The problem of shimmy of a castering wheel, such as the nose wheel of a tricycle gear airplane, is treated analytically. The flexibility of the tire is considered to be the primary cause of shimmy. The rather simple theory developed agrees rather well with previous experimental results. The author suggests that shimmy may be eliminated through a suitable choice of landing gear dimensions in lieu of a damper.

From Summary: "A simplified approximate theory is presented by means of which the laminar boundary layer over an insulated two-dimensional surface may be calculated, a linear velocity profile being assumed, and an estimate made of its effect in changing the pressure distribution over the profile upon which the boundary layer is formed. Skin friction is also determined. Comparisons of results from this theory are made with experimental results at a Mach number of 6.86 and a Reynolds number of 980,000."

"Two methods of using the concept of linearized characteristics are derived for the one-dimensional unsteady flow in a tube that is rotated about an axis perpendicular to the axis of the tube. One of the methods correponds to that used by Ferri in his basic work on the subject. Solutions are made by both methods for boundary conditions that allow analytic solutions" (p. 1).

Report presenting burst testing conducted on several designs of sound disks and disks with defects. Results were compared with tensile strength, tensile ductility, and notch tensile strength. The main purpose of the investigation was to determine the extent to which disk strength can be increased by increasing tensile strength, to investigate the extent to which a correlation exists between disk strength and mechanical properties, and to present data on the influence of several types of stress concentration on the strength of disks made from ductile and brittle materials.

Report presenting force testing in the high-speed tunnel to determine the effect of a simulated propeller slipstream on the aerodynamic characteristics of an unswept wing panel with and without nacelles. Lift, drag, and pitching moment were measured for a range of angles of attack and Mach numbers.

Report presenting a study to establish the effect of solvents on boundary lubrication by silicones. Boundary-lubrication data were obtained which are considered substantiating evidence for a hypothesis that, in solutions of solvents blended with silicones, the silicones form a closely packed and oriented absorbed film on ferrous surfaces. Results regarding room-temperature lubrication experiments, elevated-temperature lubrication experiments, low-temperature physical behavior, and effect of conventional lubrication additive are provided.

Report presenting an analysis to give a qualitative picture of the effects of wing sweep on the upwash at the propeller airplanes of multi-engine airplanes. The method was applied to two hypothetical airplanes of the high-speed long-range type, one with an unswept wing and the other with a sweptback wing. Results regarding wing upwash, total upflow for the airplanes, upwash contribution of the airplane components, nacelles inclined, and aerodynamic exciting parameter, nacelles inclined are provided.

"A structural theory is developed for the analysis of thin multicell wings with straight spars and perpendicular ribs. The analysis is intended to be suitable for supersonic wings of low aspect ratio. Deflections due to shearing strains are taken into account" (p. 1).

"With the aid of the method of small oscillations which was used successfully in the investigation of the stability of laminar velocity distributions in the presence of two-dimensional perturbations, the excitation of the unstable perturbations for the Hartree velocity distributions occurring in plane boundary-layer flow for decreasing and increasing pressure is calculated as a supplement to a former report. The results of this investigation are to make a contribution toward calculation of the transition point on cylindrical bodies" (p. 1).

Report presenting an investigation in flight at free-stream Mach numbers up to 0.77 to determine the effect of a laminar boundary layer and thin and thick turbulent boundary layers on the chordwise pressure distribution over an airfoil in the presence of shock at full-scale Reynolds numbers. Boundary-layer and pressure-distribution measurements were made on a short-span airfoil built around the wing of a fighter airplane.

Report presenting a flight investigation on a four-engine bomber to determine the effect of transient wing response in rough air on the acceleration measurements at the center of gravity of the airplane. Flights occurred in clear-air turbulence for two speed and two weight conditions. The results indicate that transient-response effects on total aerodynamic load are small for the test airplane.

Report presenting an investigation in order to study the characteristics of flow in the vicinity of a rectangular wing of aspect ratio 0.25 with a modified flat-plate airfoil section. The investigation was conducted using photographs of a tuft grid located at a number of chordwise positions along the airfoil and behind the trailing edge. Results regarding the force-tests, formation of vortices and vorticity distribution in the wake, location of vortex cores, and chordwise growth of lift are provided.

Note presenting an application of the well-known analogy between electrical and mechanical systems to the calculation of stresses and deflections of beams. The main objective of the paper is to give an explanation of the analogies in a basic manner which will enable a structural engineer to understand the process of designing the electrical circuits. Analogies are given for beams in bending and torsion with static loads and in vibrational motion.

Note presenting an extension of the Kármán-Pohlhausen method to sixth-degree velocity profiles for determining the characteristics of the compressible laminar boundary layer over an adiabatic wall in the presence of an axial pressure gradient.

"A method is presented for finding an mth-degree polynomial that passes through a specified point with (m - j) specified derivatives (l ≤ j ≤ m) and is a least-squares polynomial for other points spaced at unequal intervals of the independent variable" (p. 1).

Note presenting a method for the determination of the time lag in pressure measuring systems incorporating capillaries. The method can be used to select, design, or redesign a pressure measuring system to meet the time requirements of a particular installation. Experimental data are shown and a step-by-step sample application is presented.

Revised solutions of the laminar-boundary-layer equations for cases which involved cooling at the wall combined with large pressure gradients in the main stream produced specific-weight-flow profiles which locally exceeded free-stream values. Heat-transfer and friction coefficients, boundary-layer thicknesses, and velocity, temperature, and specific-weight-flow distributions resulting from the revised solutions are presented for Euler numbers of 0.5 and 1, stream-to-wall temperature ratios of 2 and 4, and cooling-air flow rates through porous walls designated by flow parameters of 0, -0.5, and -1.

Report presenting an exploratory investigation of the dynamic effects of fuel sloshing in tip tanks on suddenly excited bending oscillations using two simplified model beam-tank systems. Several fluids of different densities and viscosities were used in combination with various conditions of tank fullness. Results regarding the large and small beam-tank system are provided.

Report presenting a fuselage-vertical-tail combination continuously oscillated in yaw through a range of reduced frequencies and amplitudes corresponding to the amplitudes of the sustained lateral oscillation of certain airplanes. An indication of a reduction in damping in yaw appeared as the amplitude of oscillation was reduced through the range of small amplitudes investigated. Results regarding the phase angle, probable error of phase angle, damping in yaw, and probable error in the damping in yaw are provided.

Note presenting a determination of the stress and strain at the onset of crazing of polymethyl methacrylate at 23, 50, and 70 degrees Celsius. The materials tested were commercial cast polymethyl-methacrylate sheets of both general-purpose and heat-resistant grades. The results indicate that a critical strain theory for the threshold of crazing is not applicable to polymethyl methacrylate.

Results are presented of a dimensional study and an experimental investigation of the pressure rise across a shock wave which causes separation of the boundary layer on a flat plate. The experimental part of the investigation was conducted at a Mach number of 3.03 for a Reynolds number range of 2 x 10 (sup) 6 to 19 x 10 (sup) 6. The available experimental data are compared with the predictions of the present study, and the significance of the results obtained is discussed relative to certain practical design problems.

Note presenting an examination of the available information on the hail phenomenon affecting aircraft in flight. Some of the components in the report include: a digest of literature on the physical properties and formation of hail, a survey of the affect of hail on aircraft in flight from 57 cases of aircraft damaged by hail, information on hail for the benefit of pilots, forecasters, and ground personnel, and an annotated bibliography of articles about hail.

An experimental investigation of the effects of the geometry of body surface, Reynolds number, stream turbulence, and a roughness element (wire) on the reattachment of separated laminar boundary-layer flow on a bent flat plate is presented and discussed. The flow mechanisms determining reattachment of the boundary layer are analyzed and discussed.

Note presenting an investigation of the use of a consolidated porous medium as a gas-metering device and for determination of gas viscosity over a moderate range of temperature and pressure. Results of the flow tests have been employed in the determination of the viscosity of air up to approximately 900 pounds per square inch absolute at the two test temperatures of 75 and 517 degrees Fahrenheit.