Fig. 2. Aerodynamic stability determined by the slope of measured aerodynamic
torque about a rotational axis (here pitch) plotted as a function of the
angular orientation about the same rotational axis. (A) Measured aerodynamic
torques about the pitch axis for an aerodynamically stable frog. At the
equilibrium angle of rotation, no torques are acting on the frog, so it
remains at equilibrium. If a gust of wind pitches the frog's nose away from
its initial position in either the upward or downward direction, this change
in orientation relative to the airflow induces an aerodynamic torque that
tends to rotate the frog back to its initial position. (B) Measured
aerodynamic torques for a neutrally stable frog. If a gust of wind pitches the
frog's nose away from its initial position in either the upward or downward
direction, this change in orientation relative to the airflow induces no
aerodynamic torque that tends to rotate the frog back to its initial
orientation or to rotate the frog further away from its initial orientation,
so the frog remains at the angular orientation to which it was pitched. (C)
Measured aerodynamic torques for an aerodynamically unstable frog. If a gust
of wind pitches the frog's nose away from its initial position in either the
upward or downward direction, this change in orientation relative to the
airflow induces an aerodynamic torque that tends to rotate the frog even
further away from its initial position, causing the frog to diverge from its
original flight path.
