Aerotow ropes: short or long, breakable or unbreakable?

On Tuesday, November 12, 2013 9:16:19 PM UTC-7, GM wrote:
On Tuesday, November 12, 2013 11:22:14 AM UTC-5, son_of_flubber wrote:

With the dewpoint at 15d F. today, I'm ready to heat things up.







Regulations on aerotow ropes vary by region. What is the evidence to support the various approaches?







PTT (Premature Termination of Tow)(aka rope break) correlates with a number of fatal accidents. How often has a hard_to_break towrope led to a fatal accident?







Options to land after a PTT vary by airport and can be non-existent at certain altitudes. Why is an extra strong towrope not an option where the straight-ahead landing option is poor or non-existent?







In what year did the FAA set the FAR for towropes and what was the quality of towropes at that time? (obscure, but interesting question).







At the airport where I am towed, the same towrope satisfies the FAR for both the frequently towed heavier two-seater, and my less frequently towed lighter weight single place glider. Does this mean that the two-place is more likely to break the towrope?



The 80-200% rule is in the FARs but it DOES NOT APPLY to ANY glider which - at the time of US-certification (standard or experimental) - had a manufacturer's issued and approved POH, which spelled out the breaking strength of a weak-link for the CG and aero-tow hook! In some cases, these may be the same; in most cases, the aero-tow weak-link strength is lower.

In Europe, typically very strong tow ropes (mooring lines, as one US visitor to Europe called them) are used but there is a proper weak-link attached on the glider end.

A short while ago, I did launch a quick survey on the German forum to find out how many tow rope failure anyone had. The response: zero tow rope failures!

Precisely!

FAR 91.309 (the 80 - 200% rule) is for gliders whose POH didn't specify aero tow weak links (Think Schweizer). FAR 91.9 is for those which do. (Think any glider certificated under JAR-22/CS-22) If your manual specifies an aero tow weak link, 91.9 requires you to use it. 91.9 trumps 91.309 - that's the law.

The combination of 91.309 and 91.9 pretty much requires a weak links on each end of the rope with the one on the tow plane end 25% stronger than the one on the glider end. With two weak-links why would any sane person want to use a weak towrope?

We should use massively strong ropes and let the weak-links handle overloads. That way there should never, ever be a rope break. It's not what we do - and we pay the price.