Fig. 8. Aerodynamic torques measured on a full-scale physical model of
Polypedates dennysi posed in the gliding posture observed during
non-maneuvering gliding. Aerodynamic torques about the pitch (A), roll (B) and
yaw (C) axes are shown plotted against angle of attack, roll angle and yaw
angle, respectively. Lines shown on each graph are linear regressions of the
data. The linear regressions of rolling and yawing torque are taken over
smaller ranges of roll angle and yaw angle, respectively, than the linear
regression for pitching torque; the smaller range of angles reflects the lower
level of perturbations in roll and yaw angle during gliding and is consistent
with aeronautical engineering practice (McCormick,
1976). (D) Summary of
aerodynamic stability coefficients (see text for definitions of coefficients)
about the pitch, yaw and roll axes. Stability about a given axis is denoted by
negative values, and instability is denoted by positive values. At the gliding
speed (13 m s-1) and angle of attack (45°) used by P.
dennysi, the frogs are slightly stable about the pitch axis and roll
axes, and slightly unstable about the yaw axis.
