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