Bart,

Thank you for being sensitive to our friends in Austria. Our problems with
the L-13’s are nothing compared to the issues the families of the pilots
have.

You asked about the effect of exceeding limits. Your logic is correct.
Ductile metals, such as aluminum, have known performances. Stress-Strain
data is what engineers use to design structural components. It will tell
them the Elastic Limits, Elongation Limits, Ultimate Tensile Strength, and
when a Fracture will occur.

Your comment of a “Theoretical” scenario of constantly flying 20% above
the limit might result in a reduced life of the spare.

My “Theoretical” scenario would be one flight where the pilot got into
trouble and accidentally exceeded 50%. This would take the spare past it
Elastic Limits and significantly reduce it’s life. To add to my scenario,
if the limits were exceeded 10-20 years ago, the oxidization build up on
the aluminum might mask that damage. A fresh fracture would be shiny
because of the absence of oxidation.

Again, this is a theory that has almost no data backing it. However,
there are approximately 3000 Blaniks in the world that have been flying
for 2-3 decades. That is a solid record that speaks to the design life.
The L-13 in question is low time and had been over hauled. It does not
appear to be the norm.

Since this is a fatality, the investigators will get to the root cause for
the accident. They will probably review the design calculations. They
might also do a metallurgic test to determine the pedigree of the aluminum
in the spare. Their investigation will take time. We probably won’t see a
report for a year. (Again, my guess)

Andrew




At 22:21 30 August 2010, Bart wrote:
If a glider is routinely overstressed by, say, 20%...

I would like to add that the scenario above is purely theoretical and
I am not trying to suggest that the accident in Austria was caused by
anyone who has flown the glider in question in the past.

B.