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Fig. 6. Free-flight smoke visualization of the flow around the wings of Aeshna
mixta executing a roll to the right in counterstroking flight. The flow
field matches that which would be expected with conventional attached-flow
aerodynamics. (A–H) Consecutive images from a 250 Hz high speed video
recording. In (A–C) the wing is completing the upstroke and can be seen
(blue arrows) to have sliced through the smoke streams like a knife –
causing no vertical displacement. This suggests that the sections of the wing
intercepting the smoke plane are generating little or no lift. The wing
rotates in (C) and (D) at the beginning of the downstroke, and the flow
exhibits a downwards deflection indicating lift-generation, but the smoke
streams pass smoothly over the wing with no evidence of flow separation. The
flow remains attached until the end of the downstroke in (H), as the dragonfly
executes a roll to the right.
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