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 180º 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

....now redo your calculations while flying through 8 knots of sink.

Mike

On Wednesday, May 7, 2014 6:28:41 AM UTC-7, Mike the Strike wrote:
...now redo your calculations while flying through 8 knots of sink.



Mike

...and calculate the height loss while making a 180-degree turn. Taking the 12.8 seconds just mentioned at 800 feet per minute gives you a height loss of 170 feet from the airmass movement alone, plus whatever you add for the glider itself. Safety margins in severe sink disappear frighteningly quickly.

Mike

On Wednesday, May 7, 2014 9:35:46 AM UTC-4, Mike the Strike wrote:
On Wednesday, May 7, 2014 6:28:41 AM UTC-7, Mike the Strike wrote:

...now redo your calculations while flying through 8 knots of sink.







Mike



..and calculate the height loss while making a 180-degree turn. Taking the 12.8 seconds just mentioned at 800 feet per minute gives you a height loss of 170 feet from the airmass movement alone, plus whatever you add for the glider itself. Safety margins in severe sink disappear frighteningly quickly.



Mike

Now throw in wind shear and tailwind component when failure to anticipate leads to turning in the wrong direction.
Double AARRGGHH!!
UH

Can you really get 8kts of sink at 200ft? Where is the air going, into the ground?

Boggs

On Wednesday, May 7, 2014 7:20:33 AM UTC-6, Vaughn wrote:
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

You're exaggerating the stall speed differences. Regardless of what the 2-33 "manual" says, no 2-33 ever got as slow as 30 knots. 35 knots is a practical minimum speed. The flight test stall speed for a DG 1000 is 37 knots..

However, no one should consider a turn back at stall speed. Virtually all gliders will be at 50 - 55 knots so the turn radius will be essentially the same.

8 knots sink? That's a straw man argument. While extreme air movement is always possible, most PT3 incidents are in relatively benign conditions. In extreme conditions a turn back is probably moot anyway.

The point is when conditions allow, a pilot should know how to turn back safely.

On Wednesday, May 7, 2014 10:34:48 AM UTC-5, Bill D wrote:

The point is when conditions allow, a pilot should know how to turn back safely.

Precisely. It's called airmanship - knowing how to handle your plane in any conceivable situation.

If you aren't practicing something new and unusual (or at least thinking about it) on every flight, you are limiting your growth as a pilot.

My one real PTT happened at Turf Soaring (Pleasant Valley Airport) many years ago, giving a ride in old 66W - a beat up old 2-32. Tow rope was hooked up incorrectly (muddy) and released just past the end of the runway (taking off to the East) at what i guess was around 150 - 200 ft, no more. No good options other than turning back or landing in the desert; so I turned back...and had enough energy to roll back up to the surprised line boy who had just launched me. Turned the glider around, hooked up again, and the customer got his full ride the second time.

BUT--conditions were calm with light winds and no lift; and the tow was fast - and it was pretty easy to whip that big old beast around in a steep turn and bring it back to land, as I had a lot of time in 2-32s at the time. Never felt that I was too low during the turn, but didn't even try getting real slow (if you have time in 2-32s you will appreciate why!).

Yes, it can be done. But you have to know your plane WELL, and have the right conditions, and fully understand the consequences of pooching it!

Get out there and practice!

Kirk
66

At 17:01 07 May 2014, kirk.stant wrote:
On Wednesday, May 7, 2014 10:34:48 AM UTC-5, Bill D wrote:
=20
The point is when conditions allow, a pilot should know how to turn
back
=
safely.

Precisely. It's called airmanship - knowing how to handle your plane in
an=
y conceivable situation.

If you aren't practicing something new and unusual (or at least thinking
ab=
out it) on every flight, you are limiting your growth as a pilot.

My one real PTT happened at Turf Soaring (Pleasant Valley Airport) many
yea=
rs ago, giving a ride in old 66W - a beat up old 2-32. Tow rope was
hooked=
up incorrectly (muddy) and released just past the end of the runway
(takin=
g off to the East) at what i guess was around 150 - 200 ft, no more. No
go=
od options other than turning back or landing in the desert; so I turned
ba=
ck...and had enough energy to roll back up to the surprised line boy who
ha=
d just launched me. Turned the glider around, hooked up again, and the
cus=
tomer got his full ride the second time.

BUT--conditions were calm with light winds and no lift; and the tow was
fas=
t - and it was pretty easy to whip that big old beast around in a steep
tur=
n and bring it back to land, as I had a lot of time in 2-32s at the time.
N=
ever felt that I was too low during the turn, but didn't even try getting
r=
eal slow (if you have time in 2-32s you will appreciate why!).

Yes, it can be done. But you have to know your plane WELL, and have the
ri=
ght conditions, and fully understand the consequences of pooching it!

Get out there and practice!

Kirk
66

and that dear reader illustrates the problem nicely. Emergency procedures
do not have to be formulated for experienced thinking pilots. I would like
to think that I could get away with doing what Kirk has done. Emergency
procedures have to be formulated for the lowest common denominator, would a
low launches pilot be able to achieve success? Would a relatively
experience pilot who is flying minimum launches per year cope with it? That
is what formulating procedures is all about, having something that everyone
can achieve, not just the top 10%.

On Thursday, May 8, 2014 3:34:48 AM UTC+12, Bill D wrote:
You're exaggerating the stall speed differences. Regardless of what the 2-33 "manual" says, no 2-33 ever got as slow as 30 knots. 35 knots is a practical minimum speed. The flight test stall speed for a DG 1000 is 37 knots.

I knew 40 knots was conservative with the DG1000 stall speed, but that difference is less than I'd have expected. I've never flown a 2-33, but I've had Blaniks under 35 knots :-)


However, no one should consider a turn back at stall speed. Virtually all gliders will be at 50 - 55 knots so the turn radius will be essentially the same.

I've put together a spreadsheet for the calculations and In fact it turns out that for minimum loss of height in a 180º turn -- and also much smaller turn radius -- you should fly a bit faster and bank a bit steeper.

https://docs.google.com/spreadsheets...FXBnfP8tauGK1k

No matter what your stall speed or L/D, it turns out the optimum to minimise loss of height in a turn is to bank at 54.7 degrees.

This is the bank angle at which the total G loading is 1.732 (sqrt(3)) and the G available to turn you is 1.414 (sqrt(2)).

In that glass ship with 120 fpm min sink at 45 knots you're looking at 67m turn radius at 59 knots, with 24 feet loss of height in a 180º turn.

In a Blanik with 160 fpm at 42 knots you'll get a 58m turn radius at 55 knots, with 30 feet loss of height.

In a 2-33 with 168 fpm at 35 knots you'll get a 40.5m turn radius at 46 knots, with 26 feet loss of height.

Feel free to play.

On Wednesday, May 7, 2014 6:24:23 PM UTC-7, Bruce Hoult wrote:

No matter what your stall speed or L/D, it turns out the optimum to minimise loss of height in a turn is to bank at 54.7 degrees.

Feel free to play.

Thanks Bruce - I did play with this a bit. Always helpful to do the math.

Several observations pop out from the numbers:

1) The 25-30' height loss for a 180 is small compared to the 200' I always use as the minimum safe altitude to make this maneuver. Not that I'm recommending a smaller margin - there are considerations of sink and wind and clearance for the bottom wingtip in the bank.

2) Speaking of the bottom wingtip in the bank, if you subtract that height difference for each different bank angle you get a height loss for a 180 measured at the bottom wingtip that is actually minimal at a lower bank angle than 54.7 degrees. Obviously this would be most likely to apply at the end of the maneuver, not the beginning, unless there is unusual terrain.

3) Whether you include the wingtip clearance in the calculation or not, the total height loss doesn't vary all that much between 30 and 60 degrees of bank - about 6 feet of difference for the center of the aircraft and only a foot or two of difference at the lower wingtip.

The conclusion this draws me to is that the most important consideration in PTT is to make a smooth, coordinated, deliberate turn that you can manage easily - and to make sure not to dig the bottom wing into the ground. Within a pretty broad range, there isn't much percentage in optimizing the bank angle.

9B