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Development of the uses of electricity having begun approximately three decades ago, about the time that the automobile made its appearance, the application of electricity to the needs of the automobile has enabled manufacturers to meet the demands of the public for its production. When electricity was applied to starting the internal-combustion engine and to lighting the automobile 15 years later, the popularity of the automobile greatly increased. Now, 5 per cent of the weight and nearly 10 per cent of the selling price of a five-passenger sedan represent electrical apparatus that adds to the comfort and convenience of the public.

The personnel and the ground facilities that have produced such excellent results in the Air Mail Service are discussed apart from the flying equipment and its operation in the air. An airway is on the ground and the performance and safety of the pilots are dependent upon the ground facilities provided and the efficiency of the ground personnel. Pilots perform a highly important part in the operation of airlines and no matter how good the flying equipment may be, the desired results cannot be obtained without thoroughly trained and capable pilots. When selecting new pilots, the Air Mail Service looks for men who handle an airplane in a businesslike way and who are able, without taking unnecessary risks, to fly the ship without letting the ship fly them.

Following a description of airplane structure, the author discusses structural requirements and outlines the main features of properly coordinating the engineering and the manufacturing activities. He says that each of the three subdivisions of airplane design has its own series of calculations, these being related to predictions of performance before the machine is built, to stability determinations and to the design of a self-contained structure of sufficient strength to withstand any stresses developed in flight or in landing. He states also that no inspection is worth the name or the money spent on it that does not include constructive work and a knowledge at all times that the intentions of the designers are being carried out in detail so that the safety of the craft is assured. Materials used in aircraft should be light and easily workable and should possess the desired physical and chemical properties; they must have the specified cross-section and be free from defects.

Principal stresses in one type of eye-bolt have been determined in the laboratory of photoelasticity at the Massachusetts Institute of Technology by the photoelastic method. In the test, an eye-bolt, designed in accordance with a method suggested for circular eyes in a course in machine design by the Institute, was made of celluloid 0.25 in. thick, 1 in. wide on either side of the eye, with a 1.405-in. diameter of eye, and a 1.333-in. width of shank. Steel loading-plates were pinned to the broadened end of the shank and a load of 100 lb. was suspended from the bolt, which gave a mean stress of 300 lb. per sq. in. in the shank. Plain polarized light was passed through the celluloid model and the isoclinic lines, or lines of equal inclination of principal stress, were observed and recorded. Two families of lines of principal stress, designated as P and Q stresses, were determined graphically from these isoclinic lines.

Machine-repair analysis and a criticism of present-day equipment, with analytical tables based on data collected from a 5 months' study, are followed by conclusions relative to the reliability of present-day equipment. Eight types of common machine-tools are considered and the maintenance advantage of one over the other is deduced from the consolidated tables based on monthly reports. A comparison of each class of machine-tools with the others is made, as well as a summary of the weaknesses of each class from the frequency of repairs of the elementary parts. The attention of the builders is drawn to the conditions that the shop encounters with their equipment. A maintenance budget-system is described that has been installed in one plant to give the men a comparative idea of particular equipment that is running in excess of the budget time. It also serves in lieu of an inspection of the conditions of the equipment and is an indication of the time when overhauling is advisable.

The selection of machine-tools is largely a matter of judgment, based on the consideration of many variable factors. No fixed rules can be laid down, but the uses to which the machines are put are divided roughly into three classes which govern to a large extent the types of machine that should be purchased, whether they should be machines of a wide range of usefulness, standardized machines equipped with special tooling or special-purpose machines of special design capable of very large and continuous production. To determine into which of these classes the requirement for new machines falls, an analysis should be made of the following factors: (a) quantity of production required and its duration, (b) method of machining and tolerances and finish required, (c) possibility of a change in design of the product, (d) cost of production, (e) when delivery of machine is required, and (f) money available for the purchase.

Infallible performance and economical operation are the bases of successful commercial flying. Airplanes, having passed through the experimental and demonstration periods, must now prove their usefulness. Heretofore, because of military requirements, designers have fostered the use of power rather than refinement of design to obtain performance, but commercial operation demands efficiency, and in each of the four essentials, namely, dependability, size, total powerplant weight and cost, opportunity for decided improvement still exists. The requirements and limiting factors of each of these essentials are discussed in turn and the conclusion is drawn that a relation exists between the amount of thrust delivered to the air and the weight put into an airplane for its propulsion. To obtain the best over-all performance, if these terms are considered as a fraction, the numerator should have the maximum and the denominator the minimum value.

Subsequent to an historical review of die-casting, briefly stated, the author covers the subject of present die-casting practices comprehensively and conveys a large amount of specific information. Because many different methods of producing castings exist outside the sand-casting realm, he says that some confusion prevails as to the exact definition of the term “die-casting.” Such castings may be produced in metallic or in non-metallic long-life molds, or in combination with destructible cores. They may be filled by gravity and known as “permanent-mold castings”; or by centrifugal force and known as “centrifugal castings”; or by filling the mold by gravity and, after the outer skin has become chilled, pouring out the excess metal. The last named are known as “slush castings.” On the other hand, a die-casting may be defined as a casting formed in a metallic mold or die, from metal subjected to mechanical or gaseous pressure while in the molten state.

Will sheet steel that is to be used in the manufacture of automobile parts form the parts for which it is intended without breaking, buckling or pulling coarse at the sharp corners is a question, the answer to which is sought through a series of tests applied to samples of the material by the Packard Motor Car Co. Three sheets are selected from different parts of every 1000 sheets received. After sections have been removed from the ends of these sample sheets, four test pieces are taken from each sheet at specified locations and these last samples are subjected to Erichsen, Rockwell and tensile-strength tests, each of which is discussed.

Smooth operation of motor cars becomes increasingly important as average driving-speeds become higher and as the public demands greater luxury and freedom from vibration. An analysis of vibration shows that it is caused by forces which can be calculated with considerable accuracy. Vibration itself is very complex, due to the inter-relation of forces, deflection and periodicity in the parts of the engine. In this paper a number of indicating and recording instruments devised for recording the actual resultant vibration and determining its exact character are described and their operation explained. Vibration due to unbalance of rotating parts, piston unbalance inherent in four-cylinder engines, bending of the crankshaft, centrifugal force, and torsional periods are discussed. Indicator-diagrams of the various kinds of vibration are shown. Unbalanced force and elastic reaction are the two general causes of vibration.

Tests to determine the location under the hood of a motor vehicle where the air-intake of the carbureter will be exposed to the least dust were made by the agricultural engineering division of the University of California at Davis, Cal., and the results are given in the hope that they will serve a useful purpose. Of three types of dust-screen devised to catch the dust at different locations so that it could be photographed, and still would present little hindrance to passage of the air from point to point under the hood, the most effective was one of coarse hospital gauze stretched over frames set in transverse vertical positions on either side of and above the engine. The tests were made on two phaetons and a speed truck, run for less than 3 miles and following another car on a dusty road.

Utilizing an opportunity presented by a mountain-road construction-project in California, eight Class-B 3½-ton trucks were assigned to the work and a test of air-cleaners was conducted during its progress. Six trucks were each equipped with an air-cleaner; two were not. The trucks had dump-bodies and were specially prepared for the test, details of this preparation being specified. Due to varied air-cleaner design, it was not feasible to locate the cleaners identically on all the trucks, and differences in mounting may have influenced the resulting air-cleaner efficiency, but mountings were made as nearly identical as possible. Tables of average wear of piston-rings, engine cylinders and crankpins, for 1000 hr. of use, are presented, and details of how the measurements were made are stated, together with a discussion of the “growth” of pistons and of the peculiarities of wear.

Rapid wearing out of the engines of farm tractors, trucks and automobiles led the University of California to undertake a study of the dust problem and the efficiency of air-cleaners in removing field and road dust from the air before it passes into the engine. Work was begun in 1922 and several reports have been made on the methods devised and the progress made during the last 2 years. Results to June, 1924, were given in the paper published in August, 1924. The present paper gives results of the studies to the end of 1924 and includes data from tests of 12 new makes or models of air-cleaner not previously tested or not fully tested. Of outstanding importance is the discovery that the quantity of dust inspired by any cleaner or carbureter is greatly reduced if the intake is placed high and faces away from the direction of motion of the vehicle.

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Investigations indicate that detonation may be controlled by retarding the rate of combustion by chemicals added to the mixture, which serve to increase its specific heat and prevent excessive temperature, and by reducing the temperature of the walls of the combustion-chamber, so that the temperature of the charge previous to ignition will be lower and thus insure a normal rate of combustion. The present discussion is devoted to methods of controlling the temperature of the charge before and after the mixture enters the combustion-chamber, and before normal ignition occurs. Tests previously made on a poppet-valve engine and on a sleeve-valve engine revealed the impracticability of applying the laboratory methods used at that time to commercial practice and the need of eliminating some of the difficulties inherent in those methods of detonation control. The various changes made in the engine are described, including the specially designed spark-plugs.

Classes of service already provided by the street-car and the passenger automobile influence the expectations of the motorbus passenger regarding the quality of transportation service afforded by the motorbus. If an operator persuades people to ride in his motorbuses, it will be because they offer safety, economy, convenience and comfort to a greater degree than that offered by competitive transportation media. Since the public has demonstrated that, under favorable conditions, it will patronize the motorbus to an extent that yields a profit to the operators, the future success of this means of transportation lies wholly within the control of the motorbus builders and those who operate it. Of the factors that determine the degree of success attained, motorbus-body design bulks very large. Discussion of the subject is presented from the viewpoint of the passenger, as the motorbus approaches him, as he enters it and as he judges the quality of transportation it affords.

Riding-comfort is defined as the transportation of an automobile passenger in so easy a manner that the trip will be a pleasure and not a hardship. Since spring-suspension constitutes the basis of riding comfort in passenger-cars, the paper deals with some of the important factors that determine correct chassis spring-suspension. An analysis made by the National Automobile Chamber of Commerce of replies received to a questionnaire it circulated among 20,000 car-owners is presented in proof of the genuine interest the motoring public has in the riding-quality of a car and the variable factors that have an influence on spring-suspension are stated to be the type of spring used, its physical dimensions, the amounts of sprung and unsprung weight, frame construction, wheelbase dimension and the kind of material used. Horizontal, vertical and sidewise motions of a car are analyzed, and a periodicity chart is shown for passenger cars of from 112 to 116-in. wheelbase.

Balloon tires have caused the points at which the greatest trouble formerly occurred to be reversed; the greatest wear hitherto has occurred on the rear tires; now it occurs on the front. The carcasses of old tires were heavy and thick and carried a large part of the load; balloon tires are flexible and will support very little load. The air-pressure carries the load and gives greater cushioning effect. Four-ply tires have proved to be the most satisfactory and have none of the disadvantages of high-pressure tires. Balloon tires steer harder than high-pressure tires because of lower air-pressure, which necessitates a greater area of contact. Steering resistance is caused by the load on the tire and the increased area of contact. Many designers, in making the steering gear free to overcome steering resistance, make wheel-twitching possible. Shimmying may be classified as low-speed and high-speed, the latter occurring at speeds between 35 and 40 m.p.h. and being very violent.

A portable instrument of the seismograph type has been designed for measuring the riding-quality of vehicles. Headings are made by a continuously revolving counter that automatically sums up the vertical displacements of a partly suspended weight. As the counter readings are a measure of the riding-quality, a large reading indicates poor riding and, conversely, a small reading indicates good riding. An arbitrary scale graduated into revolutions of the counter per mile of travel translates the readings into riding-quality; a reading of 10 indicates “very smooth,” 20, “good,” etc. The instruments have been calibrated in a special testing-machine in which the readings can be observed under an harmonic motion of fixed period and amplitude. Comparison of the riding-qualities of balloon tires and of cord tires, made on three different automobiles run over a variety of roads, shows results that are very favorable to balloon tires.

An air-spring and a steel-spring combination has a characteristic load-curve that allows maximum flexibility in the general working-range of the axle yet has an increasing resistance to dissipate large shock-loads. By varying the compression volume in the air-spring, the load curve of the combination can be made more flexible or stiffer as occasion demands. Tests show that the steel-spring vibration alone had a duration of 5½ sec. with a period of 87.2 vibrations per min.; the combination, a 3-sec. duration with 60.0 vibrations per min. Field tests of front-axle movement were made, the test apparatus for these and other tests being illustrated and explained. The maximum axle-movement either above or below the normal line is increased when using air-springs, and the subsequent rebound shows more action on the underside of the normal line, the general tendency of the air-springs being to float the chassis on a slightly higher plane at the time of rebound.