On Sunday, December 2, 2012 10:28:45 PM UTC-7, Bart wrote:
All,



After some research I came to a conclusion that in the USA, there is

no legal requirement to use a weak link during a ground launch,

regardless of the rope/wire strength.



First question: Am I missing something? Is there something like a

ground launch version of 14 CFR 91.309?



Second question: If the glider's POH does not offer any guidance (say,

1-26), what would be an appropriate range of rope breaking strength?



Thanks!

Bart

Actually, there is a legal framework of sorts. Look at 91.9 which requires you to operate all aircraft in compliance with their POH/AFM. AFAIK, all gliders except Schweizer will have a weak link specified for ground launch in their POH/AFM. 91.9 requires you to use the POH weak link. OTOH, 91.309 exclusively applies to aero tow.

The problem is with Schweizer who never bothered to publish weak link strengths for ground launch. In fact, ground launch in general seemed to greatly confuse them. For example, the 2-33 posits the winch launch redline (Vw)as HIGHER than the maneuvering speed (Va). While I believe Schweizer knew how to calculate Va correctly, the 2-33's published Vw is pure fiction. This doesn't make me feel good about any Schweizer Vw number.

Vw is normally set at 70 - 80% of the maneuvering speed which makes a great deal of structural/aerodynamic sense. With this as a guide, the 2-33's Vw should be 44 - 50mph which would be impossibly slow for a safe launch. The bottom line is if you thinking of winch launching a Schweizer, you're a test pilot.