As part of cleaning-up the nav-radio code, I need to make a painful
change: fixing the confusion over GS maximum needle deflection.
I'm aware that there's problems with the radio reception model, but
I'm not going to attempt to address that at all - what I need to fix
in the short term is a much 'simpler' problem - the confusion over the
range of /instrumentation/nav/gs-needle-deflection.
Some aircraft (eg, the default C172, and the Primus 1000 suite) are
assuming the range is -10 to +10 degrees (matching the CDI deflection)
- others assume 3.5 degrees (1), or other things again. The Connie is
scaling the property by 1.4, and clamping to +/- 6, for example -
which just about makes sense given the actual range, but no sense at
all if the range is +/-10.
Hence, this is not about 'fixing' the code in navradio, more picking a
single definition and then fixing panels to follow that definition.
Here is what I'm going to do:
- change gs-needle-deflection to report the GS deviation *in degrees*
- add a gs-needle-deflection-norm property, reporting the
deflection as the range +/- 1.0 (I'll probably do that for the CDI as
well). 1.0 will be on the peg, 0.0 will be centred - no surprises
here, I hope.
- clamp the GS deviation to +/- 0.7 degrees in the nav-radio code (as
we clamp the CDI deflection to +/-10 degrees). This is significant,
because many panels currently work due to the value *not* being
clamped to any range. I.e there will be a peg at the sim level, not
just a a peg defined at the animation / panel level.
- update ALL the references to the property in the data directory
(that's 273 references, according to 'grep'!) to be consistent with
this.
For most cases, I'll probably switch to using the normalised property,
to avoid any future confusion (I hope) - and to avoid many scalars in
XML files based upon the 0.7-degree limit. The major benefit of all
this, apart from increased sanity in the code, will be much more
precise GS reporting in many aircraft, I hope. This may lead to end-
users reporting that flying glide-slopes has become 'harder' in some
aircraft (such as the C172) since the sensitivity will have increased
by a factor of three.
If anyone has a major objection to this, please let me know. If anyone
wants to help with fixing up panels, then *definitely* let me know.
Regards,
James
(1) - 3.5 degrees is the value you'd arrive at by examining the source
code - there is the 'magic 5' multiplier that scales the actual
deviation, +/- 0.7 degrees, by 5, in the nav radio code. As far as I
know (and based on comments in the code), no one is really sure why
the multiplier is present.
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