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