Best Rope to purchase for Auto Tows?

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I am looking for the benefit of recent experience with modern ropes
for auto tows. We fly off a 5000 foot grass runway (with a couple of
rocky spots). What size and type of rope would be best?

Bill Snead

[bildan]

On Oct 15, 9:21*pm, " > wrote:
> I am looking for the benefit of recent experience with modern ropes
> for auto tows. *We fly off a 5000 foot grass runway (with a couple of
> rocky spots). *What size and type of rope would be best?
>
> Bill Snead

Arguably the 'best' would be Amsteel Blue from Sampson Rope (~$0.41/
Ft.) 3/16" diameter would give you 5400 Lbs-F breaking strength and
weight about 1Lb/100 feet. It has about 10x the strength/weight and
15x the abrasion resistance of steel. If you prefer, it's available
in other colors.

http://www.samsonrope.com/index.cfm?rope=192

[Tim Mara]

please see http://www.wingsandwheels.com/page30.htm
I offer all types including Poly ropes, Dacron and Spectra all at very
competative prices
thanks
tim
Please visit the Wings & Wheels website at www.wingsandwheels.com


> wrote in message
...
>I am looking for the benefit of recent experience with modern ropes
> for auto tows. We fly off a 5000 foot grass runway (with a couple of
> rocky spots). What size and type of rope would be best?
>
> Bill Snead
>
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[danlj]

On Oct 15, 10:21*pm, " > wrote:
> I am looking for the benefit of recent experience with modern ropes
> for auto tows. *We fly off a 5000 foot grass runway (with a couple of
> rocky spots). *What size and type of rope would be best?

1: Based on personal experience, I would advise against using
polypropylene rope for autotow: it's much too elastic. The amount of
rubber-banding during the initial part of an autotow launch of a 1000
ft - plus poly rope is very interesting, and adds one extra,
unnecessary safety consideration to the first phase of launch: having
the rope go completely slack d/t elasticity just about the time the
glider is 15 or 20 feet off the ground and barely above stall is, in
my judgment, not desirable.

2: After the initial poly experience, our club switched to low-stretch
1/4" dacron rope in 1500' lengths from David Bradley (now via Wings &
Wheels). We actually strength-tested our ropes at first; found that
new rope broke at about 1700-1800 lb as claimed, and as the rope
abraded through being (inevitably) dragged along our highly abrasive
5000-ft runway, during a season the 100 yards of rope nearest the tow
vehicle decreased to about 1100-1200 lb (and became the actual weak
link). Your experience will be better on grass, though the fibers will
pick up sand, that will chafe internally and decrease strength.

3. Jacketed rope would wear longer but is more time-consuming to
splice in attaching hardware or when it does break, and is more
expensive. We did not try it.

4: I replaced the 1/4" steel cables of my hangar door with 1/4"
Spectra, and am very pleased with its durability and the lack of steel
slivers We are thinking of changing from Dacron to Spectra next time
we buy rope.

I would expect tow-vehicle traction to be a concern on a grass runway,
as grass is slippery. This would be mitigated with a (slow) running
start: use about 50 ft of slack rope, drive the tow vehicle about
about 10-15 mph until the slack comes out. Withf 1500 ft of woven
rope, this does not jerk the glider; meanwhile, there's less tire spin
and it's much easier on the engine and transmission. (Only an
automatic transmission is safe and durable; staying in a single gear
through the tow is highly desirable, as shifts take the power out of
the tow at poor times.)

[bildan]

On Oct 17, 3:11*am, danlj > wrote:
> On Oct 15, 10:21*pm, " > wrote:
>
> > I am looking for the benefit of recent experience with modern ropes
> > for auto tows. *We fly off a 5000 foot grass runway (with a couple of
> > rocky spots). *What size and type of rope would be best?
>
> 1: Based on personal experience, I would advise against using
> polypropylene rope for autotow: it's much too elastic. The amount of
> rubber-banding during the initial part of an autotow launch of a 1000
> ft - plus poly rope is very interesting, and adds one extra,
> unnecessary safety consideration to the first phase of launch: having
> the rope go completely slack d/t elasticity just about the time the
> glider is 15 or 20 feet off the ground and barely above stall is, in
> my judgment, not desirable.
>
> 2: After the initial poly experience, our club switched to low-stretch
> 1/4" dacron rope in 1500' lengths from David Bradley (now via Wings &
> Wheels). We actually strength-tested our ropes at first; found that
> new rope broke at about 1700-1800 lb as claimed, and as the rope
> abraded through being (inevitably) dragged along our highly abrasive
> 5000-ft runway, during a season the 100 yards of rope nearest the tow
> vehicle decreased to about 1100-1200 lb (and became the actual weak
> link). Your experience will be better on grass, though the fibers will
> pick up sand, that will chafe internally and decrease strength.
>
> 3. Jacketed rope would wear longer but is more time-consuming to
> splice in attaching hardware or when it does break, and is more
> expensive. We did not try it.
>
> 4: I replaced the 1/4" steel cables of my hangar door with 1/4"
> Spectra, and am very pleased with its durability and the lack of steel
> slivers We are thinking of changing from Dacron to Spectra next time
> we buy rope.
>
> I would expect tow-vehicle traction to be a concern on a grass runway,
> as grass is slippery. This would be mitigated with a (slow) running
> start: use about 50 ft of slack rope, drive the tow vehicle about
> about 10-15 mph until the slack comes out. Withf 1500 ft of woven
> rope, this does not jerk the glider; meanwhile, there's less tire spin
> and it's much easier on the engine and transmission. (Only an
> automatic transmission is safe and durable; staying in a single gear
> through the tow is highly desirable, as shifts take the power out of
> the tow at poor times.)

I would agree with the above. UHMWPE/Dyneema/Spectra/Amsteel Blue are
essentially the same thing and due to their high strength and light
weight are the preferred rope material. (It's good to see Tim Mara
selling Spectra at a very good price.)

We did a bunch of math on auto tow on the winch interest groups.
Straight auto tow requires a lot of room so doesn't make good use of
runway length. Going to a 2:1 "two-pulley" system with the rope
anchored at the upwind fence next to a pulley and a pulley on the tow
car converts the operation to essentially a winch and reduces the tow
car speed by half - but it also doubles the traction effort required.

The heaviest gliders require a black 10,000 DaN (2200 LbF) weak link
so the tow car would need to produce up to a 4400 LbF tractive effort
which is probably more than a grass surface can support.

Most operations serious about ground launch convert to a winch which
isn't limited by traction and does less damage to airfield grass.
Well run, a winch his faster to cycle than auto tow.