John Galloway wrote:
The main thing is; on a wire launch - never ever,
under any circumstances, pull the stick back if your
airspeed is very low. The time taken increase the
angle of attack to the point of departure into a spin
is minimal compared with the time that would have been
taken to for the airspeed to rise no matter how powerful
the winch.

That is true, and the stall speed will be a little higher - check the minimum
winch speed for your glider - it should be in the handbook. Try to avoid testing
whether it REALLY is the stall speed on your glider on winch.

John Galloway

At 06:00 30 March 2007, Bruce Greef wrote:

Roger Worden wrote:

What is the correct relationship between pitch angle
and airspeed during
ground launch, either by auto or winch? Different
sources make conflicting
statements:

1. Speed control is OPPOSITE to that during aerotow
and gliding

* SSA Soaring Flight Manual, page 13-10: 'Under most
circumstances, the best
way to reduce the airspeed is to raise the nose. During
ground launch,
however, the opposite is true ... pulling the nose
up results in an increase
in airspeed, assuming the launch vehicle has adequate
power.'

* FAA Glider Flying Handbook, page 7-16: 'The pitch
attitude/airspeed
relationship during ground launch is unique. During
the launch, pulling back
on the stick tends to increase airspeed, and pushing
forward tends to reduce
airspeed. This is the opposite of the normal pitch/airspeed
relationship.'

* This is what I was taught during autotow training.
I can't say that I have
varied the pitch enough in my few launches to have
demonstrated it.

2. Speed control is the SAME as during aerotow and
gliding

* British Gliding Association Instructors' Manual,
page 16-2: 'If the launch
speed starts to tail-off, lower the nose.' Page 16-3:
'monitor the airspeed
trend. If it is falling back towards the minimum safe
speed, lower the nose
or relax any back pressure on the stick.' BGA does
not mention attempting to
slow down: 'If the glider is starting to go too fast,
maintain the normal
climb attitude, and signal. If it remains too fast,
or gets even faster,
release.'

* During presentations on winch launch at a recent
seminar, two leading
instructors discussed lowering the nose to increase
speed and raising the
nose to decrease speed.

* This is what my experience with the Condor flight
simulator winch launch
has shown.

It seems to me that this is a critical point on which
to be clear, since I
will be winch-launching for the first time soon. I
understand that the
vectors involved are different than in aerotowing,
because the wings are
converting forward rope travel to angular motion (just
like the skeg on a
water ski!). I also understand that a properly balanced
glider using a CG
hook for winch launch will tend to nose up initially,
and will seek an
optimal climb angle naturally. Altering the climb
angle with elevator will
necessarily result in a less-than-optimal altitude
gain. But what is the
actual effect of raising or lowering the nose in a
stable ground launch
climb?

A. Is it different depending on the angle of climb?
In my experience,
autotows tend to achieve a 25- to 30-degree climb
angle, winch launch a 40-
to 45-degree climb. Does that cause a difference in
the effect of pitch
angle?

B. If #2 above is true, how did the SSA and FFA manuals
get it wrong?

C. If #1 is true, is it reversed in Britain? (Just
kidding...)



Two things active here.

If you have effectively unlimited power on the other
end of the string, then
raising the nose forces the glider to describe a larger
arc, which it achieves
by accelerating.

If you have limited power (winch power loss, or glider
too big for the winch -
unlikely in Europe with newer winches, but I have met
some very low power
winches.) OR decreasing effective headwind (remember
you are effectively fixed
to the ground in winch launch so wind gradient effects
are noticeable) THEN
raising the nose will generally decrease speed, until
you stall. Of course, if
you have a powerful winch and the appropriate controller
on the other end it may
be able to overcome the wind effect, in which case
you will get away with
raising the nose.


So both are correct.
In general, a harder pull will result in a larger arc
and higher speed on a well
matched winch. ('Under most circumstances' is the quote.)
In general, decreasing speed on a winch launch is an
alarm signal and you should
lower the nose to recover safe airspeed and anticipate
launch failure.

Bruce