SAFE Winch Launching

At 11:49 20 July 2009, brian whatcott wrote:

There is another factor worth considering in the matter of launches.

An automatic gearbox / transmission is intended to transfer as much
horse power as possible from engine to axle.

Maximizing HP in this way involves a LARGE torque at slow speed,
tapering to a low torque at high speed.

You have mentioned that the objective of a glider launch is holding the
tension constant. This is a different objective altogether!
This calls for a ramped HP, so that either a ramped throttle application

to achieve flight speed is needed, at which point that HP is held - or
as a possible alternative: running an engine at constant (max) HP, but
throwing away excess power during the ramp to flight speed.

Brian W

I don't think it's quite as simple as that. You need a lot of torque and
power to accelerate the glider up to flying speed, then a slight reduction
to allow for the safety climb and rotation and then lots of torque and
power again for the full climb. As the glider nears the top of the launch,
the climb flattens out and you need less power and torque. The cable speed
reaches a maximum as the glider starts the rotation and then drops quite a
lot as the glider enters the full climb, due to the water-skier effect, and
then continues to drop thoughout the rest of the launch.

The water-skier effect means in effect that the vertical speed is being
added to the horizontal speed, so that the maximum winch launching
airspeed would be vastly exceeeded if the cable speed is not reduced in
some way. BTW, the water-skier effect is used by water skiers themselves,
only in the horizontal axis, to gain speed for jumps and other tricks
while the ski boat continues on at a constant speed.

Oddly enough, the Skylaunch throttle stop system and automatic gearbox
seems to automatically compensate for all the above effects, except that
you have to back the throttle off near the top of the launch to avoid
overspeeding the glider.

Derek Copeland

At 11:50 20 July 2009, brian whatcott wrote:
Don Johnstone wrote:
... a "tension controlled" winch is about the craziest idea I have
ever
heard, not least because, thankfully, it would never work.

Why not?

Brian W


Because there is no direct relationship between the tension experienced at
the winch and that experienced at the glider release using wire rope.
Even with plastic rope the relationship is tenuous at best, the rope does
have some mass and in addition has an elastic quality as well. The
tensions experienced at each end of the cable can be vastly different and
are different more often than they are equal, so measuring at the winch
end tells you very little about what is happening at the glider, it may
indicate what has happened but even this is not likely to be very
accurate.

I don't think it's quite as simple as that. You need a lot of torque and
power to accelerate the glider up to flying speed,

Lets see, you have an engine from a 7000 pound road vehicle and you
are accelerating a 1,500 pound glider without even the possibility of
wheel spin and you claim you need "at lot of torque"? That doesn't
even pass a smell test.

1st and 2nd gears can/will develop so much torque at the drum you'll
break the weak link or worse. Simple arithmetic shows the GM big
block will develop 3000 pounds or more of rope tension in 3rd gear.
1st and 2nd gears are just a nuisance requiring the winch operator to
gently advance the throttle to avoid trouble.

That's just one of MANY issues related to using automotive components
in a glider winch.


then a slight reduction
to allow for the safety climb and rotation and then lots of torque and
power again for the full climb. As the glider nears the top of the launch,
the climb flattens out and you need less power and torque. The cable speed
reaches a maximum as the glider starts the rotation and then drops quite a
lot as the glider enters the full climb, due to the water-skier effect, and
then continues to drop thoughout the rest of the launch.

The water-skier effect means in effect that the vertical speed is being
added to the horizontal speed, so that the maximum winch launching
airspeed would be vastly exceeeded if the cable speed is not reduced in
some way. BTW, the water-skier effect is used by water skiers themselves,
only in the horizontal axis, to gain speed for jumps and other tricks
while the ski boat continues on at a constant speed.

Oddly enough, the Skylaunch throttle stop system and automatic gearbox
seems to automatically compensate for all the above effects, except *that
you have to back the throttle off near the top of the launch to avoid
overspeeding the glider.

Derek Copeland *

So how come do we hardly ever break weak links during the ground run????

Derek C

At 16:19 20 July 2009, bildan wrote:

I don't think it's quite as simple as that. You need a lot of torque
and
power to accelerate the glider up to flying speed,

Lets see, you have an engine from a 7000 pound road vehicle and you
are accelerating a 1,500 pound glider without even the possibility of
wheel spin and you claim you need "at lot of torque"? That doesn't
even pass a smell test.

1st and 2nd gears can/will develop so much torque at the drum you'll
break the weak link or worse. Simple arithmetic shows the GM big
block will develop 3000 pounds or more of rope tension in 3rd gear.
1st and 2nd gears are just a nuisance requiring the winch operator to
gently advance the throttle to avoid trouble.

That's just one of MANY issues related to using automotive components
in a glider winch.


then a slight reduction
to allow for the safety climb and rotation and then lots of torque and
power again for the full climb. As the glider nears the top of the
launch=
,
the climb flattens out and you need less power and torque. The cable
spee=
d
reaches a maximum as the glider starts the rotation and then drops
quite
=
a
lot as the glider enters the full climb, due to the water-skier
effect,
a=
nd
then continues to drop thoughout the rest of the launch.

The water-skier effect means in effect that the vertical speed is
being
added to the horizontal speed, so that the maximum winch launching
airspeed would be vastly exceeeded if the cable speed is not reduced
in
some way. BTW, the water-skier effect is used by water skiers
themselves,
only in the horizontal axis, to gain speed for jumps and other tricks
while the ski boat continues on at a constant speed.

Oddly enough, the Skylaunch throttle stop system and automatic gearbox
seems to automatically compensate for all the above effects, except
=A0th=
at
you have to back the throttle off near the top of the launch to avoid
overspeeding the glider.

Derek Copeland =A0

Del C wrote:
.... You need a lot of torque and
power to accelerate the glider up to flying speed, then a slight reduction
to allow for the safety climb and rotation and then lots of torque and
power again for the full climb....


Derek Copeland

Your note quoted above seems to treat torque (or thrust, or tension)
and HP as synonymous. They are not. Somebody with a physics
background could provide helpful input here....

Brian W

Don Johnstone wrote:
At 11:50 20 July 2009, brian whatcott wrote:
Don Johnstone wrote:
... a "tension controlled" winch is about the craziest idea I have
ever
heard, not least because, thankfully, it would never work.
Why not?

Brian W


Because there is no direct relationship between the tension experienced at
the winch and that experienced at the glider release using wire rope.
Even with plastic rope the relationship is tenuous at best, the rope does
have some mass and in addition has an elastic quality as well. The
tensions experienced at each end of the cable can be vastly different and
are different more often than they are equal, so measuring at the winch
end tells you very little about what is happening at the glider, it may
indicate what has happened but even this is not likely to be very
accurate.


That sounds like an interesting reply: in a comparable situation, a kite
can only carry so much line aloft, and the tension at the kite is
certainly at a different angle to that oseen by the kite flyer.

These days, a wireless sensor could be provided to measure and relay the
tension at the sailplane - but I think I am hearing that a constant
tension is not in fact wanted???


Brian W

On Jul 20, 11:28*am, brian whatcott wrote:
Don Johnstone wrote:
At 11:50 20 July 2009, brian whatcott wrote:
Don Johnstone wrote:
... *a "tension controlled" winch is about the craziest idea I have
ever
heard, not least because, thankfully, it would never work.
Why not?

Brian W

Because there is no direct relationship between the tension experienced at
the winch and that experienced at the glider release using wire rope.
Even with plastic rope the relationship is tenuous at best, the rope does
have some mass and in addition has an elastic quality as well. The
tensions experienced at each end of the cable can be vastly different and
are different more often than they are equal, so measuring at the winch
end tells you very little about what is happening at the glider, it may
indicate what has happened but even this is not likely to be very
accurate.

That sounds like an interesting reply: in a comparable situation, a kite
can only carry so much line aloft, and the tension at the kite is
certainly at a different angle to that oseen by the kite flyer.

These days, a wireless sensor could be provided to measure and relay the
tension at the sailplane - but I think I am hearing that a constant
tension is not in fact wanted???

Brian W

Constant tension during the climb phase is exactly what you want.
Read George Moore's article in this month's Soaring Magazine. Tension
telemetry is a great idea - someone please build it.

A kite string or a winch rope forms a catenary arc due to it's weight
and air drag. The tension on each end of a catenary arc is the same
except for the rope/string weight difference if the ends are at
different heights. If 2000 feet of Plasma rope were hanging
vertically the tension due to its weight is zero at the bottom and
only 20 pounds at the top - that difference doesn't matter much.

Brian,

Torque is a measure of turning or rotational force in units such as lbs.ft
or equivalent, horsepower is a measure of work done in a given period of
time (1hp = 550lb.ft/sec) and tension is a stress that produces an
elongation of an elastic physical body, usually from opposing forces. In
that you can have torque and tension without any work being done, you
really need (horse) power to make a winch launch happen.

Derek Copeland

At 17:23 20 July 2009, brian whatcott wrote:
Del C wrote:
.... You need a lot of torque and
power to accelerate the glider up to flying speed, then a slight
reduction
to allow for the safety climb and rotation and then lots of torque and
power again for the full climb....


Derek Copeland

Your note quoted above seems to treat torque (or thrust, or tension)
and HP as synonymous. They are not. Somebody with a physics
background could provide helpful input here....

Brian W

On Jul 20, 10:45*am, Del C wrote:
So how come do we hardly ever break weak links during the ground run????

Derek C

See previous post about "little old lady" style throttle advance.

At 23:36 20 July 2009, bildan wrote:
On Jul 20, 10:45=A0am, Del C wrote:
So how come do we hardly ever break weak links during the ground
run????

Derek C

See previous post about "little old lady" style throttle advance.

The reason we don't break weak links is because we take up slack at just
over tickover revs, when the engine is not producing much power or torque.
As the glider starts moving (all out) we advance the throttle over about a
2 second interval right up to the preset power stop. The automatic gearbox
then does its job and allows smooth acceleration and smooth gearbox
upchanges until a safe rotation speed is reached. The rest of the launch
is done with the gearbox in top and essentially fixed ratio.

The techniques and the way you think an automatic gearbox works, that you
have suggested up to now, are more appropriate to drag racing than winch
launching!

Derek Copeland