Glider accident while filming commercial in 2011. NTSB Report updated

On Thursday, 27 June 2013 16:28:40 UTC+1, Bill D wrote:
On Wednesday, June 26, 2013 2:40:30 PM UTC-6, Martin Gregorie wrote:



the past I've used a stopwatch and timed consistent launches as taking 5 secs from first movement until the glider started to rotate into full climb, which I assumed meant the glider was accelerating through 50 kts.



This corresponds to roughly 0.5G on average.



That's about the same result I got from UK videos. The German "windenstart" videos seem to average 1.0G (19kts/sec)acceleration. I've yet to read of an accident that can be unequivocally attributed to excessive acceleration.

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Having been winch launching since 1969 I find myself disagreeing that very rapid accelaration at the beginning of the ground run is necessarily a good thing. Being off the ground in 2-3 seconds means (approximately) going from 0-60mph in that time and which gives a rate of increase of energy into the system such that if a wing does drop then and catch then there is little chance of the pilot preventing what should have been a release +/- groundloop turning into a cartwheel/flick tragedy. 1 g acceleration means that the glider is pulled off the ground so fast that it is unlikely to drop a wing but increases the chance of disaster if it does.

We lost the pilot of a Nimbus 3 to a cartwheel accident at our club last year. The accident report not yet published so I am not saying this was a factor there but it is self evident that if a glider pilot can release the cable in time before a wingtip hits the ground then there would be zero chance of a cartwheel accident

Furthermore excessive acceleration can cause some glider types to rotate too fast in that rate of rotation can increse the stall speed at this critical time.

The BGA advice for powerful winches is 3 seconds to the intended maximum intended (not necessarily full) thottle position for the glider and winch type - with the engine rpm following a bit behind that - and that feels right to me.

See the BGA winch operations slide show at:

http://www.gliding.co.uk/bgainfo/saf.../winchops.ppsx

John Galloway

On Friday, June 28, 2013 11:50:30 AM UTC-6, wrote:
On Thursday, 27 June 2013 16:28:40 UTC+1, Bill D wrote:

On Wednesday, June 26, 2013 2:40:30 PM UTC-6, Martin Gregorie wrote:







the past I've used a stopwatch and timed consistent launches as taking 5 secs from first movement until the glider started to rotate into full climb, which I assumed meant the glider was accelerating through 50 kts.







This corresponds to roughly 0.5G on average.







That's about the same result I got from UK videos. The German "windenstart" videos seem to average 1.0G (19kts/sec)acceleration. I've yet to read of an accident that can be unequivocally attributed to excessive acceleration.



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Having been winch launching since 1969 I find myself disagreeing that very rapid accelaration at the beginning of the ground run is necessarily a good thing. Being off the ground in 2-3 seconds means (approximately) going from 0-60mph in that time and which gives a rate of increase of energy into the system such that if a wing does drop then and catch then there is little chance of the pilot preventing what should have been a release +/- groundloop turning into a cartwheel/flick tragedy. 1 g acceleration means that the glider is pulled off the ground so fast that it is unlikely to drop a wing but increases the chance of disaster if it does.



We lost the pilot of a Nimbus 3 to a cartwheel accident at our club last year. The accident report not yet published so I am not saying this was a factor there but it is self evident that if a glider pilot can release the cable in time before a wingtip hits the ground then there would be zero chance of a cartwheel accident



Furthermore excessive acceleration can cause some glider types to rotate too fast in that rate of rotation can increse the stall speed at this critical time.



The BGA advice for powerful winches is 3 seconds to the intended maximum intended (not necessarily full) thottle position for the glider and winch type - with the engine rpm following a bit behind that - and that feels right to me.



See the BGA winch operations slide show at:



http://www.gliding.co.uk/bgainfo/saf.../winchops.ppsx



John Galloway

You and the BGA are tragically wrong. You need to take another long look at that analysis. Slow acceleration is the most significant cause of the poor UK accident record. Dragging a glider along with the pilot struggling for aileron control is not conducive to winch safety.

The safest possible acceleration would get the glider away from the ground instantly, but a 1G, 2-second ground roll is safe and practical. 1G acceleration winch launches are well proven in Germany to be safer. (It also happens to be the same as that felt when laying on one's back.)

On Friday, June 28, 2013 1:04:12 PM UTC-6, Bill D wrote:
On Friday, June 28, 2013 11:50:30 AM UTC-6, wrote:

On Thursday, 27 June 2013 16:28:40 UTC+1, Bill D wrote:



On Wednesday, June 26, 2013 2:40:30 PM UTC-6, Martin Gregorie wrote:















the past I've used a stopwatch and timed consistent launches as taking 5 secs from first movement until the glider started to rotate into full climb, which I assumed meant the glider was accelerating through 50 kts.















This corresponds to roughly 0.5G on average.















That's about the same result I got from UK videos. The German "windenstart" videos seem to average 1.0G (19kts/sec)acceleration. I've yet to read of an accident that can be unequivocally attributed to excessive acceleration.







================================================== ===========================







Having been winch launching since 1969 I find myself disagreeing that very rapid accelaration at the beginning of the ground run is necessarily a good thing. Being off the ground in 2-3 seconds means (approximately) going from 0-60mph in that time and which gives a rate of increase of energy into the system such that if a wing does drop then and catch then there is little chance of the pilot preventing what should have been a release +/- groundloop turning into a cartwheel/flick tragedy. 1 g acceleration means that the glider is pulled off the ground so fast that it is unlikely to drop a wing but increases the chance of disaster if it does.







We lost the pilot of a Nimbus 3 to a cartwheel accident at our club last year. The accident report not yet published so I am not saying this was a factor there but it is self evident that if a glider pilot can release the cable in time before a wingtip hits the ground then there would be zero chance of a cartwheel accident







Furthermore excessive acceleration can cause some glider types to rotate too fast in that rate of rotation can increse the stall speed at this critical time.







The BGA advice for powerful winches is 3 seconds to the intended maximum intended (not necessarily full) thottle position for the glider and winch type - with the engine rpm following a bit behind that - and that feels right to me.







See the BGA winch operations slide show at:







http://www.gliding.co.uk/bgainfo/saf.../winchops.ppsx







John Galloway



You and the BGA are tragically wrong. You need to take another long look at that analysis. Slow acceleration is the most significant cause of the poor UK accident record. Dragging a glider along with the pilot struggling for aileron control is not conducive to winch safety.

This is what I'm talking about:
http://www.youtube.com/watch?v=Ls_VIfxOV8U

Slow acceleration CAUSES accidents.

On Friday, June 28, 2013 11:50:30 AM UTC-6, wrote:

Furthermore excessive acceleration can cause some glider types to rotate too fast in that rate of rotation can increse the stall speed at this critical time.


This is waaay over rated. Pick any glider you think is vulnerable and I'm sure there's a video on the Internet of it being launched with less than a 2-second ground roll. Acceleration alone does not cause uncommanded pitch-up.

Is an inertial-couple induced pitch-up real? Yes. But it can't happen with a tailwheel in contact with the runway and the pilot can oppose it with down elevator above the 50 knots Vw-min. That leaves the 40 to 50 knot window lasting 1/2 second at 1G acceleration where a glider's natural rotational inertia about the pitch axis and it's aerodynamic stability will prevent excessive pitch-up.

What CAN go wrong is if the pilot gets impatient with a slow acceleration and pulls up in the window of vulnerability so the inertial couple combines with up elevator to produce an excessive pitch-up. There are dozens of videos showing UK pilots doing exactly that on YouTube. The cure is simple - teach pilot to hold the nose down and wait for Vw-min before allowing the glider to rotate into a climb.