Control and Stability

 

Physical mechanisms of control and stability in insect flight


To perform complex flight behaviors, insects must be able to control the large forces and moments associated with flapping flight and maintain stability in the face of unpredictable external perturbations.  While changes in wing kinematics are likely to be involved in both of these processes, the role of other body parts such as the abdomen, head and legs is less clear.  We have previously found that the abdomen can act as a brake during slow, maneuvering flight in hawkmoths, allowing them to track the motions of oscillating flowers during feeding.  Measurements, free flight observations, and computational modeling show that abdominal flexion in these moths shifts the center of mass significantly, slowing and controlling rapid body rotations initiated by the wings.  We have recently found that abdominal motions appear to play a similar role during maneuvering flight in hunting dragonflies.


Wild orchid bees foraging over long distances face a different challenge: maintaining stability during fast, forward flight, as aerial perturbations cause bees to roll from side to side.  While these bees use their wings to increase force production and control body angle, they deal with rolling instabilities by lowering their enlarged hindlegs far below their body, increasing their rolling moment of inertia and reducing roll accelerations.  This stabilizing behavior comes at a cost,  though - lowering their legs increases body drag by 30%, leading to huge increases in the power required for flight.  The importance of the hindlegs during forward flight raises the question of whether orchid bees also use their legs for control and stability while hovering or maneuvering in unpredictable aerial environments.