(BllFs6) wrote in message ...
Hi,

found a few old WIG links last night....

these have pics of WIG hovercraft flying....

http://popularmechanics.com/outdoors...ts/print.phtml

http://www.hovercraft.com/

http://www.se-technology.com/wig/index.php


I used to have one pic showing a WIG hovercraft about 10 feet above the ground
doing a "hop"....bet it felt like a hundred feet to the operator though!

WIG hovercraft appear to have many problems....airborne stability for
one....another, dealing with mirror contacts with ground or water (waves)
without it turning into something resembling that bad landing they used to show
at the begining of the 6 million dollar man episodes....


I am not an expert on this topic but I have seen WIG hovercraft in
operation and talked to their designers.
The idea behind this design is that the aircushion makes final
break-away from the surface easy, with very little drag at the
transition. Also, touch down is very smooth.
As for wing tip contacts with water, it does not seem to be very
upsetting. The tip shapes dictate that the contact is only with the
trailing edge.
These things are cool to watch but they are mostly just a stunt,
in my humble opinion because they are slower than the hovercraft they
are derived from. Plus, they are naturally more wind-sensitive than a
hovercraft.
One reason that the hovercraft community keeps looking at WIG
technology is that light hovercraft start to fly away from dynamic
lift effects around 55-65 mph. That has been an upper speed limit,
unless one is willing to pile on weight. High performance hovercraft
can accelerate to 60 mph from a dead stop in under 10 seconds (
precise measurement is nearly impossible. Maybe with a calibrated
video camera)
That performance comes from having static nearly equal to empty
weight.


Another problem is variation of weight.....you need to make sure you CANT get
truelly "aircraft" airborne at minimum load, yet you still want to be a decent
height above the surface at maximum load....so it may make more sense to NOT
make the thing as light as possible as you would an aircraft....so that the
percentage difference between min load and max load is significantly smaller
than that of a true typical aircraft....

which aint neccessarily bad...becuase if I built one of those suckers I'd put
in a heavy duty roll cage that protected me, my neck, and ensured that I
floated upright and intact when (not if) I wrecked the thing and it ripped
apart in spectacular fashion!

Sure, that way the drag is more than if you made it as light as possible, BUT I
bet you would still be going alot faster with much less energy than you would
in an equivalent boat! And the ride would be smoother...at least until you
crashed....

The CD reduction is .8 at height = .25 wing size, .6 at .15, and .5 at .10 the
wing size...where IIRC size = chord...though it could be span....and at height
above ground effect CD = 1.0

So you can see you need to get pretty close to the ground for the WIG effect to
help much...

I'll email you the graph I have

take care

Blll