The following paper is based on the results of tests, upon duralumin columns, contained in two theses presented to the Department of Civil and Sanitary Engineering of the Massachusetts Institute of Technology.

Report presenting an investigation to determine the effect of tubing length on the indicated pressure values as ascertained in the pressure distribution measurements on the PW-9. The purpose was to determine the percentage of error in the pressure readings which might be caused by various lengths of tubing between the pressure orifices and pressure cell at the manometer. The differences in head caused by variations in the length of tubing are small, the lowest recorded being zero, the highest 2.7 percent.

Report discusses the theory of inflow of the propeller and the fact that both suctional axial velocity and suctional tangential velocity must be considered when calculating the maximum efficiency.

"The general result indicated by this study is that if desirable from any viewpoint the gap between wing and fuselage may be closed without detrimental aerodynamic effects, and with a given monoplane there is less drag if the wing is directly on top of the fuselage than if it is parasol" (p. 1).

Given here are the results of tests made to determine the effect of fuel consumption on the cylinder temperatures and the performance of a cowled Wright J-5 engine. The results of these tests indicate that enriching the mixture by increasing the carburetor size results in a reduction in cylinder head and barrel temperatures. The cylinders shielded by the magnetos or the points on the cylinder that do not receive a free flow of cooling air increase most rapidly in temperature as the mixture is leaned.

An investigation on the cowling of radial air-cooled engines was conducted in the 20-foot Propeller Research Tunnel at Langley Field. Cooling and drag tests were made with each form of cowling. The propulsive efficiency was found to be practically the same with all forms of cowling.

"The influence of different orifices on the result of measuring the same pressure distributions is the subject of this note. A circular cylinder is exposed to an air stream perpendicular to its axis and its pressure distribution is repeatedly determined. The pressures measured on the downstream half of the cylinder do not change for the orifice sizes used in the tests" (p. 1).

"The results of an investigation to determine the pressures in the open cockpit of a Vought VE-7 airplane are given. The information has been considered valuable on account of its possible effect upon the operation of instruments, particularly altimeters, due to a variation from the true static pressure which is induced by the passage of the airplane through the air. The observed values are small and the effect upon instruments is inconsiderable" (p. 1).

Methods and equipment for recording small and sometimes rapid motions by photographic means are described, and the efficacy of photographic recording in such instances is evaluated. The optical system consisting of the light source, the mirror or prism for transmitting motion to the emergent beam, and a means of bringing the rays into focus on the film are discussed. Attention is given to the critical issue of mirror mounting.

Given here are the results of experiments conducted by Colonel Costanzi of the Italian Army to determine the influence of the surrounding building in which a wind tunnel was installed on the efficiency of the installation, and how the efficiency of the installation was affected by the design of the tunnel. Also given are the results of a series of experiments by Eiffel on 34 models of tunnels of different dimensions. This series of experiments was started in order to find out if, by changing the shape of the nozzle or of the diffuser of the large tunnel at Auteuil, the efficiency of the installation could be improved.

This investigation was carried out by request of the United States Air Service in the wind tunnel of the Massachusetts Institute of Technology. The results are here published by the National Advisory Committee for Aeronautics as it is thought that they may be of general interest. Wings of the R.A.F. 6 section are tested with various angles of rake, and it is found that although rake has very little effect, a positive or negative rake of 30 degrees is the best.

Given here is a brief description of the Göttingen wind tunnel for the testing of aircraft models, preceded by a history of its development. Included are a number of diagrams illustrating, among other things, a sectional elevation of the wind tunnel, the pressure regulator, the entrance cone and method of supporting a model for simple drag tests, a three-component balance, and a propeller testing device, all of which are discussed in the text.

Note presenting an examination of horizontal buoyancy in wind tunnels, including an examination of the relative flow, static pressure gradient, horizontal buoyancy computation, and methods of computation in practical use are provided.

Note presenting an investigation of various aspects of slotted wings, including some theoretical and experimental results and characteristics of certain slotted wings currently in production.

"The subject of the choice of an airfoil section is by no means a closed one, and despite the impossibility of making a single rule serve, it is quite practicable to deduce in a strictly rational manner a series of rules and formulas which are capable of being of the greatest use if we but confine ourselves to the consideration of one element of performance at a time. There are seven such elements of performance which are here taken up in turn. The seven are of different relative importance in different types of airplanes. The seven elements are: maximum speed regardless of minimum; maximum speed for given minimum; maximum speed range ratio; maximum rate of climb; maximum absolute ceiling; maximum distance non-stop; and maximum duration non-stop" (p. 1-2).

"The vertical distribution of the pressure, temperature, and density of the atmosphere varies from day to day. Thus, rates of climb on different days cannot be compared directly, but must be corrected with reference to a standard rate of diminution of air density with increasing altitude. The following problem, therefore, has to be solved" (p. 1).

In the first series of wind tunnel tests, the drag and cross wing force of all the struts were measured at a wind speed of 30 mph and at angles of yaw from 0 degrees to 20 degrees. To determine the magnitude of the VL effect, each strut was tested at zero yaw and at a series of speeds ranging from 15 to 38 mph. Although designed as fairings for cables, part of these sections gave such high crosswind forces that they seemed to have possibilities as airfoils.

"For the calculation of the parasite resistance of an airplane, a knowledge of the resistance of the individual structural and accessory parts is necessary. The most reliable basis for this is given by tests with actual airplane parts at airspeeds which occur in practice. The data given here relate to the landing gear of a Siemanms-Schuckert DI airplane; the landing gear of a 'Luftfahrzeug-Gesellschaft' airplane (type Roland Dlla); landing gear of a 'Flugzeugbau Friedrichshafen' G airplane; a machine gun, and the exhaust manifold of a 269 HP engine" (p. 1).

"In several instances where control flaps are placed in the trailing edges of thick sections, it has appeared that a dead center (slackness or lack of control) exists about the neutral position. The condition was also experienced in the rudder action of the XB1A observation airplane. Examination of smoke pictures of the airflow around struts and airfoils indicates what may be the cause of the phenomenon" (p. 1).

Flight tests were carried out at the Langley Field laboratory of the NACA, on several airplanes for the purpose of determining their relative performance with the same engine and the same propeller. The method used consisted in flying each airplane on a level course and measuring the airspeed for the whole range of engine revolutions. In general the results show that a small change in the wing section or the wing area has but a slight effect upon the performance, but changes in those parts which cause the structural resistance have a very important effect.

In making tension tests, the slippage of the joints was noted at three points across each joint. In addition, stress strain curves were obtained for plain tension specimens, and a chemical analysis was made of the sheet.

Various details of design or arrangement of the parts of airplane structures are shown and discussed, the use of these devices having resulted in the production of structures of adequate strength, yet of a weight less than one-half of the usual construction.

Note presenting a general method followed to simplify the numerical work in hydrodynamics, which consists of neglecting quantities of a lower order of magnitude. Four of the solutions covered in this report include the theory of the lateral air forces on airship hulls, theory of wing sections in a two-dimensional flow, theory of wings with a finite span, and propeller theory.

"It is known that in a biplane the load is not distributed equally between the wings. The presence of one wing will affect the lift characteristics of the other wings. A designer must know the total load that each wing carries in order that he may design an adequate structure. The purpose here is to determine the distribution of loads between the wings of a biplane at various angles of decalage, when the gap/chord ratio is one, and there is no stagger" (p. 1).