WIND SOCKS

Hi, I guess there must be some theory for the design of windsocks out there?

Our wind sock is more like a pair of torn and laddered tights, so we need to
rebuild it.

Is there some basic theory on size (yes we have the first main ring) and
length, also the size of the outlet hole? Is it also imperative to have
material with zero permeability or is some air passing allowed? Its a 30 kt
job so on the large side!

Now if I'm really lucky, this thread will be no longer than 3 posts long.
(G) :-)

Cheers,
Malcolm...