Measurements of Unsteady Periodic Forces generated by the Blowfly Flying in a Wind Tunnel

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Abstract
A technique was developed for the measurement of the instantaneous lift and drag forces generated by the blowfly, Sarcophaga bullata, flying fixed in a wind tunnel. Apparatus for the measurement of insect-generated forces was checked in part for mean force accuracy by measurement of the drag on a circular cylinder. Our experimental device detects the sum of the aerodynamic forces and wing inertial forces as experienced by the thorax. The streamwise and vertical force waveforms show a surprising lack of higher harmonic content. Wind speeds in the neighbourhood of the known preferred flying speed were used, without an explicit attempt to nullify the mean vertical and horizontal forces to simulate free flight. Several measurements of the phase angle between the force waveform and the wing beating kinematics indicated that vertical forces in the liftward direction achieved a maximum during the downstroke and thrustward forces achieved a maximum during the upstroke.