A revised and expanded version of NNES-DC-1. The liquid thermal diffusion method for the separation of isotopes is described. The discussion includes the experimental aspects of the method, description of equipment, and the theoretical aspects of the process as applied to the design, development, and performance criteria. A short history of the liquid thermal diffusion method from 1940 to 1945 is preserted along; with a survey of relevant literature prior to 1940. The remainder of the report is concerned with theoretical aspects. (J.R.D.)

Report presenting testing in high-speed flight with a fighter airplane to determine the effect of chordwise pressure distribution resulting from a minor modification in the contour of the wing upper surface. A faired bulge was added to the contour and chordwise pressure distributions were obtained on the original and modified contours.

Note presenting symbols and definitions of various airspeed terms that have been adopted as standard by the NACA Subcommittee on Aircraft Structural Design. the equations, charts, and tables required in the evaluation of true airspeed, calibrated airspeed, equivalent airspeed, impact and dynamic pressures, and Mach and Reynolds numbers have been compiled.

Note presenting tests at high speeds to determine the drag of models, simulating propeller shanks, in the form of a circular cylinder and three airfoils with the rear 25 percent chord cut off. The results indicated that the drag of the airfoils was lower than that of the cylinder over the Mach number range investigated.

Abstract: "The half-life of polonium has been measured by a calorimetric method using samples several thousand times larger than have been previously available. The value is found to be 138.3 +/- 0.1% days."

Note presenting a well-known method of generating stream functions of an incompressible fluid flow, which involves taking the imaginary part of an analytic function of a complex variable. This paper is specifically devoted to a detailed discussion of performing computations related to obtaining flow patterns of compressible fluid from analytic functions of a compressible fluid. An example is also provided to illustrate the method.

"Knock-limited performance data were obtained for three fuels on an R-1830-75 engine in a B-24D airplane at engine speeds of 1800, 2250, and 2600 rpm, a spark advance of 25 degrees B.T.C., and carburetor-air temperatures of 85 F for 1800 and 2250 rpm and 100 F for 2600 rpm. The test fuels were a blend of 80 percent 28-R plus 20 percent triptane (leaded to 4.5 ml TEL/gal), a blend of 80 percent 28-R plus 15 percent toluene (leaded to 4.5 ml TEL / gal), and 28-R fuel. The knock-limited manifold pressure of the toluene blend depreciated more in the lean region than the triptane blend or 28-R fuel" (p. 1).

"When flying in a turn or pulling out of a dive, the airscrew exerts a gyroscopic moment on the aircraft, In the case of airscrews with three or more blades, arranged symmetrically, the value of the gyroscopic moment is J(sub x) omega(sub x) omega(sub y), where J(sub x) denotes the axial moment of inertia about the axis of rotation of the airscrew, omega(sub x) the angular upeed of the airscrew about its axis, and omega (sub Y) the rotary speed of the whole aircraft about an axis parallel to the plane of the airscrew (e.g., when pulling up, the transverse axis of the aircraft). The gyroscopic moment then tends to rotate the aircraft about an axis perpendicular to those of the two angular speeds and, in the came of airscrews with three or more blades, is constant during a revolution of the airscrew" (p. 1).

"The present report deals with the problems involved in the greater utilization and development of aircraft engine materials, and specifically; piston materials, cylinder heads, exhaust valves, and exhaust gas turbine blading. The blades of the exhaust gas turbine are likely to be the highest stressed components of modern power plants from a thermal-mechanical and chemical standpoint, even though the requirements on exhaust valves of engines with gasoline injection are in general no less stringent. For the fire plate in Diesel engines the specifications for mechanical strength and design are not so stringent, and the question of heat resistance, which under these circumstances is easier obtainable, predominates" (p. 1).

The following report provides information and results of an investigation on heavy mineral concentrates available in the placer deposits of North Carolina during the summer of 1946.

The following report describes the methods of chemical conversion of uranium fluoride to uranium trioxide.

Note presenting a study of the altered surface layers found on nitrided-steel piston rings run in nitrided-steel cylinder barrels in order to determine the physical and chemical characteristics of the altered layers and the mechanism by which the coating layers were formed. An electron and a light microscope were used to study different aspects of the materials.

None

"An extensive series of tests were conducted on riveted joints to determine the effect of rivet size and rivet pitch on the fatigue lift of joints subjected to "prying" (combined tensile and bending) loads. For each sheet thickness tested, there appeared to be a value of the ratio of rivet pitch to rivet diameter that would ensure a near maximum of the ratio of fatigue strength to static ultimate strength for the joint" (p. 1).

:Spin tests have been performed in the Langley 20-foot free-spinning tunnel on a 1/18-scale model of the Fairchild XNQ-1 airplane. The spin and recovery characteristics of the model were determined for the normal gross-weight loading and for two variations from this loading - center of gravity moved rearward and relative mass distribution increased along the fuselage. These tests were performed for two vertical-tail plan forms. The investigation also included simulated pilot-escape tests and rudder-force tests" (p. 1).

From abstract: "A sensitive method for measuring the intensity of weak neutron sources by measuring induced Mn56 beta activity after concentration by a Szilard-Chalmers process has been developed. The practical detection efficiency for Ra-Be neutron is 7.8%; the procedure is capable of detecting a neutron intensity of about one neutron per second."

"The purpose of the present report is to review briefly the geology of the Rustler Springs district, describe the occurrence of some of the acidic sulphur earth deposits...and discuss some of the economic aspects involved in production of mineral fertilizer from these deposits" (p. 5).

"The present investigation was intended to ascertain how far a tail unit is subject to disturbance by the jet of a propulsion unit. The parameters upon which this disturbing influence depends, and the values it reaches, had to be determined" (p. 1).

Note presenting a system for calculating the physical properties of supersonic rotational flow with axial symmetry and supersonic rotational flow in a two-dimensional field as determined by use of the characteristics method. Practical use of the system is based on a step-by-step procedure that requires long numerical calculations. Some applications were made to determine the external and internal flow on bodies of revolution with axial symmetry.

From Introduction: "Performance results of the tail-pipe burning investigation on the TG-180 turbojet engine and a comparison of experimental results with theoretical calculations are presented."

An investigation was conducted to determine the effects of three design modifications of the original NACA injection impeller on the performance of an R-3350 engine. Different methods of injecting the fuel into the impeller air stream were studied and evaluated from the individual cylinder fuel-air ratios and the resulting cylinder temperatures. Each impeller was tested for a range of engine powers normally used in flight operation. The relatively simple design of the original injection impeller produced approximately the same mixture- and temperature-distribution characteristics as the modified impellers of more complex design. None of the modifications appreciably affected the manifold pressure, the combustion-air flow, nor the throttle angle required to maintain a given engine power,.

Abstract: "This report includes details of the procedure along with the die and equipment descriptions for preparing tungsten copper alloy pieces."

Note presenting a theoretical investigation undertaken to evaluate the effect of small deviations from flatness on the behavior of simply supported square plates under compression, it being assumed that the proportional limit is not exceeded. Results regarding the growth of buckles with increase in load, effective width of plate, experimentally defined buckling or critical stress, critical stress and postbuckling behavior of the plate, and the Southwell plot method of predicting theoretical critical stress are provided.

Annual report from the John Sealy Blood Bank, with data regarding donors, transfusions, and other relevant information.