Dragonfly Flight: Power Requirements at High Speed and Acceleration

Most studies of insect flight deal primarily with hovering or with forward flight at constant, moderate speed. This paper reports investigations of flight characteristics that are especially relevant to the performance of dragonflies at high and/or changing velocity. Dragonflies were filmed in free flight in the field to determine velocity and acceleration. The power required for repeated acceleration is shown to be large, in some circumstances, relative to the estimated maximum available power and probable top power requirements for steady flight. Distributions of velocity and acceleration, and concomitant power requirements, differ markedly among species, however. In addition, parasite drag was measured in winds of 2–7ms⁻¹ and drag coefficients determined to be about 0.40 at Reynolds number greater than 10⁴. This result implies substantially lower power requirements at high speeds, compared to previous estimates. Other aspects of power output, including the probable magnitude of inertial power, are considered in relation to published data.