What are the forces on a tied down glider?

Bill,

As you are keen on winch launching, I wouldn't recommend a longer axle
bolt. We have had a couple of potentially serious incidents in the UK
where the winch cable has got caught around protruding mainwheel or
nosewheel axle bolts and then hung up. I suppose that this could also
happen to an aerotow rope.

Del Copeland


At 02:29 21 August 2008, Bill Daniels wrote:
Way back I needed to tie down an old TG-3 at Boulder, CO.

Like you, I decided the wings weren't strong enough but the structure
around
the main wheel was. I bought a longer bolt to replace the one that
served
as the wheel axle. Using spacers and washers much like those used on
axle

extensions seen on tail dolly wheels to engage tow out gear, I added
"spools" on each side of the main wheel.

I then made a deeply anchored concrete pad with two 1/2" steel plate
"ears"
that engaged the extended axle spools like hooks when the glider was
rolled
backwards onto the pad. The tail was chained so the glider couldn't
roll
forward enough to disengage the hooks from the spools. Just for good
measure, the nose was anchored with the tow hook. Wing stands and ropes

kept the wings from rocking.

The old TG-3 didn't even budge in a strong wind.


"Eric Greenwell" wrote in message
news:K34rk.397$lf2.251@trnddc07...
Derek Copeland wrote:
I have heard of a case where a Blanik was wrecked by a violent gust of

wind
during a storm, even though it was very well tied down. The lift on
the
wings was sufficient to lift the glider. The wingtips were both tied
down
and the mainspar was damaged beyond economic repair by the resulting
downwards bending loads!

That might have been our club's Blanik in the '80s. In retrospect, it

wasn't "very well tied down". Only the tips were tied down well to
solid

ground anchors; the fuselage was not restrained directly, and the
center

of the wing, using the factory tie down rings, was tied to a cable that

could lift a foot or so with 100-200 pounds of force.

It was that experience that makes me question a lot of the tie down
methods I see that use just the wing tips. I'm now of the opinion the
best
situation has the fuselage restrained using the towhook, or perhaps the

landing gear. If that straps and ground anchor can take 5+ Gs, it
doesn't
matter much how well the wings are restrained. The tail restraint is
probably important if very strong quartering winds are encountered.