I one of them was Paul Hansen's Sisu 1A in California the other was a
Schweizer in Texas - Houston I think. Anyway there are dozens more stories
of stakes pulling out leading to the distruction of gliders in the history
of gliding.

I don't think it's a matter of mechanical engineering, it's soil
engineering. Stakes will hold in turf or damp soil held together by strong
roots. The dry sand and gravel of western deserts just won't hold a stake
no matter how cleverly it's designed. Even half axle shafts driven in with
a sledge hammer have pulled out. The act of driving in the stake loosens
the soil enough to prevent the stake(s) from holding making the whole
exercise self-defeating.

Take a look at airport tiedowns where there's some liability involved.
These are usually 1/2 - 3/4" steel cable set in several hundred pounds of
concrete at multiple points. Anything less is a short term expediency used
under emergency conditions with no guarantees.

I spent some time working on the problem before giving up on stakes
altogether and working out the "bury the ditty bag" scheme. Even if a
dittybag does pull out of the ground, there's still several hundred pounds
of dirt tied to each wing. Ditty bags and a folding trenching tool weigh
less than stakes too. Why not find a good source of those to sell?

BTW, trenching tools have dug some pretty deep holes. I've been sold by
Marines that it's truly amazing how quick and deep you can dig when being
shot at.

"Paul Remde" wrote in message
news:5sUAk.350834$yE1.314870@attbi_s21...
Hi Bill,

That is a very strong accusation against the CLAW. Can you please give
more information about the circumstances of the 2 failures? Was the CLAW
used properly? It is designed for straight-up loads - not side-loads. I
am extremely impressed with the design of the CLAW. Until your post I
have heard only positive comments on it. It would seem to me (being a
mechanical engineer) that the CLAW is uniquely designed to grab hold more
tightly when a load is applied (from directly above).

The link to the flyties below does look interesting, but I don't agree
that it would be more robust than the CLAW.

Thanks,

Paul Remde

"Bill Daniels" bildan@comcast-dot-net wrote in message
...

"brianDG303" wrote in message
...
I always get tie down stuff from Mac's. They sell a nice strap for $5,
and check out this strap pad-

http://www.macscustomtiedowns.com/product/115/TieDowns


The CLAW- when I looked at this I decided to use flyties (
http://www.flyties.com/ ). The Claw looks like it will hold great as
long as the pulling force is directly up, but if the load moves around
it seems like the device itself would act as a lever with the near
arms prying the far stake up and out. In any case off center loads
will concentrate on individual stakes, perhaps.

Or maybe I just like the flyties better. The tool they give you to
pull the stakes out is really nice.


FWIW, I know of two gliders totaled as a result of the "claw" pulling out
of the ground. Gliders tend to repeatedly yank at their tiedowns in a
storm. This will weaken the hold of almost any stake system including the
"Claw".