Non-Steady-State Aerodynamics of the Flight of Encarsia Formosa

Abstract

Weis-Fogh (1973) demonstrated that the high lift coefficients necessary for flight in certain insects are incompatible with steady-state aerodynamics and proposed two novel mechanisms, the fling and the flip, whereby the wing movements generate circulation around the wings prior to and independently of translation. This premise is investigated for the flight of the small chalcid wasp Encarsia formosa by re-estimating the minimum steady-state lift coefficient by another method and including some possible refinements. The steady-state lift coefficient obtained in this manner is still too high for the relevant Reynolds number. An average circulation of about 3. 8 cm²s⁻¹ may be created around each wing in the fling and flip, however, and this value is higher than the circulation during translation which satisfies the Kutta-Zhukovski condition. Trailing edge vortices, with the same sense as stopping vortices, should then be shed as the wings translate. A rough calculation shows that the corresponding decrease in bound vorticity during each halfstroke is small enough to allow an average circulation remaining around the wings sufficient for flight.