What are the forces on a tied down glider?

Experts (?) in this area say that to remember something long term it should
be reviewed something like weekly for a month, then monthly, for a year,
and then yearly.

At 20:10 14 August 2008, Vaughn Simon wrote:

"Doug Hoffman" wrote in message
...
I envy your abilities. :-)

Thanks, but I don't think that I have any special abilities.

I will say this: The items that I tend to study at the last minute are

probably the things that I will NOT be able to reliably recite two weeks
after
the test. Passing a test is not proof that you will retain a
satisfactory

percentage of the material, it is only proof that you passed the test.

Vaughn

Andy wrote:


On Aug 13, 11:01=A0am, 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.

Seems like wing and tailfeather covers should help some. Maybe
a lot. The full covers I've seen (Jaxida) hang down a lot of
covering beneath the wings and horizontal stabs/elevators. To my
eye the covers might be far more effective than even open
spoilers in destroying lift.

--
Doug

** Posted from http://www.teranews.com **

Doug Hoffman wrote:

Seems like wing and tailfeather covers should help some. Maybe
a lot. The full covers I've seen (Jaxida) hang down a lot of
covering beneath the wings and horizontal stabs/elevators. To my
eye the covers might be far more effective than even open
spoilers in destroying lift.

My observation is the the wind puffs up the covers so they stand
completely off the top and bottom of the wing. In a strong wind, the
covers look like they are inflated to a high pressure, making the wing
look more like a sausage than anything else. My guess is this is a high
drag, low lift "airfoil", but I have no documentation for it.

It also provides protection from hail, which just bounces off the taut
wing covers and never gets near the wing skin.

--
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

"Eric Greenwell" wrote in message
news:x7Mok.925$xv.899@trnddc02...
My observation is the the wind puffs up the covers so they stand
completely off the top and bottom of the wing. In a strong wind, the
covers look like they are inflated to a high pressure, making the wing
look more like a sausage than anything else. My guess is this is a high
drag, low lift "airfoil", but I have no documentation for it.

--
Eric Greenwell - Washington State, USA

My observation is similar . . . except to me, the puffed up covers look like
the thick, high lift wing on a trainer.

I'd feel a lot better about covers in high winds if there were spanwise
fabric tubes sewn in to allow pipe foam insulation to be inserted for full
length spoilers.

bumper
zz
Minden
USA

On Aug 13, 7:55*pm, "bumper" wrote:
"Eric Greenwell" wrote in message

news:x7Mok.925$xv.899@trnddc02...

My observation is the the wind puffs up the covers so they stand
completely off the top and bottom of the wing. In a strong wind, the
covers look like they are inflated to a high pressure, making the wing
look more like a sausage than anything else. My guess is this is a high
drag, low lift "airfoil", but I have no documentation for it.

--
Eric Greenwell - Washington State, USA

My observation is similar . . . except to me, the puffed up covers look like
the thick, high lift wing on a trainer.

I'd feel a lot better about covers in high winds if there were spanwise
fabric tubes sewn in to allow pipe foam insulation *to be inserted for full
length spoilers.

bumper
zz
Minden
USA

The standard Jaxida covers look like this in the wind...

http://www.flickr.com/photos/darrylramm/517165653/
http://www.flickr.com/photos/darrylramm/517140648/

(maybe it was really faster than 20 knots in these photos).

Does Jaxida offer a sewn in place to insert a foam tube?

Darryl

Darryl Ramm wrote:
On Aug 13, 7:55 pm, "bumper" wrote:
"Eric Greenwell" wrote in message

news:x7Mok.925$xv.899@trnddc02...

My observation is the the wind puffs up the covers so they stand
completely off the top and bottom of the wing. In a strong wind, the
covers look like they are inflated to a high pressure, making the wing
look more like a sausage than anything else. My guess is this is a high
drag, low lift "airfoil", but I have no documentation for it.
--
Eric Greenwell - Washington State, USA
My observation is similar . . . except to me, the puffed up covers look like
the thick, high lift wing on a trainer.

I'd feel a lot better about covers in high winds if there were spanwise
fabric tubes sewn in to allow pipe foam insulation to be inserted for full
length spoilers.

bumper
zz
Minden
USA

The standard Jaxida covers look like this in the wind...

http://www.flickr.com/photos/darrylramm/517165653/
http://www.flickr.com/photos/darrylramm/517140648/

(maybe it was really faster than 20 knots in these photos).

Does Jaxida offer a sewn in place to insert a foam tube?

My covers are not Jaxidas, but are similar in design using a lighter
material (a type of Tyvek). They bulge more evenly on the top and bottom
than Darryl's Jaxida covers. Perhaps Darryl could slide one cover off
it's wing to determine if the other wing is lifting or not? It's not so
easy for me to do that because my covers attach to each other, not a
center section like the Jaxidas.

--
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

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!

Del Copeland


At 20:49 13 August 2008, Andy wrote:
On Aug 13, 11:01=A0am, 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

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.

--
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

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.

--
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

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.