Glider accident while filming commercial in 2011. NTSB Report updated

Bruce, I find your analysis helpful.

Indeed, it is metadata. However, if you have enough of it, a statistically significant picture emerges. But even so, metadata doesn't explain the detailed why and how of the picture it presents. That's the next step. At best it tells you where to look and what to look for.

I contend the 130,000 annual aero tows in the US and the related accidents are statistically significant. It's pretty simple to compare German winch launch to US aero tow for 2011. German winch launch and US aero tow suffered exactly the same number and type of accidents so the relative number of launches tells the story. 900,000 vs 130,000 is 7:1. The two countries can be said to be experts at their respective launch styles so it's a valid comparison. i.e. "Given equal levels of expertise, winch launch is 7 times safer than aero tow." I think both launch styles are equally sensitive to a lack of pilot skill.

Despite the truly excellent German winch safety record, Professor Dr. Richard Eppler at the University of Stuttgart (He of numerical airfoil analysis fame.) thinks it can be improved further and has written a paper on the subject for flight instructors. One of the insights from the paper is the concept of a minimum airspeed for winch launch that should be part of airworthiness documents and listed in flight manuals. DG was apparently listening so the DG1000 manual lists a minimum winch airspeed of 49 knots. So now in addition to Vw-max we have Vw-min. If pilots had simply ensured their airspeed was always above Vw-min, a significant number of accidents would not have happened.

Another not-so-rare accident type starts with a wing tip contacting the ground during the takeoff roll where it digs in and the rapidly accelerating glider "cartwheels". In the worst case, the glider ends up inverted and the result is fatal.

Counter-intuitively, the solution is even more acceleration to give the pilot aileron control before a wing can drop and then get him airborne where the wing can't touch the ground. More acceleration also gets the glider above Vw-min before the pilot can begin rotating into the climb. Vw-min assures enough elevator authority to prevent inertial pitch-up in high-CG, low hook gliders.

YouTube videos show a difference between UK practice and German practice. German ground rolls are pretty consistent at two seconds indicating 1G acceleration. By contrast, I've seen videos of very wobbly UK ground rolls taking as much as 15 seconds but that's an exception - most are 3 - 4 seconds.




On Wednesday, June 26, 2013 12:45:49 AM UTC-6, BruceGreeff wrote:
Meta data is data describing other data. In this case the metadata is

what is missing.



We don't have enough information for meaningful comparisons.



That is where I where I am going - and in fact gone.



You are using historical data, without enough context to draw

conclusions about current practice.



So the specific example I gave in fact demonstrates that the useful

information is often well hidden. If we use your approach you have a

statistic that supports the contention that winch launch is 100% more

dangerous than aerotow for this set of data.



Lots of problems -

1 the set is too small (the BGA vs LBA sets are statistically significant)

2 the metric and the generator are not linked. Launch method had nothing

to do with either incident. Poor airfield maintenance and pilot decision

on risk is the cause (both involved a groundloop because someone did not

cut the grass properly and the pilot decided to proceed anyway)

3 the outcome is biased by a "hidden" factor - the actual damage that

resulted in the report of damage to an airframe was traced to

progressive failure of a poor repair after an outlanding accident

decades back when the glider was a competitive two seater in Germany. It

was going to break some time soon. This flight just happened to involve

the trigger stress.



Did the launch method have much to do with the damage, not really. If

the poorly repaired wing failed during spin training, would it mean that

our spin training is dangerous?



So - to be very explicit - where I am going with my comment is that I am

concerned that you may be oversimplifying in an attempt to prove your

opinion. Where an hypothesis would be well enough constructed that is

could be proven.



If you said that the historical accident data for the period you

reviewed showed a difference in the relative safety of operations at

German versus British gliding clubs, that might even be an uncontestable

finding (102). If you compared the trends in accident rates and found

them to be stable over the period you might even be able to conclude

that this is representative of the current situation. (the numbers are

comparable)

If you had qualified the analysis by using the numbers where the

investigators concluded after careful consideration that the launch

method was the causal factor, then you could even conclude that "Winch

launch operations" are more dangerous in one than in the other.



Since you have too little "metadata" and are making conclusion without

all the painful logical and mathematical rigour that makes Business

Intelligence type metrics such a tedious business, I think it is

dangerous and misleading to make the kind of assertions you are making.



Unless you know the actual cause of every number in the set, you can't

make confident assertions.



(Humour alert) There are 10 kinds of people in the world. Those who

understand binary, and those who don't. (10 in binary = 2 in decimal) ;-)



As Bob says, is it possible? Definitely.

Does a simple integer comparison of two numbers prove the assertion? I

think you would have to question that.



Personally, I find winch launching risk to be more tractable. You can

control risk better.



But again - context is important. Winch launching an open class glass

ship with water ballast would probably be less safe than aerotowing the

same combination, all things being equal.



T59D #1771



Not sure where you're going with this, Bruce. Of course there are reasons for the differences and that's a a very important discussion to have but it doesn't affect the difference itself.



The raw accident count for the number of launches done is really metadata (To use a currently popular term.) Metadata is very valuable in seeing the big picture but not so much for analyzing the details for why it looks that way. Hopefully, the metadata will provoke that kind of detailed analysis.





--

Bruce Greeff

T59D #1771

On Wed, 26 Jun 2013 09:58:47 -0700, Bill D wrote:

YouTube videos show a difference between UK practice and German
practice. German ground rolls are pretty consistent at two seconds
indicating 1G acceleration. By contrast, I've seen videos of very
wobbly UK ground rolls taking as much as 15 seconds but that's an
exception - most are 3 - 4 seconds.

In the UK a lot of emphasis is put on having at least 50 kts *and
accelerating* before you rotate into a full climb.

I don't recall any specific comments about acceleration rates, though in
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.

This was on our club's Supacat winch with a 240 hp diesel V8 powering it.
The huge majority of the launches I've had on this winch have been like
that. I've also had a couple of launches on a Skylaunch (350hp+ V8
burning LPG), which provides a noticeably higher initial acceleration
than our V8 Supacat. I'm happy with both.

OTOH, I recently had a few much more sluggish launches with longer ground
rolls and that subjectively seemed to take forever to accelerate past 50
kts. I didn't like these at all and have promised myself that if I get
another I'll be having a discussion with the winch driver.

I'm with you on this Bill: brisk acceleration on the winch is good.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

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.

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

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.

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.