Life glider hours with winch

As Bob said, the only concern with wooden ships is adequate
maintenance which includes a timely stripdown to bare wood and
inspection of all structural components. Type of glue used is a
major factor, looking at recent issues with common glues like
Kaurit WHK.

GFRP ships like wooden ships have no life limitations based on
use, solely in hours. At least that I know of based on reading
dozena of manuals and type certificates. Looking forward to being
corrected. Have just done a life extension for an ASK21 that had
50,000+ launches and it was in great shape. Just had to replace
the main pins and stab pins as they had reached the end of their
fatigue life of 12,000 hours...

Theoretically, there’s a long fatigue life left in gliders like this when

looking at the calculations Eiri did for the PIK-20s...

At 02:02 22 March 2019, Bob Kuykendall wrote:
What I've read is that the bending forces applied to the wings
and tail
dur=
ing a typical winch launch are roughly equivalent to 3.5g flight.
That is
c=
omfortably below the load limit of every common glider.
However, it is
high=
enough that repeated launches will eventually shorten the
service life of
=
an aluminum glider. The Blanik designers understood this very
well, and
the=
original service documentation was quite explicit about logging
operations=
carefully so the service life could be tracked. Unfortunately,
most
operat=
ors did not do so.

Normal winching operations probably has no appreciable effect
on the
compos=
ite parts of a composite glider. However, I believe it was BGA
analysis of
=
repeated winch launch stresses that initiated the service bulletin
on the
s=
teel end-pins ("spigots") on Grob 102, 103 and 109 series
sailplanes.

As for wood sailplanes, my concern would mostly be around the
age and
condi=
tion of the structure, since many wood gliders are now half a
century old.
=
Since you don't feel the added stresses of winch launching the
way you
feel=
the g of vertical acceleration, it would be easy to get into the
gray
area=
between what the structure was originally built to sustain, and
what it
ca=
n actually sustain after fifty years of operation, repairs, and
deteriorati=
on.

--Bob K.