Winch Physics

This has been covered in these pages before, but it may be timely to
post it again in view of the coming fuel price squeeze and the increased
interest in winching.

This Excel spreadsheet explains mathematically why a winch system
comprised of lighter linear (rope) and rotational elements will
significantly out-accelerate a more-massively built winch. Read petrol
powered vs. Diesel powered.

The Diesel, despite its other admitted advantages (or perhaps because of
them) will take longer to "wind up". The diesel engine is more massive
than a petrol engine in the crankshaft and flywheel, and in all other
moving parts. I do not know the exact masses of the two types of prime
movers. Perhaps someone out there can contribute this information. The
dry weights of the two power plants might be sufficient information.

This longer "wind up" period results in fewer "G's" being applied to the
sailplane being launched during the acceleration from rest to flying
speed and the subsequent start of the pull-up and climb.

We find with our 454 c.i. petrol engine-powered and Plasma rope-equipped
winch that our Blanik L-13 with two souls on board (1100 lb-mass) will
be flying before we can get the throttle fully advanced. We can easily
break a 1000-lb weak link during acceleration, but can't do so with a
1360-lb "blue" link.

Quicker than this I do not know how you could go.

The numbers add up to close to 1 "G" for the heavy two-place. Since
these maths are on a spreadsheet, all items comprising the entire system
can be changed to fit your particular situation. And all units have been
worked out on both the "English" and metric systems.

My spreadsheet had nothing to do with Craig Freeman's excellent winch
design for the Permian Soaring Asscociation. Rather, I did the
spreadsheet to find out just why it was so excellent.

http://www.permiansoaring.us/ (See "Special Projects")

The Excel spreadsheet is available as an email attachment. Let me know
if you would like me to send you one.

Cheers,

Bob Johnson Midland, Texas

"Bob Johnson" wrote in message
...
This has been covered in these pages before, but it may be timely to
post it again in view of the coming fuel price squeeze and the increased
interest in winching.

This Excel spreadsheet explains mathematically why a winch system
comprised of lighter linear (rope) and rotational elements will
significantly out-accelerate a more-massively built winch. Read petrol
powered vs. Diesel powered.

The Diesel, despite its other admitted advantages (or perhaps because of
them) will take longer to "wind up". The diesel engine is more massive
than a petrol engine in the crankshaft and flywheel, and in all other
moving parts. I do not know the exact masses of the two types of prime
movers. Perhaps someone out there can contribute this information. The
dry weights of the two power plants might be sufficient information.

This longer "wind up" period results in fewer "G's" being applied to the
sailplane being launched during the acceleration from rest to flying
speed and the subsequent start of the pull-up and climb.

We find with our 454 c.i. petrol engine-powered and Plasma rope-equipped
winch that our Blanik L-13 with two souls on board (1100 lb-mass) will
be flying before we can get the throttle fully advanced. We can easily
break a 1000-lb weak link during acceleration, but can't do so with a
1360-lb "blue" link.

Quicker than this I do not know how you could go.

The numbers add up to close to 1 "G" for the heavy two-place. Since
these maths are on a spreadsheet, all items comprising the entire system
can be changed to fit your particular situation. And all units have been
worked out on both the "English" and metric systems.

My spreadsheet had nothing to do with Craig Freeman's excellent winch
design for the Permian Soaring Asscociation. Rather, I did the
spreadsheet to find out just why it was so excellent.

http://www.permiansoaring.us/ (See "Special Projects")

The Excel spreadsheet is available as an email attachment. Let me know
if you would like me to send you one.

Cheers,

Bob Johnson Midland, Texas

I can attest to Bob Johnson's statement that the Permian Soaring Association
winch is a very energetic machine. I took a launch in their L-13 last
November with Bob driving the winch and Craig Freeman coaching me from the
back seat. Bob's spreadsheets and that neck snapping launch go a long way
to convince me that the ubiquitous Chevy 454 is a very good winch engine.
In their case, the 454 is a very appropriate engine.

I still am holding out for a diesel though. Some of the older diesels were
slow to spool up but the newer electronically-controlled, turbocharged,
common-rail diesels are just as snappy as spark ignition engines according
to the operators I have spoken with. The low cost of operation, low
maintenance and massive low-end torque of diesels are real plusses.

If you plan to build a winch for any glider that might show up for a launch,
you have to consider gliders like a ASH 25 at 2200 pounds gross. My single
seat Nimbus could be over 1400 pounds with water ballast. If you add to
that the summer 15,000 foot + density altitudes of many of the very
attractive winch runways in the western USA, the power requirements go way
up.

Someone correctly pointed out that turbocharged diesels will maintain their
power to very high altitudes. However, even with sea level power, at zero
wind and high density altitude, the glider will have to be accelerated to a
far higher groundspeed to reach liftoff airspeed. It's that high cable
speed just after liftoff times the 1G cable tension that adds up to the big
HP demand.

From a practical and perhaps simplistic view, excess horsepower is no
problem since you don't have to use all that is available. Insufficient HP
is a problem you just can't get around.

Bill Daniels

On Sat, 20 Mar 2004 10:47:47 -0600, Bob Johnson
wrote:

The Diesel, despite its other admitted advantages (or perhaps because of
them) will take longer to "wind up". The diesel engine is more massive
than a petrol engine in the crankshaft and flywheel, and in all other
moving parts. I do not know the exact masses of the two types of prime
movers. Perhaps someone out there can contribute this information. The
dry weights of the two power plants might be sufficient information.

This longer "wind up" period results in fewer "G's" being applied to the
sailplane being launched during the acceleration from rest to flying
speed and the subsequent start of the pull-up and climb.

I have no idea what Diesel winches you have seen so far, but it's very
easy to break the weak link during the initial acceleration with ours.
280 hp turbo Diesel and 3.500 ft of good-old fashioned steel cable.
Wind drivers in my club are instructed not to apply full power
immediately since the acceleration is so quick that it WILL break the
weak link.
The weak link I'm talking about is the 2.000 lbs (the strongest that
is available) onr for our DG-505.


Bye
Andreas

Hi Andreas and Bill --

You're right, a 2000-lb weak link and a turbo for high altitude launches
can make all the difference in the world.

I figure Andreas' DG 505 at 615 kg gross and using all of the strength
of a 8929 N (2000-lb) weak link should get airborne (65 km/h or 35 kt)
in about 1.5 sec and take 125 kW (165 hp) out of the engine in the
process.

That's ripping the nose ring out of the bull's nose!

Cheers and all the best,

BJ

Andreas Maurer wrote:

On Sat, 20 Mar 2004 10:47:47 -0600, Bob Johnson
wrote:

The Diesel, despite its other admitted advantages (or perhaps because of
them) will take longer to "wind up". The diesel engine is more massive
than a petrol engine in the crankshaft and flywheel, and in all other
moving parts. I do not know the exact masses of the two types of prime
movers. Perhaps someone out there can contribute this information. The
dry weights of the two power plants might be sufficient information.

This longer "wind up" period results in fewer "G's" being applied to the
sailplane being launched during the acceleration from rest to flying
speed and the subsequent start of the pull-up and climb.

I have no idea what Diesel winches you have seen so far, but it's very
easy to break the weak link during the initial acceleration with ours.
280 hp turbo Diesel and 3.500 ft of good-old fashioned steel cable.
Wind drivers in my club are instructed not to apply full power
immediately since the acceleration is so quick that it WILL break the
weak link.
The weak link I'm talking about is the 2.000 lbs (the strongest that
is available) onr for our DG-505.

Bye
Andreas

Bob, let me try a different tack and look at the instantaneous power demand
at the moment of highest wire speed.

Andreas will be airborne at 65 km/h but won't really begin his climb until
over 102 km/h. At 100 km/h he is still accelerating at 10 meters per second
per second with a line pull of 615 kg. At that instant, he is demanding 169
kW or 227 HP at the glider. Since, as you pointed out, the winch engine is
also accelerating the drum and cable as well as overcoming cable friction
with the runway the real power demand at the engine is much higher.

If the glider must be accelerated to a higher ground speed because of
density altitude, the power demand goes higher still. At a 10,000 foot
density altitude he will need to go 20% faster before beginning the climb
and require 20% more power.

It's difficult to forecast the worst case power demand so I've always
advocated a large power margin to insure the power demand can always be met.

Bill Daniels


"Bob Johnson" wrote in message
...
Hi Andreas and Bill --

You're right, a 2000-lb weak link and a turbo for high altitude launches
can make all the difference in the world.

I figure Andreas' DG 505 at 615 kg gross and using all of the strength
of a 8929 N (2000-lb) weak link should get airborne (65 km/h or 35 kt)
in about 1.5 sec and take 125 kW (165 hp) out of the engine in the
process.

That's ripping the nose ring out of the bull's nose!

Cheers and all the best,

BJ

Andreas Maurer wrote:

On Sat, 20 Mar 2004 10:47:47 -0600, Bob Johnson
wrote:

The Diesel, despite its other admitted advantages (or perhaps because
of
them) will take longer to "wind up". The diesel engine is more massive
than a petrol engine in the crankshaft and flywheel, and in all other
moving parts. I do not know the exact masses of the two types of prime
movers. Perhaps someone out there can contribute this information. The
dry weights of the two power plants might be sufficient information.

This longer "wind up" period results in fewer "G's" being applied to
the
sailplane being launched during the acceleration from rest to flying
speed and the subsequent start of the pull-up and climb.

I have no idea what Diesel winches you have seen so far, but it's very
easy to break the weak link during the initial acceleration with ours.
280 hp turbo Diesel and 3.500 ft of good-old fashioned steel cable.
Wind drivers in my club are instructed not to apply full power
immediately since the acceleration is so quick that it WILL break the
weak link.
The weak link I'm talking about is the 2.000 lbs (the strongest that
is available) onr for our DG-505.

Bye
Andreas

Hi Bill --

That's right, I'm just dealing with the initial problem of accelerating
the ship off the ground. The dynamics of the climb I'm leaving to others
smarter than me.

If your experience, of which I know you have in abundance, dictates
ADDING power when the ship begins its climb, then so be it. The big
block in the PSA winch has to be backed off from 3800 rpm to 3000 rpm in
the climb when launching our L-13, even in a low-wind situation as
prevailed last Saturday. I believe Craig is pulling back just right, as
he climbs at 55 kt.

As a crazy analogy, look at the Super Hornet. With engines spooled up
and in full afterburner, it takes a tremendous shove from the steam
catapault to get the ship in the air. Once in the air it immediately
climbs out like a banshee.

Thus my gut feeling that it takes more power to accelerate to flying
speed than it does to climb.

What am I missing here?

BJ

Bill Daniels wrote:

Bob, let me try a different tack and look at the instantaneous power demand
at the moment of highest wire speed.

Andreas will be airborne at 65 km/h but won't really begin his climb until
over 102 km/h. At 100 km/h he is still accelerating at 10 meters per second
per second with a line pull of 615 kg. At that instant, he is demanding 169
kW or 227 HP at the glider. Since, as you pointed out, the winch engine is
also accelerating the drum and cable as well as overcoming cable friction
with the runway the real power demand at the engine is much higher.

If the glider must be accelerated to a higher ground speed because of
density altitude, the power demand goes higher still. At a 10,000 foot
density altitude he will need to go 20% faster before beginning the climb
and require 20% more power.

It's difficult to forecast the worst case power demand so I've always
advocated a large power margin to insure the power demand can always be met.

Bill Daniels

"Bob Johnson" wrote in message
...
Hi Andreas and Bill --

You're right, a 2000-lb weak link and a turbo for high altitude launches
can make all the difference in the world.

I figure Andreas' DG 505 at 615 kg gross and using all of the strength
of a 8929 N (2000-lb) weak link should get airborne (65 km/h or 35 kt)
in about 1.5 sec and take 125 kW (165 hp) out of the engine in the
process.

That's ripping the nose ring out of the bull's nose!

Cheers and all the best,

BJ

Andreas Maurer wrote:

On Sat, 20 Mar 2004 10:47:47 -0600, Bob Johnson
wrote:

The Diesel, despite its other admitted advantages (or perhaps because
of
them) will take longer to "wind up". The diesel engine is more massive
than a petrol engine in the crankshaft and flywheel, and in all other
moving parts. I do not know the exact masses of the two types of prime
movers. Perhaps someone out there can contribute this information. The
dry weights of the two power plants might be sufficient information.

This longer "wind up" period results in fewer "G's" being applied to
the
sailplane being launched during the acceleration from rest to flying
speed and the subsequent start of the pull-up and climb.

I have no idea what Diesel winches you have seen so far, but it's very
easy to break the weak link during the initial acceleration with ours.
280 hp turbo Diesel and 3.500 ft of good-old fashioned steel cable.
Wind drivers in my club are instructed not to apply full power
immediately since the acceleration is so quick that it WILL break the
weak link.
The weak link I'm talking about is the 2.000 lbs (the strongest that
is available) onr for our DG-505.

Bye
Andreas

On Wed, 24 Mar 2004 20:40:02 -0700, "Bill Daniels"
wrote:

Andreas will be airborne at 65 km/h but won't really begin his climb until
over 102 km/h. At 100 km/h he is still accelerating at 10 meters per second
per second with a line pull of 615 kg. At that instant, he is demanding 169
kW or 227 HP at the glider. Since, as you pointed out, the winch engine is
also accelerating the drum and cable as well as overcoming cable friction
with the runway the real power demand at the engine is much higher.

It's difficult to forecast the worst case power demand so I've always
advocated a large power margin to insure the power demand can always be met.

I'm offering German Daimler-Benz 280 hp...
Typical acceleration is about 3 seconds till liftoff (which happens
around 80 kp/h I'd estimate since the tail wheel prohibits the AoA of
the wing, and once off the ground the speed is immediately in the
green range. Precise speeds are hard to tell because due to the quick
acceleration the airspeed indicator is lagging behind.

Our winch operation typically looks like this:
The thrust lever is moved smoothly withing three seconds to a desired
engine RPM (which depends upon the wind condition and is typically
between 2.600 and 2.800 RPM for a DG505 or ASK-21).
Advancing the throttle quicker greatly enhances the risk of killing
the wek link during initial acceleration.

Shortly after the liftoff of the glider the acceleration is already
done (and the glider at a safe speed of 90-110 kp/h) and the glider
immediately starts its climb, reaching full climb angle at about 150
to 200 ft.

We sometimes even fly with pretty strong tailwinds of up to 20 kp/h
tailwind component (which should give a good comparation to the TAS
effects on high-elevation airfields). Launch height and ground run
distance are significantly reduced of course, but reaching a safe
speed for the glider is never a problem.

Launching with a Dynema cable (PU) on the winch of the other club on
our airfield didn't show much difference concerning acceleration and
tow heights (the Dynema cable is offers less than 10 percent better
launch height).
The advantages of using a "plastic" cable are rather in the handling -
splicing a Dynema cable is pure joy (although it requires the same
time (15 minutes) than doing a complete splice on a steel cable).


Bye
Andreas

The craziness is in the horsepower formula. The Super Hornet's engines at
full thrust on the carrier deck produce no horsepower at all - just thrust.
Once it starts to move, the speed term in the HP formula kicks in and the HP
output soars. A bit of trivia, at about 325 knots, one pound of thrust
equals one HP which means that at 325 knots the Super Hornet's engines with
44,000 pounds of combined thrust are producing 44,000 HP vs. 0 HP one second
before the cat shot.

Using units I am more familiar with, 1 HP= 550 foot pound seconds. Or in
the case of a winch launch, cable tension in pounds times cable speed in
feet per second divided by 550. Because of the FPS term, the HP demand
peaks at the maximum cable speed just as the glider arcs up into the climb.
Unfortunately, without an energy storage system, the winch engine has to be
sized to meet peak demand even if that demand lasts only a second or two.

Bill Daniels

"Bob Johnson" wrote in message
...
Hi Bill --

That's right, I'm just dealing with the initial problem of accelerating
the ship off the ground. The dynamics of the climb I'm leaving to others
smarter than me.

If your experience, of which I know you have in abundance, dictates
ADDING power when the ship begins its climb, then so be it. The big
block in the PSA winch has to be backed off from 3800 rpm to 3000 rpm in
the climb when launching our L-13, even in a low-wind situation as
prevailed last Saturday. I believe Craig is pulling back just right, as
he climbs at 55 kt.

As a crazy analogy, look at the Super Hornet. With engines spooled up
and in full afterburner, it takes a tremendous shove from the steam
catapault to get the ship in the air. Once in the air it immediately
climbs out like a banshee.

Thus my gut feeling that it takes more power to accelerate to flying
speed than it does to climb.

What am I missing here?

BJ

Bill Daniels wrote:

Bob, let me try a different tack and look at the instantaneous power
demand
at the moment of highest wire speed.

Andreas will be airborne at 65 km/h but won't really begin his climb
until
over 102 km/h. At 100 km/h he is still accelerating at 10 meters per
second
per second with a line pull of 615 kg. At that instant, he is demanding
169
kW or 227 HP at the glider. Since, as you pointed out, the winch
engine is
also accelerating the drum and cable as well as overcoming cable
friction
with the runway the real power demand at the engine is much higher.

If the glider must be accelerated to a higher ground speed because of
density altitude, the power demand goes higher still. At a 10,000 foot
density altitude he will need to go 20% faster before beginning the
climb
and require 20% more power.

It's difficult to forecast the worst case power demand so I've always
advocated a large power margin to insure the power demand can always be
met.

Bill Daniels

"Bob Johnson" wrote in message
...
Hi Andreas and Bill --

You're right, a 2000-lb weak link and a turbo for high altitude
launches
can make all the difference in the world.

I figure Andreas' DG 505 at 615 kg gross and using all of the strength
of a 8929 N (2000-lb) weak link should get airborne (65 km/h or 35 kt)
in about 1.5 sec and take 125 kW (165 hp) out of the engine in the
process.

That's ripping the nose ring out of the bull's nose!

Cheers and all the best,

BJ

Andreas Maurer wrote:

On Sat, 20 Mar 2004 10:47:47 -0600, Bob Johnson
wrote:

The Diesel, despite its other admitted advantages (or perhaps
because
of
them) will take longer to "wind up". The diesel engine is more
massive
than a petrol engine in the crankshaft and flywheel, and in all
other
moving parts. I do not know the exact masses of the two types of
prime
movers. Perhaps someone out there can contribute this information.
The
dry weights of the two power plants might be sufficient
information.

This longer "wind up" period results in fewer "G's" being applied
to
the
sailplane being launched during the acceleration from rest to
flying
speed and the subsequent start of the pull-up and climb.

I have no idea what Diesel winches you have seen so far, but it's
very
easy to break the weak link during the initial acceleration with
ours.
280 hp turbo Diesel and 3.500 ft of good-old fashioned steel cable.
Wind drivers in my club are instructed not to apply full power
immediately since the acceleration is so quick that it WILL break
the
weak link.
The weak link I'm talking about is the 2.000 lbs (the strongest that
is available) onr for our DG-505.

Bye
Andreas

Hi Bill:

You have flown our winch and must have felt me ease back on the throttle
to keep you from exceeding 55 kt. I'll readily concede to you and
Andreas that our winch at 6000 ft or hitched to a 2000 lb glider is not
going to perform as well as it does at Odessa's 3000 ft pulling the
Blanik.

But those two conditions are special cases and most winches will
probably never encounter the challenge they pose.

All I've tried to do is investigate the acceleration phase of the
launch.

BTW, the S-Hornet at 66,000 lb gross requires a weak link of 218,000 lb
minus the 44,000 lb thrust of the engines to attain 151 kt flying speed
in the 306 feet of flight deck it has to get away. 3.3 G's.

Bob

Bill Daniels wrote:

The craziness is in the horsepower formula. The Super Hornet's engines at
full thrust on the carrier deck produce no horsepower at all - just thrust.
Once it starts to move, the speed term in the HP formula kicks in and the HP
output soars. A bit of trivia, at about 325 knots, one pound of thrust
equals one HP which means that at 325 knots the Super Hornet's engines with
44,000 pounds of combined thrust are producing 44,000 HP vs. 0 HP one second
before the cat shot.

Using units I am more familiar with, 1 HP= 550 foot pound seconds. Or in
the case of a winch launch, cable tension in pounds times cable speed in
feet per second divided by 550. Because of the FPS term, the HP demand
peaks at the maximum cable speed just as the glider arcs up into the climb.
Unfortunately, without an energy storage system, the winch engine has to be
sized to meet peak demand even if that demand lasts only a second or two.

Bill Daniels

"Bob Johnson" wrote in message
...
Hi Bill --

That's right, I'm just dealing with the initial problem of accelerating
the ship off the ground. The dynamics of the climb I'm leaving to others
smarter than me.

If your experience, of which I know you have in abundance, dictates
ADDING power when the ship begins its climb, then so be it. The big
block in the PSA winch has to be backed off from 3800 rpm to 3000 rpm in
the climb when launching our L-13, even in a low-wind situation as
prevailed last Saturday. I believe Craig is pulling back just right, as
he climbs at 55 kt.

As a crazy analogy, look at the Super Hornet. With engines spooled up
and in full afterburner, it takes a tremendous shove from the steam
catapault to get the ship in the air. Once in the air it immediately
climbs out like a banshee.

Thus my gut feeling that it takes more power to accelerate to flying
speed than it does to climb.

What am I missing here?

BJ

Bill Daniels wrote:

Bob, let me try a different tack and look at the instantaneous power
demand
at the moment of highest wire speed.

Andreas will be airborne at 65 km/h but won't really begin his climb
until
over 102 km/h. At 100 km/h he is still accelerating at 10 meters per
second
per second with a line pull of 615 kg. At that instant, he is demanding
169
kW or 227 HP at the glider. Since, as you pointed out, the winch
engine is
also accelerating the drum and cable as well as overcoming cable
friction
with the runway the real power demand at the engine is much higher.

If the glider must be accelerated to a higher ground speed because of
density altitude, the power demand goes higher still. At a 10,000 foot
density altitude he will need to go 20% faster before beginning the
climb
and require 20% more power.

It's difficult to forecast the worst case power demand so I've always
advocated a large power margin to insure the power demand can always be
met.

Bill Daniels

"Bob Johnson" wrote in message
...
Hi Andreas and Bill --

You're right, a 2000-lb weak link and a turbo for high altitude
launches
can make all the difference in the world.

I figure Andreas' DG 505 at 615 kg gross and using all of the strength
of a 8929 N (2000-lb) weak link should get airborne (65 km/h or 35 kt)
in about 1.5 sec and take 125 kW (165 hp) out of the engine in the
process.

That's ripping the nose ring out of the bull's nose!

Cheers and all the best,

BJ

Andreas Maurer wrote:

On Sat, 20 Mar 2004 10:47:47 -0600, Bob Johnson
wrote:

The Diesel, despite its other admitted advantages (or perhaps
because
of
them) will take longer to "wind up". The diesel engine is more
massive
than a petrol engine in the crankshaft and flywheel, and in all
other
moving parts. I do not know the exact masses of the two types of
prime
movers. Perhaps someone out there can contribute this information.
The
dry weights of the two power plants might be sufficient
information.

This longer "wind up" period results in fewer "G's" being applied
to
the
sailplane being launched during the acceleration from rest to
flying
speed and the subsequent start of the pull-up and climb.

I have no idea what Diesel winches you have seen so far, but it's
very
easy to break the weak link during the initial acceleration with
ours.
280 hp turbo Diesel and 3.500 ft of good-old fashioned steel cable.
Wind drivers in my club are instructed not to apply full power
immediately since the acceleration is so quick that it WILL break
the
weak link.
The weak link I'm talking about is the 2.000 lbs (the strongest that
is available) onr for our DG-505.

Bye
Andreas

"Bob Johnson" wrote in message
...
Hi Bill:

You have flown our winch and must have felt me ease back on the throttle
to keep you from exceeding 55 kt. I'll readily concede to you and
Andreas that our winch at 6000 ft or hitched to a 2000 lb glider is not
going to perform as well as it does at Odessa's 3000 ft pulling the
Blanik.

Absolutely. Your winch has far more power than needed for the L-13 at
Odessa. Craig is one of the few winch builders in the USA that put enough
power in his winch. It'll be interesting to hear your comments about
launches on a 100+ degree day with no wind.

There's an issue that I don't have a good understanding of which is why you
and I keep fiddling with these power formulas. I think it's the density
altitude effects. DA has a very pronounced negative effect on power output
of a normally-aspirated engine combined with the need to accelerate the
glider to a higher speed. These two effects combine to really sap the
energy from a winch launch.

I find an unexpected power shortage to be quite alarming. I'd like the
power margin to be large so that under the worst imaginable conditions there
is still a considerable power reserve. Just because the power is there,
doesn't mean you have to use it.

Bill Daniels