Determination of the Effect of Horizontal-tail Flexibility on Longitudinal Control Characteristics

S. M. Harmon

Jan 1945 · National Advisory Committee for Aeronautics

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Summary: An iteration method is given for determining the longitudinal control characteristics of a flexible horizontal tail. The method permits factors such as the actual spanwise variation of elasticity and the aerodynamic induction effects due to three-dimensional flow to be accounted for to any degree of accuracy appropriate to a particular case. An analysis is included of the effects of horizontal-tail flexibility on the tail effectiveness, the hinge-moment characteristics, and the control-force gradients in a dive recovery for two modern fighter airplanes. The effects of variations in speed, altitude, elevator stiffness, and center-of-gravity movements are considered. The result of these calculations for speeds below that at which critical compressibility effects occur indicate for the two airplanes significant effects due to the tail flexibility. It appears that the location of the flexural axis of the stabilizer too far behind the aerodynamic center of the tail may cause excessive control forces in a dive recovery at high speeds.