STEVENS INST OF TECH HOBOKEN NJ EXPERIMENTAL TOWING TANK
The equations of motion describing the longitudinal stability characteristics of an uncontrolled tandem hydrofoil system in smooth water with three degrees of freedom are developed. The stability derivatives in the equations are evaluated on the basis of theoretical hydrodynamic formulas, thereby eliminating the necessity of their experimental determination. Comparison of the notions obtained from solutions of the equations with those determined from previous experimental stability tests indicate a duplication of the motion experienced in the tank tests. Variations in the location of the longitudinal center-of-gravity position are shown to lead the different types of motion, which is in agreement with the results of standard aircraft stability analyses. The additional degree of freedom in longitudinal surging is found to indicate a decrease in stability. This mode of motion is of great importance, however, for a study of stability in waves where the waves cause variations in the forward speed. The equations developed in this report may be extended to studies of motion in waves and controlled motion in incorporating the forces and moments due to wave motion and the dynamics of the control system in the equations. By assuming the resultant system of equations to be linear, the analysis may be performed by using the Laplace transform technique in the same manner as was done in the present study.