On Aug 12, 4:12*pm, Frank Whiteley wrote:
On Aug 12, 3:16*pm, ContestID67 wrote:



I was sent this link from a UK soaring friend of mine about a death
when the wings came off of a glider during a winch tow.http://www.dailymail.co.uk/news/arti...lunged-death-b...

Sad story. *A few things;

- My friend's thought was that the wing pins were left out. *Howerver,
this was the second flight of the day. *Both winch launches. *So I
would think that the wing pins were installed but the wings failed
under a winch load. *Which glider was it? *Older? *Wooden spars?
Never having had a winch launch, what happens if you don't release
back pressure at the top? *Can you pull your wings off? *Maybe
safeties on the pins were missed and the pins wiggled out on the
second flight after staying in for the first.

- I was under the impression that the BGA required parachutes for all
pilots. *Wrong? *1000 ft should have been enough to get out in time
but who knows what was happening in the cockpit or if she was 1000 MSL
or AGL at the time.

Thanks.

- John DeRosa

It was a Foka 4.

Foka-4 was a derivative of the Foka linehttp://en.wikipedia.org/wiki/Foka_%28glider%29
Cobra was the next to last iteration, with 17m being the last.http://en.wikipedia.org/wiki/SZD-36_Cobra_15
Note the comments on failures.

I don't know that the 4 had the same wing join design, but suspect it
was very similar.
There was a wing failure on a Cobra in the US and a sobering analysis.http://www.sylacaugasoaring.com/SZD%...%20WARNING.htm

The SHK has an expanding vertical pin. *There's an anecdotal story of
someone who used the right-hand to expand the pin, and finished the
job with left-hand, in the opposite direction. *The wings reportedly
departed at the top of the launch. *The pilot reportedly pulled the
tail chute on the way down.

I believe that some German studies found that successful egress and
parachute deployment below 600m is unlikely, of course there are
exceptions. *The better emergency chutes are life saving from 100ft
agl at 100kts horizontal.

Wing failure on a winch launch is very rare. *There was a K-7 at RAF
Dishforth in the UK a while back, but the investigation determined
there was prior damage to the spar which was not found following
another incident. *There was a homebuilt in Colorado that had a wing
failure due to aileron flutter during a winch launch. *After two weak
link breaks, the pilot doubled the weak link (unknown to the winch
crew). *The described flight path was one of climb, level off, climb,
level off, climb, glider breakup, crash. *The wing inspection hatch
was found early in the flight path. *What did not appear in the NTSB
report was that the pilot was refused further tows at the local FBO
after the glider had suffered significant aileron flutter on aero tow.

I winched at RAF Bicester when it was the RAF/GSA Centre. *Appropriate
weak links were always used, like any UK club. *It's not a long run,
but easy enough to climb away on the thermal day.

Steel wire rope used in many places typically has a breaking strength
of 2800-3500lbs. *The new UHMWPE 12-strand ropes (Spectra, Plasma,
Dyneema, Amsteel) now in common use are nominally 3500-5400lbs
breaking strength at similar diameters, thus use of correct weak links
are essential to avoid damaging a glider as some winches have
substantial power and there are also gusts and thermals to allow for.

Frank Whiteley

Frank's analysis is excellent.

I would only add that the wing spar loads incurred during a winch
launch is approximately that of a loop. If a glider is not approved
for loops or its age and condition is such you wouldn't loop it, don't
winch launch it.

Always use the EXACT weak link specified in the manual. If a glider's
manual doesn't specify a winch launch weak link - you're going to be a
test pilot if you winch it.

Bill Daniels