Extracting aerodynamic coefficients using direct trajectory sampling

We describe a technique to extract aerodynamic characteristics of an aircraft directly from collected trajectories. The technique was developed to investigate the low Reynold's number regime of centimeter-scale aircraft which represents a largely unstudied domain of aerodynamics and for which traditional techniques have produced limited results. This technique takes advantage of a vision tracking system that dispenses with any on-board navigation sensors and the stationary atmospheric conditions prevailing in the indoor flight experiment facility used to collect flight data. The aircraft is fitted with reflective markers on its wing, fuselage, and empennage. A broad variety of trajectories spanning the natural flight envelope were collected by hand launching the aircraft. Aerodynamic forces and moments can be determined from the vehicle's inertial acceleration; the aerodynamic angles can be determined from the vehicle's kinematics. Combining these data we can determine the aerodynamic coefficients. The results are then validated using a six degree-of-freedom model. This technique complements the traditional wind-tunnel techniques and numerical analysis tools. Thanks to its practical qualities, this technique could be useful to other fluid dynamic problems.