Abstract:

ESDU 87008 predicts semi-empirically the sideforce due to rudder deflection and its point of action on the fin, from which the rolling and yawing derivatives due to rudder deflection are easily calculated. To obtain the sideforce, ESDU data for wing lift-curve slope and for plain control effectiveness are applied to the fin with appropriate corrections. The corrections allow for body interference (which depends on the body cross-section in the region of the fin) and for tailplane position on the fin between a T-tail and a tailplane at the fin/fuselage intersection. In addition, another correction is applied for a rudder that does not occupy the whole trailing-edge of the fin. Graphs show the accuracy of the predictions by comparing them with wind-tunnel data extracted from the literature. The ranges of geometry and Reynolds number covered by the tests are quoted. The data used were in the incidence range from 0 to 10 degrees, and the effect of any control gap was neglected. The sideforce derivative is thought to be predicted to within 0.04, the yawing moment derivative to within 0.02 and the rolling moment derivative to within 0.01. A worked example illustrates the use of the prediction method. A computer program of the method is provided as ESDUpac A8708.