At 02:03 14 October 2013, Bill D wrote:
I don't get accident statistics from RAS comments.

The Dropbox link has changed. See:
https://dl.dropboxusercontent.com/u/...Acceleration.p
df


Maybe the ancient Gehrlein winches you have in the US are not
powerful enough to cause uncontrollable pitch ups, but we did
have a problem with this when we first had powerful V8 Tost
winches. K8's and the like would rocket up almost vertically
before (usually) the weak link broke. Fortunately none of them
flicked and all the pilots involved were quite switched on and
managed to get the nose down and land safely. The problem
was largely solved by opening the throttle a bit more gently at
the start of the launch. The nice thing about the Skylaunch
winches we have now is that they deliver the right amount of
power for the glider type being launched, so you get the same
ground run time for all types. So one less type conversion issue.

The acceleration induced pitch up effect is only transitory by the
way. During the ground run it is constrained by the tailwheel,
and once the glider is safely established in the full climb the pull
line and the c of g become more closely aligned. The dangerous
bit is the rotation! If the mainwheel lifts off first, the glider
pitches up to a steep angle and then the tailwheel lifts off and no
longer constrains the pitch angle, it is at this point the wings may
stall, and if any yaw is present may flick roll. The safety
message is don't over-accelerate lightweight gliders and control
the rotation rate so that it is not more than 10 degrees per
second.

Derek Copeland