On Mon, 16 Dec 2002 15:56:13 +0000 "David Luff" <[EMAIL PROTECTED]> wrote:
What about rotation (the taking-off one)? Surely in that case it rotates about the axles?Well ... sort of. In real life, yes, the gear is a pivot point. However, in the FDM sense, the ground isn't really "there" to pivot about - only a force and moment that is applied to the aircraft CG as is any other force/moment (aero, propulsion, etc.). We do not handle the rollout any differently because there is contact with the ground, really (except that the calculations are a b!t*h at very small velocities). The EOM still is working with forces and moments (rotations and translations) about the CG. When the aircraft rotates at about takeoff velocity, it is really rotating about the CG, but the CG is ALSO translating upward and slightly aft. The appearance could be taken to be physically rotating about the gear contact point with the ground, but mathematically, we are still rotating and translating about the CG.
Cheers - Dave
Jon
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