A tow hook installation done in accordance with AC 43.13-2B section 807 will
include a PLACARD stating the maximum tow line strength (1200 lbs for
Schewitzer). The installation paperwork for my Tost hook says 750 daN (1686
lbs). FAR 91.9 says no person may operate a civil aircraft without
complying with the operating limitations specified in the approved Airplane
or Rotorcraft Flight Manual, markings, and PLACARDS, or as otherwize
prescribed by the certificating authority of the country of registry.

So there is an FAR.

The POH for many glliders includes a maximum rope breaking strength, which
must be adhered to according to FAR 91.9.

4RL


wrote in message
...
On Jun 29, 12:43 pm, Tony wrote:
On Friday, June 29, 2012 2:13:42 PM UTC-5, Karen wrote:
On Jun 29, 9:25 am, Steve Leonard wrote:
On Jun 29, 7:20 am, Tony wrote:

On Thursday, June 28, 2012 9:43:36 PM UTC-5, Karen wrote:
Simple question, but why are tow hooks marked, "1200 lbs Max
weight",
like the Schweitzer type release, towing big heavy 21M ships,
ships
with water, Grobs and others over 1300 lb gross weights? Actual
pulling weight? Is there an FAR? Thanks.

1200 lbs on the towhook refers to the maximum rope strength, not the
smaximu glider weight.

And if you trace it back far enough, it probably stems from an old
NACA study on glider towing loads from the 1930s where they said "We
don't think there is ever a case where you could apply more than 1200
lbs load to a glider tow hook." And thus, we in the US are saddled
with a tow hook limitation from the days of 800 lb max weight two seat
gliders from the 1930s.
Thank you. So there is no FAR, just various 337's and field approvals?

from what i've seen the max load allowed on the towhook is usually
specified in the documentation for the installation. so yes, no FAR.

The FARs only specify the weak link requirements.