High Winds Destroys a Glider

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

I assume disassembly and storage in a trailer is out of the question?

Lift spoiler might help, but it seems to me that wind direction is so
variable that it wouldn't be 100% effective (90 degree to fuselage
centerline comes to mind as it tries to weathercock into the
wind...might be able to pull out a tiedown anchor). No hangar available
that could accomodate a 2-33 and another plane at the same time (to
split costs)?


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


--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

Got any photos !

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

Get a sturdy tail Stand!!! This is the critical factor. If you do not
reduce the lift produced by the wing, your likelihood of keeping the
glider on the ground are very poor, no matter what else you do.
Getting the wing at (or below) a zero degree angle of attack (A.O.A.)
dramatically increases your odds of keeping the ship on the ground,
especially something as light and tall as a 2-33. In a 2-33, the
A.O.A. with tail on the ground is very close to max lift - definitely
NOT what you want. This was/is standard procedure at most of the
professionally run gliders ops in the US and is discussed at length in
the old Schweizer red "bible".

Deploy drag devices and place flaps full negative, if available.

4 ft screw-in anchors are not adequate. Effective tie-downs involve
a 4+ ft hole in the ground that is belled out at the bottom and then
filled with concrete with a 2 ft long (each leg) Omega-shaped piece
of rebar set in them. Screw-in anchors are notorious for failing in
many different modes (snap, pull out, bend,). Oshkosh sees this
happen yearly.

One can backup the ropes tiedowns with chain, though not my preferred
solution; it puts too much shock load on the glider for my tastes.

Tiedowns should include: tail, nosehook, and inboard and outboard
wings. Not not forget gust locks (tied on) for ailerons, rudder, and
elevator.


A "combat" solution is to park something large and heavy (very heavy)
upwind of glider. Large dump trucks are useful.


Some very windy/rowdy places such as Tehachapi, California City, and
some airports in the southern Appalachians and Colorado have had very
few losses to wind using these strategies. Of special note is
Tehachapi where they have had 3-6 2-33's tied down for more than 25
years with NO wind-related losses. Tehachapi only uses tow rope as
tiedown material and its breaking strength is only 1200 lbs. Clearly,
they are not putting large loads on the ropes!


Significantly, wind and rotor in excess of 80 mph have been recorded
there and such conditions occur on an annual basis. Perhaps there is
a reason there are 5000 wind turbines just downwind of the
airport???

Don't reinvent the wheel! Use these proven methods. Get the nose
down, spoilers out, put in some sturdy tiedowns, and sleep better at
night!

On Apr 4, 10:28 pm, "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


We lost one in a similar way 10 years ago. Ultimately rebuilt, but
painful.
Since then we do the following.
Nose has anchor about 3 ft in front of hook. 4 foot angled stake and
chain.
Mains use 2 stakes about 3 ft apart and independent tie down
ropes(rope has a little "give" unlike chain) to rings.
Tips have single tie down anchor point added by increasing size of
bolt holding tip wheel to 1/4 inch and putting bolt thru wing to
top.
Since doing this we have had 90 MPH in a hurricane and have not lost
one -yet!

Good Luck
UH

wrote in message
oups.com...

Don't reinvent the wheel! Use these proven methods. Get the nose
down, spoilers out, put in some sturdy tiedowns, and sleep better at
night!





When ordering covers, be sure to have them sew in lift spoiler pockets,
along the top of the wing, to accept foam pipe insulation or similar.

bumper

"Scott" wrote in message
.. .
I assume disassembly and storage in a trailer is out of the question?

...
"Glider trailers parked on the field were crushed from being tossed about
like dice."

Page 8, http://www.iac78.org/newsletter/NL%20Fall-Winter%2005%20Color.pdf

(The story is about acro airplanes and a storm at Faribault MN - not
gliders)

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

I thought that this would be an interesting reprint (below my
signature) of the last page (un-numbered) of the Schweizer 2-33 manual
which details how to tie down the ship. This page may have been added
to the manual as an addendum after some accidents. The only section
in the main part of the manual (pg 1-8) which deals with tie downs
simply states;

"The 2-33 should never be left unattended in strong winds or gusty
conditions. Tie downs are at each wing where main struts are attached
and at tail wheel bracket. Be sure ropes and stakes used for tying
down are adequate and in good condition."

We had all of these recommendations except for a tail stand. In our
case, raising the tail might have lowered the force on the nose hook,
maybe preventing the hook from failing, and maybe saving the glider.
A lot of maybe's.

- John

=================

Schweizer 2-33 Tie Down Requirements

Many more sailplanes are damaged on the ground by the wind than in
flying accidents. It is usually due to leaving the ship unsecured or
using inadequate tie downs.

In the normal, tail down, ground position, the wing has a high angle
of attack. A 2-22 or 2-33 (empty wgt. 500#), facing into the wind
will be subjected to life forces as shown:

Wind Lift Net Lift
30 mph 750 250#
40 mph 1,300 800#
50 mph 2,000 1,500#
60 mph 2,900 2,400#
70 mph 3.950 3,450#
80 mph 5,200 4,700#

Therefore, it is very important that adequate tie downs are provided.
The folloing procedures are recommended:

1) Sheltered Area: Tail down, ropes(*), at wings and tail (***).
2) Unsheltered Area: Facing in the prevailing wind. Rope at wings and
tail, and chain tie down to release hook.
3) Unsheltered - High Wind Hazard: Tail support on padded stand. Rope
to wing and two ropes to tail. Short chain (5/16" welded link), tie
down to tow hook.
4) Flightline Tie Down: Short chain tie down to tow hook (tail in
air). Water filled tie tube on end of one wing.

Note:

* Minimum size of recommend ropes - 5/16" nylon or ½" manila - renew
each season. (Knots can reduce rope strength 50%)
** Size ans stype of ground anchor will depend on soil composition and
type of sailplane. In light sandy soils, anchor arm or chain longer
and set deeper. A ground anchor should be able to withstand a
vertical pull of at least 2,000#. Should not be located directly
under tie downs.
*** Ruddlelock - recommended if control locks are not used. Ailerons
and elevator can be secured with seat belt around control stick.
**** Securing the spoilers or dive brakes open will decrease lifting
forces.

ContestID67 wrote:
I thought that this would be an interesting reprint (below my
signature) of the last page (un-numbered) of the Schweizer 2-33 manual
which details how to tie down the ship. This page may have been added
to the manual as an addendum after some accidents. The only section
in the main part of the manual (pg 1-8) which deals with tie downs
simply states;

"The 2-33 should never be left unattended in strong winds or gusty
conditions. Tie downs are at each wing where main struts are attached
and at tail wheel bracket. Be sure ropes and stakes used for tying
down are adequate and in good condition."

We had all of these recommendations except for a tail stand. In our
case, raising the tail might have lowered the force on the nose hook,
maybe preventing the hook from failing, and maybe saving the glider.
A lot of maybe's.



Each glider tie down area in Boulder, CO has 4' or so chain link fence
with vinyl slats to break the wind. It disturbs the wind enough to
prevent problems. The region gets 60-70 mph wind every year with 80 mph
wind storms every few years. The power side of the airport had a plane
break loose a year or two ago, but the gliders stay put.


Shawn