Technical Note Comparison of the Hovering Efficiency of Rotating Wing and Flapping Wing Micro Air Vehicles

Trends exposing the aerodynamic efficiency of hover-capable micro aerial vehicles (MAVs) were examined. Published data for several types of MAV concepts were reviewed; these concepts encompass conventional rotating wing configurations, cyclorotors, flotors, and entomopter-like biomimetic flapping wings. The work also included assessments of the hovering performance of avian and entomological flyers. For each concept, published performance data were used to establish comparative trends for power loading as a function of the effective disk loading. No independent assessments of the quality or accuracy of the published measurements and/or calculations were performed. It is shown that the hovering efficiencies of MAV concepts lie on a simple correlation curve that is bounded by the theoretical levels of hovering performance as given by the well-known momentum theory. All hover-capable concepts that can achieve low disk loadings are shown to achieve relatively good power loadings. Such concepts, however, do not necessarily achieve the best levels of aerodynamic efficiency or figure of merit (FM). It is explained why the power loading, and not the FM, is the most objective basis on which the aerodynamic efficiency of hover-capable devices should be compared. The results show that when compared on the basis of the same disk loading, the biomimetic flapping wing systems have, at least thus far, attained lower values of FM compared to those of rotor systems. Although avian and entomological flyers operate at very low effective disk loadings with good power loadings, the available measurements suggest that they do not always achieve very high values of FM.