What are the forces on a tied down glider?

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