On Wednesday, June 26, 2013 3:38:21 PM UTC-6, Paul Ruskin wrote:
Hi Bill

So, Andreas verifies the 5 accidents the BFU lists for 2011 was all there was in 900,000 winch launches.



http://rdd.me/dstznowe says the UK suffered 12 for 180,000 launches.



How does that stack up?

UK: 1:15,000

Germany 1:180,000

Seems like Germany has a 12:1 lower accident rate.



Actually, the reference you quote above says that in 2011 there were 12 accidents plus incidents. Not the same as accidents. It's not really credible that the accident rate is 12:1 but the fatality / serious rate roughly the same, as calculated earlier. I think we're going to need to agree to differ on this one though.



It's great that the safer winch launching initiative in the UK has improved things but I think you need to find out what the Germans are doing right. I'd start by watching every "windenstart" video on YouTube. Hint: Time the takeoff rolls



OK - good thought. So I did. First five UK launches 5,2,2,4,2 seconds (roughly). First five German ones 5,4,3,3,2. Again roughly. Not a lot of difference (caveat - not a large sample and dependent on lots of other things). What was interesting was that the first two UK ones were from the same club, and used their old and new winch respectively. I think this time is largely equipment driven - could be that newer winches tend to be higher power. Don't disagree in principle though - and as I mentioned earlier, avoiding wing drop is a current focus at the moment in the UK.



On your point about minimum winch airspeed, I agree totally. It's standard teaching: (BGA Instructors' manual edition 3 page 16-1). I find it strange that gliders are placarded with maximum airspeed but not minimum.



Paul

When timing takeoff rolls, you need to find a way to consistently pick a moment when the acceleration begins. Many of the launches roll for several meters before the winch driver really hits the throttle. I choose the moment a nose wheel/skid glider's tail goes down and for tail wheel gliders when the wing runner lets go to start the clock.

To compensate a bit for this late clock start, I stop the clock when the glider's wheel is .5 - 1m above the ground. It's not perfect but then it's YouTube.

It's also necessary to estimate the wind. If there's a lot of wind noise on the sound track or the trees are obviously bending, I disregard that video. If I can see a wind sock in the background, I can estimate the wind. If there's a good sound track without wind noise, there's probably little wind.

Try that and see if your numbers change.