Dragonfly - Aerodynamics during transition to powered flight

The Dragonfly lander will enter the Titan atmosphere following an approximate 7-10-year journey through space inside its aeroshell. After atmospheric entry, deployment of the main parachute, and heatshield release, the lander will begin its transition to powered flight (TPF). TPF is a maneuver sequence used for mid-air deployment of the Dragonfly rotorcraft lander. The sequence starts just after lander release with the rotors lightly loaded and finishes when a steady-state descent condition has been attained. Mid-air deployment of a multicopter unmanned aerial system is a multidisciplinary problem involving controller choice and tuning, trajectory planning and optimization, and computational fluid dynamics analyses. This paper is an introduction to the transition of rotor flow states in TPF from the windmill brake state, through the turbulent wake state and vortex ring state, and the successful emergence into a normal operating state. A particle swarm optimized controller's nominal trajectory is plotted on a rotor aerodynamics state chart to show the trajectory's path through the flow states along the TPF maneuver. Results of preliminary CFD simulations show the variance of individual rotor thrust and power in the early stages of TPF followed by a successful stabilization of rotor performance. Interactional aerodynamic studies also characterize the pre-release flowfield around the lander to be benign at the start of the maneuver. Additionally, results for the lander in steady axial descent show a previously observed coaxial rotor shielding phenomenon of the upper rotor from the effects of vortex ring state.