302 wind calculation

On Mar 29, 1:25*pm, Darryl Ramm wrote:
On Mar 29, 9:55*am, mattm wrote:



On Mar 29, 12:31*pm, T8 wrote:

On Mar 29, 11:29 am, Darryl Ramm *wrote:

For the 180 degree wrong problem, any system that uses track and TAS/
GS difference calculations risks being 180 degrees wrong it it just
has that difference on two reciprocal tracks. If you run straight down
a ridge and do a rapid turn back the other way and fly the same track
back the other way there are two perfectly equivalent trigonometric
solutions which will give the wind from either direction. The flight
computer has absolutely no idea what direction you are crabbing the
glider into the wind.

I understand the problem of very limited information. *This is a
different problem :-).

In this case picture wind from 360, trip out on ridge with track 270,
303 shows wind from 360 @ 12, relative wind 90 degrees, arrow points
left (i.e. "wind blowing on glider" from right). *On the reverse trip,
having failed to get a wind update, the
computer now shows track 90, wind from 360 @ 12, relative wind 90
degrees, arrow points left. *See the issue? *Even in the absence of
updated wind, the relative wind should be showing 270 based on old
wind, new track. *I verified this behavior again yesterday, turning
through 45 degrees (slowly), watching track change, seeing relative
wind stay constant despite changing track until the device updated the
wind. [edit: I managed to mung the tracks up the first time].

Ignoring the 180 degree wrong wind issue, if you do do +/- 30 degree
or more track changes (not track reversals) do you get wind updates
that agree with a PDA software. What if you reset that PDA calculated
wind before each test does the wind calculated then agree?

No. *On "typical" thermal soaring days with winds under 15, but with a
shear I *know* is there, I won't get a zigzag update on the 303 unless
I alter track +/- 45, and sometimes not even then. *A single 360 turn
always works, but who wants to make such drastic maneuvers? *+/- 30 is
vastly more acceptable and that would do the trick on the older CAI
system. *My old PDA software was WP Pro 9.11. *In general, the wind on
the PDA was preferable to the 303, but less useful because I do my
final glides on the 303 (too many things to go wrong in WP, too hard
to read the PDA at high speed). *XCSoar has the nifty feature that you
can do wind calc by either circling, zigzag or both. *In zigzag only,
it out performed the 303 in yesterday's somewhat unusual conditions
(repeatedly transiting a known shear layer).

"relative wind" that is relative to track (not heading).

Understood, yes.

-Evan Ludeman / T8

Hum, interesting. *A number of flight computers have a mag compass
attachment which allows computing the wind vector in straight flight.
I had
thought the 302 had one of these, too, but now I see that it doesn't!
That
would solve this whole issue. *Did the LNav have that?

-- Matt

A compass could clearly help disambiguate the reverse track problem I
described earlier.

Some computers have a fluxgate magentometer 'compass", the LX 7000
series is the one I see mentioned most. *The main desire to have a
fluxgate magnetometer is to calculate wind without turning at all, I
don't know if any systems fold them into disambiguation track/TAS
calculations.

As mentioned earlier I've heard very few comments overall and some
negative/neutral comments about how good the LX wind calculations are
compared to standard non-fluxgate systems. I have never flown with the
LX 7000 series.

I have some concerns that trying to do magnetometer based wind
calculations with a 2D/dual fluxgate sensor (i.e. a basic compass) is
open to aircraft pitch/magnetic inclination coupling. Modern fluxgate
sensors used as a part of AHRS systems will be three axis and include
MEMS accelerometers for pitch/inclination coupling correction
(although they are still prone to acceleration/turn induced errors,
but the AHRS system can at least work out if that is going on).

I suspect many fluxgate "compasses" used in gliding computers are
simple 2D type and I wonder if this is an issue. The LX also seems to
try to detect steady straight flight (using GPS and airspeed data?)
and I am curious how much of a problem this is in practice both either
from producing inclination/pitch calculation errors or having the LX
try to prevent errors and refuse to do the calculation when the flight
is not steady (I believe it warns you when this happens). Anybody
flown with the LX series with magnetometer and want to comment on how
good the wind calcs are using he "COMPASS" setting?

Cambridge has never offered a fluxgate sensor on its flight computers
AFAIK.

Darryl

I used to fly a plane that had an LX5000 installed in it, and I
connected
my PDA running SoarPilot to the unit. It had the fluxgate compass I
believe. The wind computations were always reasonable as far as I
could tell, but I never had a chance to run a ridge with it. It
probably was
smart enough to disregard the compass when circling or accelerating,
and actually was probably using the circling drift algorithm as well.
I believe the LX160 smart vario computes wind just from circling,
when it computes it at all. It doesn't send wind data on the NMEA
stream.

-- Matt

On Mar 29, 10:55*am, mattm wrote:
On Mar 29, 12:31*pm, T8 wrote:



On Mar 29, 11:29 am, Darryl Ramm *wrote:

For the 180 degree wrong problem, any system that uses track and TAS/
GS difference calculations risks being 180 degrees wrong it it just
has that difference on two reciprocal tracks. If you run straight down
a ridge and do a rapid turn back the other way and fly the same track
back the other way there are two perfectly equivalent trigonometric
solutions which will give the wind from either direction. The flight
computer has absolutely no idea what direction you are crabbing the
glider into the wind.

I understand the problem of very limited information. *This is a
different problem :-).

In this case picture wind from 360, trip out on ridge with track 270,
303 shows wind from 360 @ 12, relative wind 90 degrees, arrow points
left (i.e. "wind blowing on glider" from right). *On the reverse trip,
having failed to get a wind update, the
computer now shows track 90, wind from 360 @ 12, relative wind 90
degrees, arrow points left. *See the issue? *Even in the absence of
updated wind, the relative wind should be showing 270 based on old
wind, new track. *I verified this behavior again yesterday, turning
through 45 degrees (slowly), watching track change, seeing relative
wind stay constant despite changing track until the device updated the
wind. [edit: I managed to mung the tracks up the first time].

Ignoring the 180 degree wrong wind issue, if you do do +/- 30 degree
or more track changes (not track reversals) do you get wind updates
that agree with a PDA software. What if you reset that PDA calculated
wind before each test does the wind calculated then agree?

No. *On "typical" thermal soaring days with winds under 15, but with a
shear I *know* is there, I won't get a zigzag update on the 303 unless
I alter track +/- 45, and sometimes not even then. *A single 360 turn
always works, but who wants to make such drastic maneuvers? *+/- 30 is
vastly more acceptable and that would do the trick on the older CAI
system. *My old PDA software was WP Pro 9.11. *In general, the wind on
the PDA was preferable to the 303, but less useful because I do my
final glides on the 303 (too many things to go wrong in WP, too hard
to read the PDA at high speed). *XCSoar has the nifty feature that you
can do wind calc by either circling, zigzag or both. *In zigzag only,
it out performed the 303 in yesterday's somewhat unusual conditions
(repeatedly transiting a known shear layer).

"relative wind" that is relative to track (not heading).

Understood, yes.

-Evan Ludeman / T8

Hum, interesting. *A number of flight computers have a mag compass
attachment which allows computing the wind vector in straight flight.
I had
thought the 302 had one of these, too, but now I see that it doesn't!
That
would solve this whole issue. *Did the LNav have that?

-- Matt

A good heading sensor would indeed allow computation of highly
accurate real-time vector winds since most glider computers already
have ground speed, track and true airspeed. 3-axis MEMS gyro
stabilized magnetometers MAY work but multi-antenna GPS derived
heading data would be better if such a device were available. (Google
"GPS heading sensor")

On Mar 29, 10:42*am, mattm wrote:
On Mar 29, 1:25*pm, Darryl Ramm wrote:



On Mar 29, 9:55*am, mattm wrote:

On Mar 29, 12:31*pm, T8 wrote:

On Mar 29, 11:29 am, Darryl Ramm *wrote:

For the 180 degree wrong problem, any system that uses track and TAS/
GS difference calculations risks being 180 degrees wrong it it just
has that difference on two reciprocal tracks. If you run straight down
a ridge and do a rapid turn back the other way and fly the same track
back the other way there are two perfectly equivalent trigonometric
solutions which will give the wind from either direction. The flight
computer has absolutely no idea what direction you are crabbing the
glider into the wind.

I understand the problem of very limited information. *This is a
different problem :-).

In this case picture wind from 360, trip out on ridge with track 270,
303 shows wind from 360 @ 12, relative wind 90 degrees, arrow points
left (i.e. "wind blowing on glider" from right). *On the reverse trip,
having failed to get a wind update, the
computer now shows track 90, wind from 360 @ 12, relative wind 90
degrees, arrow points left. *See the issue? *Even in the absence of
updated wind, the relative wind should be showing 270 based on old
wind, new track. *I verified this behavior again yesterday, turning
through 45 degrees (slowly), watching track change, seeing relative
wind stay constant despite changing track until the device updated the
wind. [edit: I managed to mung the tracks up the first time].

Ignoring the 180 degree wrong wind issue, if you do do +/- 30 degree
or more track changes (not track reversals) do you get wind updates
that agree with a PDA software. What if you reset that PDA calculated
wind before each test does the wind calculated then agree?

No. *On "typical" thermal soaring days with winds under 15, but with a
shear I *know* is there, I won't get a zigzag update on the 303 unless
I alter track +/- 45, and sometimes not even then. *A single 360 turn
always works, but who wants to make such drastic maneuvers? *+/- 30 is
vastly more acceptable and that would do the trick on the older CAI
system. *My old PDA software was WP Pro 9.11. *In general, the wind on
the PDA was preferable to the 303, but less useful because I do my
final glides on the 303 (too many things to go wrong in WP, too hard
to read the PDA at high speed). *XCSoar has the nifty feature that you
can do wind calc by either circling, zigzag or both. *In zigzag only,
it out performed the 303 in yesterday's somewhat unusual conditions
(repeatedly transiting a known shear layer).

"relative wind" that is relative to track (not heading).

Understood, yes.

-Evan Ludeman / T8

Hum, interesting. *A number of flight computers have a mag compass
attachment which allows computing the wind vector in straight flight.
I had
thought the 302 had one of these, too, but now I see that it doesn't!
That
would solve this whole issue. *Did the LNav have that?

-- Matt

A compass could clearly help disambiguate the reverse track problem I
described earlier.

Some computers have a fluxgate magentometer 'compass", the LX 7000
series is the one I see mentioned most. *The main desire to have a
fluxgate magnetometer is to calculate wind without turning at all, I
don't know if any systems fold them into disambiguation track/TAS
calculations.

As mentioned earlier I've heard very few comments overall and some
negative/neutral comments about how good the LX wind calculations are
compared to standard non-fluxgate systems. I have never flown with the
LX 7000 series.

I have some concerns that trying to do magnetometer based wind
calculations with a 2D/dual fluxgate sensor (i.e. a basic compass) is
open to aircraft pitch/magnetic inclination coupling. Modern fluxgate
sensors used as a part of AHRS systems will be three axis and include
MEMS accelerometers for pitch/inclination coupling correction
(although they are still prone to acceleration/turn induced errors,
but the AHRS system can at least work out if that is going on).

I suspect many fluxgate "compasses" used in gliding computers are
simple 2D type and I wonder if this is an issue. The LX also seems to
try to detect steady straight flight (using GPS and airspeed data?)
and I am curious how much of a problem this is in practice both either
from producing inclination/pitch calculation errors or having the LX
try to prevent errors and refuse to do the calculation when the flight
is not steady (I believe it warns you when this happens). Anybody
flown with the LX series with magnetometer and want to comment on how
good the wind calcs are using he "COMPASS" setting?

Cambridge has never offered a fluxgate sensor on its flight computers
AFAIK.

Darryl

I used to fly a plane that had an LX5000 installed in it, and I
connected
my PDA running SoarPilot to the unit. *It had the fluxgate compass I
believe. *The wind computations were always reasonable as far as I
could tell, but I never had a chance to run a ridge with it. *It
probably was
smart enough to disregard the compass when circling or accelerating,
and actually was probably using the circling drift algorithm as well.
I believe the LX160 smart vario computes wind just from circling,
when it computes it at all. *It doesn't send wind data on the NMEA
stream.

-- Matt

The LX 5000 has a magnetic compass option. That option had to be
installed and the LX 5000 wind calculation had to be set to the
"COMPASS" setting to use it in wind calculations. I understand that
SoarPilot can take the wind calculation from the LX (if configured to
do so) or do it's own internal calculations.

There are lots of permutations of configuration settings so when you
say things like "probably using..." it worry me a little :-) . Do you
know what the configuration settings were? If you get a chance to fly
with it again I'd be interested in the performance with 'COMPASS'
selected in the LX wind calculation settings and wind data read on the
LX device. I am not sure if in the combo you describe you can do a
comparison by having the LX calculate using the COMPASS setting and
have the PDA calculate using a TAS/track data to the calculations can
be compared.

Thanks


Darryl

On Mar 29, 2:08*pm, Darryl Ramm wrote:
On Mar 29, 10:42*am, mattm wrote:



On Mar 29, 1:25*pm, Darryl Ramm wrote:

On Mar 29, 9:55*am, mattm wrote:

On Mar 29, 12:31*pm, T8 wrote:

On Mar 29, 11:29 am, Darryl Ramm *wrote:

For the 180 degree wrong problem, any system that uses track and TAS/
GS difference calculations risks being 180 degrees wrong it it just
has that difference on two reciprocal tracks. If you run straight down
a ridge and do a rapid turn back the other way and fly the same track
back the other way there are two perfectly equivalent trigonometric
solutions which will give the wind from either direction. The flight
computer has absolutely no idea what direction you are crabbing the
glider into the wind.

I understand the problem of very limited information. *This is a
different problem :-).

In this case picture wind from 360, trip out on ridge with track 270,
303 shows wind from 360 @ 12, relative wind 90 degrees, arrow points
left (i.e. "wind blowing on glider" from right). *On the reverse trip,
having failed to get a wind update, the
computer now shows track 90, wind from 360 @ 12, relative wind 90
degrees, arrow points left. *See the issue? *Even in the absence of
updated wind, the relative wind should be showing 270 based on old
wind, new track. *I verified this behavior again yesterday, turning
through 45 degrees (slowly), watching track change, seeing relative
wind stay constant despite changing track until the device updated the
wind. [edit: I managed to mung the tracks up the first time].

Ignoring the 180 degree wrong wind issue, if you do do +/- 30 degree
or more track changes (not track reversals) do you get wind updates
that agree with a PDA software. What if you reset that PDA calculated
wind before each test does the wind calculated then agree?

No. *On "typical" thermal soaring days with winds under 15, but with a
shear I *know* is there, I won't get a zigzag update on the 303 unless
I alter track +/- 45, and sometimes not even then. *A single 360 turn
always works, but who wants to make such drastic maneuvers? *+/- 30 is
vastly more acceptable and that would do the trick on the older CAI
system. *My old PDA software was WP Pro 9.11. *In general, the wind on
the PDA was preferable to the 303, but less useful because I do my
final glides on the 303 (too many things to go wrong in WP, too hard
to read the PDA at high speed). *XCSoar has the nifty feature that you
can do wind calc by either circling, zigzag or both. *In zigzag only,
it out performed the 303 in yesterday's somewhat unusual conditions
(repeatedly transiting a known shear layer).

"relative wind" that is relative to track (not heading).

Understood, yes.

-Evan Ludeman / T8

Hum, interesting. *A number of flight computers have a mag compass
attachment which allows computing the wind vector in straight flight.

You know, it strikes me this thread would make a decent and probably
widely appreciated Soaring article...

On Mar 29, 11:41*am, mattm wrote:
On Mar 29, 2:08*pm, Darryl Ramm wrote:



On Mar 29, 10:42*am, mattm wrote:

On Mar 29, 1:25*pm, Darryl Ramm wrote:

On Mar 29, 9:55*am, mattm wrote:

On Mar 29, 12:31*pm, T8 wrote:

On Mar 29, 11:29 am, Darryl Ramm *wrote:

For the 180 degree wrong problem, any system that uses track and TAS/
GS difference calculations risks being 180 degrees wrong it it just
has that difference on two reciprocal tracks. If you run straight down
a ridge and do a rapid turn back the other way and fly the same track
back the other way there are two perfectly equivalent trigonometric
solutions which will give the wind from either direction. The flight
computer has absolutely no idea what direction you are crabbing the
glider into the wind.

I understand the problem of very limited information. *This is a
different problem :-).

In this case picture wind from 360, trip out on ridge with track 270,
303 shows wind from 360 @ 12, relative wind 90 degrees, arrow points
left (i.e. "wind blowing on glider" from right). *On the reverse trip,
having failed to get a wind update, the
computer now shows track 90, wind from 360 @ 12, relative wind 90
degrees, arrow points left. *See the issue? *Even in the absence of
updated wind, the relative wind should be showing 270 based on old
wind, new track. *I verified this behavior again yesterday, turning
through 45 degrees (slowly), watching track change, seeing relative
wind stay constant despite changing track until the device updated the
wind. [edit: I managed to mung the tracks up the first time].

Ignoring the 180 degree wrong wind issue, if you do do +/- 30 degree
or more track changes (not track reversals) do you get wind updates
that agree with a PDA software. What if you reset that PDA calculated
wind before each test does the wind calculated then agree?

No. *On "typical" thermal soaring days with winds under 15, but with a
shear I *know* is there, I won't get a zigzag update on the 303 unless
I alter track +/- 45, and sometimes not even then. *A single 360 turn
always works, but who wants to make such drastic maneuvers? *+/- 30 is
vastly more acceptable and that would do the trick on the older CAI
system. *My old PDA software was WP Pro 9.11. *In general, the wind on
the PDA was preferable to the 303, but less useful because I do my
final glides on the 303 (too many things to go wrong in WP, too hard
to read the PDA at high speed). *XCSoar has the nifty feature that you
can do wind calc by either circling, zigzag or both. *In zigzag only,
it out performed the 303 in yesterday's somewhat unusual conditions
(repeatedly transiting a known shear layer).

"relative wind" that is relative to track (not heading).

Understood, yes.

-Evan Ludeman / T8

Hum, interesting. *A number of flight computers have a mag compass
attachment which allows computing the wind vector in straight flight.
I had
thought the 302 had one of these, too, but now I see that it doesn't!
That
would solve this whole issue. *Did the LNav have that?

-- Matt

A compass could clearly help disambiguate the reverse track problem I
described earlier.

Some computers have a fluxgate magentometer 'compass", the LX 7000
series is the one I see mentioned most. *The main desire to have a
fluxgate magnetometer is to calculate wind without turning at all, I
don't know if any systems fold them into disambiguation track/TAS
calculations.

As mentioned earlier I've heard very few comments overall and some
negative/neutral comments about how good the LX wind calculations are
compared to standard non-fluxgate systems. I have never flown with the
LX 7000 series.

I have some concerns that trying to do magnetometer based wind
calculations with a 2D/dual fluxgate sensor (i.e. a basic compass) is
open to aircraft pitch/magnetic inclination coupling. Modern fluxgate
sensors used as a part of AHRS systems will be three axis and include
MEMS accelerometers for pitch/inclination coupling correction
(although they are still prone to acceleration/turn induced errors,
but the AHRS system can at least work out if that is going on).

I suspect many fluxgate "compasses" used in gliding computers are
simple 2D type and I wonder if this is an issue. The LX also seems to
try to detect steady straight flight (using GPS and airspeed data?)
and I am curious how much of a problem this is in practice both either
from producing inclination/pitch calculation errors or having the LX
try to prevent errors and refuse to do the calculation when the flight
is not steady (I believe it warns you when this happens). Anybody
flown with the LX series with magnetometer and want to comment on how
good the wind calcs are using he "COMPASS" setting?

Cambridge has never offered a fluxgate sensor on its flight computers
AFAIK.

Darryl

I used to fly a plane that had an LX5000 installed in it, and I
connected
my PDA running SoarPilot to the unit. *It had the fluxgate compass I
believe. *The wind computations were always reasonable as far as I
could tell, but I never had a chance to run a ridge with it. *It
probably was
smart enough to disregard the compass when circling or accelerating,
and actually was probably using the circling drift algorithm as well.
I believe the LX160 smart vario computes wind just from circling,
when it computes it at all. *It doesn't send wind data on the NMEA
stream.

-- Matt

The LX 5000 has a magnetic compass option. That option had to be
installed and the LX 5000 wind calculation had to be set to the
"COMPASS" setting to use it in wind calculations. I understand that
SoarPilot can take the wind calculation from the LX (if configured to
do so) or do it's own internal calculations.

There are lots of permutations of configuration settings so when you
say things like "probably using..." it worry me a little :-) . Do you
know what the configuration settings were? If you get a chance to fly
with it again I'd be interested in the performance with 'COMPASS'
selected in the LX wind calculation settings and wind data read on the
LX device. I am not sure if in the combo you describe you can do a
comparison by having the LX *calculate using the COMPASS setting and
have the PDA calculate using a TAS/track data to the calculations can
be compared.

Thanks

Darryl

It's been a while since I've flown that plane; it's a club plane but
I've got
my own plane now so that's what I usually fly. *It would be easy
enough
to poke into the setup panels (if anything could be considered "easy"
when it comes to the LX5000, grr) the next time someone has the plane
out. *When I used SP with the LX I know I didn't make SP do its own
wind computations. *If SP does its own (which can be forced), I know
for a fact that it only uses a circling algorithm, because there's no
heading data in the LXWPn nmea sentences.

-- Matt

Matt

Actually I believe there is is supposed to be heading data in $LXWP0
from an LX5000 if there is a compass installed (and presumably similar
later units, but obviously not the simpler LX1600 type units). I don't
know if the wind COMPASS setting is supposed to affects whether this
is placed in the $LXWP0 sentence or not (seems like a bad idea if it
does). There is also airspeed data in $LXWP0, I believe that is
supposed to be TAS in the LX5000 etc. but suspect it must be IAS in
the LX1600 since it does not know OAT. So if that is right at least a
soaring software could in principle use the TAS data from an LX5000 to
calculate wind from straight flight as long as there is some track
change. That would be interesting to compare to the LX5000 internal
wind calculated in "COMPASS" mode. The SoarPilot documentation implies
that it never uses the airspeed data from $LXWP0. Which is a pity as
it would allow comparing current PDA software TAS/track based
calculations with the LX internal COMPASS calculations. For similar
reasons I wish the SN10 would output TAS data on NMEA for us users
stuck on our PDAs who fly rental ships with SN10s installed (so if
there us a choice I will rent the Duo etc. with the C302...).


Darryl

On Mar 29, 8:35*pm, Darryl Ramm wrote:
... I wish the SN10 would output TAS data on NMEA for us users
stuck on our PDAs who fly rental ships with SN10s installed (so if
there us a choice I will rent the Duo etc. with the C302...).

Even better, the SN10 outputs the calculated wind in the NMEA stream.
As you know, the SN10 calculated wind is usually regarded the best
available.
See the following for details; your PDA software should be able to use
it:
http://www.nadler.com/sn10/SN10_PDA_Support.html

Hope that helps,
Best Regards, Dave

On Mar 29, 1:25*pm, Darryl Ramm wrote:
I have some concerns that trying to do magnetometer based wind
calculations with a 2D/dual fluxgate sensor (i.e. a basic compass) is
open to aircraft pitch/magnetic inclination coupling. Modern fluxgate
sensors used as a part of AHRS systems will be three axis and include
MEMS accelerometers for pitch/inclination coupling correction
(although they are still prone to acceleration/turn induced errors,
but the AHRS system can at least work out if that is going on).

I suspect many fluxgate "compasses" used in gliding computers are
simple 2D type and I wonder if this is an issue. The LX also seems to
try to detect steady straight flight (using GPS and airspeed data?)
and I am curious how much of a problem this is in practice both either
from producing inclination/pitch calculation errors or having the LX
try to prevent errors and refuse to do the calculation when the flight
is not steady (I believe it warns you when this happens). Anybody
flown with the LX series with magnetometer and want to comment on how
good the wind calcs are using he "COMPASS" setting?

Cambridge has never offered a fluxgate sensor on its flight computers
AFAIK.

Darryl

This kind of compass in gliders is quite problematic.
It is very hard to get sensible calibration over a
range of speeds (especially std class), and most
glider cockpits are hostile to good compass results.
Our measurements have shown nice things like
15 degree swing when gear retracts, rudder-
deflection induced swings, etc.

I have a box of compasses, none of which work
as well as the manufacturer claims, even before
installation in a glider. We don't offer a compass
because, other than:
- very fast changes (really happens crossing a
front or changing valleys in the alps), or,
- very long straight runs (50+ mile final glides
descending through big gradient/change)
.... we produce a very good result.

Hope that helps clarify,
Best Regards, Dave

On Mar 29, 9:31*am, T8 wrote:
On Mar 29, 11:29 am, Darryl Ramm *wrote:

For the 180 degree wrong problem, any system that uses track and TAS/
GS difference calculations risks being 180 degrees wrong it it just
has that difference on two reciprocal tracks. If you run straight down
a ridge and do a rapid turn back the other way and fly the same track
back the other way there are two perfectly equivalent trigonometric
solutions which will give the wind from either direction. The flight
computer has absolutely no idea what direction you are crabbing the
glider into the wind.

I understand the problem of very limited information. *This is a
different problem :-).

In this case picture wind from 360, trip out on ridge with track 270,
303 shows wind from 360 @ 12, relative wind 90 degrees, arrow points
left (i.e. "wind blowing on glider" from right). *On the reverse trip,
having failed to get a wind update, the
computer now shows track 90, wind from 360 @ 12, relative wind 90
degrees, arrow points left. *See the issue? *Even in the absence of
updated wind, the relative wind should be showing 270 based on old
wind, new track. *I verified this behavior again yesterday, turning
through 45 degrees (slowly), watching track change, seeing relative
wind stay constant despite changing track until the device updated the
wind. [edit: I managed to mung the tracks up the first time].

I have never noticed behavior like that. I'll look for that next time
I play around. Seems like a simple firmware bug that maybe might be
reproducible. Did Dave Ellis have any comments on this behavior?

Darryl

On Mar 29, 6:18*pm, Dave Nadler wrote:
On Mar 29, 8:35*pm, Darryl Ramm wrote:

... I wish the SN10 would output TAS data on NMEA for us users
stuck on our PDAs who fly rental ships with SN10s installed (so if
there us a choice I will rent the Duo etc. with the C302...).

Even better, the SN10 outputs the calculated wind in the NMEA stream.
As you know, the SN10 calculated wind is usually regarded the best
available.
See the following for details; your PDA software should be able to use
it:http://www.nadler.com/sn10/SN10_PDA_Support.html

Hope that helps,
Best Regards, Dave

Dave

OK then does SeeYou Mobile actually use that SN10 internally
calculated wind? When I've pushed on this is in the past the answer
was no.

Since SeeYou Mobile (and similar software) are able to calculate very
good winds themselves from TAS data why not just provide that (maybe
simple to pretend to be a C302 and send a w! sentence?). If your wind
is better we'll notice a difference from the SN10 display and the
SeeYou Mobile and other software displays?

Thanks

Darryl