Report presenting information about a series of modifications incorporated into light airplanes to increase safety, including decreasing the wing incidence, increasing the wing washout, increasing the area and aspect ratio of the horizontal and vertical tails, moving the elevators out of propeller slipstreams, depressing the thrust axis, and limiting the rudder travel. The new inherent safety characteristics and effects on the airplane's performance are provided.

"Charts are presented for the analysis of the stability under compression of simply supported rectangular plates with one, two, three, and an infinite number of identical equally spaced longitudinal stiffeners that have zero torsional stiffness" (p. 1).

Report in two parts: one examines the boundary conditions for an open wind tunnel with special references to the effects of the closed entrance and exit sections, while the other derives solutions of four types of two-dimensional open tunnels, including one in which the pressures on the two free surfaces are not equal.

Note presenting the method of numerical integration for calculation of beam deflection in matrix form to give it the advantages which are inherent in an influence-coefficient method. Examples are presented to show that the use of weighted matrices reduces the calculation time required to obtain a desired degree of accuracy.

Report presenting a series of tensile-strength and shear-strength tests made on age-hardened 17S-T rivets machine-countersunk in 75S-T sheets. The results of the tests indicated that the joints can be made satisfactorily with regard to both flushness and strength if the ratio of buck to diameter is kept to a certain value.

"A method for determining the streamwise flow pattern of a nonviscous incompressible fluid about an oblique airfoil from the corresponding flow pattern about the airfoil in normal position is presented and illustrated in two examples. The method can be extended to account approximately for compressibility effects by applying the Prandtl-Glauert correction factor to the flow pattern that is normal to the leading edge of the airfoil. The method is expected to be useful in determining the shape of a fuselage or nacelle having a minimum of interference with the flow over a swept-back wing" (p. 1).

Report of an investigation of the effect of forebody warp on the hydrodynamic qualities of a hypothetical flying boat with a hull length-beam ratio of 15 in smooth water and in waves. Warping the forebody planing bottom was found to appreciably increase the range of stable trim between the lower and upper trim limits of stability, although the center-of-gravity limits of stability were reduced.

"The experimental results are presented for a part of an investigation of the compressive strength of 75S-T6 aluminum-alloy flat panels with longitudinal extruded Z-section stiffeners. This part of the investigation is concerned with panels in which the ratio of the thickness of the stiffener material to the skin material varies from 0.4 to 1.0 and the ratio of stiffener spacing to skin thickness varies from 15 to 40" (p. 1).

Note presenting results of strain surveys around four reinforced circular cut-outs successively made in an axially loaded skin-stringer tension panel. Curves are presented which show the distribution of stringer and shear stresses in the panel and bending stresses in the reinforcing rings.

Note presenting a frequency-response method for determining the critical control-gearing and hunting oscillations of airplanes with automatic pilots. The method is graphical and has several advantages over the standard numerical procedure based on Routh's discriminant. Several examples are worked out to illustrate the application of the frequency-response method in determining the effect of automatic-pilot lag or lead on critical control gearing and in determining the amplitude and frequency of hunting.

Note presenting an investigation to determine the effect of automatic stabilization on the lateral oscillatory stability of a hypothetical supersonic airplane. The investigation included an autopilot sensitive to either the yawing or rolling angular velocity. The results of the investigation indicated that all the automatic pilots improved the stability of the original unstable short-period oscillation.

Note presenting a survey that has been made of the various systems of equations which have been given in the literature for the analysis of small deflections of thin elastic shell. A new system of equations has been derived for the analysis of shells, which includes the effects of transverse shear and normal stresses.

Report presenting a method for the calculation of flutter speed of a uniform wing carrying an arbitrarily placed concentrated mass. The method involves the solution of the differential equations of motion of the wing at flutter speed and does not require the assumption of specific normal modes of vibration.

Report presenting combined force and wake survey tests on three-blade model propellers in order to determine the effects of blade-width distribution on constant-speed efficiency characteristics. The most important result is the demonstration that blade-width distribution has a marked influence on the constant-speed efficiency characteristics of propellers.

"A general description of the field operations of the U.S. Weather Bureau thunderstorm project conducted in the vicinity of Orlando, Florida during the summer month of 1946 is given. The participation of NACA in this project is described and measurements of atmospheric turbulence taken by NACA are presented for one of the flights. The results indicate that some regions of thunderstorms may present no great hazard to flight, while exceptionally severe conditions of atmospheric turbulence may occur in other regions, or even in the same region, at about the same time" (p. 1).

Report presenting a wind-tunnel investigation conducted in rolling flow to determine the effects of aspect ratio and sweep on the rolling stability derivatives for a series of untapered wings. The results indicated that when the aspect ratio is held constant, an increase in sweepback angle causes a significant reduction in the damping in roll at low lift coefficients for only the higher aspect ratios tested.

Report presenting a method for the strength analysis of stiffened beam webs as applied to beams with ratios of applied shear to buckling shear less than 2.5. Results regarding critical shear stress, forced crippling failure in uprights, and web failures are provided.

"Several methods (references 1 and 2) based on gas-dynamic principles are available for reducing such measurements. The results obtained by these methods are subject to the limitation of the gas-dynamic theory which is that the mean free path of the molecules between impacts, is small with respect to the measuring device. Inasmuch as no information on the subject is to present known to be available, the purpose of the present paper is to present a method based on the concept of free-molecule theory for use in connection with this problem" (p. 1).

Report presenting an experimental investigation of a series of exhaust mufflers installed on a typical six-cylinder light-airplane engine mounted on a ground dynamometer sound. Several conclusions regarding muffler design are drawn from this testing. Since engine and propeller noise are about equal for this power-plant installation, both engine-exhaust and propeller noises must be reduced to obtain a sizable reduction in overall sound-pressure level.

From Summary: "By means of the general solutions of the hodograph equations for compressible fluids, certain solutions corresponding to solutions of the hodograph equations of an incompressible fluid are used to find flow patterns of compressible fluids. When the adiabatic equation of state is used, only a general method is outlined. The method appears to lead to the solution of the problem of subsonic flows with circulation around arbitrary bodies, as the method of Theodorsen does for incompressible fluids."

Note presenting an investigation to compare the 14S-T with 24S-T in extruded stiffeners for stiffened flat sheet panels. The tests were made with stiffened flat sheet panels with three hat-shape stiffeners. Data is provided on the strength of the two alloys as well as the effect of sheet thickness on relative stiffener strengths.

Report presenting a summary of the available information on lateral control. Some of the topics include the criterions used in lateral-control specifications, the factors involved in obtaining satisfactory lateral control, and the methods employed in making lateral-control investigations in flight and wind tunnels.

Note presenting an approximate theory of the effect of slipstream rotation on the forces on a fuselage without a wing, which represents the slipstream rotation by the flow about a vortex aligned with the longitudinal axis. A wind-tunnel investigation was made primarily to check the predictions for the lateral force on a fuselage shaped as a body of revolution.

"It has been known for some time that the velocity of sound is not the upper limit for potential flow. S. A. Chaplygin in his paper "On Gas Jets" (NACA TM No. 1063) carried out some interesting proofs on the existence of solutions and gave proofs relating to maxima and minima of certain functions. In the present paper these proofs are extended to include the supersonic potential air-flow field adjacent to the subsonic region treated by Chaplygin" (p. 1).