Water tunnel experiments were performed to determine the free-stream characteristics of a series of twelve rudders with systematic variations in the amount of flap area and flap balance. The results include plots of lift, drag, rudder moment and flap moment coefficients for a complete range of angles of attack and flap deflections. A comparison is made of the effectiveness of all-movable rudders, rudders with a fixed skeg and movable flap, and rudders with movable "skegs" and flaps. The latter were found to be by far the most effective. Rudders with fixed skegs are inferior to all-movable rudders unless the proportion of flap is very large. Flap balance does not appear desirable. Maximum flap moments, even with zero balance, are generally less than or comparable to the maximum moment of an ideally balanced all-movable rudder.

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