MacCready theory in wave

Thermals drift with the wind in classic flat land conditions. In the typical convergence lift such as in California and even the Great Basin, they are also anchored to the terrain or at least to the convergence line (usually near ridge lines) , which moves very slowly if at all. So normally need to take wind into account also in typical convergence flying. At least this is my experience.

Ramy

On Thursday, November 10, 2016 at 12:20:04 AM UTC-5, John Cochrane wrote:
Following some fun discussions with Kempton Izuno I worked out MacCready theory in wave. It turns out we should fly faster.

http://faculty.chicagobooth.edu/john...ve_macredy.pdf

Enjoy! Let me know if you see bugs.

John Cochrane

What about downwind speed to fly?
Chris

On Friday, 11 November 2016 18:34:03 UTC+2, Dan Marotta wrote:
Can you look at the sounding for Winslow, AZ for June 5, 1995 and tell
me what happened, or is that too old?

My partner and I were on safari and, on that day I ground launched from
Holbrook, AZ intending to fly to Flagstaff, then north across the Grand
Canyon at least to Heber City, UT and back south to Parowan. It was a
grand plan that didn't work out. Flying west in great lift, passing the
Meteor Crater, the lift suddenly turned off and the air went dead
smooth. I retreated and tried at least three more times before calling
my crew and sending him back to Winslow, where landed (and stood on the
corner).

On 11/11/2016 1:51 AM, krasw wrote:
On Friday, 11 November 2016 00:25:06 UTC+2, wrote:
You are quite simply incorrect. Wind direction and strength changes happen all the time when we soar. Shears are very common when these happen.
UH
No, it is not common, it is simply impossible since shear layers in free atmosphere always come with stable layer and by definition we cannot soar trough these. Please tell me where and when was the last time you did soar trough vertical shear layer. I will find sounding data to prove you wrong.. Or you can post sounding yourself (even RASP forecast sounding will do). I've been looking at soundings (real and forecast) of good gliding days for 20 years and never, not even once, have I seen wind shear in convective layer (between top of surface friction layer and inversion, to be exact). Insisting opposite is like saying apple falls upwards.

I do not blame anyone believing in strange things as most of the advanced soaring textbooks have been written by persons who have obviously little background in meteorology and have not used sounding diagram. That does not prevent them writing chapters of nonsense about interpreting them.

--
Dan, 5J

I see steady soutwesterly wind of 20 kt with no shear up to 10000 ft (6th June 00Z being your afternoon, I guess?). Sadly there is no data between 700 hPa and 550 hPa. You can check it yourself:

http://weather.uwyo.edu/upperair/sounding.html

Thanks for trying, I couldn't get anything, either.

Now it's time to begin planning for a safari this coming June...! Maybe
I'll start a new thread as plans firm up a little bit.

On 11/12/2016 12:15 AM, krasw wrote:
On Friday, 11 November 2016 18:34:03 UTC+2, Dan Marotta wrote:
Can you look at the sounding for Winslow, AZ for June 5, 1995 and tell
me what happened, or is that too old?

My partner and I were on safari and, on that day I ground launched from
Holbrook, AZ intending to fly to Flagstaff, then north across the Grand
Canyon at least to Heber City, UT and back south to Parowan. It was a
grand plan that didn't work out. Flying west in great lift, passing the
Meteor Crater, the lift suddenly turned off and the air went dead
smooth. I retreated and tried at least three more times before calling
my crew and sending him back to Winslow, where landed (and stood on the
corner).

On 11/11/2016 1:51 AM, krasw wrote:
On Friday, 11 November 2016 00:25:06 UTC+2, wrote:
You are quite simply incorrect. Wind direction and strength changes happen all the time when we soar. Shears are very common when these happen.
UH
No, it is not common, it is simply impossible since shear layers in free atmosphere always come with stable layer and by definition we cannot soar trough these. Please tell me where and when was the last time you did soar trough vertical shear layer. I will find sounding data to prove you wrong. Or you can post sounding yourself (even RASP forecast sounding will do). I've been looking at soundings (real and forecast) of good gliding days for 20 years and never, not even once, have I seen wind shear in convective layer (between top of surface friction layer and inversion, to be exact). Insisting opposite is like saying apple falls upwards.

I do not blame anyone believing in strange things as most of the advanced soaring textbooks have been written by persons who have obviously little background in meteorology and have not used sounding diagram. That does not prevent them writing chapters of nonsense about interpreting them.
--
Dan, 5J
I see steady soutwesterly wind of 20 kt with no shear up to 10000 ft (6th June 00Z being your afternoon, I guess?). Sadly there is no data between 700 hPa and 550 hPa. You can check it yourself:

http://weather.uwyo.edu/upperair/sounding.html

--
Dan, 5J

At 03:03 12 November 2016, wrote:
On Thursday, November 10, 2016 at 12:20:04 AM UTC-5, John Cochrane
wrote:
Following some fun discussions with Kempton Izuno I worked out
MacCready
theory in wave. It turns out we should fly faster.


http://faculty.chicagobooth.edu/john...docs/wave_macr
edy.pdf

Enjoy! Let me know if you see bugs.

John Cochrane

What about downwind speed to fly?
Chris

In lift, fast.
In sink, faster . . .
:-)

Perhaps this is a special case, but in our limited cross country flights in Wave in the east we sometimes will do "the death dive" from the upwind side of the mountain to the back. Flying downwind through the sink looking for the lift and then turn back into the wind. If you are near mountaintop height, the sink can be quite strong and conventional wisdom says fly fast, really fast. But the goal is to be as high as possible when you contact the up side of the wave, as you don't want to fall out the bottom. If I visualise the sinusoidal streamlines viewed from the side, it seems you would want to fly at best glide to come out with the most altitude. Up wind, clearly you want to fast as you have to overcome the wind, but downwind it seems you may want to float "on top" of those streamlines. Thoughts?

This is an interesting topic and the notion of a flight computer helping calculate speed to fly based on heading with knowledge of the orientation of the wave system would be great.

RR

One more comment / story on the subject. First a disclaimer, if you have read this far in this thread this will not be a surprise, but at the time it new to me.

I was coming back from a wave xc leg on a blue day. Without aid of my flight trace to follow my successful trip outbound, I did not fare as well on my way back.

I got low enough to need to pick between taking the upwind side of the range that was "surely working" but unlandable, or try for low wave with an easily reachable downwind airport. I chose the later. After much scratching I climbed back up, and with about a 50kt quartering head wind I had 2500 ft over glide to home.

I thought "just to be sure" I will crank up my MacCready to 5. When I did I was now showing 5000 over! Again obvious to this crowd, but the first time I had seen it happen to me.

RR

At 13:02 13 November 2016, RR wrote:
Perhaps this is a special case, but in our limited cross country flights
in=
Wave in the east we sometimes will do "the death dive" from the upwind
sid=
e of the mountain to the back. Flying downwind through the sink looking
fo=
r the lift and then turn back into the wind. If you are near mountaintop
h=
eight, the sink can be quite strong and conventional wisdom says fly
fast,
=
really fast. But the goal is to be as high as possible when you contact
th=
e up side of the wave, as you don't want to fall out the bottom. If I
visu=
alise the sinusoidal streamlines viewed from the side, it seems you would
w=
ant to fly at best glide to come out with the most altitude. Up wind,
clea=
rly you want to fast as you have to overcome the wind, but downwind it
seem=
s you may want to float "on top" of those streamlines. Thoughts?

This is an interesting topic and the notion of a flight computer helping
ca=
lculate speed to fly based on heading with knowledge of the orientation
of
=
the wave system would be great.

RR=20


Is a flight to the next bar, upwind or downwind, really any different to a
final glide? You want to arrive above a place on the ground, flying through
sink and lift. The objective is probably different, MacCready optimises
speed, you may want to do this for a wave jump, or you may want to optimise
height loss.
Welch and Irving analysed both these in The New Soaring Pilot, 40/50 years
ago
Obviously it is not always easy to know how far, but that applies whatever
theory you use.
Dave

Branko, would you consider releasing the source code for conversion to GUI ?

On Friday, 11 November 2016 00:45:54 UTC, Branko Stojkovic wrote:
John,

I haven't yet read your paper (I will as soon as I get on the plane), but before the discussion on this topic goes any further I would like to point out that I published a "Generalized Speed-to-Fly Theory" back in 1991, which covers both thermal and wave lift, and anything in between, for example thermals that drift downwind at a speed that is less than the speed of the prevailing wind.

You can download a copy of my paper he
http://trimill.com/CuSoft/PolarExplo...STF_Theory.pdf

At the time I also published a PC program called Polar Explorer which uses this theory to calculate the correct speed-to-fly in any conditions, among many other useful things it can do.

Polar Explorer program is a bit difficult to use because of the old DOS based interface. In order to run it on a Windows or Mac OS X it requires a DOS-emulator program (I use DOSBox).

The program, is now freeware and it can be downloaded from
http://trimill.com/CuSoft/PolarExplorer/index.htm

Branko Stojkovic
XYU

Colin,

I would and I already have, but the guys I gave it to a year ago haven't made any progress yet.

I wrote the code in Borland Pascal and that should make it portable to Delphi, if I'm correct. However, there are a few issues to consider. For starters, the code is poorly documented. Further, most of the 20,000 odd code lines deal with text and graphical screen handling, including a custom scripting capability that was used to create the tutorial scripts, glider and sheet libraries, etc. In my estimate, only about 10% of the code is related to the performance calculations.

Probably the best way to port the program would be to isolate the routines doing the performance calculations and then build a new interface around them.
It would also be good to convert the existing glider library to a new format.

Even doing it this way it would be require lot of work. If you're interested, email me and we can discuss it further.

Branko Stojkovic
XYU


On Monday, November 14, 2016 at 8:47:41 AM UTC-8, Colin Wray wrote:
Branko, would you consider releasing the source code for conversion to GUI ?