A theory of the aerodynamic interference between a helicopter rotor blade and a fuselage and wing in hovering and forward flight

Abstract

The Report presents a theory of the aerodynamic interference between a helicopter rotor blade and a fuselage or wing. A two-dimensional analysis is made to which a correction factor is applied to convert the two-dimensional calculations to the appropriate three-dimensional case. The pressures and forces on circular and square-sectioned fuselages and on wings are calculated for hovering flight and also the corresponding changes of lift on the blade. It is shown that large changes of blade lift occur if the blade is close to a fuselage due to the interference by the fuselage of the downwash or normal component of flow. The calculations also show that the interference effects on, and due to, a square sectioned fuselage are about half as large again as those of a circular cylinder whose diameter is the same as the length of the side of the square. The analysis is extended to cover the case of interference between a blade and a lifting wing or tailfin in forward flight. It is shown that the interference between a tailfin and tailrotor can be severe and may result in a large loss of effectiveness of the tailrotor, especially in hovering and low speed flight.