On the Definitions of Rotor and Rotorcraft Power and Performance

The origins, usage conventions, and definitions of rotorcraft aerodynamic power and performance are reviewed. The term total power is proposed to represent the combination of shaft power plus translation power (propulsive or drag), Ptotal=QΩ+DV. Total power may be divided into mechanical and aerodynamic components and sub-components (elements) that constitute a hierarchical framework, or matrix, for classifying rotor power. The mechanical power is comprised of the shaft and translation power components; the aerodynamic components include ideal, induced, and profile power. Ideal power is discussed as a key element of the framework. The derivation that links the traditional rotor performance equation and the power framework is presented. Blade-element-momentum theory is used to develop various elements of rotor power and illustrate the key fundamental characteristics of total, ideal, and induced power. The relationships of the total power components to rotor effective drag and the aerodynamic and propulsive efficiencies, L/De and ηp, are discussed.