Parachute source for gliders and winches

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

On Sunday, November 11, 2018 at 4:10:07 PM UTC-5, Dan Marotta wrote:
...On days without cross winds, just carry enough power to keep
the chute inflated until it lands.

I've never driven the winch, but I've sat in the cab and watched an international cadre of winching masters practice their art. At the two sites that I've done winch launches, operations continued in significant crosswind. Crosswinds seem to be less of a no-go with modern winches.

Additional factors make landing the parachute right in front of the winch challenging for even expert winch operators: 1)2000 foot launches means more time to drift 2)less experienced pilots (like me) that insufficiently compensate for the crosswind (by flying the launch to the upwind side of the field).

On Mon, 12 Nov 2018 20:06:57 -0800, son_of_flubber wrote:

I've never driven the winch, but I've sat in the cab and watched an
international cadre of winching masters practice their art. At the two
sites that I've done winch launches, operations continued in significant
crosswind. Crosswinds seem to be less of a no-go with modern winches.

On sites with severe cross-wind there's always the parachuteless option.
I've seen (and flown with) this setup at The Mynd,

The Mynd is on top of a long, steep north-south ridge with the runway
parallel to the ridge and close behind the soaring slope. Beyond the
runway there's an additional small rise with a valley containing moorland
and trees. When the ridge is working, launches and landings are flown in
a 90 degree cross-wind. Obviously they can't use a parachute on the
launch cable because, when the ridge is working well, the end of the
cable would end up over the hill and probably in the downwind forest: the
airfield is 250m across at its widest and scrub and trees start 100m
downwind of its lee edge.

They use a single drum winch with no parachute and the retrieval winch at
the launch point: the main cable ends in a metal triangle with the
retrieval cable on one corner and the shock rope and strop on the other.
No parachute.

During the launch a light cable streams off the small retrieval winch.
When the glider releases, the main winch is put in neutral and the
retrieval winch engages, causing the cable to snap down onto the main
runway, and shortly after that, its business end is back at the
launchpoint ready for the next launch. The two winch drivers co-ordinate
agreement about who is in gear and when by radio.


--
Martin | martin at
Gregorie | gregorie dot org

On Tuesday, November 13, 2018 at 3:37:00 AM UTC-8, Martin Gregorie wrote:
On Mon, 12 Nov 2018 20:06:57 -0800, son_of_flubber wrote:

I've never driven the winch, but I've sat in the cab and watched an
international cadre of winching masters practice their art. At the two
sites that I've done winch launches, operations continued in significant
crosswind. Crosswinds seem to be less of a no-go with modern winches.

On sites with severe cross-wind there's always the parachuteless option.
I've seen (and flown with) this setup at The Mynd,

The Mynd is on top of a long, steep north-south ridge with the runway
parallel to the ridge and close behind the soaring slope. Beyond the
runway there's an additional small rise with a valley containing moorland
and trees. When the ridge is working, launches and landings are flown in
a 90 degree cross-wind. Obviously they can't use a parachute on the
launch cable because, when the ridge is working well, the end of the
cable would end up over the hill and probably in the downwind forest: the
airfield is 250m across at its widest and scrub and trees start 100m
downwind of its lee edge.

I don't understand.

At glider release the cable is pointing up into the sky at an angle of ... well, I don't know ... let's just say more than 60 degrees.

I've never seen a cable being wound in drop below an angle of ... let's say 30 degrees (more like 45 probably, but let's go with 30) until the parachute is within 100m of the winch and speed is falling off.

Half your 250m airfield width plus 100m to the trees is 225m. Even if the cable swings around directly downwind the parachute is going to be at least sin(30)*225 = 112m up when it crosses the trees. Your trees aren't that tall.

It's a different story if the cable breaks, of course.

On Monday, November 12, 2018 at 9:06:59 PM UTC-7, son_of_flubber wrote:
On Sunday, November 11, 2018 at 4:10:07 PM UTC-5, Dan Marotta wrote:
...On days without cross winds, just carry enough power to keep
the chute inflated until it lands.

I've never driven the winch, but I've sat in the cab and watched an international cadre of winching masters practice their art. At the two sites that I've done winch launches, operations continued in significant crosswind. Crosswinds seem to be less of a no-go with modern winches.

Additional factors make landing the parachute right in front of the winch challenging for even expert winch operators: 1)2000 foot launches means more time to drift 2)less experienced pilots (like me) that insufficiently compensate for the crosswind (by flying the launch to the upwind side of the field).

I've operated quite a number of different winches and always found it easy to drop the parachute exactly where I wanted it to land. My technique is to rip the 'chute down from the sky at high speed then stop the drum to drop the 'chute directly in front of the winch. A fast recovery of the rope and 'chute minimizes crosswind effects.

Obviously, this depends on a powerful brake which can dependably stop the drum exactly when you want - some testing is required to determine this. Despite occasional screams of panic from onlookers, I have never pulled a 'chute through the rollers nor tangled the cable/rope on the drum doing this.