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FEATURES of the design of the various cylinders built by the Franklin organization in its development program leading up to the present design are discussed in this paper. The relation of waste heat to cooling-fin areas and cooling-blast velocities is shown and discussed for cylinders up to 3½-in. bore. Characteristics of the cooling system, including fan, fan housing and air housings, are discussed at length, and the authors contend that no more power, if as much, will be absorbed in the cooling system as in that of the indirect air-cooled engine. Results of tests showing the ability of the engine to cool under the severest conditions of load and temperature are given. Since the quietness of any engine is dependent upon constant valve-clearances, the authors describe in detail the method followed in the Franklin design to maintain at less than 0.003 in. any variation in clearance. A careful analysis is made for each part in the valve-gear mechanism that is affected by expansion.

AFTER stating that increased speed, mean effective pressure and piston displacement of engines have made valve conditions more difficult during the last few years, the author recalls the path which development has followed by a brief list of materials and methods of cooling. Where the stem joins the head is the hottest part of the valve. A shield for this point is shown, also a shroud to protect the end of the valve-stem guide. Cooling the valve increases its life. Salt and sodium cooling are compared, and methods of sealing the coolant in place are described. The construction and behavior of copper-cooled valves are illustrated and recounted, and a one-piece hollow-head valve is described. Reasons for valve-seat inserts are given.

THE PROBLEM of oil consumption must be solved before the problem of winter starting and winter lubrication can be solved, asserts the author, since winter starting and winter lubrication require light oils, and light oils give poor results as regards oil consumption. Eight factors affecting oil consumption are listed in the order of their importance. Some of the reasons why they affect oil consumption are given and suggestions as to methods of overcoming the difficulties are made. The author concludes that oils of low viscosity, which are required for winter starting, can be made to give satisfactory oil consumption at all engine speeds by necessary changes which probably will involve other mechanical features besides those usually considered in connection with design of the lubrication system. They may include improved bearings, oil-coolers, air-cleaners, oil-filters, better control of cylinder and piston cooling, and other factors.

MORE attention must be paid to light-weight design and to flexible combustion control if the Diesel engine is to become a serious competitor of the gasoline engine. The relative merits of existing types of combustion-chamber and injection systems used in present commercial four-cycle engines are discussed, and it is shown that the single-turbulence-chamber type offers the most promising means to high mean effective pressures at low fuel consumption. Stock high-pressure fuel-pumps and injection-valves, produced in volume by specialists, will have a great influence on the production of high-speed Diesel engines. The interrelation of combustion and injection processes in controlled-turbulence combustion-chambers is explained, and design details and test results are given of the practical application of single-chamber principles and of a stock injection system to flexible combustion control in a recently developed high-speed four-cycle engine.

AN ENDEAVOR is made herein by the author to prove by argument and charts based on data that the greatest result per dollar of car cost is obtained by the greatest piston displacement obtainable per dollar expended rather than by the greatest horsepower per dollar. Maximum result per dollar is a major principle of economics, but horsepower per dollar and piston displacement per dollar are controversial economic fundamentals. The latter is declared to be the accepted principle in the low-price car field, and the author asserts that it should be accepted in the high-price field. Price class controls the cost of the powerplant, and ingenuity of the engineering and manufacturing departments will control piston displacement. The trends in the different price classes as regards car weight, piston displacement, ratio of weight to piston displacement, and potential and actual performance in the items of economy, durability, acceleration and speed, are shown by charts and discussed.

SOME fuels marketed as aviation gasoline cause temperatures in large air-cooled cylinders 300 degrees higher than in normal operation. Piston trouble has frequently been found to result from detonation caused by such fuels. Pyrometers have not been common in the past, but now they are available at reasonable cost for instrument-board installation. Many oil companies lack adequate apparatus for determining knock values. The Pratt & Whitney Aircraft Co. maintains a limited testing-service to determine experimentally the suitability for aircraft engines of fuels that are submitted. The author urges the recognition of a high standard for undoped aviation gasoline which shall be available throughout the Country. The addition of 2 cc. per gal. of tetraethyl lead to such a fuel will make possible a change from 5:1 to 6:1 in the compression ratio of large engines, with a corresponding increase in brake mean effective pressure from 130 to 135 lb. per sq. in.

A NUMBER of the more important commercial alloys having aluminum as their base are discussed by the author, who points out their main physical characteristics and outlines methods which can be used in their fabrication, indicating in a general way which alloys are best suited to various aircraft-engine requirements. Tables are given showing chemical compositions and physical properties, including a table of physical properties of various casting alloys at elevated temperatures. Special-purpose alloys are commented upon, and also a new aluminum alloy for pistons which is beginning to find commercial application and possesses properties particularly desirable in aircraft engines. Recent developments in magnesium alloys and their application to aircraft-engine design are specified, tables of physical properties are given, and comments are made on the characteristics of the material as compared with aluminum alloys.

METHODS of operation and maintenance pertaining to a small fleet of motorcoaches are described by the author, who outlines the development of this transportation service from July, 1922, when operation was begun. An inspection system was inaugurated in which due consideration was given to the type of equipment, the nature of the service performed, average loads, the speed maintained, and the nature of the roadway over which the vehicles traveled. In this manner preventive-maintenance methods were put into effect, the results being a steady increase in efficiency. In the author's opinion, itemized costs must be kept for each unit of the fleet so that the data will be available for the month, the year to date, the last full year and, if possible, for the last several years. The figures should be embodied in a statement so that comparison can be made between similar items for each unit operated. Units differing in make or type should be grouped and averages shown for each group.

THE 4¼ x 5½-in. six-cylinder motorcoach engine built by his company is used by the author as an example of the methods governing its design, the main controlling factors being that regularly recurring maintenance operations should come in groups, so that the operator can systematize his shop-work; that all units should be interchangeable; that any operation should be completed by a trained crew in a maximum time of 2 hr.; and that removal of the engine from the chassis should almost never be necessary except for work on the main bearings and for crankshaft regrinding.

SIX CYLINDERS are used in the Chevrolet engine, because six cylinders give smoother action and a longer range of satisfactory performance than four. Maximum results per dollar has been the ideal in the design, and high output has been secured at a cost very little higher than for a four-cylinder engine. The piston displacement is large enough to give satisfactory performance without fine tuning. The bore is made as large as possible within the space required for water-cooling around the valves. The stroke is short, resulting in low inertia forces and a stiff crankshaft with the minimum amount of metal. Three main bearings are found sufficient, because of the stiffness of the shaft and the inherent balance of the groups of three cylinders. Positive lubrication is provided, without pressure. The overhead-valve mechanism is so proportioned and the cooling of the parts is so arranged that variations in expansion cancel each other and result in nearly constant valve clearance.

POINTING out the difference between scientific and industrial progress as manifested by heat theory and engine design and the Carnot and Otto cycles, the author discusses the working principles of combustion. A simple synopsis of internal combustion is presented, followed by a discussion of influence of spark-plug location on detonation and pressure rise and some observations on overcooling and flame quenching. The reasons underlying the decision to use a particular type of engine in an automobile are commented on, and this is followed by a discussion of the limitations imposed upon induction and combustion by such a choice. The advance in combustion-chamber design is traced from the early T-head through the L-head, in various forms, the overhead-valve, the hemispherical and four-valve types. Drawings of the different heads supplement the text and some comparative power curves are included.

DUAL carbureters, as equipment for eight-cylinder passenger-car engines, have recently come into special prominence and, compared with a single carbureter, give a gain in power in the middle-speed range, between 1400 and 2800 r.p.m. This is an adaptation from airplane-engine practice, in which greater power-output and better distribution have been realized by multiplying carbureter units as the number of cylinders is increased. An absence of overlapping and interfering suction-strokes and the use of larger manifold-passages are apparently responsible for this gain. Tests made on a number of eight-cylinder engines of both the in-line and the V-types confirmed this gain, which was, however, unaccompanied by any particular gain in fuel economy.

AFTER outlining the history of development of the Packard X engine, the author states the legitimate position in aviation deserved by the water-cooled aviation-engine of this type and predicts large increases in the size, speed and carrying capacity of airplanes within the near future. Passing then to a discussion of the important features of the X-type engine, various illustrations of its parts are commented upon. The cylinders are built-up from steel forgings, with all welds arranged so as to be subjected to no excessive alternating stresses. The novel features of this cylinder design lie in the fact that the valve seats are entirely surrounded by water and that water space is provided above the combustion-chamber and below the top plate of the cylinder. The cylinder-head is extremely rigid, resisting deflection and assuring the maximum integrity of valve seats. The valve ports are machined integrally with the cylinder-head and are not welded thereto as in the Liberty engine.

THE hardness or chemical composition of an iron is, by itself, no indication of the wearing property and machinability of the iron. Irons containing a large amount of free ferrite have been found to wear rapidly, whereas others having considerable pearlite or sorbite in their structure show good wearing properties. The presence in cylinder-blocks of excess-carbide spots or of phosphides of high phosphorus-content is deleterious, because such spots wear in relief and the material ultimately breaks out, acting as an abrasive that scores the surfaces. Causes of wear in cylinder-blocks are discussed, and nickel, or nickel and chromium, intelligently added to the iron is suggested as a means of obtaining the correct microstructure for a combination of good wearing properties and machinability.

COMPROMISES are necessary in designing a piston, sacrificing the quality of least importance under the given conditions. Aluminum alloy is seen as a most desirable material because of its high conductivity and low rate of absorbing heat from hot gases. Aluminum-alloy pistons are now made for oil engines with bores up to 18 in., as well as for small gasoline engines, those described in this paper having their expansion controlled by steel bands embedded in the aluminum but not bonded thereto. Slots cast in the piston allow for linear expansion of the alloy without a corresponding increase in piston diameter and change in cylinder clearance. Advantages of strut-type pistons are shown by thermal diagrams. Illustrations show large pistons and engines in which they are used. Cores and steel inserts for producing such pistons are shown also.

PROVISION is made, in the piston and rings described by the author, for an adequate flow of heat from all parts of the piston-head to the cylinder-wall by means of adequate cross-section of aluminum alloy in the head and a tongue-and-groove type of piston-ring structure which provides a greater amount of surface than is usual for heat transfer. A labyrinth oil-seal is provided which aids heat transference and prevents leakage past the piston-rings, and the heat transfer is said to be such that the heat does not destroy the oil seal between the piston and the ring. Charts are included that show the effects in reduced temperatures, oil consumption and gas leakage with the construction described. Attention is given also to a skirt construction most suitable to use with the piston-head and rings described.

REMARKABLE performance of the Wright Whirlwind J-5 engine in the transatlantic and transpacific flights of Lindbergh, Chamberlin, Byrd, Maitland, Smith, Goebel, Jensen and Brock in the summer just closed makes this paper of great timely interest. Methods of manufacture and testing that result in a degree of perfection which enables an engine to function continuously at high speed at almost full load for 40 hr. without the failure of a single part even momentarily must be of prime importance to all internal-combustion-engine production-engineers who hold reliability as an ideal. Extraordinary vigilance at every stage of production of every part is revealed by a reading of the paper to be the major factor contributing to success of the engine. Repeated tests and inspections are made of parts in process and of the engine after it is assembled.

DETAILS are given of the method of control of the engine so that quantitative and reproducible measurements of detonation and comparisons with spectra can be made. Typical data are tabulated and photographs are shown of the free-burning flames of hydrogen, carbon monoxide, methane, gasoline in a blow-torch, and the like. The spectra of explosion and of detonation in the engine confirm earlier conclusions. By means of a synchronous shutter, the spectra of radiation during the four quarters of a stroke are obtained for straight-run gasoline under detonating and non-detonating conditions for the same fuel containing tetraethyl lead, aniline and iodine as knock suppressers and for cracked-gasoline blends. The outstanding result is that, during detonation, the first-quarter spectrum extends far into the ultra-violet, that of the second quarter, a somewhat less distance; the third and fourth quarters are characterized by very little radiation energy.

THIS article reports a series of tests on the carbon-depositing tendencies of motor oils, supplementary to those reported at the 1926 Annual Meeting.4 The first investigation was concerned with conditions prevailing in passenger-car engines, the results leading to the formation by the authors of a theory explaining the relationship between certain characteristics of oils and their carbon-depositing tendencies. In the second series of tests the authors controlled the various factors to values commonly found in heavy-duty engines and in their findings confirmed the theory previously set forth. A tentative explanation offered for certain facts revealed by the tests as to the carbon-depositing tendencies of motor-oils rests on the volatility, in the combustion space of the engine, of the oils used. An approximately straight-line relationship also was established between the amount of carbon deposited per liter of oil consumed and the Conradson carbon-residue test.

ECONOMIC and other conditions that favored and practically forced the development of the light car in England, and the history of that development, are dealt with at length by the author. He recalls the light cars of the pioneer days of the automobile and then the putting on of weight about 1898 to increase reliability and riding comfort. He comments on the reaction that resulted in the advent of the cyclecar in 1911 and its quick demise because of its failure to perform satisfactorily. The keen interest of the public, however, indicated that a big business could be done in a light, efficient, cheap motor-car if it could be produced in a practical form. Genuinely light cars minus the crudities of the cyclecar began making their appearance and quickly “caught on,” due to the tax on gasoline, low selling prices, and automobile-club competitions giving the public confidence in these vehicles.