Micro aerial vehicles (MAVs) have had a recent surge of interest due to their many commercial, military and scientific applications. Their wide range of uses, such as those intended for close proximity situations, could include search and rescue missions as well as reconnaissance and surveillance.The optimal Strouhal numbers, that is the dimensionless number describing oscillating flow mechanisms, obtained for a freely flying system are found to be in the range of 0.2≤ St≤ 0.35. It has been proposed that Strouhal number selection in natural flight is not the result of an active feed back control mechanism but a limit cycle process. Theoretical phase portraits of a coupled fluid structure system show that different initial conditions are attracted to the same limit cycle and different forcing frequencies end at different limit cycles. This lends credence to the idea that if man-made flapping flight is to become viable, understanding the dynamics of Strouhal number selection will be important.
Finkel, Cyndee, "Experimental Study of Synchronization and Phase Dynamics in Flapping Foil Propulsion" (2011). Link Foundation Ocean Engineering and Instrumentation Fellowship Reports. 9.