On the optimum separation distance for minimum noise of contra-rotating rotors

Overlapping rotor systems are currently used on some urban flight vehicles and will become increasingly common in future electric propulsion, since they provide one of the most compact platform volumes per thrust. This paper presents results a detailed experimental investigation co-axial contra-rotating configuration at hover condition. A range diameters considered study 14-18 inch Tip Mach numbers investigated present 0.2. parametric is performed to investigate sensitivity radiated noise axial separation distance. An optimum distance z diameter D 0.25 has been identified, whereby minimum obtained. The reason for this explored balance between various interaction sources discussed paper. It also shown that was roughly found where aerodynamic efficiency maximum.