Flight Investigation of Lateral Control Devices for Use With Full-Span Flaps

Flight tests were made of five different lateral control devices that appeared adaptable to wings fitted with full-span flaps: Controllable auxiliary airfoils (airfoils mounted above and forward of the leading edge of the wings), external ailerons (airfoils mounted above the wing and slightly forward of its maximum ordinate), upper-surface ailerons (similar to split trailing-edge flaps except that they constitute the upper surface of the wing), ailerons that retract into the wing when in neutral, and narrow-chord conventional ailerons in combination with a special type of split flap that retracts into the under surface of the wing forward of the ailerons. The devices were tested on a small parasol monoplane.

Only the retractable ailerons and the narrow-chord ailerons in combination with the special split flap were found to be satisfactory. The absence of appreciable aerodynamic hinge moment of the retractable aileron was considered to be somewhat objectionable but this characteristic can probably be remedied by a slight modification. The external ailerons were unsatisfactory in the normal-flight range because of an irregular variation of their hinge moment with deflection and a relatively weak rolling action. These ailerons are believed to warrant further development, however, because they retain their effectiveness above the stall. The controllable auxiliary airfoils had lag as well as excessive hinge moments and hence appear to warrant no further development. The upper surface ailerons had excessive hinge moments but were otherwise satisfactory.

Experience gained in the use of flaps during these tests has indicated the desirability of a flap that can be operated quickly and easily.