Winch Launch Extreme 5200 ft

That sounds a bit frightening - 3500 fpm! What are the stresses on the
glider to get that kind of climb rate? How far away is disaster if the
pilot twitches a bit on the controls or hits some wind shear or a thermal?

Hmmm, if they are using weak links, I don't see a problem.

Stress (=force) is related to acceleration, not to speed. You can go
straight up at 1000000 fpm with the same force as at 10 fpm. Just takes
you a bit longer to reach the speed.

-Gerhard
--
Gerhard Wesp / Holderenweg 2 / CH-8134 Adliswil
+41 (0)76 505 1149 (mobile) / +41 (0)44 668 1878 (office)
+41 (0)44 668 1818 (fax)
http://gwesp.tx0.org/

Gerhard Wesp wrote:
That sounds a bit frightening - 3500 fpm! What are the stresses on the
glider to get that kind of climb rate? How far away is disaster if the
pilot twitches a bit on the controls or hits some wind shear or a thermal?

Hmmm, if they are using weak links, I don't see a problem.

Stress (=force) is related to acceleration, not to speed. You can go
straight up at 1000000 fpm with the same force as at 10 fpm. Just takes
you a bit longer to reach the speed.

Of course, the net force on the glider is zero, otherwise it would
accelerate, but the individual forces are much greater and vary during
the launch. We've all seen the wings curve up and stay that way as the
pilot rotates into the climb on a winch launch, indicating much more
lift is being generated to counteract the pull of the cable.

Surely the cable tension must be greater to provide a 3500 fpm launch
instead of a 1000 fpm launch? I'm curious about the amount of tension
needed to provide a 1000 pound glider that 3500 fpm climb.

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

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

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

Eric, perhaps you know George Moore who lives in your area. He has written
an series of papers on the forces involved in winch launch. He would be
able to provide the exact answers.

Bill Daniels

"Eric Greenwell" wrote in message
news:GBu1h.4529$WB4.3254@trndny04...
Gerhard Wesp wrote:
That sounds a bit frightening - 3500 fpm! What are the stresses on the
glider to get that kind of climb rate? How far away is disaster if the
pilot twitches a bit on the controls or hits some wind shear or a
thermal?

Hmmm, if they are using weak links, I don't see a problem.

Stress (=force) is related to acceleration, not to speed. You can go
straight up at 1000000 fpm with the same force as at 10 fpm. Just takes
you a bit longer to reach the speed.

Of course, the net force on the glider is zero, otherwise it would
accelerate, but the individual forces are much greater and vary during the
launch. We've all seen the wings curve up and stay that way as the pilot
rotates into the climb on a winch launch, indicating much more lift is
being generated to counteract the pull of the cable.

Surely the cable tension must be greater to provide a 3500 fpm launch
instead of a 1000 fpm launch? I'm curious about the amount of tension
needed to provide a 1000 pound glider that 3500 fpm climb.

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

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

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

Eric Greenwell wrote:
Surely the cable tension must be greater to provide a 3500 fpm launch
instead of a 1000 fpm launch? I'm curious about the amount of tension

No, I don't think so. And I think the climb rate is not related to the
cable length, IOW, you get the same 3500 fpm with, say, a 3000ft cable.

-Gerhard
--
Gerhard Wesp / Holderenweg 2 / CH-8134 Adliswil
+41 (0)76 505 1149 (mobile) / +41 (0)44 668 1878 (office)
+41 (0)44 668 1818 (fax)
http://gwesp.tx0.org/

Hi Eric,

On Mon, 30 Oct 2006 22:00:06 GMT, Eric Greenwell
wrote:


Surely the cable tension must be greater to provide a 3500 fpm launch
instead of a 1000 fpm launch? I'm curious about the amount of tension
needed to provide a 1000 pound glider that 3500 fpm climb.

The strongest available weak link is about 2.000 lbs which is
obviously the maximum possible tension on the cable.
A single seater's maximum allowed weak link is usually in the 1.200
lbs range.

BTW: The standard climb rate in a winch launch is usually about 3.000
ft/min, independent of glider type.



Bye
Andreas

Eric,

the forces are all the same.

there is no difference in forces strengths launching to 1000ft or to 5000ft
the applying forces just last longer thats all.

I did hundreds of take offs on the winch.
I wish we would have good winches in Australia.
Here we only have historical rubbish standing around.

Chris



"Eric Greenwell" wrote in message
news:GBu1h.4529$WB4.3254@trndny04...
Gerhard Wesp wrote:
That sounds a bit frightening - 3500 fpm! What are the stresses on the
glider to get that kind of climb rate? How far away is disaster if the
pilot twitches a bit on the controls or hits some wind shear or a
thermal?

Hmmm, if they are using weak links, I don't see a problem.

Stress (=force) is related to acceleration, not to speed. You can go
straight up at 1000000 fpm with the same force as at 10 fpm. Just takes
you a bit longer to reach the speed.

Of course, the net force on the glider is zero, otherwise it would
accelerate, but the individual forces are much greater and vary during
the launch. We've all seen the wings curve up and stay that way as the
pilot rotates into the climb on a winch launch, indicating much more
lift is being generated to counteract the pull of the cable.

Surely the cable tension must be greater to provide a 3500 fpm launch
instead of a 1000 fpm launch? I'm curious about the amount of tension
needed to provide a 1000 pound glider that 3500 fpm climb.

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

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

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

"Eric Greenwell" wrote in message
news:AFg1h.4183$WB4.3314@trndny04...
Bill Daniels wrote:
Good show!

Dyneema/Spectra winch cable allows for launches to approximately 50% of
the original cable length. Calculations show that there is really no
upper limit to the amount of Dyneema that can be used.

90 seconds to 5200 feet AGL on a winch beats the hell out of 20 minutes
on aero tow. That's especially true when the typical cost is $10 for the
launch.

That sounds a bit frightening - 3500 fpm! What are the stresses on the
glider to get that kind of climb rate? How far away is disaster if the
pilot twitches a bit on the controls or hits some wind shear or a thermal?

--
Eric Greenwell - Washington State, USA

There is a lot about modern winches and operating proceedures that will seem
counter-intuitive to US pilots trained in aero tow.so it's easy to
mis-interpret the danger signs. You can be assured that the Europeans are
at least as concerned about safety as we are and that they have carefully
worked out how to do this safely.

The glider manufacturer has carefully specified a weak link accurate to plus
or minus 5% that is the ultimate protection for the glider airframe. In
addition, modern winches are constant tension with computer controlls that
prevents the winch from applying enough force to break the weak link. The
tension is set at about 70% of the weak link strength for the main part of
the climb.

For the pilot it's just like a takeoff in a powerful airplane. Just pitch
up for desired climb airspeed. If the airspeed is high, just raise the nose
a bit more and the airspeed will decrease. If it's a bit low, lower the
nose a bit and the airspeed will increase.

If the glider hits a thermal or gust, the winch senses increasing tension
and cuts power just enough to maintain the selected tension. This pretty
much guarantees a perfect launch every time.

Make no mistake, this is a LOT of fun.

Bill Daniels

Bill Daniels wrote:
"For the pilot it's just like a takeoff in a powerful airplane. Just
pitch
up for desired climb airspeed. If the airspeed is high, just raise the
nose
a bit more and the airspeed will decrease. If it's a bit low, lower
the
nose a bit and the airspeed will increase. "


With a traditional winch of adequate power, pitching up increases
airspeed. How do these modern winches result in the reverse effect?
Does the reversal only happen once the line tension limit has been
reached?

Andy

"Andy" wrote in message
oups.com...

Bill Daniels wrote:
"For the pilot it's just like a takeoff in a powerful airplane. Just
pitch
up for desired climb airspeed. If the airspeed is high, just raise the
nose
a bit more and the airspeed will decrease. If it's a bit low, lower
the
nose a bit and the airspeed will increase. "


With a traditional winch of adequate power, pitching up increases
airspeed. How do these modern winches result in the reverse effect?
Does the reversal only happen once the line tension limit has been
reached?

Andy


A "traditional winch" doesn't control tension but tries (and often fails) to
control cable speed which doesn't relate in any logical way to glider
airspeed anyway. If the tension is controlled instead, the speed will
decrease as the pilot pitches up since this adds load to the cable which the
winch senses and slightly reduces power. This happens almost instantly so
the pilot sees the airspeed behave logically as it would in a powerful
airplane. This puts airspeed control completely in the hands of the pilot
where it belongs.

Think of it like a jet with fixed thrust. Nose up increases load on the
engine so the aircraft slows - nose down decreases load so the aircraft
accelerates.

Bill Daniels

Andy wrote:

With a traditional winch of adequate power,

There's an oxymoron. Traditional winches (new and old) pretty much
define themselves by their inadequate power.

pitching up increases
airspeed. How do these modern winches result in the reverse effect?
Does the reversal only happen once the line tension limit has been
reached?

I must have only flown off traditional winches. My experience is the
same as Bill Daniels. What over-powered monster do you fly off?

GC

Andy