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It is of course impossible to consider propeller design very much in detail in a paper of this nature. It can be said, however, that the airfoil theory, in connection with the inflow theory, has given very good results and proved exceedingly valuable for the aerodynamic design of propellers. Both theories, however, in the present state of knowledge, must be applied with a number of empirical factors. Propeller-design theories and the subject of aerodynamics are discussed mathematically, as well as the elements governing the best propeller diameter for obtaining the highest thrust. Consideration is given in detail to steel, adjustable-pitch and reversible propellers as well as to those made of laminated construction consisting of sheets of paper fabric impregnated with bakelite as a binder. The mathematical considerations that apply to propellers when reversed in flight, the time and distance required to stop when landing and the propeller stresses are enumerated and commented upon.

Automobile body building derives its origin from carriage body building, which was highly developed before automobiles were thought of. The introduction of automobile bodies fitted to a metal frame changed body builders' rules and calculations. The influence of the metal frame is discussed briefly and the limiting sizes of body members are considered also. According to the ideas expressed, the weight of bodies can be reduced if the metal frame is designed so as to support the weight of the passengers and the body. The dead-weight also can be reduced if the frame is built in proportion to the amount of weight carried, the number of passengers and the style of bodies being considered. But in the construction of enclosed bodies, as in sedans, coaches and broughams, very little weight can be saved if stability, durability and lasting quality are to be retained.

The field of body engineering is broader than it is ordinarily considered to be; the author's intention is to bring to the attention of the automotive industry the breadth and scope of body engineering and outline the way this side of the industry can be considered and developed. After describing the body engineer's position, the author then discusses at some length the conflict between art and economy in this connection. He classifies a body-engineering department under the six main divisions of body construction, open and closed; sheet metal, body metal, fenders, hood, radiators and the like; trimming; top building; general hardware; painting and enameling, and comments upon each. Following this he elaborates the reasons for need of attention to details in body designing and mentions the opportunity there is at present for bringing the materials used in body construction to definite standards.

Following a review of some of the factors that are productive of excessive weight in a motor vehicle, which causes fuel wastage, and a statement that a more thorough standardization of frames and other parts would eliminate much of this waste, the author presents in detail frame-stress calculations intended to enable the designer to proportion frames and parts with this end in view. Shearing stresses are treated in a similar manner and for a similar reason, use being made of diagrams that facilitate analysis of specific instances cited and being inclusive of a table of bending-moments derived from the diagrams. Laboratory tests of the ultimate strength, elastic limit, yield-point, elongation and reduction in area of materials are then described in some detail and the results obtained stated.

Stating that it is conceded by engineers that weight reduction is desirable economically but that it is not unusual to find that weight reduction is looked upon as incompatible with reliability and road-holding properties, the author outlines briefly the normal weight-distribution in an automotive vehicle and gives a short analysis of the power required to drive it having in mind the necessity of reducing the absolute friction-loss. The use of aluminum for various parts is debated, especially those in which reliability is distinctly a function of lightness and not of weight such as engine pistons, and the application is made general to cover all parts of an automobile in which the stresses are determined by road shocks and speed. The trend of design in general and recent research in particular are stated to be along the lines of weight reduction without any sacrifice of essentials.

The author describes the type, size and general characteristics of the engines with which the German submarines were equipped at the time of the surrender, after having personally inspected 183 of them at that time, and then presents the general details of construction of these engines, inclusive of comments thereon. The maneuvering gear for such engines receives lengthy consideration and the reliability of engines of this type is commented upon in some detail, the author having confirmed his opinion that the German submarine engine is extremely reliable. One of the controlling factors in the design is that the Germans had investigated steel casting to the point where the successful production of steel castings was an ordinary process, and the author believes this to have been largely responsible for the success of the German submarine engine.

The paper is devoted more especially to enclosed body construction, with the object of creating a closer relation between the chassis and the body designer, from the viewpoint of an automotive body constructor. After enumerating what are probably the most important materials that enter into enclosed-body construction, inclusive of glue, the author outlines what constitutes the proper seasoning of wood, this being very important because very little all-metal or steel construction has been developed as yet for enclosed bodies, owing to the fact that many parts are required that necessitate using wood. Chassis deflection is discussed in its relation to enclosed-body construction and an outline is presented of body-construction development in general. The author believes that body construction will not be changed radically until either the basic type of design or shape is transformed or there is a firmer foundation to build upon.

The author first considers the style and arrangement of the seats, the position of the rear axle as affecting the rear kick-up in the chassis frame, and the position of the rear wheels as determining the distance from the back of the front seat to a point where the curve of the rear fender cuts across the top edge of the chassis frame. The location of the driver's seat and of the steering-wheel are next considered, the discussion then passing to the requirements that affect the height of the body, the width of the rear seat, and the general shape. The evolution of the windshield is reviewed and present practice stated. Structural changes are then considered in relation to the artistic requirements, as regards the various effects obtained by varying the size or location of such details as windows, doors, moldings, panels, pillars, belt lines, etc., and the general lines necessary to produce an effect in keeping with the character of the car.

The two broad divisions of aluminum pistons from a thermal standpoint are those designed to conduct the heat from the head into the skirt and thence into the cylinder walls, and those designed to partly insulate the skirt from the heat of the piston head. Pistons of the first type seem logical for heavy-duty engines; those of the second type are better suited for passenger-car engines. The objections of wear, piston slap, excessive oil consumption and crankcase dilution are stated as being the same for aluminum as for cast-iron pistons; and these statements are amplified. Piston slap is next considered and, as this can be overcome by using proper clearance, pistons of the second design tend to make this condition easier to meet. Many tests show that when too much oil is thrown into the cylinder bores, tight-fitting pistons and special rings will not completely overcome excessive oil consumption.

The author advocates the use of the fragile aluminum crankcase as a spacer, running crankshaft bearing bolts clear through the crankcase and the cylinder base, so tieing the bearings firmly to the castiron cylinder-block and using the through-bolts also as holding-down studs for the cylinders. The results of experiments on six-cylinder engines with reference to the satisfactory utilization of engine fuel now on the market are then presented. The problem is how to carry the fuel mixture in a proper gaseous state from the carbureter into the cylinder without having the fuel deposited out meanwhile. The power developed at engine speeds of 400 to 2800 r.p.m., with and without hot air applied to the carbureter, is tabulated, the proper location of the intake manifold is discussed, and the necessary features of a satisfactory engine to utilize present-day fuel are summarized.

The annual report covering transportation by the largest British air-transport company laid particular emphasis upon the greater value of the faster machines in its service. Granted that efficient loads can be carried, the expense, trouble and danger of the airplane are justified only when a load is carried at far greater speed than by any other means. A reasonable conclusion seems to be that we can judge the progress made in aviation largely by the increased speed attainable. It is interesting and possibly very valuable therefore to inquire into the relations of power and resistance as applied to small racing machines with aircraft engines that are available.

A tendency exists in most shops to assume that brazed joints cannot be successfully heat-treated. As a consequence, many fittings used in aircraft work and assembled by brazing smaller parts together are finished and installed without being heat-treated after the brazing operation. This practice causes parts to be used that not only do not develop the available strength of the material, but which are in some cases, under internal stress due to the heating in the brazing operation. Recent experiments made at the Naval Aircraft Factory show that the assumption mentioned is entirely erroneous. The author considers this matter with a view to specifying the use of steels and brazing spelters which will permit the subsequent or perhaps the simultaneous heat-treatment of the parts.

The free, resilient, self-expanding, one-piece piston-ring is a product of strictly modern times. It belongs to the internal-combustion engine principally, although it is applicable to steam engines, air-compressors and pumps. Its present high state of perfection has been made possible only by the first-class material now available and the use of machine tools of precision. The author outlines the history of the gradual evolution of the modern piston-ring from the former piston-packing, giving illustrations, shows and comments upon the early types of steam pistons and then discusses piston-ring design. Piston-ring friction, the difficulties of producing rings that fit the cylinder perfectly and the shape of rings necessary to obtain approximately uniform radial pressure against the cylinder wall are considered at some length and illustrated by diagrams.

The author presents the practical side of the body designer's work and refers to him as being between the office and the shop, the one who stands in the way of the impatient man that wants action without preparation. The development of the body designer and body designing is reviewed and the position and duties of the designer are stated at some length. The design factors are considered in detail and the making and utilization of wax models are described, followed by a lengthy consideration of curved-surface bodies, wood body frames, style and body types. The fittings and minor design details are discussed and future designs predicted from present indications. The author explains the body designing business in detail to refute the suspicion that the working methods of body designers are different from those employed by the other members of an engineering force because body designing is different and distinct from the other branches of motor-car engineering work.

Iron ranks first of all the metals; copper, lead and zinc come fairly close together in tonnage; tin ranks next; and aluminum is fifth of the non-ferrous metals. The place of aluminum in the automotive industry is shown in a diagram and another brings out the production of copper and aluminum, both receiving comment. The metallography of aluminum alloys is discussed in some detail, as well as the phenomena of growth and aging, charts and photomicrographs being shown and commented upon. The effect of alloying on physical properties is treated in a similar manner in considerable detail and a comparison of aluminum with other metals follows. Forging alloys are described and some miscellaneous aluminum-alloy forged parts are pictured. The advantages of forging alloys are enumerated and many of their present uses specified; other contemplated uses for the newest alloy are for cast disc-wheels for passenger cars, differential carriers and cast rear-axle housings.

The development of the supercharger for aircraft engines has led to the possibility of hitherto unheard-of speed of transportation. An analysis of a definite case is presented to show the different aspects of the problem in a practical form, with a view toward determining what can reasonably be expected. An attempt is also made to arrive at a knowledge of the elements involved whose improvement will effect the greatest gain. The supercharger overcomes the deficiency of the ordinary gas engine's serious loss of power at great altitudes, due to its inability to obtain sufficient oxygen for the combustion of a normal charge of gas which, in an engine of conventional design, is essential to the development of its maximum output.

Although aluminum is the most abundant metal in the earth's crust, it was not until the early eighties that means were discovered for reducing it from its ores in such quantities and at such cost as to make it a commercial possibility. The world immediately began to find uses for this material. Two groups developed; one, assuming for aluminum properties that it did not possess, thought that it would in time replace all other metals; the other, which, reacting from the first-mentioned view due to failures and disappointments, thought it had little use. It was afterward realized that much research was necessary to make aluminum a really commercial metal. One of the main aims of the automobile engineer is to obtain lightness combined with proper strength. The paper deals with decreasing the weight of automobiles by more extended use of aluminum alloys. The physical properties of aluminum are described in considerable detail and its varied uses are enumerated.

An analysis of japanning practice as a systematized industrial operation is presented as the result of an investigation. The nature of japans is discussed and an outline given of how the apparently contradictory requirements that japans must be weatherproof, somewhat flexible, sufficiently thick to be lasting, possess enough hardness to prevent excessive scratching under ordinary service conditions and take on a brilliant finish, can be fulfilled in an ordinary industrial plant without undue expenditure, so as to accomplish the original and primary objects of applying a finish to metal parts to prevent them from too great deterioration and supply a pleasing appearance to the finished product. Adequate provision for securing a uniform product is essential. The details of this are discussed. Three ways of applying japan are explained. The considerations involved in cleaning the metal and baking japan are enumerated at some length and the methods are described.