--- Erik Hofman <[EMAIL PROTECTED]> wrote: > Jon Berndt wrote: > >>Well, to rotate the aircraft realistically the refference point > should > >>be known by the 3D modellers, but that aside. > > > > > > The rigid body rotates about the CG, not the aero ref. pt. > > Even when in motion?
In the FDM's (all of them, AFAIK), yes. Always. In reality, the aircraft will rotate about the cg in air and some other point if any of the gear are touching the ground. During takeoff rotation and landing de-rotation, for example, the aircraft will rotate about the main gear. > It seems to me there would otherwise be no need for a refference > point. It's still needed. In order to calculate the moment coefficients from measured moments, one needs to set a point on the aircraft to take the moment arms from. This has traditionally been chosen as the point 25% of the way aft along the mean aerodynamic chord. The reasoning for this is that for low speed aircraft, it is a reasonable estimate of the wing's center of pressure (i.e. where you'd place the lift vector both chord- and span-wise). In truth, this location varies with (at least) the airfoil section, wing planform, and Mach number, so when using it as a constant reference point we have to call it something different. I chose to call it the aero reference point. And since someone might reduce measured data using something other than the 1/4 chord of the MAC, this number needs to be configurable. > > Erik > > > _______________________________________________ > Flightgear-devel mailing list > [EMAIL PROTECTED] > http://mail.flightgear.org/mailman/listinfo/flightgear-devel > > __________________________________________________ Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now. http://mailplus.yahoo.com _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
