Although vertical flight has existed for many years, recent growth in unmanned aerial vehicles (UAV) and a need to operate in complex environments has led to a simultaneous growth in rotorcraft. Many of these UAVs consider co-axial rotors, which have a notable benefit in a low yaw torque. This benefit comes as the cost of complexities associated with rotor-rotor interactions. In the present work, the aerodynamics of co-axial rotors is explored in descent, ground effect, and their interaction with the ground. In descent, a flight concern arises known as vortex-ring state, which is a potentially adverse flight condition that typically leads to unsteady loads, partial loss of thrust, and/or a rise in power. The second flight condition explored is ground effect, which involves rotor operation near the surface. These flight conditions are studied using computational fluid dynamics. The findings from the present analyses explore various approaches to modeling descent and operation in ground effect. The results of the analysis provide preliminary results that suggest that a coaxial rotor has the potential to reduce the impact of thrust loss and unsteady loading associated with vortex ring state.