ACHIEVEMENTS of the last ten years in increasing the power-weight ratio of aircraft engines are stated and contributing factors are analyzed. Aluminum alloys have replaced cast iron and steel for certain parts, not entirely because of their lower weight but because of a combination of properties which better fit them for the task. Similar considerations must govern the replacement of aluminum-base alloys by those of magnesium. The most promising immediate field for the magnesium alloys is said to lie in applications wherein strength and lightness are the main considerations and high-temperature properties are of secondary importance. Properties of magnesium castings and forgings are compared with those of castings and forgings of the aluminum alloys. Features of design are discussed which should receive special attention when changing a part from aluminum to magnesium. Machining practices for magnesium are covered in some detail.
TEMPERATURE rise in the gasoline as it passes through the fuel system is the important factor in vapor lock that is within the control of the car designer. Gravity and vacuum-tank feed systems are considered briefly, including tests showing that weathering of the gasoline in the vacuum tank consists largely in removal of propane. Vapor lock in a pump system is most liable to occur on the suction side, because of the difference in pressure. Increasing the capacity of the pump for handling vapor offers little relief. Evidence is presented to show the gain made by locating the fuel line where it is protected from the heat. One example is cited to show the advantages of keeping a large flow of hot engine oil away from the pump. It is advantageous also to locate the pump where it will be cooled by the air entering the engine compartment of the car.
INCREASED quality, which is reflected through higher valve-seat hardness and improved microstructure, can be obtained by additions of nickel and chromium to automobile-cylinder iron. Different combinations of these alloys were used, and it was found that a ratio of three parts of nickel to one of chromium gives the greatest improvement in structure in conjunction with maximum hardness. The effect of prolonged heating on three representative plain irons, as well as on three nickel-chromium-alloyed irons of the same base composition, is also shown. A marked difference is revealed in these cases in favor of alloyed irons. A method is given of producing chilled roller wheels by additions of chromium in the ladle instead of using special cupola charges. This is capable of better control and results in a superior product.
NEEDING to study the ignition characteristics of Diesel-engine fuels, the authors developed an idea that was presented at a meeting of the Research Committee of the Society last June. The idea was that engine tests must be the basis of evaluation. A C. F. R. engine was converted into a variable-compression Diesel engine by substituting a new piston and a fuel-injection system for the original piston and ignition system. Test methods that have been developed are reported, together with some results that show the practicability of the procedure and its substantial agreement with data secured in other ways. It is suggested that, as some of the most desirable qualities of gasoline are undesirable for Diesel fuel, and vice versa, fuels may be divided in the future on that basis, and Diesel and gasoline engines may approach each other in compression ratio.
ALL-STEEL welded bodies for passenger-cars have many advantages over composite bodies, among them being fewer parts, doors of only two pieces, no visible outside seams, lower tops for the same headroom, less roof weight, lower center of gravity, greater safety, increased visibility, permanent quiet, economical upkeep and perfect outside lines. Wood and steel react so differently to stress that neither adds much to the strength of the other in a composite structure. Steel alone, welded into a unit structure, is lighter and less bulky. The entire side of the body is stamped from a single sheet, with the openings die formed to reenforce it. Chassis frame and body follow the same lines, so that they reenforce each other and body sills can be omitted. This plan saves 2 in. in height, as compared with some other bodies.
HEREIN the author describes methods and shows instruments, tables, scales and curves used for air navigation. The ground-speed-and-drift meter devised by him and used with such remarkable success in the round-the-world flight with Wiley Post in less than nine days, on which the author was navigator, is illustrated and described. Much has been accomplished in the last few years in providing methods and equipment for quickly and accurately determining the position and laying the correct course of aircraft, but considerable improvement remains to be made in instruments, particularly sextants. No one method of navigation can be used under all conditions; a combination of four is necessary to achieve the best results.
AIRPLANE designing is the only branch of structural engineering making any pretense of strength calculation in which such calculations are based upon a direct empirical assumption or specification of the total forces acting upon specific parts of the structure and, as a rule, having little or no relation to one another. Whether our load factors are sound throughout, no one can be certain. Although the United States Department of Commerce and the British authorities are each satisfied with its own load factors, neither has given an adequate reason for believing its practice to be right. Whereas the American and the British specifications have suggested until recently, and the British regulations still indicate, that weight of the airplane alone determines the maximum loads to which the wing structure is subjected, the author asserts positively that this is not true and that the gross weight may not even be a primary factor.
BLIND flying without special training, together with general improvement in flight control, is possible with a new simplified type of artificial horizon. The instrument in most respects provides a safer reference for control than does the natural horizon, because it deals directly with the real source of control, which is the air. Air is to the airplane as the road to an automobile; the different movements of the airplane relative to its own road of air primarily determine its control. To make such movements visible is a function of instruments, but a set of several different instruments to show separate movements of the airplane is unnecessarily complicated and expensive. A single instrument giving the unity and simplicity of the natural horizon but having a directness of reading that can be obtained only from the directly adjacent air is the remedy.
THE AUTHOR discusses the permissible interpolation interval for use in routine detonation testing as affected by octane number, engine, and adjustment of the bouncing-pin apparatus. Test results presented show that, with suitable adjustment, the use of a 10-unit interval does not materially reduce precision although it greatly reduces the time and the quantities of materials needed for the test. To determine an economical and practical method of suitably adjusting the bouncing-pin regularly and rapidly for the use of large interpolation intervals will require further research.
CONVENTIONAL automobile design is no longer suited to conditions of higher driving speeds brought about by road improvement and of smaller but more powerful engines. Study of aerodynamics and analysis of forces and motions induced in a car by location of the center of gravity and distribution of weight led the author, an ex-British naval officer, to conclude that the streamline form and the disposition of the engine behind the rear axle would result in a car giving the greatest comfort in riding and economy of power at high speed and one of pleasing appearance. The reasoning that resulted in these conclusions is set forth, and reference is made to a number of unconventional designs produced in Europe and America, such as front-wheel-drive and rear-engined cars.
STANDARDS of accuracy in forging are subject to constant revision. Accuracy depends on the equipment used, and the limit of forging accuracy was thought to have been reached because of the structural limitations in machines of existing types. However, the development of a new type of pressure machine has again caused a revision of our ideas of the accuracy attainable. Finish forging on this machine can be done on the heat remaining from forging or annealing, at a temperature below that at which scale is formed. Cold coining is also done with this machine with a high degree of accuracy and uniformity. What may be referred to as pressure machining of forgings eliminates roughing cuts, reduces the number of handlings and, in some cases, entirely eliminates further machining. Other economies resulting from uniformity are the facility with which work fits into chucks, jigs and hoppers and the uniformity in weight of parts such as connecting-rods.
AFTER DEFINING the expression “venturi cowling” and reviewing briefly the standards by which engine cooling is judged, the author discusses the subject of temperature measurement as a preface to considering the factors affecting engine cooling under venturi cowling. He states that probably the first problem confronting the designer is that of determining the area of the air-entrance passage, and gives examples of the application of the theoretical formula for determining the required entrance and exit areas. Stating that the inclusion of some sort of inter-cylinder baffle or deflector is vitally important to the design of a venturi cowl if it is to cool the engine satisfactorily, the author states that he cannot recall a venturi-cowl installation in successful commercial use in which some device of this kind is not employed. He then comments upon deflectors and gives illustrations of different types, together with the results obtained therefrom.
THE DEMAND for a successful controllable or automatic propeller is greater today than ever. Such a propeller will enable commercial aircraft to take off safely with greater loads, and it may enable multi-engine airplanes that cannot now maintain altitude with one engine dead to do so with a safe margin of power. For military aircraft it means increased rate of climb and increased speed at altitude, especially with supercharged engines. To obviate confusion in nomenclature, the authors give definitions of adjustable, controllable and automatic propellers. Distinction is drawn between the needs of different classes of airplane for different types of changeable-pitch propellers. Many propellers falling within the several classes have been designed but few are in use. Cost, weight and complication are obstacles to their commercial success. Several problems still confront the designer in this field, the chief one being that of obtaining material that is sufficiently light and strong.