Bill,

Over accelerated "Kavalierstart" winch launches often have nothing to do
with 'pilot error'. If you are already holding the stick hard against the
forward stop to try and stop the glider over-rotating, what else can you
do, apart from pulling off? Even that would leave you in a very tricky
situation, with the glider very nose high and very close to the ground!

It is quite difficult to overpower a K21, a Grob G103 or a DG1000, mainly
because they are quite heavy and need a lot of horsepower to accelerate
them. Anything lighter than this, and fitted with a belly hook, is
potentially at risk with modern powerful winches, and I include K13
two-seaters in this. I would not recommend launching on a nose hook by the
way, as you will get a very poor launch and they normally don't have a
back release mechanism.

The problem can be avoided anyway by limiting the winch power or tension
setting to what the glider type can safely handle. The Skylaunch winch
does this very well, as long as the driver sets the throttle tabs
correctly.

Derek Copeland

At 15:18 19 March 2009, bildan wrote:

I didn't accuse anyone of "hoky-poky" and certainly not the
publishers
of Aerokurier. I just said that statistics don't work very well for
accident analysis since the data set is too small to draw meaningful
conclusions. To the extent that you analyze anything with accident
statistics, it's pilot skill. That dominates the results not
equipment or procedures. Inconsistent and variable pilot skills
introduces way too much "noise" in the data. Statistics are simply
the wrong tool.

The right tool for this problem is engineering. Every single
parameter can be analyzed with measurement data. If excessive
acceleration does, in fact, reduce AOA margin, that would be very
straight forward to measure. Just install an AOA indicator,
commercial units are available, and simultaneously measure
acceleration with a tensiometer or with a simple video camera. Start
slow and work up. If the stall margin is getting smaller, you'll know
when to stop. Rock solid engineering data will also validate
mathematical models - or not.

I happen to think that the "Kavalierstart" you speak of is pure pilot
error. The pilot causes, or allows, the glider to rotate into a steep
climb before he has safe airspeed. Once over-rotated and stalled,
there is insufficient elevator authority to reverse the situation -
he's riding a kite not flying a glider. A good pilot can prevent this
at accelerations right up to the breaking strength of the weak link.
I know because I've done it.

Requite qualification: There MAY be a very small number of gliders
whose inertially induced pitch-up under hard acceleration exceeds the
elevator authority to prevent it. .