Note presenting an investigation to determine the fatigue-strength values for 24S-T aluminum alloy when subjected to various ratios of biaxial stresses. The stresses considered were both tensile. The results indicated that uniaxial fatigue-strength values in the longitudinal direction cannot be used to predict the fatigue strength, and that biaxial fatigue strength may be as low as 50 percent of the uniaxial fatigue strength.

Report presenting an investigation of pitching moments and center-of-pressure locations obtained from a landing investigation in smooth water of a conventional flying boat as compared to values predicted by general hydrodynamic impact theory. Landings were generally moderate and covered as wide a range of trim and velocities as practical. Results regarding the center of pressure and pitching moments are provided.

Note presenting a theoretical solution for the problem of the compressive buckling of flat rectangular Metalite type sandwich plates with simply supported loaded edges and clamped unloaded edges. The solution is based on the general small-deflection theory for flat sandwich plates developed in a previous report. Results regarding stability orientation and buckling curves, comparison with approximate solution, correction for plasticity, and comparison of theory and experiment are provided.

"A theoretical solution is presented for the critical axial-compressive stress of a simply supported curved rectangular panel having a central longitudinal stiffener offering no torsional restraint. The results are presented in the form of computed curves and tables. Because a panel of moderate or large curvature buckles in compression at a stress lower than the theoretical value, a method is suggested to aid in determining the critical stress for use in design" (p. 1).

Report presenting a study of the factors involved in the design of total-temperature probes for use at supersonic speeds as applied to the design of an instrument to be used in wind-tunnel calibrations. Tests of the probe showed that the calibration factor required in the conversion of the measured temperature to the true total temperature was 0.992 for a range of Mach numbers.

Note presenting an investigation conducted to determine the oxidation characteristics of molybdenum disulfide and to determine the effect of such oxidation on its role as a solid-film lubricant. A coating of molybdenum disulfide serving as a high-temperature solid-film lubricant maintained low coefficient-of-friction values during its oxidation as long as an effective subfilm of the molybdenum disulfide remained.

Contains derivations, based on a simplified theory, of approximate relations for low-speed stability derivatives of swept wings. Method accounts for the effects and, in most cases, taper ratio. Charts, based on the derived relations, are presented for the stability derivatives of untapered swept wings. Calculated values of the derivatives are compared with experimental results.

Note presenting an investigation to determine the yield strength, ultimate strength, ductility, and plastic stress-stain relations for 24S-T aluminum alloy when subjected to biaxial stresses. The data were interpreted by a generalized St. Venant theory in an attempt to predict the biaxial stress-strain relations in terms of the uniaxial tensile stress-strain relations. Stress-strain data were also obtained from flat control specimens cut from tubular specimens and compared with tension test data obtained from tubular specimens.

"By consideration of antisymmetrical, as well as symmetrical, buckling configurations, the theoretical shear buckling stresses of clamped rectangular flat plates are evaluated more correctly than in previous work. The results given, which represent the average of upper- and lower-limit solutions obtained b the Lagrangian multiplier method, are within 1 1/4 percen of true buckling stresses" (p. 1).

Note presenting a theoretical analysis, based on the linearized equation for supersonic flow, of the characteristics of triangular-tip control surfaces on thin triangular wings. The ratio of lift effectiveness to the hinge moment which resulted from control deflection was equal to the corresponding two-dimensional ratio for the same ratio of flap area to wing area.

Report presenting a study of a family of diffusing scrolls designed for use with a mixed-flow impeller and a small-diameter vaneless diffuser. Results regarding a comparison of performance of scrolls and comparison of performance of various compressor configurations are provided.

"An analytical investigation is made of the effect of shear lag on the bending vibration of wings that are designed essentially as shallow box beams, and a procedure is outlined for incorporating this effect in the determination of bending modes and frequencies. Numerical examples show that shear-lag action in a box beam can have a large influence on its vibration characteristics. The calculations indicate that even though only a small shear-lag action may be observed in a simple static deflection test of the beam, reductions in the second and higher-mode frequencies may be relatively large" (p. 1).

"The effects of outdoor weathering for 2 years and of an accelerated weathering test on the weight, dimensional stability, and flexural properties of selected reinforced plastics were investigated. The results of all tests, both in this report and the previous report (NACA TN No. 1240), indicate that none of the laboratory aging tests correlated with outdoor weathering with respect to all properties and all materials" (p. 1).

Note presenting an investigation in the 15-foot free-spinning tunnel on a research model representative of a present-day trainer or a four-place cabin monoplane, with varied moments of inertia. The tests were made for eight different wing arrangements and four different tail arrangements, including a twin tail. The results of variation of moments of inertia indicated that, within the range of the present tests, uniformly decreasing the moments of inertia led to steeper spins, higher angular and vertical velocities, and faster recoveries.

"A flight investigation in natural icing conditions was conducted by the NACA to determine the effect of ice accretion on airplane performance. The maximum loss in propeller efficiency encountered due to ice formation on the propeller blades was 19 percent. During 87 percent of the propeller icing encounters, losses of 10 percent or less were observed" (p. 1).

Report presenting an investigation to obtain some information concerning the nature and magnitude of the errors involved in computing the landing stresses for large and relatively flexible aircraft when several simplifying assumptions are made. Results regarding the exact solution and approximate solutions are provided. The results suggest that a satisfactory treatment of the landing problem may possibly be obtained from an analysis which assumes that, in landing, the aircraft is an elastic structure subject to the forces or accelerations found in a drop test in which a rigid mass is used.

Note presenting results of an investigation made to determine measurements of stability, controllability, and stalling characteristics of five light airplanes. Results regarding the longitudinal stability and control characteristics, lateral stability and control characteristics, stalling characteristics, spinning characteristics, and effect of slots on flying qualities are provided.

Note presenting hinge-moment, lift, and drag measurements made on an approximately 0.178-chord-thick NACA 6-series-type airfoil section equipped with sealed internally balanced 0.20-chord ailerons and with a 0.05-chord tab. The purpose of the investigation was to obtain the effects of aileron contour and internal-balance chord on the aileron section hinge-moment characteristics and to determine the tab effectiveness in reducing the aileron section hinge moments.

From Summary: "An investigation to determine the effectiveness of icing protection afforded by air-heating hollow steel unpartitioned propeller blades has been conducted In the NACA Cleveland icing research tunnel. The propeller used was a production model modified with blade shank and tip openings to permit internal passage of heated air. Blade-surface and heated-air temperatures were obtained and photographic observations of Ice formations were made with variations In icing intensity and heating rate to the blades. For the conditions of Icing to which the propeller was subjected, it was found that adequate ice protection was afforded with a heating rate of 40 1 000 Btu per hour per blade."

From Summary: "The icing protection afforded an internal air-heated propeller blade by radial partitioning at 50-percent chord to confine the heated air to the forward half of the blade was determined in the NACA Cleveland icing research tunnel. A modified production-model hollow steel propeller, was used for the investigation. Temperatures of the blade surfaces for several heating rates were measured under various tunnel icing conditions. Photographic observations of ice formations on blade surfaces and blade heat-exchanger effectiveness were obtained."

From Summary: "The icing protection obtained from an internally air-heated propeller blade partitioned to confine the heated air forward of 25-percent chord was investigated in the NACA Cleveland icing research tunnel. A production-model hollow steel propeller was modified with an Internal radial partition at 25-percent chord and with shank and tip openings to admit and exhaust the heated air. Temperatures were measured on the blade surfaces and in the heated-air system during tunnel icing conditions. Heat-exchanger effectiveness and photographs of Ice formations on the blades were obtained."

Note presenting an investigation to determine the order of magnitude of the important mechanical properties of honeycomb-like structures. Some of the characteristics improved by the structure include the rigidity, shear stress at proportional limit, and shear strength as compared to balsa wood. Some of the negative characteristics include the modulus of electricity, compressive stress at proportional limit, compressive strength, and tensile strength.

"New application of the Lagrangian multiplier method to stability analysis are described by means of elementary examples. The use of the method in analyzing the stability of (a) clamped plates in shear and (b) plate-stiffener combinations is demonstrated. A detailed analysis for finding upper and lower limits to critical stresses of clamped rectangular plates is presented in the appendix" (p. 1).

Report presenting the analysis of the stability derivatives of low-aspect-ratio triangular wings at subsonic and supersonic speeds, which is extended to apply to triangular wings having large vertex angles and traveling at supersonic speeds.