Test Hovercraft Equation for Science Fair Project

[hitlittle]

I need to test a equation on a hovercraft to prove it correct or incorrect for my science fair project. I would like to test hover height or how much weight the craft can hold. Any help would be appreciated.

 

[Dale]

Hi hitlittle, welcome to PF,

Try P=f/A where P is the pressure of the air under the skirt, f is the force (weight), and A is the area of the hovercraft.

 

[jack action]

The force needed to support the weight (W):

W= p_cu A_c

Where p_cu is the cushion pressure and A_c is the effective cushion area. For most current designs, the cushion pressure varies in the range 1.2-3.3 kPa (25-70 lb/ft²).

The power (P_a) required to sustain the air cushion at the peripheral gap is given by:

P_a = h_c l_cu D_c ( W / A_c ) ^3/2 ( 2 / d ) ^1/2

Where h_c is the clearance height, l_cu is the cushion perimeter, d is the density of air and D_c is the discharge coefficient (it varies from 0.5-1.0 depending on wall design but assume it is equal to 0.611 for a skirt with a straight wall). This does not included the fan efficiency and different ducting losses.

For an effective design (i.e. the pressure is used more to support the hovercraft and less to push the air out of the skirt), the following expression should be as high as possible:

K_a = A_c / ( 2 h_c l_cu D_c )

All of theses equations comes from http://books.google.ca/books?id=Blp...AA#v=onepage&q=theory ground vehicle&f=false" (chapter 8, 2nd ed.).

 

[IanLoh]

May I know what did you mean by Ac? And what is cushion perimeter?

Appreciate your help. =)

 

[jack action]

May I know what did you mean by Ac? And what is cushion perimeter?

Appreciate your help. =)

Ac is the area of the air cushion as seen from under the vehicle.

So if the air cushion has a circular shape, its area is pi * D² / 4 and its perimeter is pi * D, where D would be the diameter of the air cushion.

 

[IanLoh]

What if the hovercraft travels on water? How does it affect the power required?

And is it feasible to hover on water? Let's say, there's only one passenger with a 10 HP engine.

 

[jack action]

What if the hovercraft travels on water? How does it affect the power required?

And is it feasible to hover on water? Let's say, there's only one passenger with a 10 HP engine.

I have to say that I'm not an expert on hovercraft. I just read the one chapter - which is an intro to the subject - in the book "Theory of Ground Vehicles" by J. Y. Wong.

Hovercrafts do travel on water, but I don't know how it affects their power requirement. I think there was something in the book about it, but I'm not sure and I don't have it at hand at the moment.

 

[tnorm12]

I have built a 3' by 4' hovercraft (with rounded corners) out of plywood with a pond liner bag skirt. it it powered by either 2 battery operated leaf blowers or 1 plug in electric leaf blower. I have encountered a problem with both power sources. The hovercraft makes a loud vibrating noise when I stand/sit on it. It sounds like when you vibrate your lips together but much louder. With nobody on the craft there is a very small noise and with somebody on it its much louder. On the bottom there is a rectangular piece of plastic in the middle (16" by 4") positioned so that is 16 inches to every side (a little longer to the corners). There are 6 approx 2" holes around the middle (2 on each long side and 1 on each short side). Any suggestions of how to get rid of the noise? I assume its from not enough holes/bad positioning of the holes but i don't know.

 

[jack action]

It's probably your skirt that is not rigid enough and it is vibrating as air goes by. When you sit on it, maybe the weight is not well balanced with respect to the center of pressure of the power sources: One end is higher that the other and the sound changes.

 

[tnorm12]

that could be it jack action. I did notice that the skirt is flapping/vibrating when turned on. However the thing is in my 1st prototype i built straight off the basic online model (round 4' diameter, leaf blower, plastic 6 mil sheet for skirt, 6 holes evenly spaced around the center, bag skirt). For my 2nd prototype, the one explained before, I used a pond liner which is thicker (45 mil, almost a rubberized plastic sheet if that makes sense). Also the sound happens no matter where i sit or stand on the hovercraft. It may sound a little different when my weight changes but the basic noise is the same. I've watched two online videos (the gadget show, and something else) that were professional science people making hoverboards/hovercrafts. They did similar stuff (rectangular shap, pond liner, leaf blower (there's was gas powered but whatever) bag skirt) the main difference really is the holes in the bottom. Thats why I am thinking its coming from that. There needs to be some slack in the skirt so that air can flow in and inflate it.

 

[tnorm12]

I forgot to mention that the vibrating,rumbling noise was not present in the first protype