On Jun 23, 11:45*am, Bob Kuykendall wrote:
On Jun 23, 8:17*am, Derek C wrote:

Actually the maximum bending load on the wingspar during a winch is
equivalent to about 3 g, due to the point loading on the fuselage and
the lack of g unloading on the wings, but that still shouldn't cause a
failure...

I think that 3g equivalent load is a large enough percentage of the
limit load to constitute a fatigue concern. If I were assessing
service histories, I would definitely want to know the cycle count on
activities likely to cause that kind of load.

Thanks, Bob K.

Actually, it's probably worth worrying about any old, high-time metal
glider. Hard landings and turbulence flex the wings too. Blanik
maintenance manuals expressly limit the airframe life if used with
winch launch.

AFAIK, no composite glider has exhibited a failure mode anything like
this.