We really want to make sure that the visual model is correctly aligned with
the dynamics model. Then if the 3d model isn't sitting correctly at rest on
the ground, it could be that the gear lengths aren't set properly in the 3d
model compared to the dynamics model, or visa versa. If everything is self
consistent, it should sit nicely on the runway. And then if the pitch angle
is visually off in flight, it probably makes more sense to fix the flight
dynamics configuration to achieve the correct cruise pitch instead of
hastily rotating the visual model a few degrees to compensate for a flight
dynamics deficiency, and also a mismatch in dynamic model gear length versus
3d model gear length. I'm not saying that is the problem, just that it
seems more likely to me since we have a added a new 3d model to an existing
flight dynamics configuration.
Regards,
Curt.
On Thu, Dec 4, 2008 at 7:02 PM, gerard robin wrote:
> On vendredi 05 décembre 2008, gerard robin wrote:
> > On vendredi 05 décembre 2008, dave perry wrote:
> > > dave perry wrote:
> > > > Hi All,
> > >
> > > snip
> > >
> > > > Would it not be more realistic to rotate the 3D model about -3 or -4
> > > > degrees about the ac3d z-axis.
> > >
> > > I did not make myself clear in the initial questiion. The video link
> > > only detracted from my point. The model in the .ac file is just a
> rigid
> > > body that gets displayed when the fdm says the pitch is zero degrees
> (or
> > > perhaps zero incidence). The fdm then rotates this rigid model for
> > > other flight conditions. So if the model starts 3 or 4 degrees too
> nose
> > > high for realistic cruise, it will remain 3 or 4 degrees too high in
> > > pitch for all other rotations from the fdm. In particular, it will be
> 3
> > > or 4 degrees higher than a realistic stall at touch down, burying the
> > > tail cone in the runway.
> > >
> > > To make this clear, I opened the c172p.ac in ac3d, made a screen
> capture
> > > of the side view, then rotated the model by - 4 degrees and made a 2nd
> > > screen capture of the side view and then scaled and combined these into
> > > one small .png which is attached.
> > >
> > > My only point is that I think the rotated side view pitch (bottom
> image)
> > > looks like a c172p at cruise and the original side view (top image)
> > > looks like a c172p in level no flap slow flight. Compare the wing and
> > > horizontal stab incidence angles in the two images. In the rotated
> side
> > > view, the horizontal stab is at zero incidence while the non rotated
> > > side view shows a noticeable positive incidence for the horizontal stab
> > > which would normally require significant up elevator to maintain.
> > >
> > > Making this change will be a lot of work since the panel will be messed
> > > up. I know because I made a similar rigid rotation correction about a
> > > month after I first submitted the pa24-250.
> >
> > No if that was necessary , their is nothing else than modification of
> the
> > offset in the c172p.xml model. The panel should follow
> >
> > However i noticed that with the actual position the model has the nose
> gear
> > up above the ground.
> > An offset of -2 deg would be nice
> >
> > <path>c172p.ac</path>
> > <offsets>
> > <pitch-deg>-0</pitch-deg>
> > </offsets>
>
> oups err
> <offsets>
> <pitch-deg>-2.0</pitch-deg>
> </offsets>
>
> may be more
>
> >
> > > Dave P.
>
>
>
> --
> Gérard
> http://pagesperso-orange.fr/GRTux/
>
> J'ai décidé d'être heureux parce que c'est bon pour la santé.
> Voltaire
>
>
>
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--
Curtis Olson: http://baron.flightgear.org/~curt/
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