What are the forces on a tied down glider?

I see gliders tied down in a bewildering variety of ways, all apparently
"adequate" in the owner's mind. AT one extreme I see multiple ropes,
straps, wing stands, and load spreaders, while at the other extreme it's
just a piece of light rope (barely more than clothesline) on each wing
tip. Two questions have slowly formed in my mind...

Question 1: Is there an analysis of the forces from wind on a tied down
glider, or maybe even measurements? Perhaps there is a "best practices"
document somewhere, derived from surveys of what's worked and what's
failed? I'm not looking for lists of personal preferences (I've seen
lots of those at airports and have the pictures to prove it!), but real
data and analysis.

Question 2: What is the effect on the wind forces when the glider has
wing covers on it, such as the Jaxida covers? I assume it reduces the
lift the wing can produce, but another pilot I talked to thought it
would increase the lift. Again, I'm looking for real data and analysis.

--
Eric Greenwell - Washington State, USA
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