The geared elevator tab and tail-unit stiffness requirements

Abstract

The effect of a flexible, geared, elevator tab upon the validity of the stiffness criteria for tail-units and rear fuselages is examined. To this end, the distortions of a hypothetical, semi-rigid tail-unit under the air loads induced when the elevator is displaced are calculated for various arrangements of tab and forward aerodynamic balance of the elevator. Notice is also taken of the loss of control effectiyeness and change in elevator hinge moment resulting from these distortions. It is found that a geared elevator tab covering only a fraction of the elevator span may lead to large tip distortions and appreciable reduction of control effectiveness of the elevator if it is placed near the inboard end. From consideration of the distortions of the tab and the effect upon elevator hinge moment, a torsional-stiffness criterion for tabs is proposed.