Research Director: Dr. Keiji Kawachi
(Professor, Research Center for Advanced Science and Technology, The University of Tokyo)
Research Term: 1992～1997

Understanding how small organisms fly and move in fluids is no longer just an interesting or academic pursuit, but has become a part of interdisciplinary basic research aimed at micro-machines and other important technologies. The Kawachi Millibioflight Project took a very wide-ranging look at the motions of organisms, especially in the centimeter-to-millimeter region. As a major part of this effort, fluid dynamics was considered while carefully observing and analyzing the propulsion and control mechanisms.

Research Results

Reynolds number and types of wings: Much new information has been obtained concerning fluid dynamics, especially both theoretical and experimental proofs that though streamlined, fine-shape wings with a 10%~15% thickness ratio are appropriate for large objects; for smaller(centimeter – millimeter size) objects below a Reynolds number of 1,000, very thin wings, such as membrane-type wings, are far superior for producing lift. These membrane wings, are far superior for producing lift. These membrane wings sometimes even show corrugation in nature. At Reynolds numbers less than 100 both membrane- and hair-type wings are observed. Below Retnolds number 10 there is no suitable wing, the lift and drag being almost the same. At this point nature no longer wishes to use wings.

Hair-type wings: It has been found that some very small (millimeter size) insects have a quite unusual “hair-type” wing shape, which is much different from the membrane type. Experimental results indicate that the Thrips having such wings flies mainly by using lift force instead of drag. The motion of the wing is very similar to that of membrane wings, like that of bee or wasp.

Wing shape during flight: It has been demonstrated that the wing section shape changes during the beating motion of a dragonfly. Two kinds of measurements were performed to obtain a better understanding of this motion. The results show that the wing shape changes continuously, even during one beating motion: going downward at a positive camber to generate mainly a vertical force, but upward at a negative camber to generate main thrust. This is the first evidence to show camber change during flight, by illuminating one wing section using a laser sheet.

Neuronal control of flight: The pulses in neurons that control wing(muscular) activity were measureed by observing the color change associated with the neural firing network that controls the motion of a wing. The oxygen rate, density and distribution in the muscles were also measured suring beating.

Many new experimental techniques: Many new methods were developed to measure and analyze the flight characteristics of a wide variety of centimeter-millimeter-sized objects.

·Relation between the size of a locomotive organ and the Reynolds number

·Flow around a dragonfly wing