Airspeed control during ground launch?

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...)

As I understand it.. the SSA and FAA manuals do not have it wrong.

A report from the recent Back in the Saddle safety seminar reveals that the
"more modern" winch machines now in Europe actually are more automatic,
maintaining a set tension on the line and varying the speed on the winch.
The reports are that the pitch control for speed control is then more in
tune with the standard practice of raise to slow (more tension, auto
throttle slows down) lower to speed up, less tension more throttle to speed
up the winch and maintain the desired tension.

If you are on an auto tow there is no tension meter or "take up reel" on
auto, so the Speed control would be as described in the SSA and FAA manuals.

BT


"Roger Worden" wrote in message
et...
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...)

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

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.

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

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

Bruce wrote:
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.

The stall speed may not be a *little* higher, but substantially higher.
The BGA instructors book recommends a minimum safe winch launch speed of
stall + 50%.

Stalling on the wire often leads to an immediate spin entry with no time
to recover, so proper training is essential.

Training is also needed to embed appropriately safe actions if the cable
breaks at various heights, as (a) the pitch over to a proper recovery
angle is much higher than a pilot trained on aerotow only would expect,
(b) there is a further trap in these circumstances in that G is reduced
during the pitch over, so that any attempt to turn before full G returns
can lead to a stall and spin (stall speed reduces with lower G), and (c)
on many sites there is a critical height band where there may be only
one safe option for an abbreviated circuit, which needs to be practised
(as do all recoverise from winch launch failures).

From the perspective of several hundred winch launches via different
winches, I'd say there is no consistent answer to what to to with the
elevator to control speed. You need briefing on how that particular
winch works. There are however two clear rules:

1. If speed reduces below the safe minimum, lower the nose, and if the
speed does not pick up immediately, relase and recover.

2. If speed increases above the maximum in the latter half of the launch
(when loads are highest) and the briefed method does not immediately
reduce the speed, lower the nose slightly to reduce the load on the
glider, signal for less speed, and if you don't get is, release as before.

I'd emphasise most strongly that you can't learn safe winch launching
from reading alone - proper training is essential.

The "glider speeds up with increasing pitch" advice listed below has
annoyed me for a long time. Except for highly unusual circumstances, it's
just plain wrong. In fact, it's dangerously wrong. It is extremely
desirable that the glider pilot be able to control airspeed during a winch
launch in exactly the same way as he does under all other circumstances. He
should never be forced to deal with a reverse response.
Likely this is the result observing launches from poorly constructed winches
using automobile engines and transmissions that are allowed to "run wild"
during the launch. Automobile drive trains are designed for accelerating
heavy vehicles not launching gliders. Automotive drive trains should never
be used without extensive modifications. The Tost organization has written
extensively about this.

Without these modifications, while the gilder is rotating into the climb
portion of the launch, the automatic transmission will still be shifting up
through the gears and the torque converter will still be multiplying torque.
This often results in more line tension than is desirable and the glider
will seem to accelerate alarmingly as the nose is raised. As soon as the
transmission settles in drive and the torque converter locks up, the
pitch/airspeed relationship becomes normal where raising the nose will
reduce airspeed.

Knowledgeable winch builders who still use automotive based power trains
like Tost, gut the transmissions to eliminate all gears except the 1:1 high
gear and fit high stall torque converters that won't cause problems. Other,
still more modern winch builders like Hydrostart of the Netherlands, have
gone further by eliminating all automotive parts. Instead, they use
industrial engines and hydrostatic drives to provide exact control over
cable tension at all points in the launch. These winches provide smooth,
safe launches with a completely logical pitch/airspeed relationship. The
pilot always has control over airspeed.

Bill Daniels


"Roger Worden" wrote in message
et...
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...)

Bill,

Are you saying that the winch should be constructed so that "pitch up
= speed up" is impossible, or that the "pitch up = speed up"
relationship is not correct for any winch ?

Todd Smith

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.

Some improperly constructed winches, most notably those with automotive V8's
and unmodified automatic transmissions, can briefly cause the airspeed to
increase as the nose is raised causing the pilot to feel the launch is out
of control. This will happen while the transmission is in the lower gears.
This is one of the many reasons Tost removes 1st and 2nd gears from their
transmissions. They also fit a "looser" torque converter to provide
smoother acceleration.

As a glider pitches up on the launch, the load on the cable and on the winch
engine increases. If the winch is tension controlled, the airspeed will
decrease. If, on the other hand, the winch is capable of delilvering
essentially unlimited cable tension as would be the case when the
transmission is in 1st or 2nd gear, the glider may accelerate as the nose is
raised.

Note that this is different from normal acceleration to climb airspeed where
the nose may be rising even as the airspeed is increasing. The difference
is that there is no cause and effect relationship.

Bill Daniels

"toad" wrote in message
oups.com...
Bill,

Are you saying that the winch should be constructed so that "pitch up
= speed up" is impossible, or that the "pitch up = speed up"
relationship is not correct for any winch ?

Todd Smith

Ok, thanks. That's the physics as I understood it.

With a modern winch, I won't have to worry about reverse control. But
with an old technology ground launch, I do.

Todd