small li-ion batteries (found on old mp3 players, handhelds...) with the same voltage as what the computer fan needs, probably 5 volts.

But I'm not sure if the PC fan will produce enough air pressure (because of the number of blades found on it's propellers it might), or if the CD's surface area is enough to keep the pressure under it to make the whole thing hover...

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