Dragonfly Forewing-Hindwing Interaction at Various Flight Speeds and Wing Phasing

摘要

At positive γ_d (hindwing leads forewing), the mean total vertical force and mean total thrust of the fore- and hindwings are only slightly influenced by the forewing-hindwing interaction, while at negative γ_d (hindwing lags forewing), the forces, especially the mean total vertical force, are greatly decreased, compared with the case without interaction. The reason for the large decreases in the forces at negative γ_d is as follows: the forewing in each of its downstroke produces a downward "jet" behind it; when the hindwing lags the forewing, it moves in the jet and its effective angle of attack is greatly reduced, resulting in a large decrease in its aerodynamic force; this causes the decreases in the total vertical force and thrust. The present results might explain why dragonflies have been observed only to use positive phase differences in their flight.