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 180º 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 45º banked turn at 55 knots? Most modern gliders lose no more than 120 fpm at 45 knots in straight and level flight.. A 45º 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 45º 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 45º banked turn at 55 knots (28.3 m/s) has 115.3m radius, or 725m circumference for a full turn. A 180º 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 45º 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 180º 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.

On Tuesday, May 6, 2014 6:20:44 PM UTC-7, Bill D wrote:
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.

The discussion seems to focus exclusively on the decision height for a turn around. I think that is only one factor in making this decision. As reported by Bob T there was heavy sinking air on the departure end of the runway. Returning to the airport would have required transiting thru this air a 2nd time, which strikes me as inadvisable without much more altitude than Knauff had.

The other issue is that a tow rope break requires immediate lowering of the nose. This is done routinely at altitude, but at low altitude this means pointing the glider's nose uncomfortably down at the ground while executing a steep banked turn. If the ground is rising, as it is at Sampley, the picture seen by the pilot is even more disturbing. All that it takes is a momentary hesitation in this reflex and the outcome can be fatal.

As an aside, I once did a wind mill start in my DG400 below 1000' (over a runway). This maneuver requires achieving in excess of 90 kt airspeed. Because the engine & prop act like dive brakes, you feel like you are standing on your rudder pedals when you do this close to the ground. I got to this airspeed and the prop still didn't rotate. This meant that I had to steepen the descent even more. All of my instincts said no, but my brain said yes, which is what I did. The engine started, but I decided that this maneuver really needs to be started at a higher altitude.

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.

It's a mystery to me why some people think you can "get away with" so much more in old gliders than in those great big heavy clumsy glass ones.

Somewhere in this thread I saw a statement that you could safely turn back from 150 ft in an old glider (which I agree with), but you're a dead man if you try it below 300 ft in glass.

The differences that govern such a thing just aren't that big!

Let's look at some numbers for weight and wing area of typical training gliders (from Wikipedia):

ASK13: 290 kg, 17.5 m^2
Blanik L13: 292 kg, 19.15 m^2

PW6: 360 kg, 15.3 m^2
ASK21: 360 kg, 17.95 m^2
Puchacz: 368 kg, 18.16 m^2
Janus: 365 kg, 17.3 m^2

G103: 390 kg, 17.9 m^2
Duo Discus: 410 kg, 16.4 m^2
DG1000: 415 kg, 17.5 m^2

There's not a lot of difference in the wing areas, with individual variations bigger than the generational differences.

Yes, the glass ones weigh a bit more. How much more?

Someone flying solo in an ASK21 is at about the same all up weight as someone in a ASK13 with a smaller than average instructor in the back seat.

Someone flying solo in a DG1000 is at about the same all up weight as someone in a ASK13 with a largish instructor in the back seat.

We expect students to be able to cope with the flying characteristic differences between having an instructor and not having one -- and to cope with that difference on their first time flying alone!

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.

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.

As a UK FI(S) and FIC, previously a Full Cat instructor, this is news to me. Where is it expressed?

I thought the rule was to exercise judgement. I always address 'where would you go now' issues with students and on check flights. In most conditions and situations I would turn back from lower than 300 foot.

On Tuesday, May 6, 2014 4:41:23 PM UTC-4, 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.

Sometimes it's hard to face the fact that the glider must be destroyed to survive. Trying to save the device could be a deadly decision.

Again, I don't know what actually happened, best guess, inadvertent unintentional release. Whether he tried to turn back, or just plain didn't get the nose down quick enough during a 90 degree or lesser turn, who knows.

The only way to practice rope breaks at 100' is on a simulator (condor).

Don's suggestion that there is a rigid rule about turn back heights in the UK is a surprise to me (I am an instructor). Select the least bad option at the time. Prepare students for it by (at an earlier stage) saying 'from here I would..'. Later asking 'if the tow fails here, where would you go?'

In most circumstances from 200 foot I would turn back.

Quite right, individual clubs may have had a minimum turn back height as
advice or even a rule, the BGA has not. I write as the ex-National Coach
who produced the BGA Instructor's Manual.

At 02:47 19 July 2014, waremark wrote:
Don's suggestion that there is a rigid rule about turn back heights in
the
=
UK is a surprise to me (I am an instructor). Select the least bad option
at=
the time. Prepare students for it by (at an earlier stage) saying 'from
he=
re I would..'. Later asking 'if the tow fails here, where would you go?'

In most circumstances from 200 foot I would turn back.