Airspeed control during ground launch?

At 15:12 02 April 2007, Andreas Maurer wrote:
Hi Bill,

On Fri, 30 Mar 2007 09:49:23 -0600, 'Bill Daniels'
wrote:

The winch should be constructed such that it is not
be possible for the
airspeed to increase as a result of raising the glider's
nose. Otherwise,
the winch should be regarded as dangerous.

Is it such a problem to teach the pilot to pull the
release if his
airspeed exceeds the desired prameters?

That is exactly what we are taught to do, but making
something as counter-intuitive as 'raise nose go faster'
does strike me as dangerous in the extreme - a huge
amount of the the instruction from 1st flight is based
around 'nose down go faster, nose up go slower'. Would
you like a situation where right stick produced left
bank? I doubt it.

"Andreas Maurer" wrote in message
...
Hi Bill,

On Fri, 30 Mar 2007 09:49:23 -0600, "Bill Daniels"
bildan@comcast-dot-net wrote:

The winch should be constructed such that it is not be possible for the
airspeed to increase as a result of raising the glider's nose. Otherwise,
the winch should be regarded as dangerous.

Is it such a problem to teach the pilot to pull the release if his
airspeed exceeds the desired prameters?



Bye
Andreas


Overspeeds shouldn't be a safety problem for a well trained pilot but if it
happens frequently, it will reduce confidence in the winch/driver. For not
quite so well trained pilots, it may become a safety issue. Pilot
confidence in the system is strongly related to the consistency of the
launches. If pilots lose confidence in the winch launch system, they'll go
elsewhere.

The advantages of automatic tension control are so large that there's every
reason to adopt it. Since the tension can't exceed the breaking strength of
the weak link and certainly not the cable, these things become extremely
rare. Automatic tension controlled launches are extremely consistent
regardless of external variables - or winch driver skill.

A collateral problem related to adoption of lightweight 'plastic' winch rope
is that the winch driver can no longer see the rope sag. With heavy steel
cable, winch drivers used cable sag as a gauge of tension. And, absent
airspeed telemetry, the winch driver has no information about the gliders
airspeed. This absence of feedback leads to inconsistent launches.

To deal with lack of feedback and the possibility of overspeeds, winch
drivers just reduce power to increase margins which results in lower
launches. Highly accurate automatic tension control allows the power to be
increased while maintaining launch consistency. Higher power means higher
launches.

Bill Daniels

On Mon, 2 Apr 2007 10:01:07 -0600, "Bill Daniels"
bildan@comcast-dot-net wrote:


Pilot
confidence in the system is strongly related to the consistency of the
launches. If pilots lose confidence in the winch launch system, they'll go
elsewhere.

.... or choose to stick to the familiar aerotow...

Might this be one cause why winch launching is used that seldom in the
US?

The advantages of automatic tension control are so large that there's every
reason to adopt it.

Hmmm... as usual, I beg to differ.
Here in Germany there are hundreds of winches in use with power
ranging from 150 to 400 hp, extremely few of them equipped with
tension control (afaik only the few electric winches), yet the winch
launch works extremely well with very few safety issues.

The major cause for the wide-spread use of winches in Germany is
simplicity: By using standard truck parts such as engine and rear axle
it was (and is) easily possible to build a reliable winch for moderate
costs. Virtually any winch in Germany is homebuilt.

I think adding complex parts (such as automatic gearboxes and tension
control) raises the barrier to build an own winch significantly
(complexity, reliability, engineering effort, cost) while the
efficiency gain is negligible.

I think in order to promote winch launching in the US it might help to
heep the design as simple as possible.



A collateral problem related to adoption of lightweight 'plastic' winch rope
is that the winch driver can no longer see the rope sag. With heavy steel
cable, winch drivers used cable sag as a gauge of tension. And, absent
airspeed telemetry, the winch driver has no information about the gliders
airspeed. This absence of feedback leads to inconsistent launches.

Frankly spoken, this is contrary to my own experiences on a vast
number of winches.
A properly designed 280 hp Diesel winch doesn't need any sort of
gearbox and tension control, yet can easlily and safely launch any
glider from Grunau Baby to ASH-25E to satisfying altitudes - even with
an inexperienced winch driver, and even with plastic rope.
Not even a radio communication between pilot and winch is necessary.




Bye
Andreas

On 2 Apr 2007 15:31:32 GMT, Sally W
wrote:


That is exactly what we are taught to do, but making
something as counter-intuitive as 'raise nose go faster'
does strike me as dangerous in the extreme - a huge
amount of the the instruction from 1st flight is based
around 'nose down go faster, nose up go slower'.

I still wonder how such a rule cold be created at all.

Where I fly this rule is regarded as an urban legend and student
pilots are told accordingly to lower the nose if they get too slow.



Bye
Andreas

"Andreas Maurer" wrote in message
...
On Mon, 2 Apr 2007 10:01:07 -0600, "Bill Daniels"
bildan@comcast-dot-net wrote:


Pilot
confidence in the system is strongly related to the consistency of the
launches. If pilots lose confidence in the winch launch system, they'll go
elsewhere.

... or choose to stick to the familiar aerotow...

Might this be one cause why winch launching is used that seldom in the
US?

Andeas, you are right. This is a big reason.



The advantages of automatic tension control are so large that there's
every
reason to adopt it.

Hmmm... as usual, I beg to differ.
Here in Germany there are hundreds of winches in use with power
ranging from 150 to 400 hp, extremely few of them equipped with
tension control (afaik only the few electric winches), yet the winch
launch works extremely well with very few safety issues.

Actually, if you think about it, the diesel winch with a Vioth Turbokuppling
is very close to a tension controlled winch. Diesels have a very flat
torque curve and torque increases linearly with throttle. The Voith
coupling just passes that torque to the drum at a 1:1 ratio. If the winch
driver makes a reasonable guess as to throttle setting based on the glider
to be launched and the wind, the result will be pretty good.

Even in Germany, however, it's likely that the average tension will be 50%
to 70% of the weak link breaking load. Increasing this to 70% to 90% will
significantly increase release heights. 80% - 90% would be even better but
that will likely be more precision than the average human winch driver can
manage. Automated tension control systems can shave it as close as you
like.


The major cause for the wide-spread use of winches in Germany is
simplicity: By using standard truck parts such as engine and rear axle
it was (and is) easily possible to build a reliable winch for moderate
costs. Virtually any winch in Germany is homebuilt.

I think adding complex parts (such as automatic gearboxes and tension
control) raises the barrier to build an own winch significantly
(complexity, reliability, engineering effort, cost) while the
efficiency gain is negligible.

I think in order to promote winch launching in the US it might help to
heep the design as simple as possible.


In the US for the last 50 years or so, 'simple' has meant a V8 engine and
automatic transmission from a wrecked car. The engine will not produce
anything like a flat torque curve and transmission will run wild shifting
whenever it pleases. Combine this with gliders without CG hooks and the
results are very inconsistent leading to absurd 'rules' like "raise nose to
increase speed".


A collateral problem related to adoption of lightweight 'plastic' winch
rope
is that the winch driver can no longer see the rope sag. With heavy steel
cable, winch drivers used cable sag as a gauge of tension. And, absent
airspeed telemetry, the winch driver has no information about the gliders
airspeed. This absence of feedback leads to inconsistent launches.

Frankly spoken, this is contrary to my own experiences on a vast
number of winches.
A properly designed 280 hp Diesel winch doesn't need any sort of
gearbox and tension control, yet can easlily and safely launch any
glider from Grunau Baby to ASH-25E to satisfying altitudes - even with
an inexperienced winch driver, and even with plastic rope.
Not even a radio communication between pilot and winch is necessary.


I suspect that the average German club member has a far better idea of what
a good launch feels like and how one would drive a winch to obtain that
launch than his US counterpart. In the US, a little intellegence built
into the winch will be a big help to a fledgling winch operation.

This is even more so when it's important to achieve the highest launch
possible to compete with aero tow. Automating cable tension control allows
higher tensions to be used with safety and thus higher launches.

Bill Daniels

On Mon, 2 Apr 2007 13:29:20 -0600, "Bill Daniels"
bildan@comcast-dot-net wrote:

Actually, if you think about it, the diesel winch with a Vioth Turbokuppling
is very close to a tension controlled winch. Diesels have a very flat
torque curve and torque increases linearly with throttle. The Voith
coupling just passes that torque to the drum at a 1:1 ratio. If the winch
driver makes a reasonable guess as to throttle setting based on the glider
to be launched and the wind, the result will be pretty good.

Forget all that high-tech stuff - much too complex for an average
gliding club. Hard to design, hard to build, hard to maintain, hard to
debug, hard to repair.

Here in good ole' Europe usually a standard truck clutch is used (with
a big engine this clutch is either actuated by hydraulics or
pneumatics) to connect the engine to a standard truck rear axle.
Initial acceleration is made by moving the throttle smoothly forward
until a certain RPM is reached which depends upon glider type wind.
During the launche the throttle is slowly brought back to keep the
gliders' speed halfways constant - a couple of RPMs more or less
doesn't matter.


Even in Germany, however, it's likely that the average tension will be 50%
to 70% of the weak link breaking load. Increasing this to 70% to 90% will
significantly increase release heights. 80% - 90% would be even better but
that will likely be more precision than the average human winch driver can
manage. Automated tension control systems can shave it as close as you
like.

I don't think so.
A striong winch is easily able to enable toe glider to exceed its
particular winch-launch Vne. Usually the speed is kept about 10-15 kts
below the Vne. Release altitudes on a standard 3.300 ft rope length
are usually sufficient to thermal (1.000-1.500 ft) or fly a 7 minute
no-thermal traffic circuit.

Completely satisfying for me - and apparently for the other 30.000
glider pilots here...



In the US for the last 50 years or so, 'simple' has meant a V8 engine and
automatic transmission from a wrecked car. The engine will not produce
anything like a flat torque curve and transmission will run wild shifting
whenever it pleases. Combine this with gliders without CG hooks and the
results are very inconsistent leading to absurd 'rules' like "raise nose to
increase speed".

I can imagine that.
Until about 15 years ago the German standard winch also consisted of
an old V8 engine, coupled to a manual gear that was usually locked in
the 2nd gear. When these engines became unavailable (and the gliders
heavier) we switched to Diesel engines.


In the US, a little intellegence built
into the winch will be a big help to a fledgling winch operation.

I'm not so sure, Bill.
Intelligence is always a good thing - but what happens if the system
fails or does something unexpected? The more simple the design, the
easier it is for a small club to build and maintain a winch - and to
fix it.
I guess on any airfield in the US there's at least one mechanic who
can repair a Lycoming engine... for if your winch (a new technology
for most clubs) depends on complex closed circuits, you'll probably
get a problem sooner or later - and revert to the trusty Pawnee.



BTW:
Have you tried this to get a winch operation running?

Put an advertisement in the German gliding magazine "Segelfliegen" or
the "aerokurier", offer half a year of free board and lodging, mention
15.000 ft cloud base, and I'm sure you'll immediately find a dozen
enthusiasts who will build a usable winch for you for less than
$25.000 and provide all the training.
It would certainly help if you could offer more than an 1-26 for their
leisure flights.



This is even more so when it's important to achieve the highest launch
possible to compete with aero tow. Automating cable tension control allows
higher tensions to be used with safety and thus higher launches.

Nah... forget about the 10 percent height advantage an optimized winch
system can bring.

In 95 percent of the cases a winch launch is completely sufficient to
catch a thermal (...maybe not for a 2-33...).

Key factor for a winch operation are cost savings - and the lower
costs for a winch launch (compared to an aerotow) ought to convince
even the most stubborn club members, don't you think?

You know the deal from your club - nothing better than being able to
offer some highschool kid flying lessons for less than $3 per launch,
don't you agree?
If someone really needs 3.000 ft release altitude, he can still take
the Pawnee.





Bye
Andreas

Tell you what, Andreas, hop over to the Aero club Salland in the Netherlands
and ask for a launch on their Hydrostart winch. Ask them to explain how it
works.

Process control using simple, rugged PLC's is ubiquitous in manufacturing
facilities the world over. If this stuff were as unreliable as you say,
they'd go back to manual operations in a second. They have money to lose.
Winch tension control is very simple compared to most industrial processes
but uses the same equipment.

BTW, I like your idea of a winch group exchange. Our cloudbases often
exceed 18,000 feet. I have a couple of spare bedrooms...

Bill Daniels


"Andreas Maurer" wrote in message
...
On Mon, 2 Apr 2007 13:29:20 -0600, "Bill Daniels"
bildan@comcast-dot-net wrote:

Actually, if you think about it, the diesel winch with a Vioth
Turbokuppling
is very close to a tension controlled winch. Diesels have a very flat
torque curve and torque increases linearly with throttle. The Voith
coupling just passes that torque to the drum at a 1:1 ratio. If the winch
driver makes a reasonable guess as to throttle setting based on the glider
to be launched and the wind, the result will be pretty good.

Forget all that high-tech stuff - much too complex for an average
gliding club. Hard to design, hard to build, hard to maintain, hard to
debug, hard to repair.

Here in good ole' Europe usually a standard truck clutch is used (with
a big engine this clutch is either actuated by hydraulics or
pneumatics) to connect the engine to a standard truck rear axle.
Initial acceleration is made by moving the throttle smoothly forward
until a certain RPM is reached which depends upon glider type wind.
During the launche the throttle is slowly brought back to keep the
gliders' speed halfways constant - a couple of RPMs more or less
doesn't matter.


Even in Germany, however, it's likely that the average tension will be 50%
to 70% of the weak link breaking load. Increasing this to 70% to 90% will
significantly increase release heights. 80% - 90% would be even better
but
that will likely be more precision than the average human winch driver can
manage. Automated tension control systems can shave it as close as you
like.

I don't think so.
A striong winch is easily able to enable toe glider to exceed its
particular winch-launch Vne. Usually the speed is kept about 10-15 kts
below the Vne. Release altitudes on a standard 3.300 ft rope length
are usually sufficient to thermal (1.000-1.500 ft) or fly a 7 minute
no-thermal traffic circuit.

Completely satisfying for me - and apparently for the other 30.000
glider pilots here...



In the US for the last 50 years or so, 'simple' has meant a V8 engine and
automatic transmission from a wrecked car. The engine will not produce
anything like a flat torque curve and transmission will run wild shifting
whenever it pleases. Combine this with gliders without CG hooks and the
results are very inconsistent leading to absurd 'rules' like "raise nose
to
increase speed".

I can imagine that.
Until about 15 years ago the German standard winch also consisted of
an old V8 engine, coupled to a manual gear that was usually locked in
the 2nd gear. When these engines became unavailable (and the gliders
heavier) we switched to Diesel engines.


In the US, a little intellegence built
into the winch will be a big help to a fledgling winch operation.

I'm not so sure, Bill.
Intelligence is always a good thing - but what happens if the system
fails or does something unexpected? The more simple the design, the
easier it is for a small club to build and maintain a winch - and to
fix it.
I guess on any airfield in the US there's at least one mechanic who
can repair a Lycoming engine... for if your winch (a new technology
for most clubs) depends on complex closed circuits, you'll probably
get a problem sooner or later - and revert to the trusty Pawnee.



BTW:
Have you tried this to get a winch operation running?

Put an advertisement in the German gliding magazine "Segelfliegen" or
the "aerokurier", offer half a year of free board and lodging, mention
15.000 ft cloud base, and I'm sure you'll immediately find a dozen
enthusiasts who will build a usable winch for you for less than
$25.000 and provide all the training.
It would certainly help if you could offer more than an 1-26 for their
leisure flights.



This is even more so when it's important to achieve the highest launch
possible to compete with aero tow. Automating cable tension control
allows
higher tensions to be used with safety and thus higher launches.

Nah... forget about the 10 percent height advantage an optimized winch
system can bring.

In 95 percent of the cases a winch launch is completely sufficient to
catch a thermal (...maybe not for a 2-33...).

Key factor for a winch operation are cost savings - and the lower
costs for a winch launch (compared to an aerotow) ought to convince
even the most stubborn club members, don't you think?

You know the deal from your club - nothing better than being able to
offer some highschool kid flying lessons for less than $3 per launch,
don't you agree?
If someone really needs 3.000 ft release altitude, he can still take
the Pawnee.





Bye
Andreas

The only problem with the Hydrostart winch is that it is about the
most expensive winch around (and I haven't heard about them having
sold another one even though they do have a website and seem to have
commercialized the design)... The technology is great if you can
afford it/have the necessary resources available to the club. The guys
who build the Hydrostart are experts in their field and do related
stuff professionally resulting in an awesome winch. But the resources
they had available is not what you find in your average club and, not
surprisingly, the Aero Club Salland is one of the biggest and most
active in NL (hence the 6 drums). Interestingly enough a single drum
setup with retrieve winch could probably achieve the same launch rates
albeit at a far smaller price tag.

Process control using simple, rugged PLC's might be easy to implement
for the expert but you gotta have the expert in the first place. A
simple mechanical setup with off-the-shelf parts can be built/
maintained by a lot more people than a hydrostatic drive with PLC
based controls, no matter how simple they are. If you got the
resources, great, but for the rest of us a more conventional setup
that might lack the last 5% of performance but is reliable in daily
use is more reasonable. Only on very short fields where every meter
counts the significant extra investment those last 5% might cost you
would be really worth paying for. Otherwise I'd rather get another
nice glider for the money saved, as long as decent launches are
assured this will matter more to the members than having the fanciest
winch around.

Markus