The Longitudinal Stability of a Flying-Boat in the Planing Condition as Computed from Tank Test Data of a Hull Model

Citation

Hatton, George Anthony (1940) The Longitudinal Stability of a Flying-Boat in the Planing Condition as Computed from Tank Test Data of a Hull Model. Master's thesis, California Institute of Technology. doi:10.7907/JR58-MH75. https://resolver.caltech.edu/CaltechETD:etd-11142008-082321

Abstract

The question of “porpoising” of flying-boats has been the subject of investigation both abroad and in the United States. In Germany and England recourse has been had to the use of dynamically similar models, duplicating in the model as closely as possible all the features of the full scale flying-boat. In the towing tanks of the United States, usually a bare hull is tested, where measurements are made of resistance, load, trimming moment, and trim angle at various speeds. The results are usually furnished in the form of curves of trimming moment and draft against speed at various loadings and trim angles. Conclusions regarding “porpoising” of the full scale flying-boat cannot be drawn from the behavior of the hull alone, but it is considered possible to evaluate certain hydrodynamic stability derivatives, which, in conjunction with aerodynamic derivatives obtained from wind-tunnel tests, may be used in the stability equation to determine the behavior of the flying-boat in the planning condition. In the following discussion the aerodynamic and hydrodynamic derivatives are deduced. The aerodynamic derivatives are similar to those normally used for airplanes, but they are evaluated in terms of beam, trim angle, and other hydrodynamic terms; then the hydrodynamic derivatives are deduced, also in terms of hull dimensions and attitudes. This permits direct addition of the hydrodynamic and aerodynamic derivatives for use in the longitudinal stability equation. The criteria of stability then are applied. In addition, a factorization of the stability quartic, formulated by Dr. Millikan, is applied to determine periods of the oscillations, as well as damping factors. An example following the procedure above outlined and devised by Dr. Millikan is presented, using tank test data of a model 36 hull for hydrodynamic quantities. The aerodynamic quantities are based on an average of many modern flying-boats. The model 36 hull is selected as being fairly representative of present day flying boats.

Thesis Files