Re: GEVs

Ryan M Gill wrote:

> Yep. PACV Patrol Air Cushion Vehicle 

If it is the one I think it is, the cushion pressure was about 0.3 psi.

> > However, I am encountering another problem that could be 
> > insurmountable. GEV over water, when the pressure required to hover
> > (say 10psi) exceeds the mass of the water underneath (not very well

> > put, but I hope it gets the idea across) wouldn't the vehicle sink?


Of course it would - just like a boat which is too heavily loaded :-/

Let's see - the density of water is pretty close to 10^3 kg/m^3
(depending on salt contents, etc), and the pressure at depth h (meters)
below the mean surface (ie, don't measure where the cushion pressure
pushes the surface down <g>) should be roughly 10^3 * 9.8 * h Pa. I
think this corresponds to about 0.44 * h' psi in imperial units (h'
measured in feet).

Unless I've made a  major though error somewhere (which I quite likely
have, since it is 3 am and I've recently caught a bad cold), the
hovercraft will sink to the depth where its cushion pressure equals the
pressure of the water. If this depth is far enough down that the water
reaches the air intakes, bad things will happen <g>

If my reasoning and unit conversion is correct, a 10 psi-cushioned GEV
would sink about 22 feet down into the water before reaching the
equilibrium pressure. 

> It would have to be pretty damn high. 

Only if your GEV is very high <g>

> I would think the size of the skirt  would alleviate this. 

The size of the skirt determines the cushion pressure - a bigger skirt
for the same Mass means a lower pressure.

> The US has the LCAC which is huge and can carry > an M1. 

Cushion pressure approx. 0.8 psi. Displacement (fully loaded) 182 tons.

> The Russians have even bigger monster hover craft. 

Cushion pressure roughly 0.6 psi for all of them, including the 550 ton
one.

Regards,

Oerjan Ohlson
oerjan.ohlson@telia.com

"Life is like a sewer.
  What you get out of it, depends on what you put into it."
- Hen3ry