Hover performance of a micro air vehicle: Rotors at low Reynolds number

This investigation focused on the performance of a two-bladed, micro air vehicle rotor with variations of airfoil shape and also spanwise distributions of airfoil type and twist. Rotor performance trends were studied experimentally through load measurements and flow visualization. The objective was to determine the influence of airfoil and planform variations on the hover efficiency (or figure of merit). Performance testing results showed that a micro air vehicle blade with circular arc cambered airfoil provided a large increase in the rotor efficiency, as compared to the baseline flat plate. Variation of the leading edge shape and point of maximum camber also showed improved rotor efficiency. Rotor blades with linear distribution of airfoil camber further improved the rotor efficiency over blades with uniform camber. To provide the further basis for blade variations, a laser flow visualization experiment of the rotor wake was performed. The visualization showed evidence of a highly non-ideal inflow and spanwise distribution of lift. Correspondingly, variations of spanwise twist for flat plate, cambered blades and linearly distributed airfoils revealed more optimal rotor efficiency trends. These experimental results showed gains in figure of merit that were significant across the range of non-dimensional thrust coefficients.