The buckling failure conditions for a bar with nonprogressively variable moment of inertia J(sub n), although constant over length l(sub n), are developed.

From the described experiments it is seen that notches are a potential source of strength decrease even under static stress, which the designer must take into consideration. Section I is a general treatment of notch influence under the various types of stresses. Section II treats the influence of notches in thin sheet as is used in airplane construction.

The present report describes tests in which the stress distribution may be determined in a stiffened circular cylindrical shell loaded longitudinally at four symmetrically situated points. As being of particular importance are the cases investigated of groups of bending and arching or convexing forces, respectively. From the stress measurements on the longitudinal stiffeners, the shear stresses and the bulkhead ring stresses in the skin could be evaluated.

The present paper presents an attempt to coordinate the available theoretical and experimental data on planing surfaces so as to develop an approximate analytical method for the determination of the water resistance of a seaplane without any preliminary towing tests in the tank.