[SML] Hovercraft revolve?

[Dale Farmer]

On 2/9/2017 10:12 AM, Joe D via Stagecraft wrote:
> I have been involved with a production, where we built an revolving platform, 8ft diameter. It was about a 6" step up in height.
>
> This now has me wondering if we could have done it as a hover-craft.  I.e. 1st put down plywood the diameter of your platform, and route some channels for air passage. Then, lay down an air hose to the center.  Lay the top layer on top of that base, and connect them at the center with a pivot connection.
>
> When air is supplied, it will act like an air-hockey puck.  The benefit is that you can make a much lower profile system.
>
> It may even be possible to put the air system inside the platform itself.  Perhaps by sandwiching 3-layers of 1/4 Ply.  The middle layer has the passage for air created by using a router. Then, holes drilled through to allow the air to flow to the bottom.
>
> However, I am concerned that uneven loading may cause one part to get bogged down.  Though, I suppose as long as the air pressure is supplied to multiple points, it should work.
>
> I think the key is to keep the pressure higher than any local loading at each particular outlet.  So, if I have a 12" grid of holes, I should make sure that my Pounds per Sq Ft of load is less than the PSI of the air.  I would of course, need to make sure my source can keep up with enough air.
>
> One reference I found says a vacuum cleaner can provide around 2.7 PSI [= 370 PSF]. So, that would seem to be plenty.  The noise is, of course an issue, so the blower would have to be located elsewhere, and the air piped in.
>
> Has anyone ever taken this approach to floating a platform with the entire base of the platform acting as a single air-caster?  Any other thoughts about it?
>
> -Joe

I have seen and used such systems.  The gotcha is that the floor has to 
be fairly smooth and flat, and mostly level.   Expansion joints in 
floors let the air, and thus the lift, out fast.   They used shop air 
connections to provide the air for these things.  the larger hoses like 
jackhammers use.  and yeah, noisy.   And sweep the damned floor first. 
any dirt and grit on the floor will be blown around right into your eye, 
and any that is stuck the floor hard enough to resist the air blast will 
scratch the floor and the air caster.

As I understand the physics, the lift is provided by the cushion of air 
under the entire air caster, not just the jet of air coming through the 
opening into the air cushion.    So if you have a one square foot caster 
fed by a ten psi source, theoretical lift would be 1440 lbs. In the real 
world, somewhat less.

Dale