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After stressing the importance of transportation, the possible uses of the motor truck are considered. The increased cushioning and traction obtained from pneumatic truck tires accomplish faster transportation, economy of operation, less depreciation of fragile load, easier riding, less depreciation of roads and lighter-weight trucks. These six advantages are then discussed separately and various data to substantiate the claims made are presented. Following detailed consideration of transportation and operation economies, and depreciation of loads and roads, the practicability of pneumatic tires is elaborated, and wheels, rims and tire-accessory questions are studied. The four main factors bearing upon truck design for pneumatic tires are stated and discussed; emergency equipment for tire repair is outlined and a new six-wheel pneumatic-tired truck is described.

The discussion is largely in regard to the ability of a truck to deliver merchandise economically under a given set of external conditions. The matter of truck tire equipment is reviewed in the light of recent experiences of many operators and service men. The general functions of tires, securing traction, cushioning the mechanism and the load and protecting the road, are elaborated and six primary and seven secondary reasons given for the use of pneumatic tires on trucks within the debatable field of 1½ to 3½-ton capacity. The deciding factors in tire choice, those affecting time and those affecting cost, are stated and commented upon, the discussion next being focused on how tires affect these factors. Considerations relating to both truck and tire repairs are then reviewed.

A four-cylinder 4 by 5-in. truck and tractor engine, designed for either kerosene or gasoline fuel and having the very low volumetric compression ratio of 3.36, was used. Only by suitable adjustments was it found possible to make it show a fuel consumption as low as 0.67 lb. per b.hp.-hr.; but with a slight variation in power and only a different carbureter adjustment the fuel consumption at 600 r.p.m. increased to about 1.2 lb., or 70 per cent, emphasizing the importance of knowing what constitutes the best engine adjustment and of disseminating such knowledge. The engine and its dimensions, the experimental apparatus and the method of testing are fully described and discussed, the results being presented in charts showing performance curves. These are described, analyzed and the results interpreted.

In investigating the forces that tend to break up and destroy roads, the most destructive of these being that of impact, the United States Bureau of Public Roads devised a method of receiving the impact of a truck on a small copper cylinder and determining its amount by measuring the deformation of the cylinder. The impact values are largely dependent upon the type and construction of the truck. Unsprung weights have a great influence upon the impact value of the blow on the road surface and a reverse influence upon the body of the truck; these effects are in two different directions. The present aim of the Bureau is to investigate this impact and the effect of the unsprung weight on the road. Most of the tests have been made on solid tires, a few have been made on worn solid tires and some on pneumatic tires. The Bureau intends to elaborate all of these tests, including different types of pneumatic tire, different unsprung weights and special wheels, such as cushion or spring wheels.

In view of the inestimable services in the development of standardized transportation rendered to the Army by the Society of Automotive Engineers, particularly during the war, the author believes it important that the Society be acquainted with the intentions and policies of the War Department regarding the engineering development of motor transportation from the viewpoint of the problems and needs of the American Army. The fundamentals of the policies on motor transportation of February, 1919, as approved by the Chief of Staff, are stated and the subsequent changes discussed in some detail. Standardization of chassis as favored by the Army receives specific and lengthy consideration and the Government standardized trucks are commented upon. The standardization of body design and parts specifications are discussed in some detail. It is the policy of the Motor Transport Corps to maintain a thoroughly adequate and efficient engineering branch, which is now operative.

THIS paper records the results obtained from operating medium-weight trucks on pneumatic tires, and points out the advantages and disadvantages experienced. An analysis is made of the claims advanced in support of the use of pneumatic tires. Certain items are specified which in the author's opinion require further development before a satisfactory solution can be reached.

THE approaching exhaustion of the petroleum supply, from which nearly all of the available internal-combustion engine fuel is produced, raises two vital questions, upon the answers to which will depend the future of the automotive industry. These are (a) what fuels are to be available, from the point of view of the engine designer and (b) how much transportation can be secured from the fuel used. It is not certain that satisfactory engines can be developed to handle a wider range of fuels than those used at present. It is therefore not clear whether the trend of development will be toward two or more different grades of fuel, or toward a single mixed fuel to be used in all engines ultimately designed to burn it.

THE rapid development of heavy-duty trucks and farm tractors has made it necessary for manufacturers of engines used in such automotive apparatus to face problems regarding which there is no past experience to fall back upon. The necessity in both types of engine for maximum strength in all parts carrying excessive loads constitutes a problem of great importance, but in addition to it are others of the proper utilization of fuels at present available, lubrication under excessive load conditions over long periods of time; and, of nearly as much importance, the relation of fuels to lubricants and the effect of fuels upon lubricants. Moreover, information is to be acquired regarding the value of prospective fuels as power producers, the effects they have upon engines, lubricants, etc., comparisons of cost and the like. The tests recorded in the paper were made in an endeavor to ascertain some of these unknown values.

THE ordinary governor used on trucks and tractors is essentially a one-speed device. It gives good results at one speed, but at higher speeds “hunting” develops and at lower speeds governing is less accurate. This is because the spring must be stiff enough for maximum speed, and hence four times stiffer than it should be for half speed. The paper shows by calculations and curves the best results that can possibly be obtained; also, curves from a test showing what results are actually obtained with one well-known governor. Two new types of governor are described; in which the position of the spring is varied for different speeds. Theoretical curves also are presented and the results of tests, indicating that the new types produce the same character of curve at 800 as at 1600 r.p.m.

The paper treats the subject of ability from the point of view of its relation to the present trend in motor-truck design, setting forth some of the fundamental considerations involved. An ability formula when applied to automotive vehicles is to determine a “factor of experience” from which engine sizes and gear ratios can be calculated. While passenger-car performance is measured in terms of speed and acceleration, the latter are not the most important considerations in motor trucks, the speed of which is limited by the use of a governor. Wind resistance also is negligible at truck speeds. Practically the only resistances to be overcome by a motor truck are road friction and the force of gravity. Both road and grade resistance are in direct proportion to weight carried and are usually expressed in terms of pounds per pound.

THE design of a modification of the Class B Government standardized truck engine is presented, the principal object being a saving in weight without sacrificing either durability or safety factors. The crankcase design is rigid, but the metal is distributed so that the weight will be a minimum. The crankshafts are made of chrome-nickel steel of an elastic limit of 120,000 lb. per sq. in., which further carries out the idea of durability with low weight. The connecting-rod length is slightly more than twice that of the stroke, and this, with light-weight pistons, obviates vibration, without adding weight to the engine on account of increased cylinder height. The flywheel and bell-housing diameters were selected with a view to securing enough flywheel weight for smooth running without increasing the engine weight materially. All-steel supports reduce breakage of arms to a minimum. The manifolds are carefully designed to give economical performance, even with low-grade fuels.

EVERY plow in use should have 10 b.-hp. available. Every tractor engine should deliver continuously at least 33 hp. If the 330-cu. in. engine mentioned were as good as a Liberty airplane engine, it could deliver 57 hp. at 1000 r.p.m. The horsepower actually obtained is as follows: 41.5 in the laboratory 33.0 at the factory 29.0 when burning gasoline 23.0 when burning kerosene 21.0 with poor piston-rings 19.0 with poor spark-plugs 9.5 available at the drawbar The great engineering problem of the future lies between the 57 and the 23 hp. From 19 to 9.5 hp. is the manufacturer's problem. The main difficulties, as outlined by the figures given, lie in the combustion chamber and its ability to dissipate the surplus heat, and in the limitations of fuel. There will be no need for refiners to continue to break up the heavier fuels by processes already so successful, if by ingenuity and good understanding of thermodynamics these can be made to burn in present-day engines.

The author considers the adaptation of farming implements to the farm tractor the most important engineering problem confronting tractor manufacturers. The problems are intricate in their ramifications, all-inclusive in their scope and fundamental. They can never be solved by theoretical discussion and laboratory tests alone. Extensive field experiments are needed with the machines operated by the farmers themselves. It is the implement which does the work. The mold-board plow and the disk harrow are standard for soil preparation; the oscillating sickle, the reel and the knotter-head for harvesting; the revolving toothed cylinder and the oscillating rack for threshing. Power must be transmitted to these fundamental devices. The automotive tractor fills a place in the farm power field not successfully covered heretofore by any single prime mover.

In the past the majority of trucks have been equipped with wood wheels. These gave good service, but the results demanded under strenuous modern conditions seem, the author states, to make the substitution of steel wheels on medium and heavy-duty trucks imperative. Truck engineers and builders seem to recognize the fact, but to hesitate to make the change, chiefly because a metal wheel is somewhat higher in first cost and because some designs have not as yet rendered the service expected of them. The service return of metal wheels is given from the records and reports of the London General Omnibus Co. and the Fifth Avenue Coach Co., both of which use steel wheels exclusively. The added mileage is in excess of wood-wheel service and exceptional tire mileage is shown. The author states briefly the arguments for the hollow-spoke, hollow-rim, the hollow full-flaring spoke and the integral-hub metal wheels.

The necessity for a powerful heavy-duty truck with power transmitted through all four wheels was apparent shortly after the United States became involved in the war. An intensive study of the four-wheel-drive situation finally resulted in the design of the Ordnance four-wheel-drive truck and the modified form known as the artillery wheeled tractor. Seven factors influencing the preparation of the specifications are stated and discussed. The determination of proper gear ratios is analyzed. The considerations leading to the adoption of the universal-joint type of driving-shaft are mentioned and its application commented upon. Ten specific points of internal interchangeability of the mechanism are enumerated.

THE United States was practically unprepared in the field of military motor-transport at the beginning of the war. Due largely to the cooperation of the Society of Automotive Engineers and its members individually, this handicap was overcome and a position stronger in this respect than that of any of the other belligerents was attained. The early efforts and the cooperation between the Society and the various Government departments are described, especially with reference to the Quartermaster Corps which at that time had charge of all motor transportation. Regarding the Class B truck, it is shown that the Society acted as a point of contact between the various members of the industry and the War Department and, although not fostering any program or plan of its own, it was largely responsible for the success of the standardization program conceived and carried out by the Army.