Reduction of Hinge Moments of Airplane Control Surfaces By Tabs

An investigation was conducted in the N. A. C. A. 7- by 10-foot wind tunnel of control surfaces equipped with tabs for reducing the control forces or trimming the aircraft. Two sizes of ordinary ailerons with several sizes of attached and inset tabs were tested on a Clark Y wing. Tabs were also tested in combination with auxiliary balances of the horn and paddle types, and with a Frise balanced aileron. A tilt-surface model of symmetrical section, equipped with tabs, was tested with 40 percent of the area movable (elevator) when used as a horizontal tail and 60 percent of the area moveable (rudder) when used as a vertical tail. The half-span tail-surface model was tested with and without a reflection plane.

Complete detailed results of the tests are tabulated in standard nondimensional coefficient form. The aileron test data are discussed for one aileron movement and graphs of control force against rolling-moment coefficient are included. Curves showing the effect of the tabs as trimming or as servo-control devices are given. For the tail surfaces, the effectiveness of tabs in reducing the control force and in trimming and servo operation is discussed and figures are included.

The effect of angular velocities on the application of the data to complete airplanes is considered and also the effect of the difference in the wind-tunnel test set-up from the actual arrangement on an airplane.

The results of the tests indicated that inset tabs were superior to attached tabs for the same ration of tab/control-surface deflection. The greatest reduction is control force occurred at 0° angle of attack. The tabs could be used satisfactorily as trimming devices and also to reduce the control force for control moments as large as those ordinarily obtained by deflecting the control surface 15° or less. The reduction of hinge moments due to tabs could be added directly to the reduction due to paddle, horn, or Frise types of balance. Angles of yaw up to 20° had no appreciable effect on the reduction of hinge moments due to tabs.