ContestID67 wrote:

Last weekend a spring storm ripped through our area with 70mph local
winds and reports of a nearby microburst that took off some roofs.
This event also torn our Schweizer 2-33 out of its tie down moorings,
cartwheeled it about 30 feet and wrapped it around a tree. The
fuselage was broken in two as were both wings. An absolute total loss
to a ship that I learned to fly in. Rather sad.

The ship was tied down with stout nylon rope at the tail and both
wing's anchor points (replaced just a few week's ago). The nose was
tied down via very stout chain to the tow release. All these stout
items were anchored into the ground with 4' screw in anchors (the
stout kind) which had been in place for many years. The glider had
been flow the day before.

While we have no way or knowing what actually happened that night, we
know that the tow release's rear vertical bar (the part which is moved
when the tow release ball is pulled) was found broken and the critical
cross piece which holds the tow hook was missing. The left wing's tie
down was found broken in the middle. The right wing's tie down
deperated at a fitting. The rear tie down anchor was torn out of the
ground. There were significant divots in the ground behind the tie
down area. These are the facts, the rest is conjecture.

I believe that broken tow release allowing the curved part of the tow
hook to swing free and release the nose tiedown chain. The now
unteathered nose of the glider became airborn putting tremendous
strain on the wing tie down ropes. Finally one tie down failed and
the ship flew straight up on its tail pulling apart the other wing's
tie down and yanking the anchor from the ground. Finally the wing
tips and nose of the glider dug into the ground during the
cartwheeling. It must have been quite a sight.

The club's email dialog on this event has included talk about how not
to have this happen again. Different ideas have been floated around
including tail stands (to lower the angle of attack of the wings) and
lift spoilers. My question to you is what do you do (short of
hangaring) to protect your gliders from wind storms?

Thanks in Advance, John


John,

In 2003 a 2-33 was lost at Hinckley in almost identical
circumstances, and you are right -- it was quite a sight.
Fortunately it cartwheeled away from the line shack where we were
watching the anemometer register over 75 kts, and it also missed our
cars in the parking lot by a few feet. It was a twisted mess when it
came to rest several hundred feet away -- stopped by some heavy farm
equipment on the perimeter of the field. This aircraft was not on a
tail stand. I have the tailwheel/tie down ring assembly here to
remind me to expect the unexpected, its twisted jagged edges tell of
the extent to which the forces of nature exceed the strength of our
materials.

More interestingly in this context, at the same time we had a 2-33
which landed just prior to the microburst and rolled out to a stop
midfield. In the 2-33 were a student and an experienced instructor.
The CFIG used the aerodynamic controls and spoiler/wheel brake to
keep the aircraft aligned with the wind and on the ground until the
winds dissipated. I had wondered whether such a thing would be
possible in such a light aircraft, and so valuable lessons were
learned that day from a ring-side seat.

The nose down attitude and the deployed spoilers of the just-landed
2-33 were the keys, I think, to maintaining control of the ship.
Since we won't duplicate that forward weight distribution with empty
cockpits, a tail stand and some sort of "spoiler" arrangement on the
wings' upper surface would allow us to keep our ships from lifting
themselves out of their tie-downs in a high wind. It will be
counter-productive to leave the ship's own spoilers deployed when
tied down due to the exposure of the inner structure of the wing to
the elements and local fauna, but an external "spoiler" such as
two-by-fours lashed to the upper surface of the wings -- as is
sometimes done by bush pilots in Alaska -- can prevent the wings
from providing enough lift to break tie-downs. I suspect that the
2-33 on a tail stand won't really need the same external "spoiler"
arrangement which seems to work for Alaskan Super Cubs because the
angle of attack just won't be there to generate the lift.

How to solve the problem of the broken tow hitch is something for
which I cannot suggest an answer, except to continue to be as
certain as possible of the condition of that particular assembly
with periodic inspections throughout the season; survey commercial
operators and others to see if there is a recommended interval for
rebuilding that part of the structure, based on number of cycles;
and, to make sure that when tied down the nose chain has no slack in
it. Chains can't cushion the jerking that gusty winds can inflict on
the structure as a rope can. This harsh treatment may break a
tiedown or tow hook under conditions where a tight chain would not.
I like chains for convenience and strength but they do have their
punishing downside when slack. Of course, no tiedown, whether rope
or chain, should have any slack in it, but rope at least gives a
little bit.

The 4' tail anchor pulling out of the ground presents an almost
unbelievable scenario, but the ground is still very wet and soft in
N. IL so I suppose all bets are off under those conditions. A
seven-hundred pound glider already airborne and on its way to new
surroundings will have some momentum.

We use tail stands on all our aircraft tied out on the field and we
have had no further problems. Perhaps we have yet to be tested in
quite the same way that we were on that day in 2003, but so far so
good. I'm glad to hear that your rambling rose did not come to rest
atop flesh and blood, instead of a tree.


Jack