An Experimental Study of Drag Coefficients of a Quadrotor Airframe

This paper investigates the aerodynamic drag coefficients of a standard cross-geometry quadrotor airframe at varying pitch and yaw angles, using a wind tunnel. The quadrotor airframe was mounted in the wind tunnel at fixed pitch and yaw angles, and subjected to a range of wind flow speeds. Drag forces created by the mounting systems used were measured and removed from subsequent drag force measurements. The drag force on the airframe at these speeds and attitudes was measured, and used to identify lumped drag-area coefficients. The variability of these coefficients was observed both with and without unpowered propellers mounted on the airframe. It was found that these parameters increased with increasing angle, and were larger with propellers mounted on the airframe. Measurements were also taken at mixed pitch/yaw orientations to determine whether a relationship exists between these drag-area coefficients and ones taken at individual pitch and yaw angles. Validation was performed using computer vision estimates of projected areas and comparison with drag coefficients of geometric shapes. Fourier series models were fit to the drag-area coefficient trends to create estimator functions. The pitch axis estimator functions had adjusted R² coefficients of 0.976 and 0.932, while the adjusted R² coefficients for the yaw axis were 0.733 and 0.508 (without and with propellers respectively). The measured drag-area parameter values and fitted estimator functions provide reference values for quadrotor airframe design, simulation and controller development for model-based controllers.