Fig. 1. Conventions and terminology. (A) Sketch of an insect. The wing section is depicted by a segment drawn perpendicular to a line joining the wing base and wing tip. This segment, representing the wing chord, connects the leading edge (filled circle) to the trailing edge. (B) Sectional view of the insect wing. The free-stream velocity is denoted by U, and downwash velocity is denoted by U' (written in bold to signify their vector nature). The geometric angle of attack () is the angle that the wing section makes with U. The aerodynamic angle of attack (') is given by the angle between the wing section and the free-stream velocity deflected as a result of the downwash. (C) Phases of insect wing kinematics. Wing pronation occurs dorsally as the wing transitions from upstroke to downstroke, and wing supination occurs ventrally at the transition from downstroke to upstroke. (D,E) Linear vs flapping translation. In a linearly translating wing (D), both wing tip and base translate at the same velocity, whereas in a flapping translating wing (E), the tip rotates around an axis fixed at the base.

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