I just *know* I'm going to get totally flamed for this, but can someone
please tell me how the CG, Eyepoint, AERORP and VRP are interconnected?
Yeah, I know - RTFM.
Trouble is, I think I did R the FM (there was an article by Jon S.
Berndt himself in Issue 1, Vol1 of the Quarterly Newsletter) but it
didn't seem to answer the following questions. For that matter ISTR that
this same issue came up here a while back, but I can't find it in the
mailiing-list archives.
Here goes.
Issue 1, Vol1 of the Quarterly Newsletter states that the sim tracks an
aircraft by its CG. However, it then goes on to state that CG isn't a
useful datum for a frame of reference because it can move (as, for
instance, when fuel is used up). Indeed, CG gets specified in the
aircraft .xml file as having an [X,Y,Z] location, and evidently this
[X,Y,Z] is using some other point on the aircraft as datum.
Where is this "other point"? Just some arbitrary convenient point?
Presumably not the aerodynamic reference point, since it looks like that
also gets specified with an [X,Y,Z] coordinate in the setting of
"AERORP". Is the AERORP the point about which the "tail arm" is
referenced? Where should the AERORP be placed w.r.t the wing? Is there a
concept of "wing arm" to match the concept of "tail arm"?
I think I know what the "eyepoint" is :-). It is specified with an
[X,Y,Z] too, but in what coordinate frame?
Likewise the VRP. This is the location of the reference point of the 3D
model isn't it? Again, from what point is the VRP's [X,Y,Z] measured from?
Then there's the semi-unrelated question of the X axis. "Increasing
aftwards" it says, but along what axis of "aftwards" are we speaking? Is
it parallel (say) to the chord of the main wing or what?
Finally, back to CG again. Do I assume the the "CG" that is specified
with an [X,Y,Z] coordinate refers just to the CG of the airframe itself?
Issue 1, Vol1 of the Quarterly Newsletter states (quite rightly) that
the actual CG of a plane moves during flight duration as the fuel is
used up, but I assume that this is why you can specify tank locations
and fuel weights and rates of fuel usage. So the actual flying CG of a
plane isn't where you set "CG"?
Sorry about the interrogation, but I've realised that I seriously don't
know what I'm doing in the .xml file department here!
Thanks in advance for any insights.
Steve.
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