Report issued by the U.S. Bureau of Mines on laboratory testing developed to measure the slacking of coals. Testing methods and results are presented. This report includes tables and graphs.

Study of the bending stress in smooth skin, aluminum alloy, true monocoque fuselage sections of varying ratio of diameter to thickness.

The tests herein reported were conducted by the NACA to determine the effect of the angular position of the section of a ring cowling on the speed of an airplane having a radial air-cooled engine.

The tests, conducted at the Guggenheim Aeronautical Laboratory of Stanford University, to investigate the phenomenon of separation in the air flow past geometric shapes are described in this report.

In this mathematical investigation, made in collaboration with Dr. Wilhelm Schmidt, we interpret the temporary change (due to some disturbance) in the quantities which define the position of the airplane while in a flat spin. We further examine the effect of this change, of the means resorted to to produce the disturbance, and thus reveal the expedients available for recovering from a flat spin.

This paper presents a relative determination of the wrinkling of a plate wall beam with variable number of supports and methods of attachment. The discussion is based entirely on tests with extensometer readings and number of wrinkles, with complete web and with cutout sections. The author notes that the number of corrugations increase with added stress, keeping constant edge spacing.

"The effect of a slotted wing depends essentially on the fact that a secondary flow branches off from the main flow and passes to the suction side of the profile. It is thus possible to delay the separation greatly and increase the lift. The practical aspect of the slotted wing is less known in Germany, especially the results obtained during the last three years since the introduction of the 'auto control slot'" (p. 1).

"For some time the D.V.L. has been investigating the question of applicability of Handley Page slotted wings to German airplanes. Comparitive gliding tests were made with open and closed slots on an Albatros L 75 airplane equipped with the Handley Page "auto control slots." This investigation served to determine the effect of the auto control slot on the properties and performances of airplanes at large angles of attack. The most important problems were whether the angle of glide at small angles of attack can be increased by the adoption of the auto control slot and, in particular, as to whether the flight characteristics at large angles of attack are improved thereby and equilibrium in gliding flight is guaranteed even at larger than ordinary angles of attack" (p. 1).

The method of riveting by forming the closing head under increasing pressure or by a series of hammer blows is investigated. The question as to the best edge distance, i.e. that distance from the rivet center to the plate edge below which it is unadvisable to go and, at the same time useless to go beyond, was examined. The slippage of plates which occurs under the effect of a certain stress, does not completely disappear on unloading.

"The penetration and cone-angle of fuel sprays from open nozzles were recorded with the NACA Spray Photography Equipment. The results show that for injection systems in which the rate of pressure rise at the discharge orifice is high, open nozzles give spray-tip velocities and penetrations which compare favorably with those of closed nozzles. The spray cone-angle was the same for all tests, although open nozzles having different orifice diameters were used, and one nozzle was used both as an open and as a closed nozzle" (p. 1).

Circular describing the Vickers Viastra I, which is a commercial high-wing all-metal semicantilever monoplane. Details of the structure, fuselage, wings, fuel tanks, landing gear, tail, cabin, cockpit, characteristics, drawings, and photographs are provided.

This report describes tests of 10 full-scale metal propellers of several thickness ratios at various tip speeds up to 1,350 feet per second. The results indicate no loss of efficiency up to tip speeds of approximately 1,000 feet per second. Above this tip speed the loss is at a rate of about 10 per cent per 100 feet per second increase relative to the efficiency at the lower speeds for propellers of pitch diameter ratios 0.3 to 0.4. Propellers having sections of small thickness ratio can be run at slightly higher speeds than thick ones before beginning to lose efficiency.

Report containing tables detailing cost of mining accidents in Washington state in comparison with other states.

Report discussing both laboratory and weather-exposure corrosion tests showed conclusively that the protection afforded by aluminum pigmented spar varnish coatings applied to previously anodized aluminum surfaces was greatly superior to that afforded by the same coatings applied to surfaces which had simply been cleaned free from grease and not anodized.

From Summary: "This paper presents the results of tests of six commonly used airfoils: the CYH, the N-22, the C-72, the Boeing 106, and the Gottingen 398. The lifts, drags, and pitching moments of the airfoils were measured through a large range of positive and negative angles of attack. The tests were made in the variable density wind tunnel of the National Advisory Committee for Aeronautics at a large Boeing 106, and the Gottingen 398 airfoils, the negative maximum lift coefficients were found to be approximately half the positive; but for the M-6 and the CYH, which have less effective values were, respectively, 0.8 and 0.6 of the positive values."

This note contains the results of flight test conducted by the National Advisory Committee for Aeronautics on a low-wing monoplane equipped with leading-edge slots extending over the entire wing and flaps extending only to the ailerons, to find their effect on the lift and drag characteristics of the airplane. Curves are given showing the lift and drag characteristics of the airplane for the following conditions of the slots and flaps neutral; slots closed and flaps down; and slots open and flaps down. In addition, the high and low speed in level flight and the climbing characteristics are given. The results show that the slots used alone increase the maximum lift coefficient 54 per cent; the flaps alone increase it 38 per cent; and the slots and flaps in combination decrease the landing speed from 60 to 43 m.p.h.; increase the speed range of the airplane 40 per cent; and increase the glide angle at landing speed 4.2 degrees.

Circular describing the Guillemin J.G. 10, which is a two-place touring low-wing monoplane. Details of the wing, fuselage, engine, characteristics, drawings, and photographs are provided.

A process for the measurement of the visibility of airplanes from the pilot's cockpit is developed. The apparatus necessary for the measurements was suitably constructed and measurements of the fields of vision were made with it. The visibilities of six airplanes of different types of construction and use were measured, as well as the visibility of an automobile for comparison. An attempt was made to establish minimum visibility requirements and to express the excellence of visibility by means of a numerical coefficient.

To summarize, the experiments with balloons, sailplanes and light airplanes conducted thus far, reveal the vertical velocities of the air to be primarily dependent on the vertical temperature distribution. Stable stratifications result in up-and-down currents forced by the contour of the ground, which are readily recognized in flight and, if need be, may be avoided.

This report examines various aspects of seaplane construction; namely, stability, propulsion, water-tight bulkheads, fire protection, and construction.

"This report presents the results of tests conducted at the Langley Memorial Aeronautical Laboratory, Langley Field, Va., to determine some of the characteristics of the fuel sprays obtained from an 0.008-inch and a 0.020-inch open nozzle when injection pressures from 100 to 500 pounds per square inch were used. Fuel oil and gasoline were injected into air at densities of atmospheric land 0.325 pound per cubic foot. It was found that the penetration rate at these low pressures was about the same as the rate obtained with higher pressures. Spray cone-angles were small and individual oil drops were visible in all the sprays. Gasoline and fuel oil sprays had similar characteristics" (p. 1).

Equations are presented for two and three dimensional strut systems along with tables of equations.

A report on zinc and its alloys.

Report issued by the Bureau of Standards discussing world production of zinc and zinc alloys. History, metallurgy, and structural properties of zinc are presented. This report includes tables, illustrations, and photographs.