This article was brought to my attention on another list. I thought it would be of interest to those who followed the vortex discussion on humming bird flight earlier this year.
BTW, the article mentions "added-mass force". Does anyone know what that means? Harry Secrets of bee flight revealed http://www.newscientist.com/article.ns?id=dn8382 16:57 28 November 2005 NewScientist.com news service Helen Phillips Combining robotic modelling with slow-motion videos of airborne honeybees may have helped researchers explain the curious aerodynamics of bee flight. Aeronautical engineers had previously ³proven² that bees cannot fly. So Michael Dickinson, an insect flight expert and colleagues at Caltech in Pasadena, California, US, decided to investigate the forces actually at work during honeybee flight. In 1996, Charlie Ellington at Cambridge University, UK, showed how vortices rolling along the leading edge of many insects¹ wings were a vital source of lift. Most flying insects beat their wings in large strokes typically flapping in arcs of 145° to 165° at a frequency determined by body size to generate aerodynamic forces sufficient for flight. But this cannot explain how a heavy insect with a short wing beat, such as a bee, generates enough lift to fly. Exotic forces Dickinson and his colleagues filmed hovering bees at 6000 frames per second, and plotted the unusual pattern of wing beats. The wing sweeps back in a 90 arc, then flips over as it returns an incredible 230 times a second. The team made a robot to scale to measure the forces involved. See a video of a bee in a flap, here (5MB, .avi format). It is the more exotic forces created as the wing changes direction that dominate, says Dickinson. Additional vortices are produced by the rotation of the wing. ³It¹s like a propeller, where the blade is rotating too,² he says. Also, the wing flaps back into its own wake, which leads to higher forces than flapping in still air. Lastly, there is another peculiar force known as ³added-mass force² which peaks at the ends of each stroke and is related to acceleration as the wings¹ direction changes. The work may help engineers design rotating propellers or more stable and manoeuvrable aircraft. But ³it proves bees can fly, thank God², adds Dickinson. Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073_pnas.0506590102)
