302 wind calculation

On Mar 29, 5:44*am, T8 wrote:
On Mar 29, 1:07*am, "Paul Remde" wrote:

Hi Evan,

Your feedback is so different from all other Cambridge 302 user feedback
I've received that it makes me wonder whether your 302 is out of calibration
in some way. *Does it show accurate airspeed while in flight?

Yes, IAS right on the money. *OAT is correct and the TAS output to the
PDA is good. *XCSoar was doing very well calculating wind in "zigzag
only" mode using 302 output.

It's got current firmware, it's been back to the factory for barograph
cal and updates in the last year, I am assured it works as designed...
even after I explained to Dave Ellis about the 65 mile ridge run with
relative wind indicator 180 out of whack (flew to end of ridge, did a
wing over, got back on the ridge the other way without a wind
update). *When I called CAI/R-Track about these specific issues, all I
got for a response was "... why don't you call Richard @ Craggy
Aero." *Which I did. *I sent flight logs with annotations. *Nothing
came of this.

If anyone would like to send me a 302 to swap out and test, I'd be
happy to do so. *I'd spend money to fix this if in fact someone could
determine what needs fixing.

-Evan Ludeman / T8


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. To unambiguously solve the trigonometry it needs
some straight track away from these reciprocal headings. So all I'm
saying is seeing this type of reversal should not be completely
unexpected when flying ridges and does not necessarily indicate a
device or design problem.

If you were comparing this to wind calculated by PDA soaring software
the lack of the 180 degree reversal there might be that the PDA based
soaring software was updating its data as you flew along the ridge
with small heading change (and therefore with possible increasing
errors), or that it was simply just not aging out the old wind data.
That lack of aging out old wind data which might explain why some PDA
based software appears to work better in your situation may be
problems in other situations (e.g. rapid wind changes with altitudes
or when crossing convergence lines), but at least with that software
the pilot can decide to delete the current calculated wind (which I
will do if I suspect problems/want to force an update).

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?

---

BTW one possible point of confusion is the 303 display shows multiple
wind data, the numerical wind vector show numerical calculated winds
(directions true not magnetic) and the little arrow shows approximate
"relative wind" that is relative to track (not heading). if you are
crabbing a lot this little arrow will be wrong by that corresponding
amount and may differ from graphical arrows shown on PDA displays that
can be capable of showing heading up/track up type displays with a
wind vector.

Darryl

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 90,
303 shows wind from 360 @ 12, relative wind 90 degrees, arrow points
left. On the reverse trip, having failed to get a wind update, the
computer now shows track 270, 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.

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

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

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

On Mar 29, 12:55*pm, mattm wrote:

That
would solve this whole issue. *Did the LNav have that?

Yes, indeed. No, it didn't.

-T8

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

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, 10:42*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.

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