Coandă Effect Used to Improve the Efficiency of a Rotary Wing Aircraft

Abstract

Coandă effect is a well-known fluid mechanics phenomenon in which a jet flow attaches itself to a nearby surface and remains attached even when the surface bends away from the initial jet direction and the jet is deflected closer to the surface, up to attaching to it. Using Coandă effect, the anti-torque NOTAR system replaces the use of a tail rotor on a helicopter. A fan inside the tailboom creates a large volume of lowpressure air, which exits through two slots and creates a boundary layer of airflow along the tailboom, due to the Coandă effect. The interaction of this air flow with the downwash from the main rotor creates a force oriented as an anti-torque force, an opposed to that of the main rotor. The airflow escapes the slots tangential to the external surface of the tailboom in a parallel direction to that of the external flow. The final result is the deflection of the external flow and generation of lift forces.