Clap and fling with bristled wings: effects of varying solid membrane area

The smallest flying insects such as thrips show preference for bristled wings and the use of clap and fling kinematics to fly at Reynolds numbers (Re) on the order of 10. Overcoming drag is the greatest challenge to clap and fling at these low Re. Due to this, physical design of bristled wings is of particular interest. This study examines the aerodynamic effects of varying the ratio of solid membrane area (MA) to total area (TA) of the wing. MA/TA varied from 14-27% in thrips. Physical bristled wings models with MA/TA varying from 15-100% were tested in a robotic clap and fling model at Re from 10 to 120. Flow along the wing chord was visualized using 2D PIV and strain gauges were used for measurement of lift and drag forces. At low Re, reducing MA/TA generally resulted in lower circulation around the leading and trailing edges during both clap and fling. However, when Re was increased to 120 (relevant to larger insects such as the fruit fly), vortex shedding decreased circulation about the leading edge during clap, and the trailing edge during fling in wings with high MA/TA. Lowering MA/TA resulted in reduced lift and drag forces, but increased peak lift to peak drag ratios across the tested Re.