Bob's post below is clear and correct.

I would like to add, however, that at least my reading of accident reports
suggest that a fatal glider accident is more likely when the towline fails
prematurely. For that reason, I like to stay near the stronger end of the
FAR 80% - 200% range.

Actually, reading the POH for several German gliders, I note the weak link
for aerotow is specified as as exact figure. For example, the weak link for
both aero tow and winch for my Nimbus 2C is specified as 600 Kg (1323 Lbs)
or a blue Tost weak link. The tolerance is + or -10%. The US Airworthiness
Certificate specifies that the Nimbus 2C is to be flown as specified in the
Pilots Handbook (POH). Considering the possible flying weights, this ranges
between 95% - 160% which is a narrower range than specified in the FAR's.

Make me wonder if we should be using Tost weak links instead of old bits of
rope.

Bill Daniels

"RL" wrote in message
ups.com...
This topic is worthy of discussion, so it would be nice to avoid having
it degenerate into the typical RAS morass. I've flown at commercial
operations that use large diameter "tugboat" rope. The explanation
for this is usually something like, "Oh well, we put a knot at the
end that cuts the breaking strength in half", or "We can't afford
to keep changing those little skinny ropes...".

Let's start at the top of the list: Number one - In the US, FAR
Part 91.309(3) seems crystal clear in terms of requirements - A
towline (or weaklink) is required to be not less than 80% of max glider
weight and not more than twice the max operating weight. I am not
aware of any options in the regulations to do something different. In
fact, if you are doing something different I suspect the FAA, your
insurance company, or maybe some plaintiff's attorney might be very
interested should an accident occur.

Doug and Papa3 are right in their assessment and experience that a
glider can damage a towplane. I've seen an overstress failure of a
tow hitch which broke and bent parts in the attachment assembly.
Notwithstanding excess structural loads on the empennage, the very real
danger is the tow plane running out of pitch control in the event of a
kiting incident.

I witnessed a kiting accident caused by a glider elevator misconnect.
The glider climb resembled a winch launch with the tow plane at 50-100
feet off the ground. The tow rope broke at about the same time the
towpilot had the stick on the back stop and was pitching down. This
happened so fast, had the rope not broken as it was designed to it is
very doubtful the towplane could have either released or recovered.
There would have most likely been two fatalities that day if the tow
rope had not been the correct breaking strength.

It would take a foolhardy towpilot to believe: 1) An over-strength rope
would be legal 2) An over-strength rope could not cause structural
damage to the towplane 3) The tow pilot could react quickly enough to
release in a low level kiting incident.

The tow "system" works with multiple layers of protection if the
rope is the proper specification.

Bob