Empirical Investigation of Induced Inflow and Down wash under the Small Tandem Rotors

In this study, a multipurpose testing equipment with a sub-scale model body with tandem rotors configuration was used to carry out a number of experiments in order to understand the inflow and down wash behavior of these rotors. The results showed that for single rotor, inflow is descending except in central areas. By using the data obtained from the experiments, an approximate pattern of inflow and downwash of rotor was presented. This pattern was found to be similar to the pattern that was presented for conventional helicopters rotors under settling with power condition. This phenomenon is one of the reasons contributing to the formation of an unstable turbulent flow in the central areas of the rotor. The results showed that interacting of the two tandem rotors has an effect on the behavior of the rear rotor inflow and changes its behavior in comparison with single rotor. It was observed that the results obtained from this study were more realistic due to considering the effects of the body, actual fluctuations of the flow. The experiments in this study showed differences exist in the principles governing the aerodynamic performance of rotors used in UAVs in comparison with conventional helicopters rotors. Therefore, it is necessary to pay enough attention to these differences and behaviors in predicting the aerodynamic performance and design of this type of flying machines.