Geometric Effects on the Aerodynamic Interactions of a Wing-Propeller Combination in Hover Flight

The aerodynamic interactions between a propeller, wing, and control surface are investigated at zero freestream velocity to simulate flight conditions associated with hovering operations of a tail-sitter aircraft. Oil flow visualizations and Kiel probe surveys indicated that a thrust-producing propeller operating at zero freestream velocity generates a wake over a wing's surface that is significantly skewed towards the slipstream's downwash component. This testing also showed that a slipstream's velocity profile at a given chord location follows a bimodal distribution with a velocity deficit located behind the propeller hub. After identifying distinctive slipstream characteristics associated with this unique flight condition, additional testing was performed focused on determining the influence of a propeller's rotational direction, distance from a wing's leading edge, radius, and pitch on the resultant lifting force and pitching moment. Test results demonstrated that propeller directionality did not significantly impact the wing's aerodynamic loads. Similarly, the lifting force and pitching moment appeared largely insensitive to changes in propeller standoff distances between 0.5R and 1.5R. The wing's aerodynamic loads increased linearly with the amount of thrust generated by a propeller. For a given control surface deflection, similar thrust-normalized lifting forces and pitching moments were generated regardless of propeller radius and pitch. These thrust-normalized loads increased proportionally with control surface position for small to moderate deflections. Relating the wing's lifting force and pitching moment to propeller thrust provides a succinct method for estimating the aerodynamic loads required to model the flight dynamics of a tail-sitter VTOL aircraft operating at hovering flight conditions.