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Fatal crash Arizona



 
 
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  #21  
Old May 7th 14, 01:30 AM posted to rec.aviation.soaring
Mike the Strike
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Posts: 935
Default Fatal crash Arizona

On Tuesday, May 6, 2014 4:56:44 PM UTC-7, Don Johnstone wrote:
At 22:22 06 May 2014, Bill D wrote:

On Tuesday, May 6, 2014 2:41:23 PM UTC-6, Don Johnstone wrote:




Frankly I would be horrified to be required to conduct a turn back at


=20


200ft, I would suggest that this is one of those occasions where the


dang=


er


=20


of practice is to great to justify.




If you should check out in the USA, you'll be required to demonstrate


compe=


tence in this maneuver. Every pre-solo student is required to do so and


mo=


re than a half century of safety records do not suggest a problem. In


fact=


, even with low performance gliders, there's quite a large safety margin..


T=


he most likely outcome is a pilot will find the glider uncomfortably high


f=


or a downwind landing requiring full spoilers and a slip.




The logic is simple - it's better to have pilots trained for the option.


N=


o one says a pilot is required to turn back or that 200' is always


adequate=


to do so. What is illogical is to suggest a pilot be required to crash


in=


unlandable terrain when a safe option exists to land on the departure


runw=


ay.




What are you trying to save? The pilot or the aircraft? The priority should

be survival of the soft bit, that is you and me.

As an instructor with nearly 50 years experience I know that when I

initiate an emergency procedure I do so allowing a margin to ensure my

survival if it does not work out, I have been bold but never certifiable.

Most living instructors have the same survival instinct. That is why I have

lived long enough to do 10,000 launches, and of course landings. It has

already been hinted that the practice you describe involves modifying what

you normally do, in my view that probably makes it pretty useless and not

real preparation for the event. If you did carry out the training in

exactly the same way as the possible real event you might find that the

results were very different, not to mention painful. I will stick with my

300ft thank you, I know it works. Low turns, below that height may have

been acceptable in old wooden gliders, the minimum height in T31 and T21

gliders was 150ft, but for modern glass gliders it is just far too low, you

only have to look at the accident statistics to see that low final turns

figure to a large degree in accidents so why plan for it?

I repeat a controlled descent with wings level is far more likely to have a

better result than hitting the ground in a turn or even worse spinning in

trying to avoid it.



PS Despite all that there have been times when I have initiated a practice

emergency and very quickly wished I had not, no plan survives first

contact.


I should also add that over the years, I have retrieved various sailplanes that made controlled landings into terrain in Arizona, including mesquite bushes, palo verde trees and ironwood trees. Only one of these aircraft was seriously damaged and all the others have been repaired. No pilot was seriously injured. Level flight into quite evil terrain does appear a much better option than a sharp turn at low altitude, with a significant possibility of stall/spin or uncontrolled ground impact.

Mike
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  #22  
Old May 7th 14, 02:07 AM posted to rec.aviation.soaring
Bill D
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Posts: 746
Default Fatal crash Arizona

On Tuesday, May 6, 2014 4:08:26 PM UTC-6, Mike the Strike wrote:
On Tuesday, May 6, 2014 1:41:23 PM UTC-7, Don Johnstone wrote:

While in no way do I wish to speculate on the cause of this accident or




indeed suggest that my comments in any way address the cause of this




accident.




I feel that comment is needed on some of the things said here. We have a




rule here in the UK, launch failure on aerotow below 300ft a landing should




be made ahead, or slightly to one side. No attempt should be made to turn




back below this height.




The reason is simple, a controlled crash into difficult terrain is likely




to result in a better outcome than an uncontrolled arrival on the airfield.




The important bit to keep intact is the bit you are sitting in, the rest of




the glider does not really matter too much. The best chance of achieving




that is flying to the ground with the wings level. It has only happened to




me once, there was a field ahead but it was full of the Tiger Moth tug that




had landed in the middle. I discovered that there was just enough space for




a Skylark 2 as well. I have no doubt that a turn back would have resulted




in an accident. I was at 250ft agl max.




If there really is nowhere to land ahead you should really ask the




question, "should I be taking a launch".




Frankly I would be horrified to be required to conduct a turn back at




200ft, I would suggest that this is one of those occasions where the danger




of practice is to great to justify.




I have also voiced my concern at this tow termination training. Most times, it is a planned event and the towplane flies a modified pattern to give the trainee the best opportunity of returning to the launch runway. I have done several of these and they are not problematic. They also don't much resemble what happens in the real world when a rope break or disconnect is unplanned.



I have had only one of these in nearly 50 years of gliding. In one of my biannual tests, the instructor reassured me that no low altitude rope breaks would be simulated and then pulled the plug on me at a hair under 200 feet. Being unplanned. my reaction time was much longer - you have to work through the "holy ****, the tow rope's gone" thought process before taking any action. I landed successfully, but not on the departure runway - a story for another day. it did teach me that I didn't want a rope break under 200 feet and preferably not under 500 feet!



I have had several ropes break on the initial acceleration but none in the air. I have had three tugs lose power - two on the take-off run and one during climb-out. From my experience, I am skeptical that rope breaks between take-off and 200 feet are common enough to warrant the attention and training they get here in the USA..



I can also comment on the weather the day of the accident. It was perhaps one of the strongest (and highest) blue days I have seen in Arizona. The atmosphere was stable and dry under a dominant high-pressure system. Thermals were created by heating the air so much it had to rise, but these conditions resulted in very narrow, very strong, often multi-core, thermals surrounded by vicious sink and turbulence. These can be challenging if encountered on tow and can rapidly erode any height margin you have. You can expect to bash your head a few times (and perhaps your shins) on a day like this. Good when you're high, but nasty below pattern altitude.



Mike


Mike,

Turns do not cause stall/spin accidents. In fact, the steeper the turn, the greater the stall margin. That's because elevator authority is progressively used up making the glider turn as the bank gets steeper until the angle of attack can't be raised above stall. Try it. You'll find many gliders will run out of up elevator before they can be stalled at bank angles over 45 degrees.

Low turns don't cause stall spins either - they just insure there will be a permanent record should one occur. Pilots spin gliders unintentionally at higher altitudes too but they don't tell anybody.

Spins happen because the pilot stalled the glider, not because the pilot was turning.

The root cause of stall/spin accidents is pilot incompetence although it may not be their fault. Pilot training in gliders skips over an important area that is well covered in airplane training - its called ground reference maneuvers. If a student is drilled in low turns, it's less likely they will spin in on turns to final.
  #23  
Old May 7th 14, 02:20 AM posted to rec.aviation.soaring
Bill D
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Posts: 746
Default Fatal crash Arizona

On Tuesday, May 6, 2014 5:56:44 PM UTC-6, Don Johnstone wrote:
At 22:22 06 May 2014, Bill D wrote:

On Tuesday, May 6, 2014 2:41:23 PM UTC-6, Don Johnstone wrote:




Frankly I would be horrified to be required to conduct a turn back at


=20


200ft, I would suggest that this is one of those occasions where the


dang=


er


=20


of practice is to great to justify.




If you should check out in the USA, you'll be required to demonstrate


compe=


tence in this maneuver. Every pre-solo student is required to do so and


mo=


re than a half century of safety records do not suggest a problem. In


fact=


, even with low performance gliders, there's quite a large safety margin.


T=


he most likely outcome is a pilot will find the glider uncomfortably high


f=


or a downwind landing requiring full spoilers and a slip.




The logic is simple - it's better to have pilots trained for the option.


N=


o one says a pilot is required to turn back or that 200' is always


adequate=


to do so. What is illogical is to suggest a pilot be required to crash


in=


unlandable terrain when a safe option exists to land on the departure


runw=


ay.




What are you trying to save? The pilot or the aircraft? The priority should

be survival of the soft bit, that is you and me.

As an instructor with nearly 50 years experience I know that when I

initiate an emergency procedure I do so allowing a margin to ensure my

survival if it does not work out, I have been bold but never certifiable.

Most living instructors have the same survival instinct. That is why I have

lived long enough to do 10,000 launches, and of course landings. It has

already been hinted that the practice you describe involves modifying what

you normally do, in my view that probably makes it pretty useless and not

real preparation for the event. If you did carry out the training in

exactly the same way as the possible real event you might find that the

results were very different, not to mention painful. I will stick with my

300ft thank you, I know it works. Low turns, below that height may have

been acceptable in old wooden gliders, the minimum height in T31 and T21

gliders was 150ft, but for modern glass gliders it is just far too low, you

only have to look at the accident statistics to see that low final turns

figure to a large degree in accidents so why plan for it?

I repeat a controlled descent with wings level is far more likely to have a

better result than hitting the ground in a turn or even worse spinning in

trying to avoid it.



PS Despite all that there have been times when I have initiated a practice

emergency and very quickly wished I had not, no plan survives first

contact.


So, you're saying the pilot will be safer if they don't learn to perform the return to runway maneuver when it's safe to do so?

I can assure you that the higher a glider's performance, the safer it is. It's the old, low L/D gliders that can run out of altitude before getting lined up with the runway.


  #24  
Old May 7th 14, 03:28 AM posted to rec.aviation.soaring
son_of_flubber
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Posts: 1,491
Default Fatal crash Arizona

I just practiced 10 simulated PTOTs at my home field using Condor. It gave me a better perspective on my options. I will practice again with different wind directions and speed.


  #25  
Old May 7th 14, 04:35 AM posted to rec.aviation.soaring
Bob Whelan[_3_]
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Posts: 396
Default Fatal crash Arizona

On 5/6/2014 5:56 PM, Don Johnstone wrote:
Major Snip...

I will stick with my
300ft thank you, I know it works. Low turns, below that height may have
been acceptable in old wooden gliders, the minimum height in T31 and T21
gliders was 150ft, but for modern glass gliders it is just far too low...

Snip...

Volunteers for testing whether a lower-speed/higher-rate glider (T21/T31
certainly qualify) requires less height to execute a course reversal compared
to a higher speed/lower-sink rate modern plastic one? While testing, please do
contact the ground in controlled flight...

...you
only have to look at the accident statistics to see that low final turns
figure to a large degree in accidents so why plan for it?


Because: a) it happens (statistics); and b) (IMO) we reasonably safely can?
(That's certainly NOT the case when practicing the inadvertent departure from
controlled flight in the pattern.) And the skill might be good to have in
one's skill set? I'm not trying to be snarky, but it's the *uncontrolled*
ground contact that jumps out from the death statistics I've seen.

I repeat a controlled descent with wings level is far more likely to have a
better result than hitting the ground in a turn or even worse spinning in
trying to avoid it.


Roger both thoughts...especially that last one!

It's not "merely" the broken rope Joe Glider Pilot needs to be prepared for
as "the" source of an in-pattern prematurely terminated tow. Except for
training flights, I've never had an in-pattern premature tow termination...but
I know of lots of others who "for real" have, with causes including (off the
top of my head) unlatched canopies, passenger idiocy, improperly connected tow
rings and almost certainly more I'm forgetting.

Stuff happens. Prepare - mentally, training, muscle memory - accordionly.

Bob W.
  #26  
Old May 7th 14, 05:41 AM posted to rec.aviation.soaring
Robert M
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Posts: 25
Default Fatal crash Arizona

Why is anyone aero towing with a tow hook that will back release? To me it is a basic safety issue. It is not just this latest tragic accident, I have seen more wild gyrations and damages brought on by aero towing with a C.G.. hook than with a nose hook that does not back release. There are, I think, very few glider models that cannot be retro fitted with a forward hook that does not back release. To those who admire the so called "Zuni hook", well I have one on my desk right now, it is a poor piece of engineering.

In Germany regulations have been enacted setting currency standards that one must meet before using a C.G. hook for aero tow.

It would be interesting to analyze damage claims on aero launches, sorted by nose, E-85 or similar, tow hooks against back releasing C.G. hooks.

But then maybe I should not make a big issue of it as I am in the glider repair business.

Robert Mudd
Moriarty, NM
  #27  
Old May 7th 14, 07:55 AM posted to rec.aviation.soaring
Bruce Hoult
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Posts: 961
Default Fatal crash Arizona

On Wednesday, May 7, 2014 1:20:44 PM UTC+12, Bill D wrote:
So, you're saying the pilot will be safer if they don't learn to perform the return to runway maneuver when it's safe to do so?

I can assure you that the higher a glider's performance, the safer it is. It's the old, low L/D gliders that can run out of altitude before getting lined up with the runway.


I agree with you. I'm shaking my head every time I read this thread.

In a modern glass glider (such as the DG1000's I instruct in) with a 40 knot stall speed and being towed at 70 knots you should be able to execute a safe 180 turn with *zero* loss of height.

Just slowing down from 70 knots towing speed to 55 knots gains you 80 ft on top of whatever you already had.[1]

How much height do you lose in a 45 banked turn at 55 knots? Most modern gliders lose no more than 120 fpm at 45 knots in straight and level flight.. A 45 banked turn gives 1.41 Gs (1/cos(45)), which needs sqrt(1.41) = 1.19 times more speed for the same angle of attack and L/D. 45 knots times 1.19 is 53.6 knots. So 55 knots in a 45 turn has a little more margin above stall than 45 knots in straight and level. The sink rate will be 120 * 1.41 = 170 fpm.

Converting to SI and using a=v^2/r, a 45 banked turn at 55 knots (28.3 m/s) has 115.3m radius, or 725m circumference for a full turn. A 180 turn (362m) will take 12.8 seconds. In 12.8 seconds at 170 fpm you'll lose 36 feet.

So the height loss in the turn is only about half the height gained from slowing down from towing speed to circling speed!

It would actually be better to start turning immediately, but these calculations assume you delay (deliberately or not) and climb straight ahead (no pull-up required) for several seconds before starting the turn.

With 18m wingspan in a 45 bank your wingtip is 18m/2*sin(45) = 6.4m or 21 ft below you.

So you theoretically could do this from absolutely zero height, with nearly 20 ft to spare.

I wouldn't want to try it! But from 100ft? No problem at all. IF you start from normal towing speed and reasonably benign weather conditions.

Even if you're releasing from a sick tug that's slowed to 55 knots, you'll be fine from 200 ft.


Another post mentioned that glider pilots make mistakes when flying close to the ground because they are not trained to do so and don't do "ground reference" manoeuvres like power plane pilots do.

Obviously that person lives in very flat ground, because I can assure them that here we're flying close to ridges and peaks a LOT, from almost the first flight, doing 180 turns at the end of ridge lift runs, or circling low over a peak or head of a gully looking for a thermal. We'd very often be only 100-200 ft or so above the terrain while doing so.


[1] handy formula: X knots of kinetic energy is worth (X/5)^2 feet of gravitational potential energy. e.g. 70 knots = (70/5)^2 = 14^2 = 196 ft. 50 knots = (50/5)^2 = 10^2 = 100 ft. Less drag loses of course. You'll never turn speed into quite that much height, and you'll need more height than that to get speed. But the differences are large in a high performance glider at moderate speeds.
  #28  
Old May 7th 14, 12:49 PM posted to rec.aviation.soaring
James Metcalfe
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Posts: 35
Default Fatal crash Arizona

At 06:55 07 May 2014, Bruce Hoult wrote:
[1] handy formula: X knots of kinetic energy is worth (X/5)^2 feet of

gravitational potential energy. e.g. 70 knots = (70/5)^2 = 14^2 = 196 ft.
50 knots = (50/5)^2 = 10^2 = 100 ft. Less drag loses of course.
You'll never turn speed into quite that much height, and you'll need more
height than that to get speed. But the differences are large in a high
performance glider at moderate speeds.

...or you could use my rule of thumb: a change of speed of 10 knots IAS
gives
you (or costs you) the number of feet in height of the speed you arrive at.

For example:
70 knots to 60 knots : plus 60 feet
60 knots to 70 knots: minus 60 feet
70 knots to 50 knots (i.e. 70 to 60, then 60 to 50) : (60+50) = plus 110
feet

(N.B. Done without undue delay, and at sea level - more height change at
greater altitudes. Height in feet, IAS in knots, works for a change of
speed of 10 knots. Results
are realistic but approximate.)

  #29  
Old May 7th 14, 01:19 PM posted to rec.aviation.soaring
James Metcalfe
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Posts: 35
Default Fatal crash Arizona

At 11:49 07 May 2014, James Metcalfe wrote:
60 knots to 70 knots: minus 60 feet

sorry - s.b. minus 70 feet

  #30  
Old May 7th 14, 02:20 PM posted to rec.aviation.soaring
Vaughn
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Posts: 154
Default Fatal crash Arizona

On 5/7/2014 2:55 AM, Bruce Hoult wrote:
On Wednesday, May 7, 2014 1:20:44 PM UTC+12, Bill D wrote:
I can assure you that the higher a glider's performance, the safer

it is. It's the old, low L/D gliders that can run out of altitude
before getting lined up with the runway.
I agree with you. I'm shaking my head every time I read this thread.

In a modern glass glider (such as the DG1000's I instruct in) with a
40 knot stall speed and being towed at 70 knots you should be able to
execute a safe 180 turn with*zero* loss of height.


The comparison isn't quite as simple as just looking at L/D. Turn
radius also has a lot to do with your chances of making it back to the
field, and turn radius is proportional to the SQUARE of airspeed.

Compare your example (40 knot stall) with a (horrors) 2-33. The highest
stall listed for a 2-33 is around 30 knots. If you do the math, you
will find that your DG1000 has nearly double the turn radius of the
slower glider.

Vaughn

 




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