This report continues the work presented in NACA-TM 605 and expands the scope to include the change in specific number of wrinkles from direction x to z, so that b and f become variable in direction z. Moreover, it seems likely that b and f increase from the edge toward the center if the sheet is infinitely thin.

"Noting that the stiffness of the girder increases very rapidly as Beta increases, the result can be summed up as follows: When the cross stress preponderates in one direction and when the web plate is to be given the dimensions commensurate to its stresses, it is advisable (regardless of any ensuing structural difficulties) to set the uprights at about Beta = 120 degrees, thereby lowering the weight of the plate wall 15 percent (in contrast to Beta = 90 degrees), and raising the stiffness 55 percent. But, when the cross stresses alternate and are approximately of the same intensity in both directions, or, if the web plate thickness is determined by other structural reasons, then Beta = 90 degrees should be chosen" (p. 1).

The object of this report was to develop the structural method of sheet metal girders and should for that reason be considered solely from this standpoint. The ensuing methods were based on the assumption of the infinitely low stiffness in bending of the metal web. This simplifies the basis of calculations to such an extent that many questions of great practical importance can be examined which otherwise cannot be included in any analysis of the bending stiffness of the buckled plate. This report refers to such points as the safety in buckling of uprights to the effect of bending flexibility of spars, to spars not set parallel, etc.

Memorandum presenting an evaluation of elektron, which is the lightest of the light metals and is of particular interest for aircraft construction. Some of its chemical properties, particular alloys and wrought materials that can be made using elektron, and some of the potential ways in which the material might be used are provided.

Report discussing the design of the wind vane described rests on the following line of reasoning: An airplane, originally in equilibrium about its C.G. is assumed to be deflected from this position through an angle (delta)i, the variation (delta)i being so sudden that the path of the C.G. and the airplane speed do not change while it is taking place. The aerodynamic forces acting on the wings, tail surfaces, fuselage, etc., which, as a whole, exerted a zero moment (M(sub G) = 0) about the center of gravity at the instant of equilibrium, now exert a moment M(sub G) not equal to 0.