Using Plasma Rope For Winch Tows

Mark Busse wrote:
...
We have not had any launches with strong headwinds in fact there has
been little or no wind at all. The steel launches we made were
700'-900' then the Plasma were 1000'-1200' I wish we could pull out
1500' more rope maybe someday.
...

I find these heights abnormally low. I expect about 40% of cable length,
this is what we used to reach in my club with steel cable and no wind, now
the engine does no more provide its full poweer, so the height is sligtly
reduced (350m instead of 400m with 1000m cable).

On Thu, 31 Jul 2003 09:11:43 +0000, Robert Ehrlich
wrote:

Mark Busse wrote:
...
We have not had any launches with strong headwinds in fact there has
been little or no wind at all. The steel launches we made were
700'-900' then the Plasma were 1000'-1200' I wish we could pull out
1500' more rope maybe someday.
...

I find these heights abnormally low. I expect about 40% of cable length,
this is what we used to reach in my club with steel cable and no wind, now
the engine does no more provide its full poweer, so the height is sligtly
reduced (350m instead of 400m with 1000m cable).

Indeed. We are also testing a PE-cable instead of steel cable, with a
cable length of about 3.300 ft, and height difference between seteel
and the light PE cable is very hard to tell - definitely not an as
huge difference as Mark writes.
Bye
Andreas

...
We have not had any launches with strong headwinds in fact there has
been little or no wind at all. The steel launches we made were
700'-900' then the Plasma were 1000'-1200' I wish we could pull out
1500' more rope maybe someday.
...

I find these heights abnormally low. I expect about 40% of cable length,
this is what we used to reach in my club with steel cable and no wind, now
the engine does no more provide its full poweer, so the height is sligtly
reduced (350m instead of 400m with 1000m cable).

My guess is that you are out side of north america. European winch
technology is far ahead of anything we do in the states. Although we do seem
to be experimenting more with the type of cable material a little more. The
fact that we are even talking about it in the states is a huge change from
just ten years ago.

We have been auto towing (off and on) for several years with Dacron rope and
are quite happy with it.

wy

"wy" wrote in message
et...

...
We have not had any launches with strong headwinds in fact there has
been little or no wind at all. The steel launches we made were
700'-900' then the Plasma were 1000'-1200' I wish we could pull out
1500' more rope maybe someday.
...

I find these heights abnormally low. I expect about 40% of cable length,
this is what we used to reach in my club with steel cable and no wind,
now
the engine does no more provide its full poweer, so the height is
sligtly
reduced (350m instead of 400m with 1000m cable).

My guess is that you are out side of north america. European winch
technology is far ahead of anything we do in the states. Although we do
seem
to be experimenting more with the type of cable material a little more.
The
fact that we are even talking about it in the states is a huge change from
just ten years ago.

We have been auto towing (off and on) for several years with Dacron rope
and
are quite happy with it.

wy

I suspect release heights will get higher as pilots get more comfortable
with the new winch. I find US pilots are extremely reluctant to enter the
full climb attitude until 200 - 400 feet AGL which significantly reduces the
height achieved.

This conservatism is appropriate when a group is learning new procedures but
it does limit launch heights.

Bill Daniels

Bill Daniels wrote:

"wy" wrote in message
et...

...
We have not had any launches with strong headwinds in fact there has
been little or no wind at all. The steel launches we made were
700'-900' then the Plasma were 1000'-1200' I wish we could pull out
1500' more rope maybe someday.
...

I find these heights abnormally low. I expect about 40% of cable length,
this is what we used to reach in my club with steel cable and no wind,
now
the engine does no more provide its full poweer, so the height is
sligtly
reduced (350m instead of 400m with 1000m cable).

My guess is that you are out side of north america. European winch
technology is far ahead of anything we do in the states. Although we do
seem
to be experimenting more with the type of cable material a little more.
The
fact that we are even talking about it in the states is a huge change from
just ten years ago.

We have been auto towing (off and on) for several years with Dacron rope
and
are quite happy with it.

wy

I suspect release heights will get higher as pilots get more comfortable
with the new winch. I find US pilots are extremely reluctant to enter the
full climb attitude until 200 - 400 feet AGL which significantly reduces the
height achieved.

This conservatism is appropriate when a group is learning new procedures but
it does limit launch heights.

Bill Daniels


I think the time at which you enter the full climb attitude should not
be determined by your altitude but rather by your speed. The main reason
you should not go to quickly to a high nose up attitude is the risk of
stall in case of cable break. In this case, a push down to 0g causes a
ballistic recovery path with a modern glider having a near zero drag
(compared to other involved forces), i.e. the glider flies an arc of a
parabola with a nearly constant horizontal component of speed. This means
that if you start the recovery at 100km/h and 45 degrees nose up, the
horizontal component is 100*sqrt(2) ~ 70km/h and you will reach the top
of the parabola with a speed of 70 km/h, i.e. above stall speed On the
other hand, even with a lot of altitude margin, if you have a cable break
with a high nose up attitude and you don't immediately push to 0g, you
are probably going to stall. If you do it starting from a to low speed, you
will need to continue at 0g past the top of the parabola in order to recover
a speed above the stall speed, and diving toward the ground at low altitude
is a thing any pilot would be reluctant to do.


As "wy" guessed, I am in Europe, more precisely in France. Winches are very
common in Germany and some other european countries, but in France, up to
a not very long time ago, the situation was very similar to that in the US. At the
time when a lot of gliders were built in France, a lot of them had no CG hook.
My knowledge on the subject is only from hearing what older pilots are saying,
since I started only in 1995, but as far as I understand, winch launching in
these years (50 to 80) was perceived as an old fashionned launching method
superceeded by aero tow. The availability of a lot of Rallye's dropped by the
army as tow plane helped that. Now the raising cost of maintenance of these
old planes, the complaints of neighbours of airfields against their noise
and the vanishing of the financial helps from the state are causing a renewed
interest for winching. But a lot of old mentalities remains. There are several
big clubs in the vicinity of Paris (more than 100 members), but my own one is
the only one owning and using a winch. And despite the efforts of the fans
of winch (I am one of them) the winch is highly underused (lowest year 2001 with
only 3 launches).

"Robert Ehrlich" wrote in message
...
Snip-----

I think the time at which you enter the full climb attitude should not
be determined by your altitude but rather by your speed. The main reason
you should not go to quickly to a high nose up attitude is the risk of
stall in case of cable break. In this case, a push down to 0g causes a
ballistic recovery path with a modern glider having a near zero drag
(compared to other involved forces), i.e. the glider flies an arc of a
parabola with a nearly constant horizontal component of speed. This means
that if you start the recovery at 100km/h and 45 degrees nose up, the
horizontal component is 100*sqrt(2) ~ 70km/h and you will reach the top
of the parabola with a speed of 70 km/h, i.e. above stall speed On the
other hand, even with a lot of altitude margin, if you have a cable break
with a high nose up attitude and you don't immediately push to 0g, you
are probably going to stall. If you do it starting from a to low speed,
you
will need to continue at 0g past the top of the parabola in order to
recover
a speed above the stall speed, and diving toward the ground at low
altitude
is a thing any pilot would be reluctant to do.

Absolutely true. Airspeed is the key.

As "wy" guessed, I am in Europe, more precisely in France. Winches are
very
common in Germany and some other european countries, but in France, up to
a not very long time ago, the situation was very similar to that in the
US. At the
time when a lot of gliders were built in France, a lot of them had no CG
hook.
My knowledge on the subject is only from hearing what older pilots are
saying,
since I started only in 1995, but as far as I understand, winch launching
in
these years (50 to 80) was perceived as an old fashionned launching method
superceeded by aero tow. The availability of a lot of Rallye's dropped by
the
army as tow plane helped that. Now the raising cost of maintenance of
these
old planes, the complaints of neighbours of airfields against their noise
and the vanishing of the financial helps from the state are causing a
renewed
interest for winching. But a lot of old mentalities remains. There are
several
big clubs in the vicinity of Paris (more than 100 members), but my own one
is
the only one owning and using a winch. And despite the efforts of the fans
of winch (I am one of them) the winch is highly underused (lowest year
2001 with
only 3 launches).

I wouldn't have guessed. Sounds just like the USA.

Bill Daniels

I concur - it is about speed (and to some extent altitude), not climb
angle.

The secret is in the winch driver, and the pilot knowing what they are
doing and ensuring a smooth and rapid acceleration appropriate to the
specific aircraft being launched.

We try to have the winch at "full throttle" (which varies depending on
what you are launching) in a smooth 4 second roll. That way the glider
is not snatched, but acceleration is rapid, minimising chances of wing
drops and other excitement.

If your aircraft is set up and trimmed properly you find that the whole
plot works fairly automatically.

Once the tail lifts you are at a speed where you have elevator authority
.. If you move the stick to the neutral position most aircraft lift off
as their speed increases beyond the speed needed to support the weight
(stall) Continuing the slow pull up with progressively more back
pressure on the stick initiate a safe climb, with the aircraft still
accelerating strongly.
By the time you are 100m down the runway and 20m up you have reached
close to Vw, at which point it is safe to rotate into the steep climb. A
smooth but relatively quick rotation will have you safely launching to
maximum height. Because you have enough speed to recover from a cable
break or winch failure, altitude is not particularly important unless
you are very low. If you fly a smooth pull-up into the climb you will
not be at your steepest angle below 30-40m (100+feet)

Some gliders have a tendency to over-rotate or kite, but that is
restricted to older designs as far as I know. In these it is unwise to
pull up too hard under any circumstances.

Interestingly enough if your winch has sufficient torque you will find
that steep climbs actually increase your speed, because you are
describing a larger arc. If your winch does not have sufficient power
reserves you can slow things down by pulling too hard, which is
extremely dangerous.

On Thu, 7 Aug 2003 07:52:53 -0600, "Bill Daniels"
wrote:



The boundary on the high side of acceleration is the tendency of some
gliders with high CG's, low hooks and limited down elevator authority to
pitch-up uncontrollably when a threshold acceleration is exceeded.

Please tell me the names of these gliders. I have NOT heard of a
single one yet that showed this behaviour. Not one.


Some winch operations deliberately accelerate the glider to a point above
the Vw airspeed limit at the start of the launch. A short excursion above
Vw at the start has no adverse effect on wing loads. Of course, the
airspeed must fall below Vw as the glider enters the full climb attitude.

I wonder whyt use this should have. If the pilot decides to pull back
he will enter a highspeed stall as quickly as if he was slower. And as
long as he's in the 55-60 mph range his speed will always be
completely sufficient to recover if he has a rope break at low
heights.
Having high speed and a steep climb angle is the perfect trigger for a
rope (or weak link) break, therefore it's not a good idea to be too
fast in my opinion.


This is a situation that cries out for precise winch instrumentation and
automation. This is why a glider to winch data link is so promising. I
envision a device in the glider that allows the pilot to set the desired
acceleration and airspeed before the launch - in effect setting the launch
parameters of the winch to fit a particular glider/pilot combination.

No idea why you get the idea why such a thing ought to be necessary -
but in my club (as well as in all other clubs I know, and these are
many) the winch drivers are perfectly capable of doing a safe and
efficient winch launch (none of them being a proffessional winch
driver, but having winch duty only half a dozen of days per year).
They get told what glider they are going to tow, and adjust the power
accordingly.


It is also a case where large power reserves are needed. This is the reason
the new generation of high power winches are so popular.

The advantages of a high power winch?
The ability to reach sufficient heights in a double-seater even with a
10 kts tailwind.

Bye
Andreas

"Andreas Maurer" wrote in message
...
On Thu, 7 Aug 2003 07:52:53 -0600, "Bill Daniels"
wrote:



The boundary on the high side of acceleration is the tendency of some
gliders with high CG's, low hooks and limited down elevator authority to
pitch-up uncontrollably when a threshold acceleration is exceeded.

Please tell me the names of these gliders. I have NOT heard of a
single one yet that showed this behaviour. Not one.

In my experience the K8 pitch-up was near uncontrollable when winching. If
you had winched it previously you learnt the theoretically correct
procedure, which was:

a. Stick back to get the nose skid up.

b. Stick central to run on the main wheel; and then

c. (*Immediately the main wheel left the ground) Knuckles hard into the
instrument panel and wait for the pitch to become controllable.

On anything but the softest of take-ups (a) and (b) disappeared, as the
glider was flying before you could react, so the *real* procedure was stick
full forwards as soon as the glider moved.

Once full pitch control was re-established the rest of the launch was fine,
but the first two seconds were only semi-controlled, and that only if you
knew what to expect. I never saw a first flight in the K8 where the pilot
reacted in time to prevent an uncontrolled pitch-up as soon as the main
wheel left the ground. And our winch was not any kind of high-powered
monster.

All the glass gliders I've seen winching behaved well, but the K8 was ...
interesting.

I learnt flying gliders on a Ka7/Ka8 combo (only winching), later
instructing, and I never came across a behaviour of a Ka8 as you describe
it. Completely simple and controlable.

--
Bert Willing

ASW20 "TW"


"Chris Reed" a écrit dans le message de
...
"Andreas Maurer" wrote in message
...
On Thu, 7 Aug 2003 07:52:53 -0600, "Bill Daniels"
wrote:



The boundary on the high side of acceleration is the tendency of some
gliders with high CG's, low hooks and limited down elevator authority
to
pitch-up uncontrollably when a threshold acceleration is exceeded.

Please tell me the names of these gliders. I have NOT heard of a
single one yet that showed this behaviour. Not one.

In my experience the K8 pitch-up was near uncontrollable when winching. If
you had winched it previously you learnt the theoretically correct
procedure, which was:

a. Stick back to get the nose skid up.

b. Stick central to run on the main wheel; and then

c. (*Immediately the main wheel left the ground) Knuckles hard into the
instrument panel and wait for the pitch to become controllable.

On anything but the softest of take-ups (a) and (b) disappeared, as the
glider was flying before you could react, so the *real* procedure was
stick
full forwards as soon as the glider moved.

Once full pitch control was re-established the rest of the launch was
fine,
but the first two seconds were only semi-controlled, and that only if you
knew what to expect. I never saw a first flight in the K8 where the pilot
reacted in time to prevent an uncontrolled pitch-up as soon as the main
wheel left the ground. And our winch was not any kind of high-powered
monster.

All the glass gliders I've seen winching behaved well, but the K8 was ...
interesting.