MacCready theory in wave

[John Cochrane[_3_]]

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.cochrane/soaring/docs/wave_macredy.pdf

Enjoy! Let me know if you see bugs.

John Cochrane

[Chris Rollings[_2_]]

At 05:20 10 November 2016, 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.cochrane/soaring/docs/wave_macredy.pdf
>
>Enjoy! Let me know if you see bugs.
>
>John Cochrane
>

Faster into wind, same speed as for thermals cross-wind, slower than
inter-thermal down-wind.

[krasw]

torstai 10. marraskuuta 2016 7.20.04 UTC+2 John Cochrane kirjoitti:
> 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.cochrane/soaring/docs/wave_macredy.pdf
>
> Enjoy! Let me know if you see bugs.
>
> John Cochrane

Good read as usual, thanks. But:

"In classic thermal lift, the thermals drift with the wind, so MacCready theory is unaffected by wind speed."

is simply not true. Windspeed inside thermal column can easily be only 50% of what it is outside thermal. Just think what would happen if wind speed would be same everywhere: thermals would be completely round and symmetrical no matter what the windspeed is as there would be no shear to distort the cylindrical shape.

[John Cochrane[_3_]]

Actually, it turns out it's not the same crosswind. Since you have to crab in to the wind, and since wave lift does not drift you cross wind, you also fly faster in crosswind. Not as much as upwind. But in 40-60 mph crosswinds, not uncommon in wave, the effect is substantial.

John Cochrane

[Matt Herron Jr.]

On Thursday, November 10, 2016 at 6:59:10 AM UTC-8, krasw wrote:
> torstai 10. marraskuuta 2016 7.20.04 UTC+2 John Cochrane kirjoitti:
> > 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.cochrane/soaring/docs/wave_macredy..pdf
> >
> > Enjoy! Let me know if you see bugs.
> >
> > John Cochrane
>
> Good read as usual, thanks. But:
>
> "In classic thermal lift, the thermals drift with the wind, so MacCready theory is unaffected by wind speed."
>
> is simply not true. Windspeed inside thermal column can easily be only 50% of what it is outside thermal. Just think what would happen if wind speed would be same everywhere: thermals would be completely round and symmetrical no matter what the windspeed is as there would be no shear to distort the cylindrical shape.

Hmm,

I think it's the vertical component that distorts the shape, not the horizontal wind. We agree that a parcel of air in the core is rising faster than air on the edge of the thermal. Therefor it's slope is more vertical. It take less time to climb 1000 feet than the parcel next to it. That shorter time means it is blown downwind less than slower vertical parcels and therefor the core tends to pile up on the upwind side of the thermal.

Matt

[krasw]

On Thursday, 10 November 2016 17:27:32 UTC+2, Matt Herron Jr. wrote:
>
> Hmm,
>
> I think it's the vertical component that distorts the shape, not the horizontal wind. We agree that a parcel of air in the core is rising faster than air on the edge of the thermal. Therefor it's slope is more vertical. It take less time to climb 1000 feet than the parcel next to it. That shorter time means it is blown downwind less than slower vertical parcels and therefor the core tends to pile up on the upwind side of the thermal.
>
> Matt

I was talking about horizontal wind field. What you say makes no sense.

[David Hirst]

>
> Enjoy! Let me know if you see bugs.
>
> John Cochrane

Good article, John. Now, if I was proof-reading it, I'd suggest adding a few more axis labels to the plots and the legends. On P1, the sentence "Going upwind to wave lift is just like flying through no wind to thermal lift.." should be changed to "Going upwind in wave lift is just like flying through no wind in thermal lift...". My first reading of that sentence was that the pilot was pushing upwind in zero lift (or the frequent heavy sink) to get to the wave band, whereas your analysis assumes that the pilot is in wave lift constantly.

My 2c.

DH
TX

[Matt Herron Jr.]

On Thursday, November 10, 2016 at 9:26:31 AM UTC-8, krasw wrote:
> On Thursday, 10 November 2016 17:27:32 UTC+2, Matt Herron Jr. wrote:
> >
> > Hmm,
> >
> > I think it's the vertical component that distorts the shape, not the horizontal wind. We agree that a parcel of air in the core is rising faster than air on the edge of the thermal. Therefor it's slope is more vertical. It take less time to climb 1000 feet than the parcel next to it. That shorter time means it is blown downwind less than slower vertical parcels and therefor the core tends to pile up on the upwind side of the thermal.
> >
> > Matt
>
> I was talking about horizontal wind field. What you say makes no sense.

OK, lets take another shot at it. Would you agree that hypothetically if the air in the thermal was not rising then the windspeed in the "not rising thermal" would be the same as the surrounding windspeed? (I neglect the effect of rotational speed of the "thermal" which would increase windspeed on the downwind portion of rotation and reduce windspeed on the upwind portion of rotation). If so, then it is the vertical velocity component of the thermal that changes its shape.

Also, the horizontal windspeed in a thermal cannot be 50% less than the surrounding windspeed. This is a myth. If this were true, then I could extract way more energy out of a thermal by flying upwind inside of it, and downwind outside of it (like dynamic soaring) My velocity would build up and I could use that kinetic energy to climb...

[Matt Herron Jr.]

On Wednesday, November 9, 2016 at 9:20:04 PM UTC-8, 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.cochrane/soaring/docs/wave_macredy.pdf
>
> Enjoy! Let me know if you see bugs.
>
> John Cochrane

John,

Help me understand the goal, and assumptions. Are we trying to maximize XC speed assuming there is a long band of constant lift at the same altitude and we are traversing 90 deg to the wind? Or are we trying to maximize climb rate so we can glide to the next area of lift? Or are we trying to calculate speed to fly between 2ndary and primary upwind?

Thanks,

Matt

[krasw]

torstai 10. marraskuuta 2016 20.48.18 UTC+2 Matt Herron Jr. kirjoitti:
> On Thursday, November 10, 2016 at 9:26:31 AM UTC-8, krasw wrote:
> > On Thursday, 10 November 2016 17:27:32 UTC+2, Matt Herron Jr. wrote:
> > >
> > > Hmm,
> > >
> > > I think it's the vertical component that distorts the shape, not the horizontal wind. We agree that a parcel of air in the core is rising faster than air on the edge of the thermal. Therefor it's slope is more vertical. It take less time to climb 1000 feet than the parcel next to it. That shorter time means it is blown downwind less than slower vertical parcels and therefor the core tends to pile up on the upwind side of the thermal.
> > >
> > > Matt
> >
> > I was talking about horizontal wind field. What you say makes no sense.
>
> OK, lets take another shot at it. Would you agree that hypothetically if the air in the thermal was not rising then the windspeed in the "not rising thermal" would be the same as the surrounding windspeed? (I neglect the effect of rotational speed of the "thermal" which would increase windspeed on the downwind portion of rotation and reduce windspeed on the upwind portion of rotation). If so, then it is the vertical velocity component of the thermal that changes its shape.
>
> Also, the horizontal windspeed in a thermal cannot be 50% less than the surrounding windspeed. This is a myth. If this were true, then I could extract way more energy out of a thermal by flying upwind inside of it, and downwind outside of it (like dynamic soaring) My velocity would build up and I could use that kinetic energy to climb...

I would say that if you have a thermal without vertical speed you have no thermal. Yes, vortex-like vertical structure of thermal bubble affects vertical shape of thermal, but that has nothing to do with horizontal wind discussed here. And no, it is not a myth, I and many others can see it with out own eyes using modern wind measusing inertial variometer. Usually windspeed difference between thermal center and surrounding is less that 50%, maybe 20-30%, but in well formed cloudstreet it is almost a rule that windspeed halves in best lift. There is not a shadow of doubt that thermal acts as a "semi-transparent" barrier to surrounding windfield. If the wind would not change, we would not need the skill of centering thermal, one single centering correction at the beginning would be enough since thermal would be perfectly round and symmetrical. I'm still waiting to find one that fits the description.

[John Cochrane[_3_]]

Matt:

The idea: you have a good idea that there is wave lift ahead, either upwind or crosswind. You have a good idea how strong that wave lift will be, or at least you are confident enough that you won't stop for less than x knots of wave lift.

Now, how fast should you fly to that lift? As usual, flying faster gets you there lower, but flying slower gets you there higher.

The general answer is, as always, set the MacCready value to something and speed up through sink and slow down through lift as told. This is easier in wave as the lift and sink generally come on more smoothly and predictably.

But what do you set the MacCready value to? Pretty clearly something higher than the lift you expect to find, i.e. the minimum lift you would stop for.. Since the wave lift does not drift downwind it's better than thermal lift of the same magnitude. But how much better?

The whole point is to work that out. So, for example, if you're flying in a 40 knot crosswind and expect the wave to be 2 knots when you get there (Last weekend, Mendocinos, exactly the situation that caused me to write this), you should set the Mc to 3.5, not 2.0.

John Cochrane BB

[John Cochrane[_3_]]

Yes, thermals don't drift fully with the wind. The major reason is wind shear. The wind is stronger at altitude than below. That's why we can sometimes slope soar or wave soar cumulus clouds. That's why we do better than expected upwind, and worse than expected downwind. Someday I'll work up a set of tables for that...

John Cochrane

[Matt Herron Jr.]

On Thursday, November 10, 2016 at 11:06:12 AM UTC-8, krasw wrote:
> torstai 10. marraskuuta 2016 20.48.18 UTC+2 Matt Herron Jr. kirjoitti:
> > On Thursday, November 10, 2016 at 9:26:31 AM UTC-8, krasw wrote:
> > > On Thursday, 10 November 2016 17:27:32 UTC+2, Matt Herron Jr. wrote:
> > > >
> > > > Hmm,
> > > >
> > > > I think it's the vertical component that distorts the shape, not the horizontal wind. We agree that a parcel of air in the core is rising faster than air on the edge of the thermal. Therefor it's slope is more vertical. It take less time to climb 1000 feet than the parcel next to it. That shorter time means it is blown downwind less than slower vertical parcels and therefor the core tends to pile up on the upwind side of the thermal.
> > > >
> > > > Matt
> > >
> > > I was talking about horizontal wind field. What you say makes no sense.
> >
> > OK, lets take another shot at it. Would you agree that hypothetically if the air in the thermal was not rising then the windspeed in the "not rising thermal" would be the same as the surrounding windspeed? (I neglect the effect of rotational speed of the "thermal" which would increase windspeed on the downwind portion of rotation and reduce windspeed on the upwind portion of rotation). If so, then it is the vertical velocity component of the thermal that changes its shape.
> >
> > Also, the horizontal windspeed in a thermal cannot be 50% less than the surrounding windspeed. This is a myth. If this were true, then I could extract way more energy out of a thermal by flying upwind inside of it, and downwind outside of it (like dynamic soaring) My velocity would build up and I could use that kinetic energy to climb...
>
> I would say that if you have a thermal without vertical speed you have no thermal. Yes, vortex-like vertical structure of thermal bubble affects vertical shape of thermal, but that has nothing to do with horizontal wind discussed here. And no, it is not a myth, I and many others can see it with out own eyes using modern wind measusing inertial variometer. Usually windspeed difference between thermal center and surrounding is less that 50%, maybe 20-30%, but in well formed cloudstreet it is almost a rule that windspeed halves in best lift. There is not a shadow of doubt that thermal acts as a "semi-transparent" barrier to surrounding windfield. If the wind would not change, we would not need the skill of centering thermal, one single centering correction at the beginning would be enough since thermal would be perfectly round and symmetrical. I'm still waiting to find one that fits the description.

I would like to hear more about the science/physics that support your contention about horizontal wind velocity in thermals and a semi-transparent wind barrier. I can be convinced, but so far not so much.

As far as correcting for downwind drift in thermals, the reason is this; In the presence of wind, (and in particular, wind shear as John mentions below) the thermal rises at an angle. if the glider were going up at the same rate as the air in the thermal we would not need to correct for this as you state. However, we have a sink rate. Because of this we are constantly and slowly falling out the bottom of this tilted thermal. We must make upwind corrections in our circles to stay in the lift.

[krasw]

torstai 10. marraskuuta 2016 21.28.25 UTC+2 John Cochrane kirjoitti:
> Yes, thermals don't drift fully with the wind. The major reason is wind shear. The wind is stronger at altitude than below. That's why we can sometimes slope soar or wave soar cumulus clouds. That's why we do better than expected upwind, and worse than expected downwind. Someday I'll work up a set of tables for that...
>
> John Cochrane

Uhhh... No. There is practically no wind shear in convective layer, apart from surface friction layer, unless you put a mountain to disturb flow. The convection transfers momentum of airflow vertically up and down, resulting uniform *average* wind field vertically. Please look at flatland soundings of any convective day, shear layers under cloudbase do not exist.

What you are describing with slope soaring is windshear across inversion layer. Wave can exist only in stable layer above inversion (where hydrostatic stability acts as a "spring" force), whereas convection requires layer of constant potential temperature, ie. neutral stability. Sometimes inversion layer undulates and this makes it possible to contact wave close to cumulus base (cumulus penetrates to inversion). It is not slope or ridge soaring, there is no heated ridge creating slope wind.

[[email protected]]

On Thursday, November 10, 2016 at 3:06:19 PM UTC-5, krasw wrote:
> torstai 10. marraskuuta 2016 21.28.25 UTC+2 John Cochrane kirjoitti:
> > Yes, thermals don't drift fully with the wind. The major reason is wind shear. The wind is stronger at altitude than below. That's why we can sometimes slope soar or wave soar cumulus clouds. That's why we do better than expected upwind, and worse than expected downwind. Someday I'll work up a set of tables for that...
> >
> > John Cochrane
>
> Uhhh... No. There is practically no wind shear in convective layer, apart from surface friction layer, unless you put a mountain to disturb flow. The convection transfers momentum of airflow vertically up and down, resulting uniform *average* wind field vertically. Please look at flatland soundings of any convective day, shear layers under cloudbase do not exist.
>
> What you are describing with slope soaring is windshear across inversion layer. Wave can exist only in stable layer above inversion (where hydrostatic stability acts as a "spring" force), whereas convection requires layer of constant potential temperature, ie. neutral stability. Sometimes inversion layer undulates and this makes it possible to contact wave close to cumulus base (cumulus penetrates to inversion). It is not slope or ridge soaring, there is no heated ridge creating slope wind.

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

[Branko Stojkovic]

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 here:
http://trimill.com/CuSoft/PolarExplorer/Generalized_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

[John Cochrane[_3_]]

It's all that I derived and more -- I didn't do angles other than 0 or 90. Well, maybe the tables are of some practical use!
John Cochrane BB

[krasw]

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.

[Roy Garden]

At 05:20 10 November 2016, 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.cochrane/soaring/docs/wave_mac
redy.pdf
>
>Enjoy! Let me know if you see bugs.
>
>John Cochrane
>

The speed to fly for wave lift is simple.
In lift, fly fast.
In Sink, fly faster.

_never_ fly crosswind in sink.

When flying upwind (to a primary for example) your speed needs to be
set by your gps not your Asi.
in zero lift, fly upwind at your best glide speed (as read by your gps)
over the ground (assuming a fairly flat polar on your glider)
To clarify that further, best glide + windspeed = airspeed to cross upwind

in zero lift.
In sink, keep ramping that ground speed up as the sink increases, the
only limit being Vne on your Asi (corrected for Alt, back to Tas)

Mcready will not work in wave as it doesn't know what the windspeed is
and that is the critical thing for setting your into wind ground speed.

What flatland thermal pilots need to do first, is stop pointing the glider

where they want to go, Crab, almost always (except when flying directly
into or down wind, which is almost never)

And picking where to fly is more important than how fast you fly.
if you need to cross wave bars, do it at a Bridge or where the lift is weak

(as the sink will be weak too)

So, things to do in wave.
1) Ditch the McReady ring, it doesn't apply as it doesn't know what the
windspeed is.
2) Crab, almost everywhere.
3) in lift, fly fast, in sink, fly ridiculously fast. (up or downwind,
never
cross wind, never)

Unless you are pole squatting for badge purposes or just don't like the
gel coat on your glider, Va is minimum speed on a halfway decent wave
day, Vne is a good indicator that you probably shouldn't go too much
faster when crossing sink.

Said slightly tounge in cheek.
But really, crab ! everywhere.
And fly faster (much faster than you think)

[Dan Marotta]

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

[Ramy[_2_]]

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

[[email protected]]

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.cochrane/soaring/docs/wave_macredy.pdf
>
> Enjoy! Let me know if you see bugs.
>
> John Cochrane

What about downwind speed to fly?
Chris

[krasw]

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 Marotta]

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

[Roy Garden]

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.cochrane/soaring/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 . . .
:-)

[RR]

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

[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

[David Salmon[_3_]]

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

[Colin Wray[_3_]]

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 here:
> http://trimill.com/CuSoft/PolarExplorer/Generalized_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

[Branko Stojkovic]

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 ?