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