Dragonfly wings - note the more reinforced structure in the
leading third of each wing
Dragonflies are very manoeuvrable in flight. The flight muscles can
adjust stroke-frequency, amplitude, phase between forewings and
hindwings, and angle of attack independently for each of the four wings.
For the purposes of description, four main flying modes are recognised:
counter-stroking, in which forewings and hindwings move up and
down about 180° out of phase - this pattern is generally used in
phased-stroking, where the hindwings cycle about 90° before the
forewings - this provides more acceleration for manoeuvres
synchronised-stroking, where the forewings and hindwings move in
gliding, where the wings are held without beating for free
gliding, gaining lift in updrafts, or during mating
Dragonflies use a variety of lift-inducing mechanisms, for example
classical lift at low angles of attack, supercritical lift at high
angles of attack close to the stall, vortex production, especially along
the leading edge of the forewings, and vortex-shedding. The angle of
attack is the most important variable controlling aerodynamic mechanisms
(Thomas et al, 2004)
http://tolweb.org/notes/?note_id=2471 (accessed 3/11/05).
A.L.R., Taylor, G.K., Srygley, R.B., Nudds, R.L., and Bomphrey, R.J.
(2004) Dragonfly flight: free-flight and tethered flow visualisations
reveal a diverse array of unsteady lift-generating mechanisms,
controlled primarily via angle of attack. Journal of
Experimental Biology, 207, 4299-4323.