Fig. 1. (A) Depictions of the vortex-ring and continuous-vortex gaits. (B)
Cross-sectional view of the wing profile. Lift produced during flapping
provides weight support (upward force) and thrust (horizontal force). In the
vortex-ring gait, lift is produced only during the downstroke, providing
positive upward force and forward thrust. In the continuous-vortex gait, lift
is produced during both the upstroke and the downstroke. The downstroke
produces a positive upward force and forward thrust; the upstroke produces a
positive upward force and rearward thrust. Partial flexion of the wing during
the upstroke reduces the magnitude of the rearward thrust to less than that of
the forward thrust produced during the downstroke, providing net positive
thrust per wingbeat (adapted from Rayner,
1986,
1988).
