"A study has been made of the heating requirements for the cyclic de-icing of hollow steel propellers fitted with two types of internal electric heaters. Solutions to the transient-heat-flow equations depicting the cyclic de-icing of propellers were obtained by use of an electrical analogy. The study showed the impracticability of using an internal tubular heater and illustrated the advantages of employing an internal shoe-type heater, which distributes the heat more evenly to the blade surface" (p. 1).

"Measurements of propeller efficiency loss due to ice formation are supplemented by an analysis to establish the magnitude of efficiency losses to be anticipated during flight in icing conditions. The measurements were made during flight in natural icing conditions; whereas the analysis consisted of an investigation of changes in blade-section aerodynamic characteristics caused by ice formation and the resulting propeller efficiency changes. Agreement in the order of magnitude of efficiency losses to be expected is obtained between measured and analytical results" (p. 1).

From Summary: "A Bragg X-ray spectrometer equipped with a volume-sensitive Geiger counter and Soller slits and employing filtered molybdenum Ka radiation was used to obtain a set of diffracted intensity curves as a Punction of angle for supercooled water. Diffracted intensity curves in the temperature region of 21 to -16 C were obtained. The minimum between the two main diffraction peaks deepened continuously with lowering temperature, indicating a gradual change in the internal structure of the water. No discontinuity in this trend was noted at the melting point. The internal structure of supercooled water was concluded to become progressively more ice-like as the temperature is lowered."

"The thermal conductivity of low-density ice has been computed from data obtained in an experimental investigation of the heat transfer and mass transfer by sublimation for an iced surface on a flat plate in a high-velocity tangential air stream. The results are compared with data from several sources on the thermal conductivity of packed snow and solid glaze ice. The results show good agreement with the equations for the thermal conductivity of packed snow as a function of snow density. The agreement of the curves for packed snow near the solid ice regime with the values of thermal conductivity, of ice indicates that the curves are applicable over the entire-ice-density range" (p. 1).

From Summary: "The effects of ice formations on the section lift, drag, and pitching-moment coefficients of an unswept NACA 65A004 airfoil section of 6-foot chord were studied.. The magnitude of the aerodynamic penalties was primarily a function of the shape and size of the ice formation near the leading edge of the airfoil. The exact size and shape of the ice formations were determined photographically and found to be complex functions of the operating and icing conditions."

Note presenting an experimental study of the wet-surface temperature and stream conditions that result in ice-free surfaces for bodies in flight through icing clouds, and the results obtained are compared with values calculated using an analytical method. Two symmetrical airfoil models, one of diamond shape and the other of double-circular-arc contour, were used in the investigation. Results regarding the chordwise variation of pressure distribution, chordwise variation of recovery factor, the diamond airfoil, and circular-arc airfoil are provided.

"A series of test flights was conducted by the U. S. Navy over a 3- year period to evaluate the effects of icing on the operation of the ZPG-2 airship. In supercooled. clouds, ice formed only on the forward edges of small protuberances and wires and presented no serious hazard to operation. Ice accretions of the glaze type which occurred in conditions described as freezing drizzle adversely affected various components to a somewhat greater extent" (p. 1).

A procedure proposed for use in the design of air-heated systems for the continuous prevention of ice formation on airplane components is set forth. Required heat-transfer and air-pressure-loss equations are presented, and methods of selecting appropriate meteorological conditions for flight over specified geographical areas and for the calculation of water-drop-impingement characteristics are suggested. In order to facilitate the design, a simple electrical analogue was devised which solves the complex heat-transfer relationships existing in the thermal-system analysis.

"The problems associated with providing icing protection for the critical components of a typical turbojet transport airplane operating over a range of probable icing conditions are analyzed and discussed. Heating requirements for several thermal methods of protection are evaluated and the airplane performance penalties associated with providing this protection from various energy sources are assessed. The continuous heating requirements for icing protection and the associated airplane performance penalties for the turbojet transport are considerably increased over those associated with lower-speed aircraft" (p. 1).

"The effect of modifying the gas passage of hollow metal airfoils by the addition of internal fins and partitions was experimentally investigated and comparisons were made among a basic unfinned airfoil section and two airfoil designs having metal fins attached at the leading edge of the internal gas passage. An analysis considering the effects of heat conduction in the airfoil metal was made to determine the internal modification effectiveness that may be obtained in gas-heated components, such as turbojet-inlet guide vanes, support struts, hollow propeller blades, and thin wings" (p. 1).

"A study has been made of the heat requirement for the cyclic de-icing of hollow steel propellers fitted with external blade heating shoes. Solutions to the equations for the heat flow in cyclic heating of propellers were obtained, using an electrical analogy. The study showed how the energy requirement for propeller de-icing with existing blade shoes could be decreased, and illustrated the effect of blade-shoe design on the energy requirement. It was demonstrated, for example, that by increasing the heating intensity and decreasing the heating period from those currently used the energy requirement could be decreased in the order of 60 percent" (p. 1).

Note presenting an investigation of the effects on porous-material permeability characteristics of the absolute pressure level, choking of the flow, bending the material, and other factors. Experiments showed permeability characteristics to be appreciably affected by absolute pressure level, flow choking, and thickness of the material. Results regarding testing with wire cloth and sintered metal are provided.

Note presenting measurements made of the resistance to air flow of a series of perforated metal sheets with open areas ranging from less than 1 percent up to 41 percent. The results showed that the permeability of a perforated sheet is governed principally by its open-area ratio. The number of holes per square inch, the sheet thickness, and the shape of the individual holes had little or no effect on permeability.

Note presenting a low-turbulence wind-tunnel investigation of an NACA 64A010 airfoil section with continuous suction through its porous surfaces to determine its ability to maintain extensive laminar flow behind finite surface disturbances and at angles of attack other than 0 degrees. Generally, application of area suction permitted only a small increase in the size of a finite disturbance required to cause premature boundary-layer transition as compared with the nonsuction airfoil.

Note presenting an investigation to determine the combined effects of surface cooling, pressure gradients, nose blunting, and surface finish on boundary-layer transition. Data were obtained for various body shapes at a Mach number of 3.12 and Reynolds numbers per foot as high as 15 x 10(exp 6). Results regarding the effect of extreme cooling, effect of pressure gradient, effect of blunting, effect of surface roughness, and roughness as cause of transition reversal are provided.

Note presenting a simplified method for determination of the critical height of three-dimensional roughness particles required to promote premature transition of a laminar boundary layer on models of airplanes or airplane components in a wind tunnel with zero heat transfer. The method has been applied to various types of configurations in several wind-tunnel investigations.

Note presenting an investigation at low speed of the two-dimensional characteristics of a 10.51-percent-thick symmetric airfoil with area suction for boundary-layer control near the leading edge. The lift and suction-flow characteristics were determined with different porous surfaces consisting of perforated plates and sintered steel for various suction velocity distributions obtained by varying the permeability arrangement.

"Measurements were made of the resistance to air flow of commercially available porous materials. Three general types of porous media were tested - granular (sintered materials), fibrous (felt cloths and filter papers), and perforated. The flow-resistance characteristics of the porous materials tested are presented in a form intended to assist in the selection of materials for applications to boundary-layer control using area suction" (p. 1).

From Summary: "A flight investigation has been made of the practical problems associated with the use of porous-leading-edge suction. The wing leading edge of the test airplane was porous over approximately 83 percent of the span and the first 8 percent of the chord on the upper surface. Various other extents of suction area within these limits were also tested."

"Measurements were made of the resistance of fibrous-glass compacts to normal air flow. The flow resistance was related to the thickness and density. As a porous material for boundary-layer-control applications using area suction, the fibrous-glass compact could be made to any desired thickness and permeability and sandwiched between perforated rigid surfaces" (p. 1).

Report presenting an analysis of the sound-pressure field of a rotating propeller in forward flight in free space by replacing the normal-pressure distribution over the propeller associated with thrust and torque by a distribution of acoustic pressure doublets acting at the propeller disk. The result is presented for a moving and a fixed observer.

Calculations have been made for the icing limit of a diamond airfoil at zero angle of attack in terms of the stream Mach number, stream temperature, and pressure altitude. The icing limit is defined as a wetted-surface temperature of 320 F and is related to the stream conditions by the method of Hardy. The results show that the point most likely to ice on the airfoil lies immediately behind the shoulder and is subject to possible icing at Mach numbers as high as 1.4.

"The effects of primary and runback icing and frost formations on the drag of an 8-foot-chord NACA 651-212 airfoil section were investigated over a range of angles of attack from 20 to 80 and airspeeds up to 260 miles per hour for icing conditions with liquid-water contents ranging from 0.25 to 1.4 grams per cubic meter and datum air temperatures of -30 to 30 F. The results showed that glaze-ice formations, either primary or runback, on the upper surface near the leading edge of the airfoil caused large and rapid increases in drag, especially at datum air temperatures approaching 32 F and in the presence of high rates of water catch" (p. 1).

"An empirical relation has been obtained by which the change in drag coefficient caused by ice formations on an unswept NACA 65A004 airfoil section can be determined from the following icing and operating conditions: icing time, airspeed, air total temperature, liquid-water content, cloud droplet impingement efficiencies, airfoil chord length, and angles of attack. The correlation was obtained by use of measured ice heights and ice angles. These measurements were obtained from a variety of ice formations, which were carefully photographed, cross-sectioned, and weighed" (p. 1).