A report in two parts: one is a brief review of methods available to helicopter designers for obtaining desired stability characteristics by modifying airframe design and the other is a review of some of the methods of predicting rotor stability derivatives.

From Summary: "Data from ditching investigations conducted at the Langley Aeronautical Laboratory with dynamic scale models of various airplanes are presented in the form of tables. The effects of design parameters on the ditching characteristics of airplanes, based on scale-model investigations and on reports of full-scale ditchings, are discussed. Various ditching aids are also discussed as a means of improving ditching behavior."

"A coincidence Geiger counter system was constructed for the absolute measurement of the activity of radioactive substances made in a cyclotron. The average beam current in the cyclotron can be calculated from the number of disintegrations per second observed, the half-life of the radioactive substance, and the reaction cross section" (p. 1).

Report presenting the use of molybdenum disulfide as a solid film lubricant in applications where designs or temperatures preclude liquid lubricants is dependent on successful bonding of the powder to the surface to be lubricated. An investigation was conducted to determine the basic mechanism of bonding and to extend application of the bonding to a variety of materials. Results regarding an examination of electron diffraction of MoS2 dusted and rubbed on steel, adherence of dry powders to metals, chemical action in bonding mechanism, other resin-forming liquid vehicles, bonding of MoS2 and other powders to various materials, and analysis of solid film by electron diffraction are provided.

Note presenting a qualitative approach to the problem of the effect of frequency and temperature on fatigue, as the theoretical and experimental results do not always seem to match. The fatigue problem is examined from the viewpoint of a two-component system.

Note presenting a study of Stokes' stream function for subsonic or supersonic flow past axisymmetric bodies of small slope. The first-order equation is found to be nonlinear. It can be linearized if one seeks only the formal order of accuracy of the slender-body approximation.

Note presenting tests to determine local heat-transfer coefficients and friction factors for fully developed turbulent flow of air in a smooth electrically heated tube with an inside diameter of 0.87 inch and a length of 87 inches. Testing occurred at high ratios of wall to fluid bulk temperatures. Results regarding the predicted temperature and velocity distributions, Nusslet numbers, friction factors, velocity distributions, and temperature distributions are provided.

Note presenting a survey of the chromium-cobalt-nickel ternary phase diagram at 1200 degrees Celsius by means of microscopic and X-ray diffraction studies on 110 vacuum-melted alloys prepared from commercial metals of the highest purity available. Three distinct phases are noted.

Note presenting a discussion of a semiempirical profile correction factor which enables the estimation of the wave drag due to thickness at supersonic speeds for three-dimensional wings with arbitrary airfoil section through use of previously calculated drag coefficients. Application of the correction factor to the known drag coefficients of some rhombic-profile wings yielded estimates for the drag coefficients of parabolic-arc-profile wings that were in good agreement with theoretically calculated values.

"An isothermal survey was made of certain portions of the chromium-cobalt-nickel-iron quaternary system at 1200 degrees Celsius. The iron content was varied up to 30 percent to include the range of commercial chromium-cobalt-nickel alloys. As a part of the quaternary system, the cobalt-chromium-iron ternary system was also studied" (p. 1).

Note presenting the principle of complementary energy in the nonlinear elasticity theory, which is shown to be derivable from the principle of potential energy by a Legendre type of transformation. The expression of the complementary energy is derived for homogeneous and sandwich plates and shells with large deflections. The stress-strain relations are derived for homogeneous shells, sandwich plates, and sandwich shells.

Report presenting a study in which heavy hydrogen (deuterium) was substituted in turn for regular hydrogen in each of five possible hydrogen-producing operations in the coating process. The gas that evolved when coated steel specimens fishscaled after firing was collected and analyzed with the mass spectrometer.

Note solving basic equations of Karman and Chien by representing the shape of a torsion box by means of a Fourier series. The coefficients of the series are determined by conventional methods. Results obtained for angles of twist and normal stresses are in good agreement with results of Karman and Chien except at sharp corners.

Report presenting normal accelerations and airspeed data collected with NACA V-G recorders in transport airplane operations from 1933 to 1945, which are summarized and analyzed with respect to gusts and gust loads. The accelerations experienced in most operations equaled or exceeded the limit-gust-load-factor increment, on average, twice in 107 flight miles. Results regarding the acceleration experience, gust experience, probable airspeed, and maximum airspeed are provided.

Note presenting bending-moment distributions that were measured on a model helicopter rotor blade under hovering and simulated forward-flight conditions. curves of maximum-bending-moment distribution are presented for all test conditions. Resonance studies have also been made on three sets of blades of different stiffnesses for the purpose of comparing the experimentally determined resonance peaks with those indicated by theory.

The test method presented shows that the "toss energy" contributed by the apparatus for brittle materials is negligible. The total toss energy is considered to consist of two components: (a) recovered stored elastic energy and (b) kinetic energy contributed directly by the apparatus. The results were verified by high-speed motion pictures of the test in operation.

Report presenting an investigation of a 1/19-scale model of an unswept-wing trainer airplane in the 20-foot free-spinning tunnel to determine the rocket spin-recovery characteristics of the model for comparison with available full-scale-airplane results. A rocket was attached to each wing tip to fire in a direction to apply an antispin yawing moment about the Z body axis. Results regarding the full-scale spin recoveries by rockets, model spin recoveries by rudder reversal, model spin recoveries by rockets, and mass changes associated with installation of emergency device are provided.

Note presenting an investigation of some of the possible mathematical troubles that may occur in the iterative procedure so much in use in present-day aerodynamics. The analysis indicates the general undesirability of determining the velocity potential or the stream function in the form of a series whose coefficients are analytically developed in a power series of some parameter.

Note presenting a survey of the 1200 degrees Celsius isothermal sections of the iron-nickel-molybdenum and the cobalt-iron-molybdenum ternary systems. The phases occurring in the systems were identified by means of x-ray diffraction and by etching methods, and the phase boundaries at 1200 degrees Celsius were determined microscopically, using the disappearing phase method with quenched specimens. Results regarding the specific phases and phase diagrams are provided.

Report presenting calculation studies to evaluate the influence that wing bending flexibility has on the structural response to gusts for three twin-engine transports and one four-engine bomber. The manner in which dynamic response factors for acceleration and bending moment vary with different assumed airplane operational factors is shown.

In this study in which an airplane simulator with one degree of freedom (pitch) was used, results were determined for three conditions of airplane dynamics. For an undamped natural frequency of 1/2 cps with a damping ratio of 0.18 and for an undamped natural frequency of 1 cps with a damping ratio of 0.11, moderate longitudinal stick forces and displacements were desired.

Note presenting flight tests conducted with a medium-size single-rotor helicopter, of which one blade was equipped with strain gages, to determine the relative effects of atmospheric turbulence and moderate maneuvers on the periodic rotor blade moments. The results indicate no significant increase in the total blade moments due to atmospheric turbulence of moderate pull-up maneuvers which produced center-of-gravity acceleration increments of less than about 0.15g. Results regarding moment records, maximum vibratory moments, harmonic analysis of moment records, and applicability of NACA helicopter VGHN recorder surveys are provided.

Report presenting external wave drag of bodies of revolution moving at supersonic speeds, which can be expressed either in terms of the geometry of the body or in terms of the body-simulating axial source distribution. The second of the methods is found to be more tractable.

Report presenting a study of the lubrication of steel by a series of stable fluorine- and chlorine-substituted methane and ethane derivatives. Several compounds containing fluorine and two or more chlorine atoms per molecule functioned as boundary lubricants to reduce friction and to prevent surface welding and metal transfer.