Airspeed control during ground launch?

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