Fig. 11. Smoke visualization of tethered dragonflies flapping, but not generating any lift. (A) The dragonfly Aeshna grandis is flapping, but the aerodynamic angle of attack is sufficiently close to zero to generate no lift – as evidenced by the lack of any vertical displacement of the near-wake (red arrows). The wake shows that the wings have swept a straight path during the downstroke. In (B) (Aeshna mixta) the wake again shows that the wings can maintain an angle of attack at, or close to, zero, even when the forewing sweeps a curved path on the upstroke.