On 1/4/2012 6:11 PM, Markus Graeber wrote:
I am in the process of writing up some regulations for aerotowing to
standardize operations and ensure safe procedures for us here in
Colombia. The civil aviation authorities don't know a thing about the
intricacies of aerotowing so we are on our own with how we want to go
about it. Hence the desire to implement something that resembles best
bractices across the gliding world.

I have been reviewing information/regulations from Germany, the US,
the UK, Australia and New Zealand as well as manufacturer information
and manuals.

Snip of excellent research summary...

So the quick summary of my take so far on all this with regards to
aerotow ropes is:

- Minimum aerotow rope breaking load of 2248 lbf (1000 daN)
- General purpose length of aerotow rope for standard daily ops of 50m/
165 feet
- Use of 2 weak links, one on the glider end, one on the tow plane end
- Weak links with the Tost reserve setup, 899 lbf (400 daN) on the tow
plane end, 661 lbf/300 daN on the glider end

Looking forward to comments, suggestions, experiences etc. Thanks in
advance,

Markus Graeber
Aeroclub de Colombia
Gliding Colombia/Vuelo a Vela Colombia

Hello Markus,

Seems like a great "good news/bad news" situation you're faced with...the good
news of having a blank sheet of paper & the bad news being (non-bureaucratic)
you have to do all the filling in of it. I hope the Powers That Be eventually
see fit to buy into your conclusions/suggestions...

Off-the-cuff thoughts follow...
- "Real" (as in metallic, testable, precision-made) weak links at both ends
seem to me to be eminently sensible & much preferred over "knots in rope"
sort of weak links. While only Tost (so far as I'm aware) makes these, anyone
with access to spec-ed metal, standard machine tools, and a pull tester could
easily "roll their own." Hence, spec-ing such doesn't necessarily build
"whiney" up-front costs. IM(U.S.-based)O, the U.S. FAA approach of specifying
*only* breaking strengths probably has worked as well as it has mainly because
historically the U.S. has been primarily an aero-tow operation. Kinda-sorta
related, personally I wouldn't winch launch without a "metal-spec" weak link
at the glider end.
- I think you're right to "ignore DA-40-like" plane-specific special cases in
any spec-ing you do. Let plane manufacturers rule out/self-limit any newer
models they roll out. It probably won't be in our lifetimes
non-manufacturer-spec-ed acceptable towplanes (e.g. Pawnees and Super Cubs in
the U.S.) vanish. Don't self-create problems for your country/self.
- Avoid the "over specification" swamp. For example, don't specify max/min
rope length or strength. (Well, OK, maybe some motherhood words about an
aerotow rope having to be stronger than either weak link, just to satisfy the
lawyer crowd.) On the winch side, if some bubba wants to build a monster winch
using chain as the cable, a glider-end weak link should adequately protect the
glider and its educated, qualified and current pilot (and passenger, if any),
which I would suggest is the proper/sufficient goal. Let education and "the
market" address all the other glider-launching, safety-related issues.

You should get some interesting feedback!

Regards,
Bob W.