Aerotow ropes: short or long, breakable or unbreakable?

On Wednesday, November 13, 2013 8:17:22 AM UTC-5, Tom wrote:
The reality is there have indeed been fatalities due to over-strong tow ropes, and one of the preventative measures is to use a rope designed to break in case of over-stress.

The problem is that rope degradation is not recognized and defective ropes are used until they fail prematurely.

Is it a problem that we use tow ropes of a type that is subject to rapid degradation? The structural part of the rope is exposed to abrasion and UV. The open weave of the rope allows grit to penetrate and destroy the rope from the inside out. We use ropes that are dirty and show signs of "acceptable" wear. We test our ropes by towing the next glider.

Rock climbers approach this problem differently. Their ropes are designed to minimize the penetration of grit. The function of the outermost wrapping of the rope is to protect the structural core from grit. When the outermost protective wrapping is worn, the rope is discarded. In the old days, rock climbers would wash their ropes in the washing machine to remove micro grit.

Three questions:
1)Would a simple visual inspection find 99.9% of bad tow ropes before they break (Prematurely)? Do "good" towropes ever break?
2)Are we using the right type of rope?
3)Is there a way to test a tow rope on the ground without destroying it?

If you applied a known load to a tow rope (on the ground) and measured the elongation, would this not give an objective estimation of the condition of the rope? (As fibers break or weaken, the rope will elongate more under a known load). If the elongation is outside the limits, the rope is retired.

Would a magnifying glass improve the visual inspection process?

On Thursday, November 14, 2013 9:28:52 AM UTC-5, son_of_flubber wrote:

The problem is that rope degradation is not recognized and defective ropes are used until they fail prematurely.

Not at my club.

The rope requires a preflight inspection, just like our gliders and airplanes. If you aren't doing this, you are doing it wrong.

T8

On Thursday, November 14, 2013 9:55:42 AM UTC-5, Evan Ludeman wrote:
On Thursday, November 14, 2013 9:28:52 AM UTC-5, son_of_flubber wrote:



The problem is that rope degradation is not recognized and defective ropes are used until they fail prematurely.


The rope requires a preflight inspection, just like our gliders and airplanes. If you aren't doing this, you are doing it wrong.


I thought it was obvious that "used until they fail" refers to the specific ropes that failed prematurely on tow. Are you saying that visual preflight inspection will detect 99.99% defective ropes before they fail in the air?

One problem is that ropes are not retired when they show "normal wear", and visual inspection is very subjective. I was surprised to see what is considered "normal wear" in AZ where the tow rope is regularly dragged through grit. The effects of grit sawing away at the fibers inside the weave of the rope cannot be seen from the outside.

Are we gonna fly today or will the eight hour test and evaluation session
use up all available daylight?


"son_of_flubber" wrote in message
...
On Wednesday, November 13, 2013 8:17:22 AM UTC-5, Tom wrote:
The reality is there have indeed been fatalities due to over-strong tow
ropes, and one of the preventative measures is to use a rope designed to
break in case of over-stress.

The problem is that rope degradation is not recognized and defective ropes
are used until they fail prematurely.

Is it a problem that we use tow ropes of a type that is subject to rapid
degradation? The structural part of the rope is exposed to abrasion and UV.
The open weave of the rope allows grit to penetrate and destroy the rope
from the inside out. We use ropes that are dirty and show signs of
"acceptable" wear. We test our ropes by towing the next glider.

Rock climbers approach this problem differently. Their ropes are designed
to minimize the penetration of grit. The function of the outermost wrapping
of the rope is to protect the structural core from grit. When the outermost
protective wrapping is worn, the rope is discarded. In the old days, rock
climbers would wash their ropes in the washing machine to remove micro grit.

Three questions:
1)Would a simple visual inspection find 99.9% of bad tow ropes before they
break (Prematurely)? Do "good" towropes ever break?
2)Are we using the right type of rope?
3)Is there a way to test a tow rope on the ground without destroying it?

If you applied a known load to a tow rope (on the ground) and measured the
elongation, would this not give an objective estimation of the condition of
the rope? (As fibers break or weaken, the rope will elongate more under a
known load). If the elongation is outside the limits, the rope is retired.

Would a magnifying glass improve the visual inspection process?

On Thursday, November 14, 2013 10:50:46 AM UTC-5, Dan Marotta wrote:
Are we gonna fly today or will the eight hour test and evaluation session

use up all available daylight?

Good point. Time is limited.

If an elongation test would detect weakening ropes, you would only need to do it once a week or so because many forms of degradation is gradual. If you had a permanent jig for testing elongation, it would take 10 minutes. Or you could test the ropes at the beginning of wave season when you know they are gonna get stressed (or even better, you could replace your ropes at the beginning of wave season).

Ever have a rope break at Moriarty? I know that you have a lot of grit.

On Thursday, November 14, 2013 10:18:20 AM UTC-5, son_of_flubber wrote:
On Thursday, November 14, 2013 9:55:42 AM UTC-5, Evan Ludeman wrote:

On Thursday, November 14, 2013 9:28:52 AM UTC-5, son_of_flubber wrote:







The problem is that rope degradation is not recognized and defective ropes are used until they fail prematurely.





The rope requires a preflight inspection, just like our gliders and airplanes. If you aren't doing this, you are doing it wrong.





I thought it was obvious that "used until they fail" refers to the specific ropes that failed prematurely on tow. Are you saying that visual preflight inspection will detect 99.99% defective ropes before they fail in the air?



One problem is that ropes are not retired when they show "normal wear", and visual inspection is very subjective. I was surprised to see what is considered "normal wear" in AZ where the tow rope is regularly dragged through grit. The effects of grit sawing away at the fibers inside the weave of the rope cannot be seen from the outside.

So... is this operation experiencing rope failure without overload? In 27 years in the sport, I've never seen this. If I did see it I'd change my procedures.

At some of my favorite places to fly, a PTT at 50 - 300' has some significant risks, so we take launch prep fairly seriously, the tow plane pre-launch checkout includes a warmup flight, etc. We don't break ropes, we inspect them visually and service them before they get ugly. We have no need for an ASTM approved test program....

On Thursday, November 14, 2013 11:35:41 AM UTC-5, Evan Ludeman wrote:

So... is this operation experiencing rope failure without overload?
That does not tell us that their current procedure has a reasonable safety margin.
In 27 years in the sport, I've never seen this.
If I did see it I'd change my procedures.

Wait for a failure before evaluating procedures??

At some of my favorite places to fly, a PTT at 50 - 300' has some significant risks, so we take launch prep fairly seriously, the tow plane pre-launch checkout includes a warmup flight, etc. We don't break ropes, we inspect them visually and service them before they get ugly. We have no need for an ASTM approved test program....

The collective wisdom and experience of many people have developed the status quo, and I'm sure that it makes sense on balance, but does anyone know how close to failure ropes get before they are retired?

And there is the matter of how our uncertainty about the rope affects training and flight reviews. I watched a glider enter a spin after a "simulated rope break" during a biennial flight review (glider totaled, no injuries, pilot retired). Maybe "that should not have happened", but I'm left with the impression that PTT simulation is risky.

That the probability of a PTT is currently high enough to justify the risk of PTT simulation is part of my motivation. Can the probability of a PTT be lowered to the point that the risk of PTT simulation is no longer justified? How far can better rope material choice and better (practical) inspection go towards eliminating the possibility of PTT?

On Thursday, November 14, 2013 11:36:01 AM UTC-6, son_of_flubber wrote:

That the probability of a PTT is currently high enough to justify the risk of PTT simulation is part of my motivation. Can the probability of a PTT be lowered to the point that the risk of PTT simulation is no longer justified? How far can better rope material choice and better (practical) inspection go towards eliminating the possibility of PTT?

In over 2500 hours of glider flying, and maybe 700 towing, I've never had a rope break.

As a tow pilot, I inspect the rope at the start of the day, and when there is a break in the action (as part of laying out the rope behind the towplane to get it out of the way).

I've had two (2) PTTs in that time - neither caused by a rope breaking. One was an incorrectly hooked up Schweizer to hook (muddy) that gave me a PTT at about 200' in a loaded 2-32 (quick 180 and rolled back to the doofus who had hooked me up and made him do it again, correctly) and once when the tow pilot ran out of gas and released his end without telling me (but the funny thing was that it happened at exactly 3000' agl and I released at the same time - we never did find that rope!).

And all this at glider fields all over the US.

So I really think our procedures are pretty sound. Can ropes break? Of course. So can tow releases, weak links, etc...

As far as PTT training being dangerous - you can tow with a steel cable and still get a PTT. So yes, it is very important. And really, it's not a Chuck Yeager bit of airmanship, after all...spinning off a PTT is remarkably bad flying - and probably the sign of someone who was scared of stalls or steep banks at low altitude and didn't really know how to fly to the limits of his glider. You want to worry about something, worry about the currency and proficiency of your fellow glider pilots!

Kirk
66

Tow ropes do break, but in my experience it’s pretty rare. I’ve been soaring for only 8 years, primarily off of grass fields, and out of about 20,000 tows that have occurred during that time at the two sites I’ve flown from, I know of only 6 rope breaks. Four of those breaks occurred above 2,000 feet AGL, during slack line removal practice. One break occurred above 1,000 feet AGL, when a glider got high and upset the tow plane. One break occurred at about 10 feet AGL, when the tow rope came apart in its middle via unraveling.

The first four breaks don’t really bother me at all. The fifth break bothered a whole bunch of us, but not from a tow rope standpoint! The sixth break was initially disturbing, but we quickly discovered that a poorly manufactured batch of rope had been imported into the country (the substandard nature of the rope was pretty obvious simply by running the line through your hand).

Most of our tow rope wear occurs where the line is wrapped twice through the round part of the Tost ring. Pilots and line men see this area “growing hair” at the inspection done just before hook-up, and a worn tow rope gets rejected quickly. Our line men use a short stick with a metal hook in its end to guide the rope as the tow plane taxis into take off position. The feel of the rope going through this hook is a virtual mini-inspection, and has resulted in our finding knots as well as rope damage caused by trees and rocks.

-John, Q3

On Thursday, November 14, 2013 1:27:22 PM UTC-5, kirk.stant wrote:
after all...spinning off a PTT is remarkably bad flying - and probably the sign of someone who was scared of stalls or steep banks at low altitude and didn't really know how to fly to the limits of his glider.

I agree that it "should not have happened", but the pilot in the front seat had thousands of hours over decades of flying in multiple gliders. He had been a top glider pilot at one time. He put off his retirement from flying for too long.

I'm confident flying after a PTT if there is a place to land, but as Evan notes there are fields where the options after a PTT at 50-300 AGL are limited. I fully subscribe to Evan's emphasis on pre-flight inspections.