FRY, SN*; SAYAMAN, R; DICKINSON, MH; ETH/University of Z�rich; Bioengineering, CalTech; Bioengineering, CalTech: Instantaneous flight power in the fruit fly Drosophila

Hovering fruit flies are required to generate sufficient flight power to overcome aerodynamic and inertial forces. The aerodynamic models developed by Ellington (1) provide the theoretical framework for estimating flight power based on time-averaged flight parameters. Based on these methods, muscle power was previously estimated at around 60 W/kg (2). This approach is limited by the required assumptions and the estimate of several input parameters. Furthermore, the experiments relied on tethered flying fruit flies, whose behavior is subject to an unknown bias. Using 3D high speed videography and a dynamically-scaled robotic wing (3), we measured the precise time course of 3D wing motion and flight forces in free and tethered flying fruit flies. Based on these data, we calculated the instantaneous mechanical power during hovering flight. A lower estimate of mean muscle power of 108 W/kg is calculated from the mean of mechanical power, assuming perfect elastic storage of kinetic energy. Without elastic storage, muscle power increases only slightly to 126 W/kg. The cost of wing acceleration is therefore minor and is further reduced by elastic storage, confirming previous results (4). Our measurements of muscle power are substantially higher than the previous estimates, which were in part based on unrealistic input parameters. We also find that flight power in tethered flight is significantly reduced to 65-77 W/kg. Taken together, the measurement of instantaneous wing motion and flight forces in free flight provides a more detailed and robust method to analyze the power requirements of insect flight. References: (1) Ellington,C (1984) Phil Trans R Soc Lond B 305,1-181 (2)Lehmann,F and Dickinson,MH (1997) J Exp Biol 200,1133-1143 (3) Fry,SN, Sayaman,R and Dickinson, MH (2003) Science 300,495-498 (4) Dickinson,MH and Lighton,JRB (1995) Science 268,87-90