Safety of winch launch vrs. aero tow?

Hi Bill --

I 'member my O-Nine Two oil field piano wire breaking at the half way
point during a tow in Roy Schlemeyer's old SGS 2-22. I yelled "Oh, line
break" or something to that effect and recall the glider innards debris
collected since the last ice age floating up and dancing before my eyes
as I dumped the stick full forward. Was it half a second before I
reacted? Can't believe I waited that long. And when the astronauts tell
you that zero-g is exhilarating, believe it.

Luckily, I had been well briefed by Roy as to what to expect. It has
been theorized that some people are "allergic" to zero-g and they
instinctively jerk the stick full back instead of push full forward.
Unfortunately, this is the last mistake they ever make and we can no
longer interview them as to why they did this.

There, we're back to the original question, "Is winch launch safer than
aerotow?" The answer? -- scroll down


















IT DEPENDS!


Thanks and good to hear from you again.

BJ



Bill Daniels wrote:

"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

Earlier, JJ Sinclair wrote:

Its been a long time now, but a group was
auto-towing a Cherokee at Air Sailing, NV...

I'm not sure, but I believe that was actually a Don Mitchell design
called the Nimbus III-B (no relation to the later Schempp-Hirth
product of similar name). That was in 1973:

http://www.ntsb.gov/NTSB/brief.asp?ev_id=85473&key=0

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com

"Bert Willing" wrote in message ...
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 :-)



Agree, the way they often do it in Germany is useless. Glider having
to tell the guy at the phone what he's supposed to then tell the
winch. It's so simple if the winch has a radio.

Our winch has had a radio for decades. Even when we used to give the
lauch signals with a flag! About fifteen years ago we switched to
telephone to give the launching commands but as soon as the glider has
left the ground the guy at the phone says _nothing_ more. Then only
the glider pilot says either 'faster' or 'slower' over the radio.
Since we have the wire tension indicated to the winch driver these
commands have become very rare and so have cable breaks.

As long as we're sitting around the campfire and also to show you I can
go both ways, I 'member a time only a couple of years ago that I
experienced the dreaded aerotow line break at 200 ft and 60 kt over the
outbound fence.

I looked out front and it wasn't too exiting, so I gingerly turned
ninety to the left and the scenery looked some better, but not the
greatest, so I REALlY gingerly gave it another ninety to the left and
was really impressed this time as I found I was perfectly lined up with
the takeoff runway. And I recall I hadn't lost too much of my original
60 kt. Will wonders never cease!!

I thought "OK now God, you've made it possible for me to do this little
magic trick perfectly the first time I tried it in front of all my
friends and hangar bums, give me your hand again and let's try just one
more."

So I pulled spoilers, checked gear down and rolled up to my exact
takeoff spot.

And as I popped the canopy, my good friend who shall remain nameless,
said "S--t!, you've gone and lost us another Tost ring, somebody go back
to the hangar and see if they can find another tow rope". It was his
turn to tow, so I pushed back. Nobody else said a word.

Safety lecture from a dummy follows:

I don't remember to this day why I ninetied to the left. During the
previous year's biannual when Juan Batch pulled the plug on me over his
outbound fence, turning right was the correct choice because in that
direction lay the wind, which blows one back over the airport. This
improves the scenery like you wouldn't believe.

When I tried the trick for real solo, the wind lay to my left. I'd like
to think it was instinct. But I believe it was a coin toss.

Anyway, thank God. And Juan.

It Depends

BJ






Bob Johnson wrote:

Hi Bill --

I 'member my O-Nine Two oil field piano wire breaking at the half way
point during a tow in Roy Schlemeyer's old SGS 2-22. I yelled "Oh, line
break" or something to that effect and recall the glider innards debris
collected since the last ice age floating up and dancing before my eyes
as I dumped the stick full forward. Was it half a second before I
reacted? Can't believe I waited that long. And when the astronauts tell
you that zero-g is exhilarating, believe it.

Luckily, I had been well briefed by Roy as to what to expect. It has
been theorized that some people are "allergic" to zero-g and they
instinctively jerk the stick full back instead of push full forward.
Unfortunately, this is the last mistake they ever make and we can no
longer interview them as to why they did this.

There, we're back to the original question, "Is winch launch safer than
aerotow?" The answer? -- scroll down

IT DEPENDS!

Thanks and good to hear from you again.

BJ



Bill Daniels wrote:

"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

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.

The subject under discussion is a club that is thinking about trying a new
launch system, winch launching and now pay-out winch. My point in posting on
this subject is to show what can happen when unskilled club members try a new
system.
JJ Sinclair

"JJ Sinclair" wrote in message
...


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.

The subject under discussion is a club that is thinking about trying a new
launch system, winch launching and now pay-out winch. My point in posting
on
this subject is to show what can happen when unskilled club members try a
new
system.
JJ Sinclair

OK, JJ, If they are unskilled and insist on REMAINING unskilled, I'll give
you the point. Everybody starts out unskilled, however - I don't hold that
against them.

I don't think you are dissing ground launch, you're just warning that any
group needs to realize that there is a steep learning curve ahead of them.
I'll agree with that.

They've learned to fly gliders however, so they can't be dumb. I think they
can learn to operate a winch safely and enjoyably IF they take the trouble
to learn the art and science of it. There are lots of books to read and
this medium, the internet, connects us with the world where there is a
wealth of knowledge about ground launch.

If someone wanted to do the world of ground launch a great favor, they would
start a web site where the collective wisdom of the world could be displayed
so that anyone wishing to undertake winch launch could go there and get an
education.

Any volunteers?

Bill Daniels

I say learn and enjoy.

Bill Daniels

On Wed, 29 Oct 2003 16:48:38 +0100, "Bert Willing"
wrote:

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 :-)

Don't forget that you rarely do 100 launches per day at your current
airfield with "Vent arriere" messages each 3 minutes, interfering with
launches...

(Yes - I'm envious!)

Of course you are correct - it's nice to have a direct connection
between pilot and winch driver.
My club at Landau has never had such a (radio) communication, and we
seldom miss it. Sometimes the Ka-8 gets too fast (and releases early),
but otherwise I cannot remember and disadvantages of not having a
glider-winch connection.
It's more a question of winch driver practice - drivers with little
practice tend to judge the speed wrong and need corrections.

To add some spice - I personally watched two bad winch accidents, each
had to do with power failure of the winch/too low airspeed. In both
cases there was direct radio communication between glider and winch.






Bye
Andreas

In article ,
Bob Johnson wrote:

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.

You are making some totally contradictory and inconsistent claims there.

If max torque and max HP occur close together then they must both drop
off precipitously after that.

If the torque curve is flat then HP will be increasing linearly with
RPM, max torque and max HP will be very far apart.


It is quite likely that you do have maximum torque at around 3000 RPM,
but if for example the torque curve is flat enough that the torque at
the 5000 RPM redline is still 60% or more of that at 3000 RPM then that
(redline) is exactly where maximum power will be.

-- Bruce

To add some spice - I personally watched two bad winch accidents, each
had to do with power failure of the winch/too low airspeed. In both
cases there was direct radio communication between glider and winch.


Of course having radio connection does not mean you can just let the
launch happen. You still have to fly it and react to whatever
situation arises. First, you have to use the radio. Second you have to
use it before it's to late and third and most important: never rely on
the use of radio of having any effect on the launch.
I still fail to understand why any winch or cabel failure should lead
to an accident. With or without radio. With or without wind. With or
without water ballast.
Be prepared.

Marcel

Bob Johnson wrote:

As long as we're sitting around the campfire and also to show you I can
go both ways, I 'member a time only a couple of years ago that I
experienced the dreaded aerotow line break at 200 ft and 60 kt over the
outbound fence.

I looked out front and it wasn't too exiting, so I gingerly turned
ninety to the left and the scenery looked some better, but not the
greatest, so I REALlY gingerly gave it another ninety to the left and
was really impressed this time as I found I was perfectly lined up with
the takeoff runway. And I recall I hadn't lost too much of my original
60 kt. Will wonders never cease!!

I thought "OK now God, you've made it possible for me to do this little
magic trick perfectly the first time I tried it in front of all my
friends and hangar bums, give me your hand again and let's try just one
more."

So I pulled spoilers, checked gear down and rolled up to my exact
takeoff spot.

And as I popped the canopy, my good friend who shall remain nameless,
said "S--t!, you've gone and lost us another Tost ring, somebody go back
to the hangar and see if they can find another tow rope". It was his
turn to tow, so I pushed back. Nobody else said a word.

Safety lecture from a dummy follows:

I don't remember to this day why I ninetied to the left. During the
previous year's biannual when Juan Batch pulled the plug on me over his
outbound fence, turning right was the correct choice because in that
direction lay the wind, which blows one back over the airport. This
improves the scenery like you wouldn't believe.

When I tried the trick for real solo, the wind lay to my left. I'd like
to think it was instinct. But I believe it was a coin toss.

Anyway, thank God. And Juan.

It Depends

BJ


This raises the interesting question of the height loss during a 180 degrees
turn in a glider or an airplane with a dead engine. I recently had a dicsussion
about that with a friend who is a power pilot and on this occasion made again a
small computation I had already made on this matter. As I never have seen
these results elsewhere, I think it may useful to show that here. Assume
you fly your turn wit an angle of attack which correspond to the speed V
when flying straight and wings level, and that the vertical sink speed
in the same conditions wuold be Vz, then during this 180 degrees turn
flown with a bank angle phi, the height loss is pi*V*Vz/(g*sin(phi)*cos(phi)),
and the turn is flown at speed V/sqrt(cos(phi)). The optimum (minimal
height loss) is when sin(phi)*cos(phi) is maximum, i.e. phi = 45 degrees,
and the product V*Vz is minimum. A glance on a typical glider polar will
show that this last thing is obtained with V just below min sink speed, but
as it is not easy to find how many below, let's assume the turn is done
at min sink speed, this is not very far from the optimum. For a typical
glider with min sink of .6 m/s at 80 km/h (22.2 m/s) the height loss is
8.5 m, for a typical airplane with min sink of 3 m/s at 120 km/h (33.3 m/s)
the height loss is 64 m. This explains why the 180 degrees turn back to
the runway over the outbound fence succeeds in a glider but not in a power
plane.

In the case mentioned above, the speed (60kt) was far over the optimum,
however the result is as expected not catastrophic. Assuming a bank angle
of 45 degrees, the equivalent speed in straight flight would be multiplied
by 1.18, this gives 26 m/s or 93 km/h. Assuming the sink speed is 1 m/s in these
conditions, we get a height loss of 16.6m. This is for a poor glider (L/D =
26 at 93 km/h).