Parachute source for gliders and winches

On Sun, 11 Nov 2018 14:10:03 -0700, Dan Marotta wrote:

The simple response to that is:Â* Don't drag it on the ground.Â* When I
was driving a winch back in the 90s, the technique was to increase
throttle sufficiently after the glider releases to keep the parachute
inflated and drop the chute right in front of the winch. The driver had
to have the skill to stop the drum before the chute got jammed in the
rollers.Â* On days without cross winds, just carry enough power to keep
the chute inflated until it lands.


Spot on for normal operation, but there is one unavoidable difference if
you're using Spectra rope.

On steel cable, you do the last launch of the day, suck the cable in,
pack the winch up and tow it back to its roost and everything is fine.

But if you do the same with Spectra rope, it will destroy the winch drums
because tightly wound Spectra is likely to crush the drum in overnight
cold, so after the last launch both cables are pulled out again. The
winch then pulls them in slowly enough to avoid inflating the chute. This
leaves the ropes loose enough on the drums to prevent crushing problems,
but has also dragged the 'chutes along the ground for the length of your
airfield.


--
Martin | martin at
Gregorie | gregorie dot org

I hesitate (not really) to ask how you learned what the Spectra could do.

I've only launched and driven with steel cable or plain rope with auto tow.

On 11/11/2018 4:26 PM, Martin Gregorie wrote:
On Sun, 11 Nov 2018 14:10:03 -0700, Dan Marotta wrote:

The simple response to that is:Â* Don't drag it on the ground.Â* When I
was driving a winch back in the 90s, the technique was to increase
throttle sufficiently after the glider releases to keep the parachute
inflated and drop the chute right in front of the winch. The driver had
to have the skill to stop the drum before the chute got jammed in the
rollers.Â* On days without cross winds, just carry enough power to keep
the chute inflated until it lands.

Spot on for normal operation, but there is one unavoidable difference if
you're using Spectra rope.

On steel cable, you do the last launch of the day, suck the cable in,
pack the winch up and tow it back to its roost and everything is fine.

But if you do the same with Spectra rope, it will destroy the winch drums
because tightly wound Spectra is likely to crush the drum in overnight
cold, so after the last launch both cables are pulled out again. The
winch then pulls them in slowly enough to avoid inflating the chute. This
leaves the ropes loose enough on the drums to prevent crushing problems,
but has also dragged the 'chutes along the ground for the length of your
airfield.



--
Dan, 5J

On Sun, 11 Nov 2018 16:44:19 -0700, Dan Marotta wrote:

I hesitate (not really) to ask how you learned what the Spectra could
do.

There was feedback in S&G from early adopters about it and, when we
bought the Skylaunch I'm fairly certain it was in the operating manual.

Disclaimer: I regularly serve as part the airfield's normal operating
crew, but at the launchpoint and driving the cable tow-out truck. I had
some winch training on the Supercat, but don't drive the Skylaunch.

I've only launched and driven with steel cable or plain rope with auto
tow.

I never seen auto tow used - its very much a dieing art over here due to
the availability of good modern winches. Our longest cable run is just on
1km (3270 ft) long. Typical calm weather launches get to 1400ft but I've
had 2600-2700 ft on windy days with a decent velocity gradient in both
ASK-21 and SZD Juniors.


--
Martin | martin at
Gregorie | gregorie dot org

On Sunday, November 11, 2018 at 6:26:47 PM UTC-5, Martin Gregorie wrote:
On Sun, 11 Nov 2018 14:10:03 -0700, Dan Marotta wrote:

The simple response to that is:Â* Don't drag it on the ground.Â* When I
was driving a winch back in the 90s, the technique was to increase
throttle sufficiently after the glider releases to keep the parachute
inflated and drop the chute right in front of the winch. The driver had
to have the skill to stop the drum before the chute got jammed in the
rollers.Â* On days without cross winds, just carry enough power to keep
the chute inflated until it lands.


Spot on for normal operation, but there is one unavoidable difference if
you're using Spectra rope.

On steel cable, you do the last launch of the day, suck the cable in,
pack the winch up and tow it back to its roost and everything is fine.

But if you do the same with Spectra rope, it will destroy the winch drums
because tightly wound Spectra is likely to crush the drum in overnight
cold, so after the last launch both cables are pulled out again. The
winch then pulls them in slowly enough to avoid inflating the chute. This
leaves the ropes loose enough on the drums to prevent crushing problems,
but has also dragged the 'chutes along the ground for the length of your
airfield.


--
Martin | martin at
Gregorie | gregorie dot org

Martin,

steel cables do have the tendency to crush drums when not wound up after the last launch loosely, particularly if you were winching during a warm/hot summer day and experience a drop in temperature over night. Spectra is less affected by temperature swings but it is so tightly packed on the drum after the launch that it can crush a drum if left in that condition. We always pay out the line after the last launch and haul it it in at moderate speed, i.e. 1st gear at idle.
Dragging the chute several thousand feet over any kind of surface is just plain nuts! No wonder you are wearing it out in no time. Tie an old tire to the end, if you desire some resistance.

Uli
'AS'

Did Bill and Martin just agree on a winch related topic?!

On Sun, 11 Nov 2018 15:54:13 -0800, AS wrote:

steel cables do have the tendency to crush drums when not wound up after
the last launch loosely, particularly if you were winching during a
warm/hot summer day and experience a drop in temperature over night.

When we used steel cable we didn't do anything special - just put the
winch, a Supacat, away with the cables wound from the last launches.
Maybe the Supacat drums were stronger than I realised: certainly the
whole winch looked to have been made with surplus battleship parts from
its air-cooled V8 diesel engine onward.

When we replaced the Supacat with a Skylaunch (and later added a Tost
that had been upgraded by Skylaunch) we switched to Spectra and the pull
out and rewind loosely after the last launch. Our field is mown grass
which doesn't obviously harm the heavy duty canvas and webbing parachutes
we use.

What I said initially applies only to those lightweight Fruity chutes.


--
Martin | martin at
Gregorie | gregorie dot org

It's true that Spectra (Dyneema) has a thermal coefficient of expansion at 180 - 200 M/(MxK) - roughly 20X that for steel and 10X that for aluminum. Leaving it wound tightly on a cold night probably has caused drums to fail.

However, there's no need to drag the 'chute - that's what old tires are for.. Keep a couple handy with an eye-bolt through the tread to attach the rope to. Pulling a tire across the whole airfield can be done quickly at the end of the day leaving the Spectra wound loosely enough not to cause problems.

On Sunday, November 11, 2018 at 4:26:47 PM UTC-7, Martin Gregorie wrote:
On Sun, 11 Nov 2018 14:10:03 -0700, Dan Marotta wrote:

The simple response to that is:Â* Don't drag it on the ground.Â* When I
was driving a winch back in the 90s, the technique was to increase
throttle sufficiently after the glider releases to keep the parachute
inflated and drop the chute right in front of the winch. The driver had
to have the skill to stop the drum before the chute got jammed in the
rollers.Â* On days without cross winds, just carry enough power to keep
the chute inflated until it lands.


Spot on for normal operation, but there is one unavoidable difference if
you're using Spectra rope.

On steel cable, you do the last launch of the day, suck the cable in,
pack the winch up and tow it back to its roost and everything is fine.

But if you do the same with Spectra rope, it will destroy the winch drums
because tightly wound Spectra is likely to crush the drum in overnight
cold, so after the last launch both cables are pulled out again. The
winch then pulls them in slowly enough to avoid inflating the chute. This
leaves the ropes loose enough on the drums to prevent crushing problems,
but has also dragged the 'chutes along the ground for the length of your
airfield.


--
Martin | martin at
Gregorie | gregorie dot org