Studying the effect of the tail on the dynamics of a flapping-wing MAV using free-flight data

The effects of the horizontal tail surface on the longitudinal dynamics of an ornithopter were studied by systematically varying its surface area, aspect ratio and longitudinal position. The objective was to improve the understanding of the tail effect on the behaviour of the ornithopter and to assess if simple models based on the tail geometry can predict the steady-state conditions and dynamic behaviour. A data-driven approach was adopted since no suitable theoretical models for ornithopter tail aerodynamics are available. Data were obtained through wind tunnel and free-flight experiments. Fourteen tail geometries were tested, at four different positions with respect to the flapping wings. Linearised models were used to study the effects of the tail on the dynamic behaviour. The data show that, within the tested ranges, increasing the surface area or aspect ratio of the tail increases the steady-state velocity of the platform and improves pitch damping. Results also suggest that the maximum span width of the tail significantly influences the damping properties, especially when the distance between the tail and the flapping wings is large, which likely relates to the induced velocity profile of the flapping wings. Steady-state conditions can be predicted accurately based on the tail geometry even when extrapolated slightly outside the original measurement range. Several trends were identified between model parameters and tail geometry, but further research is required before these trends can be applied as a design tool.