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ALUMINUM-TIN alloys which promise to be excellent bearing materials are the result of an intensive research and development program carried out by the authors. After testing a number of aluminum alloys for antiscoring qualities, fatigue resistance, and mechanical stability in operation, they concluded that the optimum bearing characteristics are found in alloys having a plastic, low-melting phase and a relatively hard phase uniformly distributed throughout an aluminum solid solution matrix of moderate hardness. Tin, affording ease in alloying and resistance to corrosion in lubricating oils, furnishes the best plastic constituent. Pure aluminum-tin alloys do not possess the strength needed in highly stressed bearings. The addition of silicon forms a hard constituent which increases strength markedly. Antiscuffing qualities are improved also, although ductility is reduced.

DYNAMICALLY loaded bearings on which the load alternates or rotates in direction and on which the load intensity is constant or varies are discussed here. Practical bearing engineering, the authors say, has neglected this type although it represents the most important bearings in aircraft and automotive engines. The relative load-carrying capacity of a finite-length bearing is shown by the authors to be proportional to the expression: (2 load rpm - journal rpm). The test setup used to prove the formula is described by the authors. Oscillograph records are presented which show the change in oil film thickness as the load conditions are varied. The effect of running out of oil, on oil film thickness is demonstrated by the authors to be identical to approaching the critical value of zero load-carrying capacity as defined by the expression in the previous paragraph. A method for investigating the capacity of engine bearings is also discussed by them.

FUNDAMENTAL concepts of combustion, too often overlooked, explain many puzzling episodes of erratic engine operation which can not be blamed on mechanical, electrical, or carburetion failures. Powerplants in flight are not being operated under the same conditions of warm air, warm engine, and warm carburetor air used during development and determination of carburetor settings. The lack of heat results in inadequate preparation of the fuel for combustion. The author reviews here the basic principles governing the aircraft engine's requirements for fuel and air.

No startling increases in traction or traction efficiency are envisioned for the near future by Mr. O'Harrow for tractors operating on the usual surfaces; only with a few extreme conditions will large-scale improvements be made. He reached this conclusion after an analysis of tractor operation on many different surfaces. He discovered that to attain sufficient traction to transmit large horsepowers at a comparatively low speed - and at high efficiency - is an extremely complex job.

LIQUID-OXYGEN injection, especially in combination with water injection, has proved to be a practicable means of improving power output of aircraft engines at altitude. Its use for limited periods in nonservice installations has increased speed, rate of climb, and operational ceiling without increasing the tendency toward knocking. The injection system can be readily applied to existing aircraft. It is remarkably light in weight - a system weighing 180 lb, including about 100 lb of oxygen, will increase the power of an R-2800 by 300 hp for 16 min. Maximum permissible boost is limited by engine cooling.

The material known as 75ST is a new high strength aluminum alloy that can be used in certain aircraft structural applications to effect a saving in weight or an increase in strength or both over designs using other alloys. However, the structural engineer should be well acquainted with the advantages and limitations of this material before utilizing it in design.

THE theory of the untuned viscous damper is developed mathematically here by Mr. O'Connor to show that its characteristics are such as to make practical the use of silicone fluid as a damping medium. That this type of damper achieves a high relative efficiency throughout a wide range of damping is indicated by a consideration of a simple mass system. The performance of a damper applied to the mass elastic system of a typical 6-cyl gasoline engine is predicted to be satisfactory over a range of speeds and values of the damping constant. An exact tabular method and a simpler approximate method are proposed for calculating the maximum amplitude and the frequency at which it occurs. The approximate value of optimum damping can also be found by a simple procedure.

AS the result of a six years' study of photographs taken at 40,000 and 200,000 frames per sec, Mr. Miller has become convinced that knock is best explained by a combination of the detonation-wave and the autoignition theories. In other words, he feels that knock is actually caused by a detonation wave that follows autoignition of the end gas. As Mr. Miller shows in this paper, the results of many earlier research programs also favor the combined theory.

NO German development in the field of diesel engines is worth applying immediately to American units, Mr. Rosen finds, although some of the design refinements he describes might improve performance. His information comes from files of the United States Naval Technical Mission in Europe, of which he was a member. The Germans concentrated on reducing weight per horsepower. Supercharging is the principal means by which output was improved. Both speed and bmep were increased to reduce cubical dimensions. Considerable work was done on fuels testing. A universal fuel test engine tested a variety of combustion systems at varying compression ratios. Another machine was well suited for determining cetane numbers of diesel fuels. Government and industry had invested 4,000,000 marks in a laboratory for the study of stress problems, chiefly those of crankshafts.

COMBUSTION roughness associated with lateral flywheel vibration can be controlled more effectively by adding a suitable damping system to the flywheel than by altering combustion-chamber shape. The authors reach this conclusion because their quantitative study shows that the degree of shock excitation is dependent on different pressure characteristics at different engine speeds. At 1000 rpm, low rates and accelerations of pressure rise, obtainable by proper combustion-chamber design, will reduce combustion roughness. However, at 3500 rpm, it is maximum pressure - which is not dependent on combustion-chamber design - that governs vibration intensity. If vibration is to be diminished by a reduction in maximum pressure, either the spark must be retarded or the volumetric efficiency decreased. Maximum kinetic energy proved to be the most suitable criterion of disturbance over the entire range of engine speeds.