Dragonfly aerodynamics

It has been questioned why dragonflies have 2 sets of wings. 2 pairs of wings add nothing to lift, it is thought the second pair decreases lift, nor manoeuvrability. Instead of an second set of wings, flies have halteres which function as gyroscopes and give them significant manoeuvrability. Dragonflies are still highly manoeuvrable—they can appear stationery from the vantage of their moving prey—they may just use a different mechanism to flies.

Modelling of dragonfly flight suggests that 2 sets of wings can decrease energy requirements if they beat out of phase.

Despite efforts at understanding the implications of flapping flight with two pairs of wings, previous studies have generally painted a rather disappointing picture: interaction between fore and hind wings reduces the lift compared with two pairs of wings operating in isolation. Here, we demonstrate with a mechanical model dragonfly that, despite presenting no advantage in terms of lift, flying with two pairs of wings can be highly effective at improving aerodynamic efficiency. This is achieved by recovering energy from the wake wasted as swirl in a manner analogous to coaxial contra-rotating helicopter rotors. With the appropriate fore–hind wing phasing, aerodynamic power requirements can be reduced up to 22 per cent compared with a single pair of wings, indicating one advantage of four-winged flying that may apply to... dragonflies...

So a second pair of wings decreases the energy requirements of dragonflies by a significant amount. A useful design feature and seen elsewhere in the biosphere—V formation bird flight decreases energy requirements by half by decreasing drag.