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▪ Abstract  In this review we describe the aerodynamic problems that must be addressed in order to design a successful small aerial vehicle. The effects of Reynolds number and aspect ratio (AR) on the design and performance of fixed-wing vehicles are described. The boundary-layer behavior on airfoils is especially important in the design of vehicles in this flight regime. The results of a number of experimental boundary-layer studies, including the influence of laminar separation bubbles, are discussed. Several examples of small unmanned aerial vehicles (UAVs) in this regime are described. Also, a brief survey of analytical models for oscillating and flapping-wing propulsion is presented. These range from the earliest examples where quasi-steady, attached flow is assumed, to those that account for the unsteady shed vortex wake as well as flow separation and aeroelastic behavior of a flapping wing. Experiments that complemented the analysis and led to the design of a successful ornithopter are also described.

The design of micro aerial vehicles requires a better understanding of the aerodynamics of small low-aspectratio wings. An experimental investigation has focused on measuring the lift, drag, and pitching moment about the quarter chord on a series of thin at plates and cambered plates at chord Reynolds numbers varying between 60,000 and 200,000. Results show that the cambered plates offer better aerodynamic characteristics and performance. It also appears that the trailing-edge geometry of the wings and the turbulence intensity in the wind tunnel do not have a strong effect on the lift and drag for thin wings at low Reynolds numbers. Moreover, the results did not show the presence of any hysteresis, which is usually observed with thick airfoils/wings.

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