| The complex, non-linear motions of flapping insect wings, coupled with their small size and mass, mean that insects do not generate lift via the same aerodynamic mechanisms used by large birds and man-made aircraft. The majority of studies into the aerodynamic mechanisms of lift production by insects have employed insect species that are functionally two winged and thus the complex nature of the interaction of wing couples, specifically forewing-hindwing interactions, has been largely unexplored. The objective of this thesis was to characterize, using high-speed digital cinematography, dye flow visualization of model wings and volumetric 3-component digital particle image velocimetry, the interaction between forewing-hindwing couples during straight flight and during steering in locusts; a functionally four-winged insect that flies with a steeply inclined stroke plane. Kinematic analyses determined biologically relevant values of key kinematic variables defining the position of forewings and hindwings during the downstroke. The fluid structure over the hindwing, including the presence of a hindwing leading edge vortex, was found to be very sensitive to the presence of a forewing at moderate and high angles of attack. The separation angle between forewing and hindwing was not as important as the difference in elevation angles of the forewing and hindwing during the downstroke. In general, wing-wing interactions result in the abolishment of a LEV on the hindwing by preventing separation at the leading edge. It is hypothesized that this results in a decrease in lift produced by the wing couple. Kinematic observations during steering attempts are consistent with this strategy to decrease lift produced by the wing couple on the inside of the turn path. |
