Winch Launch Safety Study

On Mar 19, 12:26*pm, wrote:
Bill,
the statistics covers accidents and launches in the period from
2002-2008. Brought to an annualized figure that means there were an
average of 1,449,500 glider launches every year for the period. That
is, the analysis covers about 10,146,500 launches of all types in
Germany and the accidents that resulted from these. That's a pretty
big sample. The sample also covers 60 winches in France, listed
separately. (the only accidents in France involved electric winces)

In Germany, for the period (2002-2008), there was a yearly average of:
712,500 - Winch Launches
237,000 - Aero tows
500,000 - Motorglider take offs (fixed position motors)

The number of motorized glider take offs is not indicated, but the
number of their accidents is, which comes out to 5.3% of all glider
launch accidents involves this type of launch.

I don't think the sample is too small.

Your statement that one could simply install an AOA indicator to allow
the pilot to avoid exceeding the AOA misses the point entirely. The
point is that exceeding the AOA occurs because of what the winch does,
not the pilot - namely, excessive initial launch speed/tension/power
resulting in an uncontrollable excessive initial pitch up movement
that ends with a stall and flip into the ground at high speed within
seconds.

The only aircraft type pattern mentioned is that involving GROBs.
These types were never involved in flip ins during inititial launch.
Another anomaly is that in 45% of all accidents involving broken weak
links Grobs were involved - indicating the certified strength of the
weak links for Grobs are not strong enough.

I think the analysis is very thorough and makes strong
recommendations. What you are doing, strong initial acceleration
launches (which I presume exceed 1g rope tension), is what they are
saying should be avoided. Later in the launch phase, it's OK to
increase tension beyond 1g, but not in the initial danger zone.

I think understand, Tommyto is Derek Copeland using one of his
hundreds of aliases.

The statistics are interesting but prove little without actual
engineering measurements. What the statistics do suggest is that
pilot incompetence is sadly not rare and that someone should do some
actual certified engineering measurements.

To increase the weak link strength without engineering data to insure
that is in fact safe is grossly irresponsible - and illegal in every
country in the world except the UK. In any event, the final and only
authority on that subject is holder of the type certificate - Grob
itself. (US pilots note that weak link strengths are set under JAR-22
to a prescribed value with a +or- 10% tolerance as part of a types
airworthiness certificate - read your POH.)

To suggest that pilots are crashing due to the weak links being too
weak would be hilarious if not so tragic and I'm quite sure the LBA
and/or DAeC made no such suggestion.

Weak link failure accidents are 100% pilot error and 0% hardware
deficiency. Pilots must EXPECT wire or weak link failures and be
prepared to deal with them safely. Pilots who can't handle a launch
failure with big safety margins should be grounded for extensive
retraining.

I did NOT suggest using an AOA indicator to help the pilot avoid
"exceeding the AOA" [OF STALL?] although that is a great idea. What I
did suggest is using it as an engineering measurement tool to
determine if increased acceleration was causing an increase in AOA.

My measurements suggest the exact opposite - that increasing the
acceleration REDUCES the maximum AOA. Other measurements suggest that
even gliders with a strong inertial pitch up tendency will break their
weak link under strong acceleration long before running out of
elevator.

If you want statistics, they seem to show that over rotation leading
to stalls on the wire occur mainly on weak winches and auto tow -
always as the result of premature pilot induced pitch up - as in
counting 6 seconds and pulling up without consulting the ASI.