Evaluation of static stability derivatives from standard yawing tests

Abstract

An analytical and experimental investigation was made to determine the possibility of predicting the static and rotary directional stability derivatives of a flying boat of the conventional short afterbody type. Starting with the angle of trim obtained from a tank test at a specified load and speed, the extent of the wetted areas of forebody and afterbody is computed on the basis of available empirical relations available for planning processes. It is shown that for a range of pre-hump speed the lateral forces due to the yaw can be obtained by consideration of the inequality of loading on two sides of the bottom due to the change of the effective angles of attack resulting from vectorial addition of the angles of deadrise, yaw, and trim. It is also shown that this action results in identical position of centers of pressure for the vertical and lateral forces. On this basis, the static and rotary stability derivatives for yawing motion are computed. The experimental verification of the methods in regards to static derivatives was made for three operating speeds at C(V) of 2.63, 2.46, and 2.34. A reasonable agreement of the test and analysis data is shown for the two higher speeds, but the agreement at the lowest speed is uncertain, probably because of the lack of necessary data on the configuration of the wake of the forebody. Such data are presently available only for C(V) of 3.0 and above. The work was done at the Graduate School and Experimental Towing Tank of Stevens Institute of Technology in partial fulfillment for the degree of Master of Science