The flow around the air vehicle is affected by the strong vortices generated at the propeller blade tips. Flow interaction varies continuously with time due to the unsteady propeller motions. Therefore, the designer has to consider the entire air vehicle, integrating its aerodynamic characteristics (i.e. aerodynamic forces), and its propulsion system (such as propellers, engine inlet, etc.), rather than just isolated airframe or propeller. Micro air vehicles operate at the low Reynolds numbers, typically between 100,000 and 200,000. For such low Reynolds numbers, the flows around the airframe can involve laminar separation bubble formation, transition, and reattachment, which can all be influenced by the wake vortices generated behind the propeller and hence influence the overall aerodynamic performance significantly. Therefore, a detailed investigation on the propeller effects is critical to understand the overall MAV performances

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