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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.

FROM Karavodine's inefficient tube in 1908 through American developments after the recovery of German V-1 bombs, Mr. Edelman sketches the history of pulsating jet engines. Work in the United States has centered on instrumentation, tube geometry, fuel injectors, air inlet valves, fuel properties, and performance estimation. Realized performance is still low in comparison with predictions of best possible performance; but the author suggests use of the pulsating jet for helicopters having jets at the blade tips, for gliders, for starting turbines of aircraft gas turbine powerplants, and for auxiliary power with conventional aircraft.

TROLLEY coaches have a lower cost of operation per seat per mile in the range of 800 to 3500 passengers per hour than do either motor buses or trolley cars, the author's curves show. Outside this range, motor buses are most economical for lighter traffic and trolley cars for heavier traffic. Many passengers prefer trolley coaches to buses and streetcars, according to a Columbus, Ohio, poll. Other users of the street appreciate curb loading, which permits traffic to pass coaches at stops. Because of the relatively small amount of wear, the life of the vehicle is limited by obsolescence rather than by mechanical failures.