Spectra winching question

We (Greater Boston Soaring Club) had our first Spectra "glider flinging"
session today and were surprised that we saw no altitude improvement
after switching from steel cable. The winds were not favorable and our
heights may improve in time. .... But that's not the question.

We have the option of launching from either asphalt or turf. From a
Spectra wear point of view, which would be preferred?

Tony V. LS6-b "6N"

On Jun 19, 7:17*pm, Tony V wrote:
We (Greater Boston Soaring Club) had our first Spectra "glider flinging"
session today and were surprised that we saw no altitude improvement
after switching from steel cable. The winds were not favorable and our
heights may improve in time. .... But that's not the question.

We have the option of launching from either asphalt or turf. From a
Spectra wear point of view, which would be preferred?

Tony V. LS6-b "6N"

Launching from turf will extend the rope's life but people launching
from asphalt are also reporting good rope life. The rope tends to
come off the ground far more quickly than steel cable so it suffers
less abrasion regardless of the surface. FWIW, Spectra, (HMWPE) has
10 - 15 times the abrasion resistance of steel.

The major advantage of turf over asphalt is temperature - black
asphalt can get hot in the sun. However, Spectra's rated strength is
valid to 150F (To advertize a strength value, the manufacturer has to
set a maximum temperature - i.e. "Critical temperature".) Strength
trends downward above that until it melts around 283F. It's not
likely your asphalt will exceed 150F.

There are two major failure modes (Other than winch damage.) one is
"snagging" where individual fibers catch on sharp objects and get
broken. This results in "fuzzing" which, counter-intuitively,
actually protects the remaining fibers from further abrasion damage.
The other is melting.

Most rope damage is caused by poorly designed winches. Big crossed
rollers collect rings of melted Spectra indicating the rope has been
terminally damaged. If the rope is stiff and shiny, it's been melted
by the winch. It should remain soft and pliable for it's whole life.
It's worth investing in a Spectra-friendly fairlead for your winch.
(e-mail me and I'll send you drawings and photos of one.)

Whatever the ultimate failure mode, if you get 1500 launches or so,
the extra per-launch cost of about $0.50 is trivial for most people.

As to release height, the advantage of light ultra high strength
synthetic rope depends on runway length. The longer rope you start
with, the greater the relative benefit. Below 4000 feet or so, there
isn't much height gain but at 10,000 feet it's really significant.
But, even with short runways, you still get the safety and handling
benefits which, in themselves, are worth it

On Jun 19, 9:07*pm, bildan wrote:
On Jun 19, 7:17*pm, Tony V wrote:


Whatever the ultimate failure mode, if you get 1500 launches or so,
the extra per-launch cost of about $0.50 is trivial for most people.

The cost difference of UHMWPE ropes over steel amortized over 1500
launches is about $1.05/launch if purchased in bulk. If you need to
splice, that will be cheaper than splicing steel. You should do a lot
less splicing that with steel. For 3/16" 12 strand, I recommend
making a fid from a 10 1/2 knitting needle bonded with a 9/32" round
brass tube. Field splices using a 12" 3x tuck splice in either
direction are fine. Leave the proper splice for non-flying days.

I would suggest actually amortizing your first run over 1000 launches
until you get some experience with your actual results. That puts the
cost differential nearer $1.58/launch. At that rate, you should be
well on your way to funding replacement rope before you exhaust your
current length.

Costs are based on 5000ft bulk purchases at best available prices.

Impact damage from loops striking parts of the winch causes breaks.
Loops may result for both design and operational issues. Snagging
objects on the ground can have similar results. I'm aware of a club
that damaged $200 (~500ft) worth of Dyneema 75 that way recently. The
more power your winch has, the more technically sophisticated your
line feeds should be as the tendency to 'melt' the line increases with
load. Your launches will be higher also but the real gains from the
reduced weight of these ropes shows up when the run length approaches
5000ft. 5000ft of UHMWPE (3/16") is 50 lbs. The same length of steel
is over 300 lbs. The winch should be at the fence. Your airport is
only about 3100ft max. I don't think you'll see 100ft different in
launch heights.

If you can use a soft surface for retrieves, I'd recommend it. Runway
verges work fine and keep the line clear of the hard surface so it may
be used by other aircraft while the glider winch launch is staging.
Up slack may pull some of the line onto the hard surface for a very
short while, but it'll be in the air right away.

Frank Whiteley

On Jun 19, 8:17*pm, Tony V wrote:
We (Greater Boston Soaring Club) had our first Spectra "glider flinging"
session today and were surprised that we saw no altitude improvement
after switching from steel cable. The winds were not favorable and our
heights may improve in time. .... But that's not the question.

We have the option of launching from either asphalt or turf. From a
Spectra wear point of view, which would be preferred?

Tony V. LS6-b "6N"

Besides anything else that has been said one core component and its
effect on launch height that is almost always overlooked is the
parachute. The drag a big, unwieldy parachute creates even when it is
folded during the launch can have a much bigger effect than
differences in cable weight etc. Just using a well designed parachute
with a low profile when folded can easily get you a couple of hundered
feet compared to some drag monster commandeered from some other
unrelated application...

Markus Graeber

We have had excellent results from a mirage F1 drag chute.

Light, low drag when closed, very fast stable opening.
Tough as one could hope for - we get ~2500 launches on rough stony earth
before condition demands replacement. Unfortunately the surplus stock we
obtained when the F1s were retired is now used up. Soon we will have to
get a new chute.

Much smaller solid canvas chutes have worse drag , shaking and opening
on launch behaviour.

Drag is influenced by shape and material/surface.

On 2011/06/20 07:58 AM, Markus Graeber wrote:
On Jun 19, 8:17 pm, Tony wrote:
We (Greater Boston Soaring Club) had our first Spectra "glider flinging"
session today and were surprised that we saw no altitude improvement
after switching from steel cable. The winds were not favorable and our
heights may improve in time. .... But that's not the question.

We have the option of launching from either asphalt or turf. From a
Spectra wear point of view, which would be preferred?

Tony V. LS6-b "6N"

Besides anything else that has been said one core component and its
effect on launch height that is almost always overlooked is the
parachute. The drag a big, unwieldy parachute creates even when it is
folded during the launch can have a much bigger effect than
differences in cable weight etc. Just using a well designed parachute
with a low profile when folded can easily get you a couple of hundered
feet compared to some drag monster commandeered from some other
unrelated application...

Markus Graeber

--
Bruce Greeff
T59D #1771 & Std Cirrus #57

On Jun 20, 6:55*am, BruceGreeff wrote:
We have had excellent results from a mirage F1 drag chute.

Light, low drag when closed, very fast stable opening.
Tough as one could hope for - we get ~2500 launches on rough stony earth
before condition demands replacement. Unfortunately the surplus stock we
obtained when the F1s were retired is now used up. Soon we will have to
get a new chute.

Much smaller solid canvas chutes have worse drag , shaking and opening
on launch behaviour.

Drag is influenced by shape and material/surface.

On 2011/06/20 07:58 AM, Markus Graeber wrote:









On Jun 19, 8:17 pm, Tony *wrote:
We (Greater Boston Soaring Club) had our first Spectra "glider flinging"
session today and were surprised that we saw no altitude improvement
after switching from steel cable. The winds were not favorable and our
heights may improve in time. .... But that's not the question.

We have the option of launching from either asphalt or turf. From a
Spectra wear point of view, which would be preferred?

Tony V. LS6-b "6N"

Besides anything else that has been said one core component and its
effect on launch height that is almost always overlooked is the
parachute. The drag a big, unwieldy parachute creates even when it is
folded during the launch can have a much bigger effect than
differences in cable weight etc. Just using a well designed parachute
with a low profile when folded can easily get you a couple of hundered
feet compared to some drag monster commandeered from some other
unrelated application...

Markus Graeber

--
Bruce Greeff
T59D #1771 & Std Cirrus #57

It's certainly true parachutes can hurt the height achieved.
Fortunately, there are alternatives.

Traditionally, parachutes were there to prevent steel cable from
kinking and tangling - Spectra/Dyneema rarely does either. Some clubs
have eliminated the parachute and just let the soft rope fall. Others
have used ~20" diameter plastic drag disks cut from the bottoms of
plastic barrels which are far cheaper and tend to protect the weak
link hardware. The drag disk can also eliminate the need to remove
and fold up an expensive parachute for the rope retrieve - just let
the disk drag behind the retrieve car.

Spectra/Dyneema rope forces a lot of changes in winches and
operational procedures.

Bill D

Spectra/Dyneema requires far less drag in the system than steel.

Europeans have tens of thousands of winch launches of experience with
Spectra/Dyneema rope on us and as far as I hear they don't see real
advantages (meaning they are switching back to steel). Neither in
life expectancy nor in launch height or ease of splicing are there
significant reasons to abandon steel. In fact, the winch guillotine
has to be modified to cut Spectra, much more difficult than severing a
steel cable.
Unless you are winching from a really nasty surface I'd say that the
steel cable is still overall the best material to go with.

Spectra/Plasma/Dyneema doesn't store energy the way steel cable does.
When cable breaks under tension, you get a huge tangle that has to be
dealt with. Hands, cable, winch, all get damaged. With the Dyneema, the
rope just falls with little or no tangling. That alone is worth the cost
to me.

On Jun 20, 10:02*am, Herbert kilian wrote:
Europeans have tens of thousands of winch launches of experience with
Spectra/Dyneema rope on us and as far as I hear they don't see real
advantages (meaning they are switching back to steel). *Neither in
life expectancy nor in launch height or ease of splicing are there
significant reasons to abandon steel. *In fact, the winch guillotine
has to be modified to cut Spectra, much more difficult than severing a
steel cable.
Unless you are winching from a really nasty surface I'd say that the
steel cable is still overall the best material to go with.

Citations?

The only people I know of who switched back were the ones who refused
to make the necessary changes to their winches and operational
procedures. And, perhaps, those with really short runways where there
is little gain in height.

If you want to see a really big difference in height, roll out 3000
meters of steel cable on one drum and the same amount of Spectra on
the other and see which one gets a glider higher. The aerobatic guys
in Germany got a ASK-21 to 1700 meters (5577') AGL - try THAT with
steel. They are most certainly not going back to steel.

However, for many, it there's no choice since insurance companies are
very aware that industries who previously used steel cable (wire rope)
have switched to Spectra for worker safety reasons saving the lives of
hundreds of workers a year. Wire rope is really nasty stuff. OTOH,
Spectra is really sweet to work with. It's easy to see the day when
wire rope is made illegal for any application where people are exposed
to it.

Yes, Spectra is much more difficult to cut with a guillotine which is
a testament to it's toughness - and to steel's weakness. However,
simple changes to guillotines allow them to cut Spectra.
Specifically, guillotines with a "shearing" action just won't work.
The tough Spectra pushes the blades apart and jams the works. The
only design proven to work reliably is a "chopping" guillotine where a
sharp blade cuts the rope against a brass block. This is just one of
the changes needed for Spectra.

On 6/20/2011 12:02 PM, Herbert kilian wrote:

Unless you are winching from a really nasty surface I'd say that the
steel cable is still overall the best material to go with.


In our case, our insurer (Costello) said it's going to be synthetic rope
or nothing.

Thanks for all the replies. Every one has been quite helpful!!

Tony