How to get maximum height on a winch launch?

Hi Bill, Glad to see you are coming round to my way
of thinking, that the rotation into the full climb
should be gentle and controlled, and should not put
you in an unrecoverable position if the launch fails
for any reason.

The exact position to hold the stick during a winch
launch is very type dependent. Gliders with way back
c of g hooks, such as the K21, K8 and Pirat will require
the stick to be held neutral or even forward of neutral
during the full climb. Gliders with slightly further
forward hooks such as the K13 will need the stick held
fairly well back, although probably not on the back
stop. Gliders with single 'compromise' hooks such as
the Slingsby Skylark and the Bocian will need the stick
to be held on the back stop if they are to climb at
all steeply.

The best advice I can give to Dan G is to look at the
wingtips during the launch and find what stick position
will hold them at about 45 degrees to the horizon AND
give a safe speed. If you have a low powered winch
you may have to adopt a lesser angle.

Derek Copeland

At 15:18 13 December 2006, Bill Daniels wrote:
Dan, your questions concern me. Full up elevator is
dangerous on a winch
launch. All modern

At 15:18 13 December 2006, Bill Daniels wrote:
Dan, your questions concern me. Full up elevator is
dangerous on a winch
launch. All modern trainers like ASK 21's or Grob
103's will fly an almost
perfect launch without the pilot touching the controls
if trim and winch
power are right. Demonstrating hands off launches
is a good start to winch
training. (The take home lession is the launch will
be nearly perfect if the
pilot doesn't screw it up.)

You should be using just enough elevator to keep the
airspeed where you want
it. (Typically 55 - 60 knots, depending on the glider)
The basic principle
is that the winch driver controlls power and the glider
pilot controlls
airspeed. If it requires large amounts of up elevator
to control airspeed,
signal for less power. As you point out, some gliders
with high CG
locations like a K8 will need nearly full down elevator
from the start to
control the natural pitch up. It shouldn't need much
up elevator at all
later.

The winch driver should be slowly backing off the power
as the glider
approaches the top of the launch. Take a good look
at George Moores charts
that show cable tension - tension is a direct function
of winch power.

In any event, there's very little additional height
that can be achieved
late in the launch. Pulling hard near the top just
loads up the glider and
may break the weak link. (You are using the correct
Tost weak links,
right?)

Suggestion: Get a copy of a good glider flight simulator
like Condor and
practice lauches on a computer. There's a lot to learn
with a good sim. I
use Condor as an 'animated white board' when I teach
winch ground school.

Bill Daniels

'Dan G' wrote in message
roups.com...
Thanks Bill, that document is very interesting.

There is one thing in particular I am unsure about
however - how much
up elevator I should be putting in. With the K8, I
fly the launch at
50-55kts with the stick fully back for perhaps the
last 30% of the
launch after smoothly transitioning from full forwards
on the ground
run through neutral once in the full climb, until
I feel the glider
being pulled level, when I relax the aft pressure
in anticipation of
putting the nose down to reuce cable tension prior
to releasing. (This
later movement often results in quite an increase
in speed, which I
convert to height after releasing. Is this an indication
I'm releasing
back pressure too early, or the winch driver not backing
off the
throttle enough?)

With a K21, which winch drivers here (which includes
me) are told to
give 'full power all the way up' from our Oldsmobile
V8. Climb speed is
at lesst 65kts and I'm reluctant to pull back too
hard. Why? A K21
launches on a black weak link (1,000kg). I imagine
full up elevator in
a K21 would produce enough lift to break that at well
below max winch
speed, 81kts.

Is there a way to calculate how much lifting force
full up elevator
should produce for any given airspeed? Or should I
not be putting full
up in? If not, just how far should I bring the stick
back, and when?


Bill Daniels wrote:

If you join the Yahoo group 'winchdesign' and look
in the files section,
there are a series of truely excellent papers in the
folder 'Winch
Dynamics
and Performance' by George Moore. (soargsm)

Essentially what George determened is that the major
sensitivities a
1.Field length
2. Headwind
3. Cable tension as a percentage of glider flying
weight.
4. Weight & drag of the cable

There is very little extra height to be gained by
agressive technique
beyond
just hitting your target airspeed and holding it there
with smooth
control
inputs. This gives an angle of attack just slightly
greater than that
for
best L/D. If you want help with this, put some AOA
strings on the canopy
sides and calibrate them for L/D max and Vmin sink.
Of course, it goes
without saying that you should never put yourself
in danger by rotating
into
the climb so quickly that a recovery from a rope break
is impossible.
Smooth and accurate flying are what you want.

So, if you want to get higher, get a longer field
with more wind, replace
steel with high strength Dyneema and get a winch that
can accurately hold
tension at 80 - 90% of the weak link.

Bill Daniels

'Dan G' wrote in message
ups.com...
I'm interested in learning how to get the maximum
possible height on a
winch launch, without compromising safety in any
way.

This question has two parts really - how should the
pilot fly the
launch (pretty much how should he operate the elevator
during the
launch), how fast should the glider fly, and how
should the winch
driver feed the power in? For the sake of argument,
let's assume the
glider is a K13.

For reference, I fly from an airfield with a 3,300'
long cable, and the
maximum height I achieve repeatedly is 1,700'. Headwind
typically goes
from around 10kts at the ground to something like
(I estimate) 20kts at
height.

Derek Copeland wrote:

The exact position to hold the stick during a winch
launch is very type dependent. Gliders with way back
c of g hooks, such as the K21, K8 and Pirat will require
the stick to be held neutral or even forward of neutral
during the full climb.

My Pirat will fly a very nice winch launch which is almost completely
independent of anything the pilot chooses to do with the stick! It's
not so much the fore-and-aft position of the hook, I think, as the
vertical one: since it is at the bottom of a deep fuselage there is a
considerable nose up pitching moment during the ground run. As soon as
it takes off, therefore, it does a lovely rotation into full climb all
by itself: full forward stick has no effect at all.

Gliders with single 'compromise' hooks such as
the Slingsby Skylark and the Bocian will need the stick
to be held on the back stop if they are to climb at
all steeply.

All the Bocians I have ever flown had C of G and nose hooks. The Pirat
manual specifically permits winching on the nose hook: using full back
stick and forward trim from the "All Out", and warning that it will
only give 60% of normal release height. I have never tried this, for
several reasons, one being that I rather like having the back release
there ...

Ian