Free-Body Modeling of the Stability and Control of Submarines. Volume I - Text. Volume II - Figures

Abstract

An experimental study of the dynamic control and stability of submarines has been made by means of small-scale, free-running, powered and controlled models at the California Institute of Technology, Hydrodynamics Laboratory. The experimental and theoretical basis of the modeling of the behavior of fully submerged submarines is discussed. The design and construction of the models are described, and development of experimental techniques is outlined. The experimental program was conducted with models of two full-scale submarines -- the U.S.S. Odax and the U.S.S. Albacore -- to (1) evaluate the efficacy of small-scale modeling, and (2) to predict control characteristics of a boat of radically new design. Satisfactory agreement between the dynamic behavior in free flight of the small-scale (120:1) model and the Guppy-type submarine Odax is demonstrated for one type of maneuver. Zig-zag maneuvers in the vertical plane were chosen for this purpose because of their simplicity and suitability for comparison with available full-scale data. The model's diving planes were made to reproduce the time-sequence of the diving plane motions of the full-scale submarine and the resulting depth and inclination responses compared to those of the full size vessel. The consistency of the model's behavior was evaluated from repeated tests with each of four selected control programs for which only a single full-scale test was run. Predictions of the dynamic control and maneuverability characteristics of the U.S.S. Albacore (AGSS 569) Scheme IV submarine, which marks a radical departure in hull design, were made with a 100 to 1 scale model. This model was built at about the same time that the keel was laid for the prototype ship. The studies made with this model were divided into three parts: (1) Control characteristics in the vertical plane. (2) Turning characteristics with rudder control alone. (3) Turning characteristics with depth control, and with combination depth-and-roll control. The tests under item (1) were made with two sets of appendages (tail structure, bow planes, and bridge fairwater), for which only minor differences in control response were found and no measurable difference noted in directional stability. Items (Z) and (3) were made with one set of appendages (corresponding to those first used on the prototype) and with Froude-scaled model velocity. Specific maneuvering problems, such as the determination of control plane programs required to execute optimum dives or horizontal turns without changing depth, are solved by successive approximation with the model. The tests show that a high degree of prescience is required and that precise execution of the control program is necessary to successfully accomplish an optimum maneuver. Comparison of the behavior of the two models shows that the Albacore has a greater degree of directional stability and a faster response to its controls than the Odax. This is certainly due to its better hydrodynamic design. The Albacore model also demonstrated much better consistency in it- own behavior than did the Odax model. This is due in part to better design and in part to the improvements made in the techniques of building and operating the models and in processing the model test data. At the time of this writing, no detailed comparisons have been made between results obtained with the Albacore model and those of the sea trials of the prototype which were made in the fall of 1955. The few spot comparisons which were made (but not included in this report) show good agreement. Detailed comparisons of these two sets of tests will be made at the David Taylor Model Basin (under whose supervision the sea trials were conducted) and will be the subject of a separate report.

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