Insects were the first animals to fly through earths atmosphere, hitting the skies hundreds of millions of years before dinosaurs managed the same feat. Unlike planes, insects have not evolved jet engines that thrust themselves through the world at incredible speeds. Instead, insects must flap wings to generate forces strong enough to support their entire body weight. But what does this flapping achieve?
If we take the traditional aerodynamic approaches that we use in planes and apply it to the body and wings of an insect, we predict that insects should not generate enough lift to fly. Misinterpretation of this finding has lead to the common misconception that scientists are baffled that insects can still fly. In reality, insects and aircraft rely on different mechanisms to generate lift, aircraft use stable aerodynamic flows while insects use unstable aerodynamic flows. Insect wings are normally relatively small compared to those of aircraft. This is because insects flap, and flapping wings requires muscles. The larger and heavier your wings are, the more muscles you need to flap them. This creates a positive feedback loop, where bigger wings need more muscle, which increases your weight, meaning you need to flap even harder to support the additional weight, which needs more muscle again, which increases your weight again, and so on…. Therefore insects are a good example of a flying machine optimised for generating maximum lift from the lightest, smallest wings available. And the solution for doing so, is to generate unstable aerodynamic flows.
Lift is all about air pressure. If you can produce an air pressure differential between above and below your body, your body will be lifted accordingly. And the easiest way to produce an air pressure differential is to alter the speed that air is moving at. Fast moving air has a lower pressure than slow moving air, so wings are designed to speed up the flow of air passing across their top surface. Flapping insect wings utilise very specific movements and wing angles to generate what we call Vortices. A vortex is a circular airflow, and in this pattern the air speed is generally very high. If you can generate large, fast vortices on the upper surface of your wing, you will generate a large pressure differential, and a significant amount of lift. This is exactly what insects do, and it is the secret to them generating such incredible amounts of lift, using such tiny, lightweight wings.
The paper that I am now working on is investigating the sensory neuroscience of how insects achieve and maintain these unstable airflows. If your flight relies on generating very specific air flow patterns, it makes sense to monitor air flow and react when it fails to perform as intended. We are trying to describe a novel air-flow sensing system on the wings of dragonflies, which performs this very role.
Hopefully I will have more to show in the future!