Fatal crash Arizona

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.

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

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.

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.

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.

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.)

At 11:49 07 May 2014, James Metcalfe wrote:
60 knots to 70 knots: minus 60 feet
sorry - s.b. minus 70 feet

On Wednesday, May 7, 2014 11:49:46 PM UTC+12, James Metcalfe wrote:
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

It's nearly the same formula. If you made it "every 12.5 knots IAS" instead of 10 then it'd be nearly exact.

The derivative of my formula (X/5)^2 i.e. X^2/25 is X/12.5. So gaining or losing X feet at X knots takes roughly 12.5 knots of speed change.

Doing it using the speed you're changing *to* is clever, as it makes some allowance for drag losses. However your height estimates are systematically biased 20% too large.

If you said 70 to 50 is (60+50)-20% = 110-22 = a gain of 88 ft then that would be good.
And 50 to 70 is (60+70)-20% = 130-26 = a loss of 104 ft, which is pretty good too.

If you're doing something like "how high can I zoom to after a 140 knot low pass and still have 60 knots for the circuit?" then I'm not convinced that adding up eight numbers is easier than calculating two squares and subtracting them :-)

By me: 28^2 - 12^2 = ~800 - ~150 = 650 ft (784-144 = 640 if you do it exact)
By you: 130+120+110+100+90+80+70+60 = 760 ft
By you with my -20% correction: 760 - 152 = 608

(remember folks, that's 140 knots at the END of the low pass, not the start!)

At 23:50 07 May 2014, Bruce Hoult wrote:
However your height estimates are systematically biased 20% too large.
Well, about 8% for a pull-up, and 17% for a dive - at the high-speed end of
the scale.
(Better and worse, respectively, at the low-speed end.) Whereas your rule
is about 10%
low throughout.

By me: 28^2 - 12^2 = ~800 - ~150 = 650 ft (784-144 = 640 if you do it
exact)
By you: 130+120+110+100+90+80+70+60 = 760 ft
By you with my -20% correction: 760 - 152 = 608
And the truth (from v^2 = u^2 + 2gh ... whence we both started, I'm sure)
is 708.66 ft. (I
knew you'd like the ".66" ;o) )

Spreadsheet he http://tinyurl.com/mzokpyk for those amused by such
things.

But of course these are both rules of thumb, intended more to give better
understanding
than for exact calculation. I have more often referred to mine in
discussing recovery of
lost speed low on finals (or after a low winch-launch failure) than for the
120kt beat-up
case!

On Friday, May 9, 2014 4:44:38 AM UTC+12, James Metcalfe wrote:
At 23:50 07 May 2014, Bruce Hoult wrote:
(Better and worse, respectively, at the low-speed end.) Whereas your rule
is about 10% low throughout.

Yes, it's deliberately biased a little to the low side from the true (as you note) /4.7516 to make it more of a "guaranteed to pull up that far". Also useful for "I'd like to be down on that ridge line, but I don't want to overspeed". Of course in that case the height difference is going to be pure guess anyway.

I've contemplated using /4 for dives where you want to make sure you have some minimum speed, but I think that overdoes it. /4.5 would be better but not easy to calculate in your head.