Bulletin presenting an investigation of the effects of various camouflage paints and painting procedures on the drag characteristics of a 60-inch-chord low-drag airfoil in the NACA two-dimensional low-turbulence pressure tunnel.

Report presenting an investigation of the effectiveness of suction slots as a means of extending the laminar boundary layer in flight at high Reynolds numbers on an NACA 35-215 airfoil. The results showed that, with a slot spacing of about 5 percent of the chord, the laminar boundary layer could be maintained to or slightly beyond 45 percent of the chord.

Report details the methods of determining the heat-transfer rate, pressure drop, and drag power of high-altitude radiators. Performance charts are provided for a wide range of design variables.

Report discussing tests on the N9M-2 airplane to evaluate the airplane efficiency factor and to investigate the characteristics of the aeroboost in the elevon control system. The efficiency factor compared reasonably well to conventional airplanes and the aeroboost system and valve-chatter tests were satisfactory.

Report discussing testing to check the improvement of 3 or 4 miles per hour in the maximum speed of the P-51B airplane as a result of sealing the wing-gun access doors and flap-spar lightening holes. Large variations in speed were observed during testing, so additional testing and analysis was carried out to determine the effects of various factors that were suspected of contributing to the inconsistency of the plane's performance.

From Summary: "This paper deals with the single problem if circular shell-supported frames subjected to concentrated loadings. A mathematical attack is developed and presented in the form of nondimensional-coefficient curves."

Report presenting an investigation made of the flow downstream from a two-dimensional grid, formed of parallel rods. The two-dimensional character of the flow was insured by end plates normal to the rods and covering the entire flow field. The nature of the flow was determined primarily by means of total-head measurements.

Report presenting testing of fifty-eight lightened and five unlightened aluminum-alloy channels as simply supported beams in pure or simple bending produced by loads parallel to the plane of symmetry, and fifty-three lightened and four unlightened aluminum-alloy channels with loads parallel to the back. Four types of testing occurred with various types of support and loading.

Note presenting a least-squares procedure adapted to numerical calculation for the approximate solution of the Prandtl lifting-line equation. Sufficient data are tabulated to permit a solution of the equation by purely numerical methods for an arbitrary symmetrical variation of the chord and the angle of attack.

Report presenting an investigation of the shape of stress-strain curve for a material, especially when the material is subjected to compression, which may cause materials to become unstable at stresses beyond the elastic range. The ratio of stresses to effective modulus is explored in equation form.

Note presenting an effective value of Poisson's ratio for 18:8 Cr-Ni steel computed from values of tensile and torsional moduli of elasticity obtianed in earlier investigations by use of an appropriate formula.

"An empirical equation has been developed that gives the approximate amount of ovalization for tubes under bending loads. Tests were made on tubes in the d/t range from 6 to 14, the latter d/t ratio being in the normal landing gear range. Within the range of the series of tests conducted, the increase in ovalization due to a compression load in combination with a bending load was very small" (p. 1).

From Summary: "The various types of hydrodynamic instability - including porpoising, skipping, and yawing - that may be encountered during take-off or landing of a flying boat are described and the piloting technique required for efficient take-offs and landings is discussed. Suggestions are made for assisting a pilot to become familiar with the take-off and landing qualities of a flying boat that is new to him."

Report presenting a survey of the technical information contained in the literature on the subject of lubrication, friction, and wear of aircraft engine piston rings.

Note presenting a torsion test to failure for a monocoque box of 24S-T aluminum alloy. The box had a rectangular section and was reinforced by Z-stringers, antirolls, bulkheads, and corner posts.

Report presenting experiments with a flat reinforced sheet model, the longitudinals of which were loaded axially. Two groups of sheets, one with one panel and one with two panels, were cut out and the stress distributions in stringers and sheet was measured with electric strain gages.

Report presenting calibrations in axial tension over the strain range from 0 to 0.0024 are presented for 15 types of single element multistrand wire strain gages. The majority of the gages showed significant differences between the calibration factors for strain increasing and strain decreasing. Improvement in gage performance after preloading was apparent in most cases.

From Summary: "A unit oil system and oil-weighing device designed for laboratory engine tests to permit the remote measurement of oil-flow rate and oil consumption is described. The system regulates the oil pressure and temperature and is closed to make possible the accurate measurement of blow-by gas. The oil is weighed by a self-contained diaphragm and pilot-valve assembly, which uses compressed air as the transmitting medium. Several of those unit systems have given satisfactory service for more than a year."

Note presenting axial fatigue tests made by the resonance method on 10 specimens from airplane wing beams. The specimens contained several types of stress raiser, such as rivets, holes, fittings, splices, reinforcing plates, and so forth. The results show a greater fatigue stress concentration factor for the wing-beam specimens than for drilled coupons machined from the flanges or for parallel strip coupons containing idle rivets.

"A systematic account is given in part I of the use of dimensional analysis in constructing similarity conditions for models and structures. The analysis covers large deflections, buckling, plastic behavior, and materials with nonlinear stress-strain characteristics, as well as the simpler structural problems" (p. 1).

Note presenting an investigation of several laminated glass windshields to determine their suitability for use in airplanes with pressurized cabins. The various constructions of the extended portions of the windshields which serve for mounting purposes included plastic alone, plastic and one sheet of glass extended, plastic extension reinforced with an aluminum strip, and plastic extension reinforced with a steel strip. The results indicated that the laminated windshields with plastic-mounting extensions reinforced by aluminum or steel were resistant to creep and bursting at pressures of the order that will be encountered in service.

Report presenting a note in two parts regarding simplified truss stability criteria. The first part covers the development of simplified criteria for the stability of planar pin-jointed trusses against buckling in the plane of the truss. The second part constitutes a report on tests carried out to verify the validity of the criteria developed in part one.

Report presenting experiments with both curved and flat reinforced sheet models, the longitudinals of which were loaded axially. The stress distribution in longitudinals and sheet was measured with electric strain gages.

From Summary: "Charts are presented for rapidly determining the principal strains and stresses, the maximum shear strain and stress, and the orientation of principal axes from data on 45 degree strain rosettes. The charts may be used for analyzing the conventional data consisting of strains measured along three gage lines 45 degrees apart, but their application is more direct if the rosette data are obtained by means of special circuits that require the use of four gages 45 degrees apart."