Figure 4.

Right-handed body-fixed axis system. The axis system is centred on the centre of volume of the body, including the head. The x-axis is defined as the long axis of the body, calculated using principal components analysis. The y-axis is parallel to the line joining the two wing bases. Pitch, roll and yaw are signed positive in the directions of the curved arrows. Angular accelerations about the pitch axis, and linear accelerations along the x- and y-axes are expected to be correlated with symmetric changes in the wing kinematics. Angular accelerations in roll and yaw, and linear acceleration along the y-axis are expected to be correlated with asymmetric changes in the wing kinematics.