On 01/31/2007 10:04 AM, Torsten Dreyer wrote:
> I just checked you patch to hsi.xml where you tied the rotation of the
> compass
> rose to the heading of the heading-indicator.
> This leads to a drift of the compass rose due to precession and internal
> errors as one can see in Instrumentation/heading_indicator.cxx
> This is ok for a standard directional gyro, but the hsi implemented here is a
> slaved gyro since there is no way to correct the compass rose.
Did you /observe/ such drift, or is it just a theory?
Any such theory is inconsistent with my observations. I
have performed the following check in the c182rg, and
I suggest that others should do a similar check.
0) Apply my patch to hsi.xml
1) Initialize the aircraft on a taxiway or runway and start
the engine.
2) Observe that the HSI indication agrees with the compass.
3) Fail the instrument using the popup menu.
4) Turn the aircraft by some good-sized angle.
5) Observe that the HSI indication no longer agrees with
the compass.
6) Unfail the instrument.
7) Observe that it rapidly re-orients itself to agree
with the compass ... as you would expect for a properly
slaved HSI (although perhaps a bit too rapidly for 100%
realism).
> I agree, that the hsi does not respond to the serviceable flag from the
> heading indicator and there is no way to fail the 2d instrument,
Agreed (unless/until my patch has been applied).
> but I think
> your patch make things worse, since it makes the instrument unusable after
> some time. This is unrealistic.
I see no evidence of this.
If you have actual evidence of this, please explain.
> A better solution might be to wrap the transformation into a condition that
> checks the servicable flag and leave the driving property at the original
> value.
>
> I suggest to not commit the patch since it is not a bug but a missing feature.
There is no missing feature here. The slaving feature is not missing,
and the serviceability-flag feature is not missing. If your HSI is
supposed to be slaved but is not, then you have *two* bugs. My patch
fixes one of the bugs, without making the other better or worse.
Note that in the c++ code, there are two backends:
*) heading_indicator_dg
*) heading_indicator_fg
The latter is slaved, while the former is not. In all aircraft I
have checked, the HSI is mated to the slaved version. If that is
not true for your aircraft, then that's your problem ... and any
such problem (or lack thereof) should be completely orthogonal to
my hsi.xml serviceable patch.
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