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The title of this paper fully indicates its scope. The author presents an intimate picture of conditions prevailing at the war front which affect the operation and maintenance of war trucks, and these two factors in turn indicate the trend that design should take. The training of the mechanical transport personnel of the Army is also gone into at some length. The English and American trucks used earlier in the war consisted of about nineteen different makes and forty-two totally different models, resulting in a very serious problem of providing spare parts and maintenance in general. In the British Army transportation comes under an Army Service Corps officer called the Director of Transport and Supplies. At the outbreak of the war these officers had had little mechanical experience, horses being employed principally. In the French Army motor vehicles were used to a greater extent before the war, under the artillery command.

The author outlines methods for producing high-speed engines with high mean effective pressure and gives data resulting from several years' experimental work. He discusses the desirable stroke-bore ratios; valve area, weight, dimensions, location and timing; compression ratios; ignition requirements; and the location and means for operating camshafts and other valve-actuating mechanism. Data are given regarding the best material and dimensions for pistons and the desirable number of rings. The physical characteristics of alloy steel desirable for use in connecting-rods are mentioned. Similar data, including dimensions and factors controlling the construction of the crankshaft and its bearings are included. The relation of the inertia stresses set up by reciprocating parts to those due to the explosion and compression pressure on the piston head is indicated, and the maximum total stress deduced.

The author points out the necessity of obtaining dynamic or running balance of rotating parts, especially in automobile-engine construction. He discusses the manifestations of the lack of static and running balance, such as vibration and high bearing pressures. Formulas are supplied for calculating bending moments and centrifugal forces in a crankshaft that is out of balance. Methods for obtaining static balance are described and the possible conditions existing after static balance is obtained are treated, with especial reference to the existence of one or more couples. Descriptions are given of two representative machines that are used to locate couples and correct for them. The principles of operation are made clear and advantages and disadvantages of each type are brought out fully.

The author discusses in this paper a few of the problems involved in the design of ignition equipment. Some of these problems have been solved and some remain to be solved. The early history of the development of ignition apparatus is traced, reference being made to the vibrating coil type of ignition operated by dry cells or storage batteries, various types of magneto and dual-magneto systems, and combined generator and storage battery systems. The balance of the paper refers more particularly to batteries and ignition proper. The two types of battery ignition, open-circuit and closed-circuit, are described and the current characteristics of each are shown graphically by means of curves. Some of the problems encountered in the development of present battery systems are next considered and such topics as reduction of inertia in the contact-arm, overcoming harmonic vibration, advantages of one-piece cams and the function and design of the condenser are treated in detail.

After a few general introductory remarks the author outlines the operating requirements for tractors, and takes up the matter of the proper sizes of tractors, stated in horsepowers per given number of plows. The use of lower-grade fuels, value of water in the engine, cylinder construction, methods of lubrication and design of drive-wheels are the subjects covered by the balance of the paper.

The author first compares mineral oils with certain other liquids in order to point out clearly certain of their characteristics. He then shows the economic benefits that would result from making more of the crude available for use as fuels. He discusses such topics as cracking methods in use, advantages of dry gas, initial flame propagation, gas producers, hot mixtures, wet mixtures and difficulties of correcting existing engines. He concludes by proposing as a solution of the gasoline problem the more general use of superheated homogeneous fixed dry gases made in vaporizing devices independent of engine cylinders, and outlines means for attaining this end. Performance data covering the use of mixtures of kerosene and gasoline on several cars are included in a table, and several charts throughout the paper illustrate many of the topics discussed.

The author states that the objects of the paper are to define and trace the development of the various processes of carburetion, and to offer such suggestions along these lines as may assist the investigator in developing motorboats, automobiles and self-contained unit motor cars for railway purposes. The surface carburetor is mentioned chiefly as of historic interest. In considering the jet carbureter the author discusses the proportion of gas desired, the effect of the varying inertia of the air and the liquid gasoline and the breaking up of the combustible needed. Following sections review the devices for using kerosene, such as gasoline jet carbureters to which heat is applied, devices of the fixed gas type, the introduction of combustible directly into the cylinder, forcing combustible directly upon a hot surface in the cylinder and devices which raise the combustible to the boiling point.

This paper emphasizes the importance of using standardized testing equipment in order that mental calculations may be avoided in interpreting the reports of other engineers. The situation and environments of the engine-testing plant, cooperation among the men conducting tests, standardized methods of conducting tests, value of venturi meters and testing of accessories are among the subjects discussed in the first part of the paper. The subject of the testing of engine cooling systems is treated at some length, the importance of obtaining operating conditions being emphasized. The paper concludes with two sections covering spark-plug testing and tests for preignition.

This paper first traces the early development of aviation engines in various countries. The six-cylinder Mercedes, V-type twelve-cylinder Renault, and six-cylinder Benz engines are then described in detail and illustrated. Various types of Sunbeam, Curtiss, and Austro-Daimler are also described. The effect of offset crankshafts, as employed on the Benz and Austro-Daimler engines, is illustrated by pressure and inertia diagrams and by textual description. The paper concludes with a section on the requirements as to size of aviation engines, four curves showing the changing conditions which affect the engine size requirements. These curves relate to variations of temperature, air density, engine speed, airplane speed and compression ratio required to compensate for decrease in air density, all as related to varying altitude.

This paper deals only with water-cooled engines, the cooling system being considered as made up of four main units-the water jacket, the circulating system, the radiator and the fan. Water-jacket problems are first considered, followed by a comparison of pump and gravity (thermosyphon) systems of circulation. The next section is devoted to radiator requirements. The balance of the paper relates to the fan. Five curves show graphically the correlations of the various factors of cooling, power consumed, air velocity and volume, engine speed, fan speed, air and water temperatures and the element of time, the results applying to different types and sizes of fans. These curves are of service in the selection of fans for radiator cooling purposes. The classification of fans, fan power consumption and speed, fan belts and pulleys, disadvantages of high fan speed, types of fan bearings, and applications of fans are the subjects next taken up.

The forces necessary to induce and maintain gasoline engine speeds of 3000 r.p.m. or faster, as well as other forces closely associated with high speeds, are numerous. The author has, however, confined his discussion to the three most important groups of forces upon which, in the main, the smooth running and the life of an engine depend. The different component forces were determined in respect to two engines of equal capacity for twenty-four crank positions, uniformly spaced at intervals of 30 degrees, which constitutes two revolutions and one complete cycle in the case of four-stroke cycle engines. Medium-sized six and twelve-cylinder engines were chosen for investigation. Corresponding components were combined as resultant forces and graphically represented in magnitude and direction. Several such characteristic diagrams of the resultant forces acting upon crankpins and main bearings of the two engines investigated are reproduced throughout the paper.

This paper contains a brief description of the Entz electric transmission. Wiring connections are given of the several speeds, for electric braking, for starting the engine and for charging the battery. The statement is made that the electric transmission eliminates and does the work of the friction clutch, the clutch pedal, the transmission gears, the flywheel and separate starting and lighting systems.

The efficiency of the automobile engine, as operated on the Otto cycle, is thought by the author to be too low, and he therefore suggests a method of improving it. He considers the various losses by which heat is dissipated in internal-combustion engines and finds that the best opportunity for increasing thermal efficiency is by an increased expansion of the charge. The author suggests that this expansion be carried 50 per cent further than is ordinarily done. In order to obtain higher efficiency at part load, the suggestion is made that instead of throttling the mixture, the admission valves be closed earlier. In case the expansion is 50 per cent longer than the induction stroke and the cut-off takes place earlier as the load becomes lighter, it will be necessary to vary the fuel opening inversely with the air induced. It is suggested that the fuel valve and cut-off lever be connected together and operated by the accelerator pedal or hand lever on the steering wheel.

The paper gives the value of certain factors in engine design that are good practice and uses these values to calculate the horsepower of a four-cylinder engine. The author holds that the deciding factor in comparing four-cylinder engines with those of the same displacement but with a greater number of cylinders, is the thermal efficiency. Both the cooling medium and the mechanical losses increase in proportion to the number of cylinders. He suggests in closing, that the demand for power output beyond the possibilities of four cylinders must be met by the use of a greater number.

The author confines his discussion to engines used on pleasure cars, inasmuch as practically all commercial vehicles use the four-cylinder type. The performance expected of their cars by automobile owners is outlined, particularly as regards performance, durability and maintenance cost. In-asmuch as the horsepower required is often determined by the acceleration demanded, the argument in favor of four-cylinder engines is based mainly on a comparison of its acceleration performance with those of engines having a larger number of cylinders. A number of acceleration curves are given for these engines. The paper next considers smoothness of operation at low, medium and high running speeds, asserting that the decrease in inertia forces due to lighter reciprocating parts has made it possible to increase the speed and thus reduce remarkably the vibration of the four-cylinder engine.

The author describes a number of detailed developments that took place during the working out of a line of worm-driven trucks. The details of front axle and steering parts are dealt with at length, the reasons for the final constructions being clearly explained and the constructions themselves well illustrated. Details concerning difficulty with the Hotchkiss type of drive on heavy trucks, troubles with drive-shafts and lubrication of the worm wheel are all covered thoroughly; spring-shackle construction and lubrication, radiator and hood mounting come in for detailed attention and the question of governors is interestingly covered. Brief reference is made to the influence of unsprung weight, the differences between truck and pleasure car practice in this respect being pointed out.

The author outlines the constructions that have performed cially that four-cylinder engines carried under a hood are the most satisfactory. The defects revealed by war service are given in considerable detail, the author finding that all of the trucks used had developed some weak point. Radiators and springs are specified as a general source of trouble. The author outlines a number of operating troubles developed under the existing conditions of operation and gives examples of the way these have been remedied. Considerable attention is paid to the methods of operating trucks away from made roads. The methods of fitting chains to the wheels, and the use of caterpillar attachments are described. Dimensions are given for bodies and a number of suggestions made as to their proper construction.

The results are given of laboratory investigations made of a number of different types of carbureters, showing the relation between their gasoline and air consumptions over a wide range. This relation is plotted on so-called quality diagrams, on which is indicated the range between which high power and high efficiency can be expected. A description is given of a carbureter arranged in two stages, the first being used at light load and the second coming into action when the throttle is nearly open, thereby more than doubling the carbureter capacity. Engine performance curves are presented showing the result when only one or both stages of this carbureter are used.

The author considers the effects of velocity variation on the operation of a car and states that this variation is absorbed mainly by the flywheel. A formula is given for calculating the pressure on universal bearings. Various methods of protecting and lubricating joints are described. A number of European types of joints are illustrated. A much larger number of types of joints are used abroad in-asmuch as each maker usually makes his own design instead of purchasing it from a specialist as is the usual practice in this country. In conclusion the paper describes types of joints using flexible material, such as leather or spring steel.

The author outlines in a general way the relation of car performance to modern engine development. He considers particularly weight reduction and torque performance of high-speed engines, giving the undesirable characteristics attending the increased torque range gained by higher speed. He next discusses the relation of torque to total car weight, to acceleration and to hill-climbing ability and suggests a method of determining the value of a car in terms of its performance ability. The author holds incorrect those systems in which the amount of lubrication is in proportion to speed only; and in which oil for crankshaft and crankpin bearings must cool as well as lubricate them. He shows a system designed to solve these oiling problems. Static, running and distortion balance of a rotating mass are defined by the author, who shows how they apply to a large number of types of crankshafts.