302 wind calculation

Does anyone have any insight into how a 302 calculates wind? How good
is it in regards to wind a straight flight with very little turning?
How valuable is it on a ridge? What does it need in order to
calculate
probable wind one 360 turn, part of a turn, two turns?
Any information is appreciated.

Today was an interesting day to test instruments. Winds varied from
about 15 kts at 2600 to 26 kts at 3600 and favored a local ridge which
added its own influence. It wasn't anywhere near good enough to go
anywhere, so (unusually) I flew local, tested out XCSoar for the first
time in flight and played with vector wind on the 302.

I stand by my assessment of the 302 being inferior to the latest
versions of the LNav+GPSNav. That older system would get good vector
winds under normal thermal soaring cruise conditions as long as you
were not flying in an arrow straight line. It would also frequently
get useful updates on a meandering ridge. The 302 requires GPS track
changes of close to 90 degrees to get a decent vector wind. Lesser
changes will sometimes get updates, but frequently the updates will be
a little funny -- definitely at odds with other recordings in the same
airmass and therefore suspect. I think it's probably quicker, faster
and more efficient to do a 360 turn if you really need a wind update.
I've only ever been willing to do that once on a racing task, but it
does work.

XCSoar, happily, does vector wind in cruise quite nicely using the
302s GPS and TAS output. Nothing bad to say about this at all. It
seems likely that it will out perform the 302. I'll be interested to
see how this works in normal XC soaring.

Darryl: my apologies for jumping down your throat. I *don't* think
the 302 works as well as you say it does. In fact I think the vector
wind in cruise capability it has is next to useless for performance XC
and racing (my main interest) but clearly it does work in a limited
sort of way that I can see *would* be useful for exploring a
convergence, perhaps also wave, etc. Different strokes.

-Evan Ludeman / T8

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?

Best Regards,

Paul Remde

"T8" wrote in message
...
Today was an interesting day to test instruments. Winds varied from
about 15 kts at 2600 to 26 kts at 3600 and favored a local ridge which
added its own influence. It wasn't anywhere near good enough to go
anywhere, so (unusually) I flew local, tested out XCSoar for the first
time in flight and played with vector wind on the 302.

I stand by my assessment of the 302 being inferior to the latest
versions of the LNav+GPSNav. That older system would get good vector
winds under normal thermal soaring cruise conditions as long as you
were not flying in an arrow straight line. It would also frequently
get useful updates on a meandering ridge. The 302 requires GPS track
changes of close to 90 degrees to get a decent vector wind. Lesser
changes will sometimes get updates, but frequently the updates will be
a little funny -- definitely at odds with other recordings in the same
airmass and therefore suspect. I think it's probably quicker, faster
and more efficient to do a 360 turn if you really need a wind update.
I've only ever been willing to do that once on a racing task, but it
does work.

XCSoar, happily, does vector wind in cruise quite nicely using the
302s GPS and TAS output. Nothing bad to say about this at all. It
seems likely that it will out perform the 302. I'll be interested to
see how this works in normal XC soaring.

Darryl: my apologies for jumping down your throat. I *don't* think
the 302 works as well as you say it does. In fact I think the vector
wind in cruise capability it has is next to useless for performance XC
and racing (my main interest) but clearly it does work in a limited
sort of way that I can see *would* be useful for exploring a
convergence, perhaps also wave, etc. Different strokes.

-Evan Ludeman / T8

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

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

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