Safety of winch launch vrs. aero tow?

Bob Johnson wrote:

Robert --

I would like to learn how they do this.

The experiment I was talking about was done in another club,
so I have no direct information about it. However, when our winch
correctly delivers its power, we also get about 40% of cable length,
i.e. 400m with 1000m cable.

Our Blanik has perhaps the best
located CG hook on any sailplane I'm aware of, although some would say
the bridle is somewhat awkward to use.
On a typical tow, with the Blanik weighing about 1100 lb, the 300 hp
winch engine throttle is advanced to the forward stop in 3 seconds and
at this time the engine is already rapidly approaching redline 5000 RPM.
At this point the Blanik is already beginning its climb and the throttle
is eased.

There are some differences with what happens in my club: the reduction
ratio is not the same by us, engine RPM is 1800-2000. We never get
near redline, although the throttle is kept to the forward stop for
2 seaters (ASK21) until the glider seen from the winch crosses the
angle between the front window and the top window, i.e. cable angle
near 45 degrees. Our engine has only 200 hp.

This quick takeoff and climb performance is still not fast enough to
load the ship and its occupants to more than about 0.8 - 0.9 G
horizontal acceleration, which I think one would have do to attain any
more than the 1/3 line length releases we are attaining.

We limit our climb airspeed to 55-60 kt, which I believe is the POH
recommendation. Very little if any back stick is necessary, and the
Blanik attains the 55 kt climb pretty much on its own until the last
part of the 45 second tow, when some back stick is applied to counter
the downward (with respect to the ground) pull of the rope. Our
Spectra/Dyneema/Plasma plastic rope weighs less than its full 66 lb when
partially wound on the drum, so line weight (and its necessary
acceleration and ground contact friction) for us is practically
negligible.

If there is a better setup anywhere in the world, I would sure
appreciate a description.


Maybe a reduction ratio on the engine allowing full throttle without
crossing redline, keeping full throtte longer during the climb, climbing
at 60 kt rather than 55 kt. And probably a higher nose up attitude during
the first part of the climb, which would be allowed with more power and
speed during this phase. But maybe the difference is only due to the
better aerodynamic of the ASK21 compared to the Blanik. I don't remember what gliders
were used in the experiment I reported about, but probably modern
gliders, certainly not Blaniks (almost unknown in France).

Thanks for your reply,

Andreas Maurer wrote:

On Wed, 29 Oct 2003 10:02:06 +0000, Robert Ehrlich
wrote:

Why telephone rather than radio? Radio let everybody know what is
happening, rather than only the two persons at both end of telephone.
Likely mandatory when there is some other activity in parallel (aero
tow, power flying ...).

Nothing worse than someone else interfering during the critical phase
of a winch launch (initial acceleration).


A worse thing would be someone interfering not to the communication but
to the launch itself because he is not aware of the launch. Of course
this is a discipline that everybody has to observe, i.e. don't use
the radio for anything else when a winch launch is in progress. This
also implies that every glider or tow plane has a working radio, which
is the case by us.

On Wed, 29 Oct 2003 14:48:37 +0100, Andreas Maurer
wrote:

On Wed, 29 Oct 2003 10:02:06 +0000, Robert Ehrlich
wrote:


Why telephone rather than radio? Radio let everybody know what is
happening, rather than only the two persons at bot end of telephone.
Likely mandatory when there is some other activity in parallel (aero
tow, power flying ...).

Nothing worse than someone else interfering during the critical phase
of a winch launch (initial acceleration).

True enough, and you wouldn't want the continuous stream of "take up
slack....take up slack....all out...all out" occupying a common-use
channel either. We use radio to control launch but its on a dedicated
channel (sorry - I don't know the frequency) that is separate from our
tugging frequency and is one that I've never heard interference on.
One benefit is that as well as the winch, the cable truck, golf
buggy[1] and office are all on the channel so the launch marshal can
talk to anybody he needs to.

[1] an excellent and economical way of moving gliders about.


--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

Any others? Certainly there have been a few at Torrey Pines over the
decades, though environmental factors have been a big player there.

Frank Whiteley

Its been a long time now, but a group was auto-towing a Cherokee at Air
Sailing, NV. The initial flights were made with a pulley attached to a stake in
the ground and car driver heading straight for the glider. After several
flights they decided to put the pilley on the car and NOBODY knew that would
DOUBLE the glider speed. The driver "Stood on it " hard and finally obtained
his briefed 50 mph. The glider was now doing 100 and pilot was unable to
release due to excessive tow line pressure. The wings came off and pilot was
killed.

About 20 years back, a group was auto-towing a Monarch at Kingdon, Ca. That
went so well, they decided to hook it up to a tow plane. The ship did several
PIO's as the pilot tried in vain, to release. He survived, but doesen't
remember anything after the 3rd grade.

My pilot licence still reads, "Aero-Tow- Only"
JJ Sinclair

"Bob Johnson" wrote in message
...
Eggert --

Those are really good numbers for your winch.

With V8 300 HP (GMC 454 c.i., 7.4 L), and 5000 ft (1550 m) Plasma line
laid out, we are getting the rule of thumb 1/3 cable length releases of
1700 ft (525 m). This is into 10-15 kt wind. Much over that, we leave
the Blanik in the barn!

BJ
Midland, Texas

Bob, When winching, the wind is your friend. Quitting at 15 knots is not
necessary. I have winched into 35 knots and higher winds and the results
are spectacular. Each 10 knots of headwind is the equivalent of about 40
additional HP.

The thing that often severely limits the altitude gained is a slow pitch-up
profile at the start of the launch. The final height achieved is largely
determined by the profile flown in the first few seconds of the launch.

Now, as everyone has pointed out, you need to be careful here. Safety at
the start of the climb is a combination of airspeed, altitude and attitude.
The more you have of the first, the faster you can get the second two and
the higher you will get.

I've done calculations, simulator runs (X-Plane) and flight test to prove
the following point. If you have 60 knots in a glider with a stalling
airspeed of 40 knots, you can be in full climb attitude at zero altitude and
still have a large safety margin. Practice this way - at several thousand
feet AGL, zoom the glider into a 50 degree nose-up attitude. As the
airspeed decays to 60 knots, yell "WIRE BREAK", delay 0.5 seconds
(simulating reaction time) and pitch forward at zero G. Watch the airspeed
and altitude, you'll see what I mean. (For winch CFI-G's, this is a great
way to teach how to handle wire breaks.)

If you have (or simulate) a wire break at this point and start a zero G
pitch over after a .5 second delay, the minimum airspeed during the
parabolic ballistic trajectory will be about 50 - 55 knots when the glider
reaches apogee at an altitude of about 100 feet AGL. So there you are at
100 feet and 55 knots in a normal gliding attitude - not exactly a
problematic situation, just land straight ahead. The reason this works is
that the glider's induced drag at zero G is minimal so the airspeed decay is
mainly just due to gravity and the glider follows a parabolic trajectory
until the pilot re-establishes one G at the normal glide attitude.

I need to repeat that I am not advocating a rocket blast-off kind of climb
profile but a smooth transition into the full climb without undue delay
equipped with a full understanding of the safety margins.

Bill Daniels

Nothing worse than an additional communication step between pilot and winch
driver. Did that for 10 years in Germany, happy to do it by radio ever since
I left Germany, hadn't had an interference from others on the same
frequencies for the last 13 years :-)

--
Bert Willing

ASW20 "TW"


"Andreas Maurer" a écrit dans le message de
...
On Wed, 29 Oct 2003 10:02:06 +0000, Robert Ehrlich
wrote:


Why telephone rather than radio? Radio let everybody know what is
happening, rather than only the two persons at bot end of telephone.
Likely mandatory when there is some other activity in parallel (aero
tow, power flying ...).

Nothing worse than someone else interfering during the critical phase
of a winch launch (initial acceleration).

Bye
Andreas

"JJ Sinclair" wrote in message
...

Any others? Certainly there have been a few at Torrey Pines over the
decades, though environmental factors have been a big player there.

Frank Whiteley

Its been a long time now, but a group was auto-towing a Cherokee at Air
Sailing, NV. The initial flights were made with a pulley attached to a
stake in
the ground and car driver heading straight for the glider. After several
flights they decided to put the pilley on the car and NOBODY knew that
would
DOUBLE the glider speed. The driver "Stood on it " hard and finally
obtained
his briefed 50 mph. The glider was now doing 100 and pilot was unable to
release due to excessive tow line pressure. The wings came off and pilot
was
killed.

About 20 years back, a group was auto-towing a Monarch at Kingdon, Ca.
That
went so well, they decided to hook it up to a tow plane. The ship did
several
PIO's as the pilot tried in vain, to release. He survived, but doesen't
remember anything after the 3rd grade.

My pilot licence still reads, "Aero-Tow- Only"
JJ Sinclair

JJ, you've had some bad experiences and I'm sorry for that. But you have to
realize that there are hundreds of thousands, if not millions of winch
launches all around the world that go off without a hitch simply because the
people involved know what they are doing.

If we take the trouble to learn from them and not try to re-invent the
wheel, ground launch becomes very safe and enjoyable. (The first thing to
learn is not to use a Schweitzer-type tow release for anything at all,
period.)

Bill Daniels

On our field communication between pilot and winch driver is mostly by 4.6mm
steel cable. Works fine and very direct :-)
And in germany communication between winch and start point on air band radio
(only) is not allowed, you may use a radio on some other frequency.

Tjeerd


"Bert Willing" schrieb im
Newsbeitrag ...
Nothing worse than an additional communication step between pilot and
winch
driver. Did that for 10 years in Germany, happy to do it by radio ever
since
I left Germany, hadn't had an interference from others on the same
frequencies for the last 13 years :-)

--
Bert Willing

ASW20 "TW"


"Andreas Maurer" a écrit dans le message de
...
On Wed, 29 Oct 2003 10:02:06 +0000, Robert Ehrlich
wrote:


Why telephone rather than radio? Radio let everybody know what is
happening, rather than only the two persons at bot end of telephone.
Likely mandatory when there is some other activity in parallel (aero
tow, power flying ...).

Nothing worse than someone else interfering during the critical phase
of a winch launch (initial acceleration).

Bye
Andreas

Eggert -

You are exactly right with those finer points of flying the launch.
Thanks for adding those to the thread.

Also we will want to try maybe 60-65 kt in the climb next time we go
out.

Cheers,

BJ

Eggert Ehmke wrote:

Bob Johnson wrote:

I would like to learn how they do this. Our Blanik has perhaps the best
located CG hook on any sailplane I'm aware of, although some would say
the bridle is somewhat awkward to use.
On a typical tow, with the Blanik weighing about 1100 lb, the 300 hp
winch engine throttle is advanced to the forward stop in 3 seconds and
at this time the engine is already rapidly approaching redline 5000 RPM.
At this point the Blanik is already beginning its climb and the throttle
is eased.

As a winch driver, I allways try to leave the throttle in the position it
has when the plane leaves the ground, for about the first 1/3 of the climb.
Then I slightly slow down, depending on the wind and the climb angle of the
plane. This can mean full throttle for a double seater and almost idle for
a Ka8 with strong headwind. This method works in all wind conditions.

With an ASK21 or Grob G103, the ground roll is not longer than 2 or 3
seconds. The first ca. 100 feet we keep a flat attitude, than we go
slightly into a climb angle of about 40 degrees.

We limit our climb airspeed to 55-60 kt, which I believe is the POH
recommendation.

This seems a bit slow for me, but may be correct for the Blanik. The ASK21
has a recommended speed of about 60 kt, and 65 is no problem. More speed
means more lift too.

Very little if any back stick is necessary, and the
Blanik attains the 55 kt climb pretty much on its own until the last
part of the 45 second tow, when some back stick is applied to counter
the downward (with respect to the ground) pull of the rope.

In the last part of the climb it is even important to give the stick a
little forward, so the angle between cable and plane does not exceed the
point where the backrelease is triggered. That way you can stay longer on
the rope, getting higher. Also the release is much softer.

Just my 2 cents...
Eggert

Robert -

Those are all good points, see my reply to Eggert.

Our engine is petrol fueled. Despite Google's best efforts, I have not
yet located a Torque/HP/RPM curve for our very common 7.4 L engine, but
have heard that it develops max torque and HP at about 3000 RPM and
further that the curves are fairly flat at this point.

Our drum speed is around 400 RPM for about a 7-8/1 overall reduction
using first gear of our automatic tranny. We have lately begun bringing
in the parachute in second gear, which reduces engine wear and tear
considerably.

In addition to raising the unflapped climb speed to 65 kt, we also have
the option on our Blanik L-13 model to let out the Fowler flaps and
climb at a reduced airspeed. We have not yet tried the flaps during tow
to my knowledge.

You may be using a Diesel, which could account for your good performance
at lower revs.

Thanks,
BJ

Robert Ehrlich wrote:

Bob Johnson wrote:

Robert --

I would like to learn how they do this.

The experiment I was talking about was done in another club,
so I have no direct information about it. However, when our winch
correctly delivers its power, we also get about 40% of cable length,
i.e. 400m with 1000m cable.

Our Blanik has perhaps the best
located CG hook on any sailplane I'm aware of, although some would say
the bridle is somewhat awkward to use.
On a typical tow, with the Blanik weighing about 1100 lb, the 300 hp
winch engine throttle is advanced to the forward stop in 3 seconds and
at this time the engine is already rapidly approaching redline 5000 RPM.
At this point the Blanik is already beginning its climb and the throttle
is eased.

There are some differences with what happens in my club: the reduction
ratio is not the same by us, engine RPM is 1800-2000. We never get
near redline, although the throttle is kept to the forward stop for
2 seaters (ASK21) until the glider seen from the winch crosses the
angle between the front window and the top window, i.e. cable angle
near 45 degrees. Our engine has only 200 hp.

This quick takeoff and climb performance is still not fast enough to
load the ship and its occupants to more than about 0.8 - 0.9 G
horizontal acceleration, which I think one would have do to attain any
more than the 1/3 line length releases we are attaining.

We limit our climb airspeed to 55-60 kt, which I believe is the POH
recommendation. Very little if any back stick is necessary, and the
Blanik attains the 55 kt climb pretty much on its own until the last
part of the 45 second tow, when some back stick is applied to counter
the downward (with respect to the ground) pull of the rope. Our
Spectra/Dyneema/Plasma plastic rope weighs less than its full 66 lb when
partially wound on the drum, so line weight (and its necessary
acceleration and ground contact friction) for us is practically
negligible.

If there is a better setup anywhere in the world, I would sure
appreciate a description.


Maybe a reduction ratio on the engine allowing full throttle without
crossing redline, keeping full throtte longer during the climb, climbing
at 60 kt rather than 55 kt. And probably a higher nose up attitude during
the first part of the climb, which would be allowed with more power and
speed during this phase. But maybe the difference is only due to the
better aerodynamic of the ASK21 compared to the Blanik. I don't remember what gliders
were used in the experiment I reported about, but probably modern
gliders, certainly not Blaniks (almost unknown in France).

Thanks for your reply,