Dynamic flight stability of a bumblebee in forward flight

The longitudinal dynamic flight stability of a bumblebee in forward flight is studied. The method of computational fluid dynamics is used to compute the aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis are employed for solving the equations of motion. The primary findings are as the following. The forward flight of the bumblebee is not dynamically stable due to the existence of one (or two) unstable or approximately neutrally stable natural modes of motion. At hovering to medium flight speed [flight speed u _e = (0-3.5) m s^-1; advance ratio J = 0-0.44], the flight is weakly unstable or approximately neutrally stable; at high speed (u _e = 4.5 m s^-1; J = 0.57), the flight becomes strongly unstable (initial disturbance double its value in only 3.5 wingbeats).