Aerodynamic Forces. The position of the net CM was approximated throughout
the turn using a mass-distribution model of the body and tail, head, and
wings (Fig. 3). The torso and tail were represented by a single point-mass,
because the effect of tail movements on net CM were assumed to be minor
and are difficult to model. The head and 14 chordwise strips per wing were
modeled as point-masses, with time-varying positions based on segment
kinematics (Fig. 3). The two wings together constitute approximately 1∕8th
of a pigeon’s body mass. The motion of the flapping wings causes the net
CM to move substantially relative to a pigeon’s torso CM, necessitating
the time-dependent, non-body-fixed CM calculations.