Energy-turn-rate characteristics and turn performance of an aircraft

Abstract

Specific energy of turn (SET), which is defined as the energy required to overcome drag per unit mass per turn, is a simple concept for evaluating the turn effectiveness of an aircraft. The characteristics of SET vs turn-rate show up the effects of drag polar and wing loading under the given conditions of flight. The simplicity of constant thrust/weight curves and constant C_Lmax curves in the SET-turn-rate plane permits a convenient separation of their effects on the achievable peak sustained and transient turn-rates. SET is shown to be an absolute minimum at a certain optimum turn-rate for the given configuration, wing loading, and flight conditions. The optimum turn-rate is generally larger than that needed for maximum lift/drag. Analytical expressions of optimum turn-rate, minimum SET, and an index of flatness of the SET-turn-rate curve are obtained on the basis of a recent representation of the drag polar, which seems to be an acceptable approximation over a large range of angles of attack. An example is given to indicate possible applications to parametric studies.