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
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

One sample has been in evidence for years on the back page of the SGS
2-33 POH. --JHC

Just some facts, Eric. At Stead 2 gliders that were tied down at wing
tips and tail with 3/8" poly rope, broke all 3 ropes and performed a
near perfect half loop landing upside down after experiencing a
reported 100 knot wind (ships were tied down facing the wind).

At Minden 2 ships did much the same maneuver after experiencing about
the same wind (Winter storm frontal passage).

Raising the tail to get a negative angle of attack and locking the
spoilers open can go a long way in preventing the above OR, put it in
the box!
JJ

On Aug 13, 11:01*am, Eric Greenwell wrote:
I see gliders tied down in a bewildering variety of ways, all apparently
"adequate" in the owner's mind.

Perhaps the real question is how well does it have to be tied down to
satisfy the insurance company that you were not negligent.

Another significant factor is what is it tied too. We seem to take
for granted that tie down wires etc that we find at the airport are
secure, but I've seen a whole line of cable and the anchors pulled out
of the ground. I used to trust the rings on the ramp at Hobbs until
one year I cleared all the dirt out of the hole and found the rings
corroded almost all the way through. Last time I flew there I dug
around until I found a good one and tied the CG hook to it.

Others would say why worry - put it in the box!

Andy

On Aug 13, 2:49*pm, Andy wrote:
Others would say why worry - put it in the box!

Kinda hard to do that if:

1) You've landed away from home and are waiting for the box to arrive

2) Touring in a self-launcher without a chase crew

JJ Sinclair wrote:
Just some facts, Eric. At Stead 2 gliders that were tied down at wing
tips and tail with 3/8" poly rope, broke all 3 ropes and performed a
near perfect half loop landing upside down after experiencing a
reported 100 knot wind (ships were tied down facing the wind).

At Minden 2 ships did much the same maneuver after experiencing about
the same wind (Winter storm frontal passage).

Raising the tail to get a negative angle of attack and locking the
spoilers open can go a long way in preventing the above OR, put it in
the box!

Does anyone know the force required to break those ropes; for example,
were the ropes tested afterwards for breaking strength?

Was there any analysis of the forces on the gliders? A 100 knots might
destroy a glider, even if the ropes held. That happened to our club
Blanik years ago in winds of about 70 mph.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Aug 13, 1:58*pm, 5Z wrote:
On Aug 13, 2:49*pm, Andy wrote:

Others would say why worry - put it in the box!

Kinda hard to do that if:

1) *You've landed away from home and are waiting for the box to arrive

2) *Touring in a self-launcher without a chase crew

Williams Soaring is selling JJ's little tie-down kit that can be
carried in the ship.
JJ

"John H. Campbell" wrote in message
...
One sample has been in evidence for years on the back page of the SGS 2-33
POH. --JHC

Yes, and some would say unfortunately, it works. Just look at the
improbable population of 2-33's still in existance.

Bill D

There's a tiedown technique I developed 40 years ago when I decided that
steel stakes were too heavy and often didn't work in soft ground.

I bought some stout 10 gallon nylon bags with 1/2" nylon rope closures and a
lightweight folding shovel "trenching tool" from a military surplus store.
Three bags and one shovel were much lighter and took less space in the
glider than the steel screw-in stakes they replaced. The idea was to dig
holes and put the dirt in the bags and push the filled bags into the holes,
then tie the glider to the nylon ropes.

After using them, I tried to pull the bags out of the ground with a truck
but gave up and left the bags in the ground when the truck almost got stuck.
Even if the glider was able to pull a bag out of the ground, the
considerable weight of the dirt filled bag would still hold the glider. On
the other hand, steel stakes pulled out easily.

I've just heard that these bags are still available through military
sources.


"5Z" wrote in message
...
On Aug 13, 2:49 pm, Andy wrote:
Others would say why worry - put it in the box!

Kinda hard to do that if:

1) You've landed away from home and are waiting for the box to arrive

2) Touring in a self-launcher without a chase crew

On Aug 13, 2:01*pm, Eric Greenwell wrote:
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
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes"http://tinyurl.com/y739x4
* * * New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org

If at all possible, add a nose tie down. This limits the angle of
attack available and can be a big safety margin adder.
Good rule of thumb is at twice stall speed, wing is generating 4 times
gross weight in lift.
For 2-33's, we use 2 tiedowns on each main, a tiedown on the tips, and
a nose tiedown. Smaller ships use tips and nose.
We had a blow away due to a failed chain in 80 mph winds about 15 yr
ago. Once you have one, you realize extra tiedowns are cheap.
Heinz W had his ASH-25 off the ground in gust front and was saved by
nose tiedown.
UH