Report presenting a method for the analytical determination of the natural coupled frequencies and mode shapes of vibrations in the vertical plane of tandem helicopters. That information is then used to calculate the response of the helicopter to applied oscillation forces. Calculated response curves show how the vibrations of the cockpit vary with frequency and method of application of oscillating forces applied at the hubs.

Note presenting a determination of the time-average characteristics of boundary layers over a flat plate in nearly quasi-steady flow. The time averages were found without specifying the plate velocity explicitly except that it is positive and has an average value. Some remarks on the heat-transfer problem are also provided.

Results of an experimental investigation of the structural damping of six full-scale helicopter rotor blades, made to determine the variation of structural damping with materials and methods of construction, are presented. The damping of the blades was determined for the first three flapwise bending modes, first chordwise bending mode, and first torsion mode. The contribution of structural damping to the total damping of the blades is discussed for several aerodynamic conditions in order to point out situations where structural damping is significant.

From Summary: "Values of nondimensional normal component of induced velocity in the lateral plane of a uniformly loaded lifting rotor are given in the form of graphs and tables. The values were computed by use of the Biot-Savart relation using the assumption that the wake vortex distribution consists of a uniform, semi-infinite elliptic cylinder. The necessary auxiliary equations are given so that the graphs or tables of the induced velocity ratios nay be used to estimate numerical values of the normal component of induced velocity and the associated flow angle in the lateral plane of any given rotor or set of laterally disposed rotors."

Note presenting measurements of ignition delays for mixtures of ethane, n-butane, isobutane, hydrogen, or propane with oxygen and nitrogen using a flow system with two experimental procedures. Delays were measured over a range of temperatures for each gas. Results regarding a comparison among fuels and effect of experimental procedure on absolute values of ignition delay are provided.

A wind-tunnel investigation has been made at low speed to determine the effects of vertical fins placed ahead of the vertical tail on the directional stability and damping-in-yaw characteristics of a swept-wing model under steady-state oscillatory conditions. Various sizes of fins were used above and below the fuselage center line. The vertical-tail size also was varied.

From Summary: "Experimental measurements have been made of the zero-lift drag rise at transonic speeds of a family of triangular plan form wings of varying thickness and aspect ratio mounted on a cylindrical body. Together with the transonic similarity parameters, the results of the tests are used to define the range of applicability of the transonic area rule for wings of triangular plan form. The significance of the test results is discussed."

"The rate and area of cloud droplet impingement on several two-dimensional swept and unswept airfoils were obtained experimentally in the NACA Lewis icing tunnel with a dye-tracer technique. Airfoil thickness ratios of 6 to 16 percent; angles of attack from 0 deg to 12 deg, and chord sizes from 13 to 96 inches were included in the study. The data were obtained at 152 knots and are extended to other conditions by dimensionless impingement parameters" (p. 1).

Report presenting an investigation in the helicopter test tower to determine experimentally the effects of compressibility on the hovering performance and blade pitching moments of a helicopter rotor with NACA 63(sub 2)-015 airfoil sections. The results indicated that two-dimensional airfoil-section data provide a reasonable basis for predicting the onset of compressibility losses and that the differences in Mach number for drag divergence between airfoils shown by two-dimensional data are realized in rotor tests.

Note presenting tests made of stiffened cylinders of 2024 aluminum alloy under internal pressure and cyclic torsion. Fatigue cracks that developed in the skin resulted in both gradual and explosive types of failure. Results regarding the 30-inch cylinders, 48-inch cylinders, and effect of the pressurizing medium are provided.

Report presenting results of fatigue-crack-propagation studies conducted during fatigue tests of nine complete wings from C-46 airplanes. Static tests of the wings with fatigue failures are also described. Results regarding fatigue-crack propagation and residual static strength testing are provided.

Note presenting fatigue tests performed on notched and unnotched sheet specimens made of 2024-T3 and 7075-T6 aluminum alloys and of SAE 4130 steel. The steel was tested in two conditions: normalized and heat-treated to a tensile strength of 180 ksi. The primary focus was on the life range from 2 to 10,000 cycles.

Report presenting a discussion of flight-test and analysis methods for some selected helicopter vibration studies. The analytical methods described are based on the determination of the power spectral density of the force and of the response due to the force through use of analog frequency-analysis technique. Results regarding the coupled response with wood blades, coupled response with metal blades, comparison between flight and ground tests, comparison of flight results with theory, suggestions for refined flight-test technique, and natural-vibration measurements are provided.

Report presenting ignition-delay characteristics of approximately 90 fuel-oxidant combinations determined in a modified open-cup apparatus at -40 degrees Fahrenheit. Freezing temperatures of acids were determined as well as viscosities of several fuels at moderate and low temperatures. Results regarding fluid properties of fuels and oxidants at low temperatures, an ignition study of the acid oxidants, an ignition study of fuels, and practical aspects of working with the oxidants and fuels are provided.

Report presenting a study of the use of the incomplete time response to a unit impulse as a device to analyze lightly damped linear systems. The incomplete time response to a unit impulse computed from an incomplete time response and complete input adequately describes a light damped linear system without requiring an estimate and correction.

Report presenting three modifications to the leading-edge region of the NACA 64A010 airfoil section, which were designed and tested two-dimensionally at both low and high subsonic speeds. The modifications increased the low-speed maximum lift coefficient of the symmetrical reference section, largely by increasing the angle of attack at which stall occurred.

An investigation was conducted in order to determine the effectiveness of blowing a jet of air over the flaps of a wing equipped with a 50-percent-chord sliding flap and a 25-percent-chord plain flap in deflecting a propeller slipstream downward for vertical take-off and the results are presented herein. The effects of a leading-edge slat, ground proximity, end plate, and propeller position were also investigated. The tests were conducted in a static-thrust facility at the Langley Aeronautical Laboratory.

Note presenting an investigation of the transfer of heat from a metallic ribbon to water, under transient conditions, for initial water temperatures from 76 to 203 degrees Fahrenheit and average heat-generation rates per square foot of square area of 3, 10, and 20x10(exp 5) Btu per hour per square foot. Results regarding the nucleate boiling region, film boiling region, and critical heat flux are provided.

Tests have been conducted on the Langley helicopter test tower to determine the vertical drag and pressure distributions on flat panels mounted below a helicopter rotor. Calculations of the vertical drag by use of a strip-analysis procedure outlined in the paper and the assumption of a fully contracted wake agreed well with the experimental results over the range from 0.2 to 0.64 rotor radius beneath the plane of zero flapping. The pressure increase caused by the passage of the blade over the panel is a maximum at about the 0.8 radius spanwise station. At this station, the pressure decreases from 10 times the disk loading per blade at 0.05 radius beneath the rotor plane of zero flapping to one-half of the disk loading per blade at 0.64 radius beneath the plane of zero flapping.

The lift and pitching-moment characteristics of a body alone, six triangular wings of various aspect ratios, and the combinations were measured at Mach numbers of 1.50 and 2.02 at a Reynolds number of 5.5 million (based on the body length) for angles of attack up to 5.5 degrees. The total lift and pitching-moment interference were determined and compared with theory. The agreement was found to be good.

Report presenting generalized expressions and charts which depend on the shock Mach number, initial state of the gas, and an enthalpy parameter for the temperature, pressure, density, and flow velocity behind a shock wave.

Report presenting the problem of the three-point body of revolution that has minimum wave drag, based on linearized supersonic-flow theory, which has been solved formally without resorting to slender-body approximations. The evaluation of the source-distribution function, as well as body shape, requires numerical procedures.

Report presenting an initiating system designed using data obtained from full-scale experimental and accidental airplane crashes. It is designed to act rapidly and so that accidental operation is improbable. In order to provide an extra layer of safety for airplanes carrying crash-fire protection, it would be desirable to have a way to restore fuel and oil flow to the engines after the system has ceased functioning.

Report presenting a generalized procedure that permits a rapid determination of the core lengths of crossflow gas-to-gas heat exchangers. Some of the variables that must be prescribed include the inlet states of each fluid, the available pressure drops for each fluid, the required temperature change of one fluid, the fluid heat capacities, and the core configuration.