Report presenting an analysis of the measurements of drag-angle oscillation of a helicopter rotor made with the helicopter apparatus to determine both the natural frequencies and the damping required to prevent excessive drag-angle-oscillation response to various throttle and control movements. Results regarding symmetrical oscillations, unsymmetrical oscillations, blade damping, and general discussion are provided.

Report presenting a wind-tunnel investigation to determine the boundary-layer and stalling characteristics of the NACA 63-009 airfoil section. Pressure distributions, tuft studies, and boundary-layer measurements were obtained. A localized region of flow separation was found to develop on the upper surface of the airfoil near the leading edge.

Note presenting an investigation of the use of measured static pressures in a vaneless-diffuser passage for determining centrifugal-compressor performance. The general effects of diffuser-wall-surface friction were studied to locate the regions in the vaneless-diffuser passage where the most valid evaluation can be made by the static-pressure method.

Note presenting meteorological data from flight observations in icing conditions during the first 5 months of 1948. A total of 335 measurements of liquid-water content and mean-effective drop diameter were obtained by the multicylinder method in the course of 40 flights in icing conditions covering most of the northern United States. Information regarding the discontinuous character of icing clouds, variation of average liquid-water content with extent of icing conditions, and variation of drop diameter from year to year and with geographic location are provided.

"Results are presented of calculations for the elastic buckling load of a simply supported flat rectangular plate of uniform thickness subjected to unequal compressive stresses at two opposite edges, with a linear variation of stress between the two edges. The difference between the compressive stresses at the two loaded edges is equilibrated by shear stresses along the other two edges. The results show that a plate with a linear stress gradient will buckle at an average stress that is lower, but at a maximum stress that may be appreciably higher, than the uniform compressive buckling stress of the same plate" (p. 1).

"This report is the second phase of a broad program of study of the transient motions of helicopters in autorotative flight. The first phase (reference 1) dealt with the steady-state condition of autorotative vertical descent. This report is concerned with the the transition from the steady condition of hovering to the steady autorotative descent" (p. 1).

"This report is the result of the first part of a broad program to analyze the transient motions of a helicopter, which occur in the various phases of flight following power failure" (p. 1).

From Introduction: "Although the aerodynamic characteristics of the components of such configurations may be well known, the mutual interference resulting from combining the wings, as well as the wings and body, may be so great that is desirable to study the aerodynamic properties of the complete configurations. Two methods of handling this problem are presented in this report. The first method is essentially an extension of the theory for slender wing-body combinations of reference 1 to determine the load distribution, forces, and moments exerted on slender cruciform-wing and body combinations inclined simultaneously at small angles in pitch and yaw. "