Andy Ross writes:
> Whatever convention we pick should be an easily explainable and
> identifiable from the *shape* of the airframe only. Not everyone
> has a POH handy, very few people have W&B or C.G. numbers, and even
> things like the centerline are subject to argument on some
> aircraft. Referencing the ground plane is especially bad, since
> the gear are going to compress differently depending on load.
>
> Remember that many/most 3D model authors aren't particularly
> interested in aerodynamics, and may very well be working from
> photographs and 3-views only. Forcing these people to look up a
> reference datum from an unfamiliar source is only going to
> discourage them.
Someone has to write an aerodynamic model before a 3D model is any
use. The aero designer needs to publish the reference datum she used
in a README, and then the 3D designer can simply follow it. Actually,
all of the aero designers will have to agree on the datum. I can live
with a modified version of Jon's suggestion:
x-origin as specified by the TCDS (free online) and/or POH,
defaulting to the tip of the nose/spinner when not available.
y-origin at the centreline.
z-origin at the height of the nose tip.
> And, quite honestly, what's the actual advantage to using a
> reference datum anyway? No one does weight and balance
> calculations in Blender. :)
Well, it does give you the location of (say) the back seat on the
X-axis. More importantly, once we implement dynamic W&B more easily
in FlightGear, it will be nice to have the model mesh up; even now,
using the published W&B datum (from the TCDS or the POH) gives you a
few numbers more easily in the aero modelling (like where to put
the fuel tank) -- if you're using the same datum, errors will be
easier to spot and the file will be easier for others to understand.
All the best,
David
--
David Megginson, [EMAIL PROTECTED], http://www.megginson.com/
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