Re: [Flightgear-devel] Turn ball fix & JSB notes

[Tony P. <ap...@ea...>]

On Tuesday 28 August 2001 02:34 pm, you wrote:
> >      vUVWdot = mVel*vPQR + vForces/Mass;
> > +
> > +    // Body-frame acceleration is similar, but it includes gravity
> > +    // too, and does NOT include the mVel*PQR fictitious force (which
> > +    // is an artifact of the accelerated reference frame used here).
> > +    // Note that the gravity vector is the Z unit vector times the
> > +    // "local to body" matrix.
> > +    vBodyAccel = vForces/Mass;
> > +    vBodyAccel(1) -= 32.1 * State->GetTl2b(1, 3);
> > +    vBodyAccel(2) -= 32.1 * State->GetTl2b(2, 3);
> > +    vBodyAccel(3) -= 32.1 * State->GetTl2b(3, 3);
> >
> >      vNcg = vUVWdot*INVGRAVITY;
>
> Another thing that is suspicious here, to me. vBodyAccel gives an
> acceleration vector in body axes. You are adding the effects of gravity in
> body frame. This would be correct, except that now vForces includes
> gravity, as mentioned in the previous email. Also, you wrote: "it uses
> F=ma to calculate the acceleration relative to the _earth_ frame". This is
> not what you are doing, above. You are calculating, here, the accels in
> body frame. I do not see them being transformed to inertial, or "earth"
> frame, anywhere. But, I may be missing something, here. Can you explain
> this misunderstanding?

Gravity is already there, at least in the current code.   Check out 
FGInertial::Run()


>
> Jon
>
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-- 
Tony Peden
ap...@ea...
We all know Linux is great ... it does infinite loops in 5 seconds. 
-- attributed to Linus Torvalds