Someone has said that, in theory, a bumblebee should not be able to fly. Can you provide any information about who said this and why?
The flight of the bumblebee
Many people must have said it because it is true. And it is true not only of bumblebees, but of most, if not all, flying insects. That is to say, it is true according to the conventional aerodynamic principles employed in the design of fixed wing aircraft. But since bumblebees can fly--after a fashion, clearly some other aerodynamic theory is needed to account for the fact.
Conventional aerodynamics generally deals with steady motions, such as a wing moving in a straight line at a constant speed. Thus, it is assumed that for a given portion of an insect wing, the lift generated at a particular moment is indentical to that generated by a wing moving uniformly at the same speed and in the same direction (McNeill, 1996).
But insect wings do not move in a straight line at constant speed. They flap up and down, which means that they continually change in both direction and speed. They also rotate axially with each change between upward and downward motion. According to a study by Ellington and others (1996), it is the constant change in motion that explains the ability of insects to generate the lift necessary for flight.
These authors photographed streaks of smoke flowing past both a tethered hawkmoth, and also a mechanical insect model, or "flapper," located in a wind tunnel. The pictures revealed an intense leading edge vortex created during the down-stroke. The vortex developed first adjacent to the body of the insect at the beginning of the downs-stroke and extended along the wing to spill off at the end. Apparently, the vortex constitutes an area of reduced pressure above the wing and adds sufficient lift to make flight possible not only for hawkmoths but, presumably, for bumblebees as well.
But what have others to say?