Why don't flight computers adjust STF for wind?

[Kevin Christner]

My understanding is that modern flight computers (which seem to have 10X more features than anyone could possibly use) don't make adjustment to STF calculations for the wind. From my reading of recent "authoritative" sources (Brigliodori, Kawa) it is optimal to increase speed into the wind and decrease speed downwind, relative to non-adjusted McCready. Also of critical importance to me would be a final glide optimizer. Currently when making a final glide I "move the dial" up and down in McCready speeds as I get close to final glide. Often changing the McCready value up into the wind and down with the wind leads to lower required altitude.

Am I missing anything?

2C

[[email protected]]

On Friday, January 10, 2014 1:10:45 PM UTC-6, Kevin Christner wrote:
> My understanding is that modern flight computers (which seem to have 10X more features than anyone could possibly use) don't make adjustment to STF calculations for the wind.

They do make very good adjustments for the wind in the sense that if you dial in MacCready 3 into the wind they will tell you you need a lot more altitude than if you dial in MacCready 3 going downwind.

The speed to fly calculation is not affected by wind, as long as thermals drift with the wind. You still fly MacCready 3 airspeed in MacCready 3 lift. The final glide calculation is also not affected by wind. You still leave a 3knot thermal when you hit the MacCready 3 altitude, corrected for wind.

There are second order effects -- thermals don't drift exactly with the wind, you may be able to bump more or less effectively depending on wind, etc. But it would take a whole new generation of theory and software to begin to quantify these effects.

The optimal MacCready setting is affected by wind, when you're going in to a turnpoint. You want to both fly faster and be choosier about thermals going to an upwind turnpoint, and fly slower and take weaker lift going to a downwind turnpoint. This is currently handled by just increasing or decreasing the MacCready setting, which is what Brigliadori and Kawa are advocating..

The setting choice can be done quantitatively, see "upwind and downwind" here

http://faculty.chicagobooth.edu/john.cochrane/soaring/index.htm

The only thing a flight computer can productively add is this calculation. I've been bugging the CN folks do implement this for a while. All it takes is to present the equivalent after-turnpoint mac cready setting for the current value. But they answer (correctly, from a business standpoint) "we're not putting in a number that only you care about!"

John Cochrane

[Kevin Christner]

> The only thing a flight computer can productively add is this calculation.. I've been bugging the CN folks do implement this for a while. All it takes is to present the equivalent after-turnpoint mac cready setting for the current value. But they answer (correctly, from a business standpoint) "we're not putting in a number that only you care about!"

If Brigliadori and Kawa care, it might be worth adding!

2C

[Steve Leonard[_2_]]

I think I would modify John's statements just slightly. He says "You want to both fly faster and be choosier about thermals going to an upwind turnpoint, and fly slower and take weaker lift going to a downwind turnpoint."

I would say, you want to fly faster 'after the last climb going into an upwind turnpoint' and be choosier about thermals (particularly the last one before the turnpoint) when going to an upwind turnpoint and 'be more willing' to fly a little slower, or take a weaker climb (particularly the last one before the turn) when going to a downwind turnpoint.

Key is that theory is different when trying to maximize altitude over the ground at a fixed point some distance away then it is to maximize achieved cross country speed through the air.

Sound about right, John?

[Dave Nadler]

George Moffat:
"Always go into an upwind turnpoint low"

Anonymous:
"Yep, Ol' George sure landed out a lot of his competitors with that one!"

See ya, Dave "YO electric"

[[email protected]]

On Friday, January 10, 2014 3:10:57 PM UTC-6, Dave Nadler wrote:
> George Moffat:
>
> "Always go into an upwind turnpoint low"
>
>
>
> Anonymous:
>
> "Yep, Ol' George sure landed out a lot of his competitors with that one!"
>
>
>
> See ya, Dave "YO electric"

no matter downwind or upwind ... use the horseshoe theory :) cheers S9

[Chris Rollings[_2_]]

If you are gliding from one thermal to another, optimum speed is the same
whether you are going into wind, downwind or no wind, it just depends on
the rate of climb achieved in the next thermal. If you are gliding to a
point on the ground, final glide or round a turn-point, then optimum speed
will be higher into wind than downwind.

At 19:10 10 January 2014, Kevin Christner wrote:
>My understanding is that modern flight computers (which seem to have 10X
>mo=
>re features than anyone could possibly use) don't make adjustment to STF
>ca=
>lculations for the wind. From my reading of recent "authoritative"
>sources=
> (Brigliodori, Kawa) it is optimal to increase speed into the wind and
>decr=
>ease speed downwind, relative to non-adjusted McCready. Also of critical
>i=
>mportance to me would be a final glide optimizer. Currently when making
a
>=
>final glide I "move the dial" up and down in McCready speeds as I get
>close=
> to final glide. Often changing the McCready value up into the wind and
>do=
>wn with the wind leads to lower required altitude.
>
>Am I missing anything?
>
>2C
>

[Eric Greenwell[_4_]]

Doesn't it depend on what you are trying to optimize?

* if it's maximizing your arrival height at a point, then you do use a
different STF for upwind and downwind

* if it's minimizing the time for a final glide, then you use the same
STF, based only on your current rate of climb

* if you are approaching a turnpoint, it's not about classic McCready
STF, but about risk management: fly the MC STF and you might have to
take thermal while going upwind; fly more slowly so you can use a
thermal on the downwind side, but risk a lower course speed because you
are flying slower than the MC optimum.

Or putting it in "classic" terms, for the "rounding the turnpoint"
situation: Always fly the MC STF, but leave your thermal as soon as you
can glide around the turnpoint to your next thermal. A practical example
is a big dust devil or gaggle short of the turnpoint: go to the
gaggle/dust devil after rounding the turnpoint, not before.

Chris Rollings wrote, On 1/10/2014 11:35 PM:
> If you are gliding from one thermal to another, optimum speed is the same
> whether you are going into wind, downwind or no wind, it just depends on
> the rate of climb achieved in the next thermal. If you are gliding to a
> point on the ground, final glide or round a turn-point, then optimum speed
> will be higher into wind than downwind.
>
> At 19:10 10 January 2014, Kevin Christner wrote:
>> My understanding is that modern flight computers (which seem to have 10X
>> mo=
>> re features than anyone could possibly use) don't make adjustment to STF
>> ca=
>> lculations for the wind. From my reading of recent "authoritative"
>> sources=
>> (Brigliodori, Kawa) it is optimal to increase speed into the wind and
>> decr=
>> ease speed downwind, relative to non-adjusted McCready. Also of critical
>> i=
>> mportance to me would be a final glide optimizer. Currently when making
> a
>> =
>> final glide I "move the dial" up and down in McCready speeds as I get
>> close=
>> to final glide. Often changing the McCready value up into the wind and
>> do=
>> wn with the wind leads to lower required altitude.
>>
>> Am I missing anything?
>>
>> 2C
>>
>


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl

[Kevin Christner]

On Saturday, January 11, 2014 2:35:45 AM UTC-5, Chris Rollings wrote:
> If you are gliding from one thermal to another, optimum speed is the same
> whether you are going into wind, downwind or no wind, it just depends on
> the rate of climb achieved in the next thermal. If you are gliding to a
> point on the ground, final glide or round a turn-point, then optimum speed
> will be higher into wind than downwind.

This is true from an optimal speed perspective. Kawa and Brigliodori's point (I think) has to do with increasing search range. Flying faster upwind and slower downwind increases your search range. Also, if you've ever looked at a graph for flying slightly faster or slower than optimum MC bumping up or down one know has very little effect on total speed. Finding a better thermal (or a thermal at all) would make you faster or keep you from going Aux Vauche...

Thoughts?

2C

[[email protected]]

On Saturday, January 11, 2014 1:35:45 AM UTC-6, Chris Rollings wrote:
> If you are gliding from one thermal to another, optimum speed is the same
> whether you are going into wind, downwind or no wind, it just depends on
> the rate of climb achieved in the next thermal. If you are gliding to a
> point on the ground, final glide or round a turn-point, then optimum speed
> will be higher into wind than downwind.
>

Not quite true on final glide. If you're in a 3 knot thermal, you climb until you hit the Mc 3 glide height, and then set off at the Mc 3 speed to fly, and the wind makes no difference to this calculation. It does not make sense to sit in a Mc 3 thermal, drifting downwind, to get higher and then bash home at the Mc 4 speed just because it's in to the wind.

This presumes that the goal is speed, not stretching a glide.

This also ignores the fact that it's often easier to bump thermals into the wind, but much harder to scratch low going into the wind than downwind. Those features argue for a bit more aggressive approach early on an into-wind final glide, and a much more conservative approach later on an into-wind final glide. All my final glide disasters have been going in to stiff winds! When down to 1000 feet, it's awfully nice to be drifting downwind while you hunt around in those half know thermals.

John Cochrane

[Steve Leonard[_2_]]

On Saturday, January 11, 2014 2:35:45 AM UTC-5, Chris Rollings wrote:
> If you are gliding from one thermal to another, optimum speed is the same
> whether you are going into wind, downwind or no wind, it just depends on
> the rate of climb achieved in the next thermal. If you are gliding to a
> point on the ground, final glide or round a turn-point, then optimum speed
> will be higher into wind than downwind.

Then, on Saturday, January 11, 2014 4:18:33 PM UTC-6, Kevin Christner wrote:
> This is true from an optimal speed perspective. Kawa and Brigliodori's point
> (I think) has to do with increasing search range. Flying faster upwind and
> slower downwind increases your search range. Also, if you've ever looked at a
> graph for flying slightly faster or slower than optimum MC bumping up or down
> one know has very little effect on total speed. Finding a better thermal (or
> a thermal at all) would make you faster or keep you from going Aux Vauche....
> Thoughts? 2C

Take your polar, see what your speed is for MC3. Let's say it is 75 knots. Calculate your L/D from the polar. Now, fly into a headwind, say 5 knots, and determine your L/D over the ground. Now, check your L/D flying at 80 knots into that same 5 knot headwind. Did your L/D go up or down? Try adding another 5 knots to the cruise speed and see what happens with your L/D.. Try subtracting 5 knots and calculate your L/D Now, bump the headwind to 10 knots, then 15, and 20. Figure out how strong the headwind has to be for your L/D to actually go UP by flying at 80 or 85 knots indicated versus 75 knots indicated. Think you will find that flying faster into the wind will only increases your search range when the MC is low and the wind speed is high.

As for increasing your search range when flying down wind, why slow down since you have the tailwind increasing your search range?

But, those are increasing glide distance over the ground, which is not the same as maximizing cross country speed.

And, as BB said, MC for final glide is climb rate for your last thermal. Not more if the final glide will be into the wind. Altitude required increases for a headwind, but speed to be flown does not change because of wind.

Steve Leonard

[Chris Rollings[_2_]]

My earlier post was referring to the theoretical considerations. The
essential point is that the thermals drift with the wind, applying simple
McReady theory gives maximum achieved average speed through the air, any
variation gives a lower average airspeed and therefore also a lower average
ground speed.

In the real World, for the last 40 years, my teaching and practice, in
UK/NW Europe conditions, has been: default setting 1 knot, if you're
getting low or it doesn't look good ahead set 0 knots, if it's a really
good day and you're high and going well set 2 knots, if it's a fantastic
day, the best you've ever flown on and you look like setting a record, set
3 knots. If you are tempted to set 4 knots, land, take 2 asperin and lie
down, you're feverish. For strong thermal areas like the American South
West, South Africa and Australia, add one knot to all the above, except
perhaps the 0 knot case.

You go faster flying between 6 knot thermals with 2 knots set than you do
flying between 4 knot thermals with 4 knots set. The lower setting you
use, the greater your range and the greater your chance of finding the
really good thermals.

This doesn't apply on final glide, when you do need to allow for head or
tail wind and you should use the instantaneous rate of climb when you leave
the thermal, not the average.

At 04:11 12 January 2014, Steve Leonard wrote:
>On Saturday, January 11, 2014 2:35:45 AM UTC-5, Chris Rollings wrote:=20
>> If you are gliding from one thermal to another, optimum speed is the
>same=
>=20
>> whether you are going into wind, downwind or no wind, it just depends
on=
>=20
>> the rate of climb achieved in the next thermal. If you are gliding to
a=
>=20
>> point on the ground, final glide or round a turn-point, then optimum
>spee=
>d=20
>> will be higher into wind than downwind.=20
>
>Then, on Saturday, January 11, 2014 4:18:33 PM UTC-6, Kevin Christner
>wrote=
>:
>> This is true from an optimal speed perspective. Kawa and Brigliodori's
>po=
>int
>> (I think) has to do with increasing search range. Flying faster upwind
>an=
>d
>> slower downwind increases your search range. Also, if you've ever
looked
>=
>at a
>> graph for flying slightly faster or slower than optimum MC bumping up
or
>=
>down
>> one know has very little effect on total speed. Finding a better
thermal
>=
>(or
>> a thermal at all) would make you faster or keep you from going Aux
>Vauche=
>....
>> Thoughts? 2C
>
>Take your polar, see what your speed is for MC3. Let's say it is 75
>knots.=
> Calculate your L/D from the polar. Now, fly into a headwind, say 5
>knots=
>, and determine your L/D over the ground. Now, check your L/D flying at
>80=
> knots into that same 5 knot headwind. Did your L/D go up or down? Try
>ad=
>ding another 5 knots to the cruise speed and see what happens with your
>L/D=
>.. Try subtracting 5 knots and calculate your L/D Now, bump the
headwind
>t=
>o 10 knots, then 15, and 20. Figure out how strong the headwind has to
be
>=
>for your L/D to actually go UP by flying at 80 or 85 knots indicated
>versus=
> 75 knots indicated. Think you will find that flying faster into the
wind
>=
>will only increases your search range when the MC is low and the wind
>speed=
> is high.
>
>As for increasing your search range when flying down wind, why slow down
>si=
>nce you have the tailwind increasing your search range?
>
>But, those are increasing glide distance over the ground, which is not
the
>=
>same as maximizing cross country speed.
>
>And, as BB said, MC for final glide is climb rate for your last thermal.
>N=
>ot more if the final glide will be into the wind. Altitude required
>incre=
>ases for a headwind, but speed to be flown does not change because of
wind.
>
>Steve Leonard
>
>

[KiloKilo[_2_]]

Not sure it's true ... but I recall Bill Bartell(US comp pilot) initially misunderstood MC ... and would set his MC value to altitude/1000 ... i.e. 5000' MC = 5 .... 2000' MC = 2.

He had some pretty good comp results during this period - as I recall.

:-)

kk

[[email protected]]

> In the real World, for the last 40 years, my teaching and practice, in
> UK/NW Europe conditions, has been: default setting 1 knot, if you're
> getting low or it doesn't look good ahead set 0 knots, if it's a really
> good day and you're high and going well set 2 knots, if it's a fantastic
> day, the best you've ever flown on and you look like setting a record, set
> 3 knots. If you are tempted to set 4 knots, land, take 2 asperin and lie
> down, you're feverish. For strong thermal areas like the American South
> West, South Africa and Australia, add one knot to all the above, except
> perhaps the 0 knot case.
>
>
>
> You go faster flying between 6 knot thermals with 2 knots set than you do
> flying between 4 knot thermals with 4 knots set. The lower setting you
> use, the greater your range and the greater your chance of finding the
> really good thermals.
>
>
This reflects current practice, and it's really interesting. "Range" doesn't really describe the reason, I think. In the southwest USA at 10,000' we have tons of range, we don't stop for under 6 knots, yet flying at 100 knots does better than 120 (go look up mc 6 speed!), and 95 won't kill you.

I think the reason is more that flying at warp speed, you (or at least I) lose the feel of the air; I can't adjust slightly to benefit from gliding through rising air. And, I might fly right through that great thermal and not feel it.

John Cochrane

[krasw]

On Friday, 10 January 2014 22:01:28 UTC+2, wrote:

> There are second order effects -- thermals don't drift exactly with the wind, you may be able to bump more or less effectively depending on wind, etc. But it would take a whole new generation of theory and software to begin to quantify these effects.
>
>
> John Cochrane

Yes, theoretically *if* thermals would drift perfectly with wind, there wouldn't be any windshear across thermals, resulting that they would be completely symmetrical (round). Or they would ascend at impossible angles (2 m/s thermal drifting in 20 m/s wind would result 1:10 angle).

Flying under clouds with real-time wind information is quite revealing.

krasw

[Jim White[_3_]]

This was exactly my understanding until I read Brigliadori. On pages 359
through 364 they make a pretty good case for flying a bit faster into wind
on task due to the slope of thermals and vice versa, all with worked
examples.

Jim

At 07:35 11 January 2014, Chris Rollings wrote:
>If you are gliding from one thermal to another, optimum speed is the same
>whether you are going into wind, downwind or no wind, it just depends on
>the rate of climb achieved in the next thermal. If you are gliding to a
>point on the ground, final glide or round a turn-point, then optimum
speed
>will be higher into wind than downwind.
>

[Steve Leonard[_2_]]

On Monday, January 13, 2014 2:34:40 AM UTC-6, krasw wrote:
>Yes, theoretically *if* thermals would drift perfectly with wind...

Uh oh. Next problem. If thermals don't drift at the same speed as the wind, how accurate is that wind speed your computer derrives from drift while you are thermalling?

Steve

[Andrew Brayer]

On Friday, January 10, 2014 2:10:45 PM UTC-5, Kevin Christner wrote:
> My understanding is that modern flight computers (which seem to have 10X more features than anyone could possibly use) don't make adjustment to STF calculations for the wind. From my reading of recent "authoritative" sources (Brigliodori, Kawa) it is optimal to increase speed into the wind and decrease speed downwind, relative to non-adjusted McCready. Also of critical importance to me would be a final glide optimizer. Currently when making a final glide I "move the dial" up and down in McCready speeds as I get close to final glide. Often changing the McCready value up into the wind and down with the wind leads to lower required altitude.
>
>
>
> Am I missing anything?
>
>
>
> 2C

what flight computer are you running?

[Dave Nadler]

On Monday, January 13, 2014 11:17:35 AM UTC-5, Steve Leonard wrote:
> On Monday, January 13, 2014 2:34:40 AM UTC-6, krasw wrote:
> >Yes, theoretically *if* thermals would drift perfectly with wind...
>
> Uh oh. Next problem. If thermals don't drift at the same speed
> as the wind, how accurate is that wind speed your computer derrives
> from drift while you are thermalling?
>
> Steve

It is well known that thermals do not exactly drift with the wind.
Consider the inertia of the heated parcel of air as it rises through
increasing wind aloft...
Hang-glider pilots have known for decades to fly upwind in thermal
wind shadows.

Not all flight computers use drift while thermalling to estimate
wind! For example, the ILEC SN10 does not...

Hope that helps,
Best Regards, Dave "YO electric"

PS: Steve, how's the first SN10 ever delivered to a customer treating you?

[Eric Greenwell[_4_]]

Steve Leonard wrote, On 1/13/2014 8:17 AM:
> On Monday, January 13, 2014 2:34:40 AM UTC-6, krasw wrote:
>> Yes, theoretically *if* thermals would drift perfectly with
>> wind...
>
> Uh oh. Next problem. If thermals don't drift at the same speed as
> the wind, how accurate is that wind speed your computer derrives from
> drift while you are thermalling?

My experience with a 302 and SeeYou Mobile was the differences were
small compared to other variations due to time, location, and altitude,
and small enough that I usually didn't notice any difference. But, there
may be places that do have bigger differences, and I just didn't fly there.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

[Kevin Christner]

>
> what flight computer are you running?

Most recently an Oudie, but for example with a 10kt headwind best L/D over ground would be better at MC 1 than MC 0.

[krasw]

On Tuesday, 14 January 2014 04:46:19 UTC+2, Eric Greenwell wrote:
> Steve Leonard wrote, On 1/13/2014 8:17 AM:
>
> > On Monday, January 13, 2014 2:34:40 AM UTC-6, krasw wrote:
>
> >> Yes, theoretically *if* thermals would drift perfectly with
>
> >> wind...
>
> >
>
> > Uh oh. Next problem. If thermals don't drift at the same speed as
>
> > the wind, how accurate is that wind speed your computer derrives from
>
> > drift while you are thermalling?
>
>
>
> My experience with a 302 and SeeYou Mobile was the differences were
>
> small compared to other variations due to time, location, and altitude,
>
> and small enough that I usually didn't notice any difference. But, there
>
> may be places that do have bigger differences, and I just didn't fly there.
>
>
>
> --
>
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
>
> email me)

I think many computers (or software) counts for wind variations due altitude. For flying in convective conditions this is just plain wrong and misleading. Wind doesn't change much (or at all) between altitude just over surface friction layer (few hundred meters) and cloudbase. This is because convection effectively mixes airmass momentum in convective layer. (Wave and mountains are of course different matter). Most important variations are due location and time.

[Dave Nadler]

On Thursday, January 16, 2014 3:04:17 AM UTC-5, krasw wrote:
> I think many computers (or software) counts for wind variations due altitude.

You think? For example?

> For flying in convective conditions this is just plain wrong and misleading.

Actually, it can and often does change significantly
(out in USA west for example). But, the more important
input to final glide is completely differing wind on
final glide from the point the glide is planned (think
final glides to Minden or Gawler, or any mountain site).

Hope that helps,
Best Regards, Dave "YO electric"

[krasw]

On Thursday, 16 January 2014 14:23:20 UTC+2, Dave Nadler wrote:
> On Thursday, January 16, 2014 3:04:17 AM UTC-5, krasw wrote:
>
> > I think many computers (or software) counts for wind variations due altitude.
>
>
>
> You think? For example?
>

SeeYou Mobile.


>
>
> > For flying in convective conditions this is just plain wrong and misleading.
>
>
>
> Actually, it can and often does change significantly
>
> (out in USA west for example). But, the more important
>
> input to final glide is completely differing wind on
>
> final glide from the point the glide is planned (think
>
> final glides to Minden or Gawler, or any mountain site).
>
>
>
> Hope that helps,
>
> Best Regards, Dave "YO electric"

If you find sounding taken from a) flatland, b) during afternoon, c) with convective conditions, and d) wind changing direction and strength within convective layer, I would be more than interested in seeing it.

I have limited knowledge of Australian or western US geography, but I probably wouldn't classify Minden or areas east of Gawler flatland.

[Mike the Strike]

A few points from a south-western US perspective:

1) MacCready setting should be close to your achieved average climb. With 'ten-knot" thermals, we often find a climb average of 4 to 6 knots - you have to find them and center them as well as climb!

2) Wind speed and direction often does change with altitude, but this is not a major factor until final glide.

3) The best practice to approach an upwind turnpoint is with the minimum altitude for safety. You don't need to change MacCready setting, but don't carry excess height flying against the wind.

4) If in doubt, I use a MacCready setting of 3 - I have never found zero or 1 to be useful as it has no margin for safety. (I don't think I could live anywhere where a MacCready setting of 1 is the norm!)

Mike

[Eric Greenwell[_4_]]

Mike the Strike wrote, On 1/17/2014 7:12 AM:
> 4) If in doubt, I use a MacCready setting of 3 - I have never found
> zero or 1 to be useful as it has no margin for safety. (I don't think
> I could live anywhere where a MacCready setting of 1 is the norm!)

Many of us use two MC settings: for me, the STF vario is set to 1 or 2
(3 on amazing days); the flight computer MC setting is usually set to 4
(5 or 6 as the area between airports gets scarier).

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)