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FUELS for use in aircraft engines are discussed with reference to their antiknock value, volatility, vapor-locking and engine-starting properties, gum content and availability, and to antiknock agents. The usefulness of a fuel for spark-ignition engines is stated to be limited by its tendency to heat the cylinder and the piston unit. Definite evidence is available that the tendency of fuels to heat the cylinder unit is not always in accord with their tendency to cause audible knocking. The fuel required depends upon the compression ratio of the engine, its volumetric efficiency, the design, size and temperature of the cylinder unit, and the rate of revolution. Mid-Continent Domestic Aviation gasoline having an approximate antiknock value of 50 octane-50 heptane gives excellent results if the engine output is kept within the limitations of this fuel but is not suitable for many modern aircraft engines if flown wide open at sea level.

THIS paper was prompted by the numerous inquiries received by the Bureau of Standards from airplane owners and airport operators regarding the grades of gasoline that are suitable for aircraft use and the suggestion that the Bureau test all brands of commercial aviation gasoline and publish the results or that the Department of Commerce issue approved type certificates for certain standard grades of aviation gasoline. The purpose of the author in presenting the paper was to open discussion on the subject, and in this he was very successful. The problem of a suitable fuel and its general distribution throughout the Country for aviation use is complicated by considerable divergence of opinion among aircraft-engine manufacturers as to the kind of fuel preferred and by wide differences in detonation characteristics of gasolines of like volatility.

TAKING as basic requirements such fundamental characteristics as can be largely separated from the problem of wing design or assumed as attributes of the complete airplane, the author discusses the independent variables consisting mainly of the geometrical characteristics that can be varied to obtain maximum performance without changing the basic requirements. He develops a weight and a drag equation, each founded on the chosen basic requirements and including in the simplest possible form the combined effect of the independent variables. The terms in these equations are defined and the equations are applied to a low-wing monoplane in power and gliding fight and to a rectangular-wing biplane in gliding flight. The results are tabulated in some instances but are principally shown on charts. The accuracy of the results obtained is stated to depend largely upon the proper choice of approximations with an appreciation of their limitations.

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.

AFTER defining the function of transport as the transfer of persons and things from one part of the earth's surface to another in the minimum time and at the minimum cost, and dividing modern transport into human, animal and mechanical, the author proceeds to describe the part played by commercial motor-vehicles in the Country's economic structure. Since food and drink are necessities of life, the first examples of motor-truck transportation discussed include the haulage of milk, bakery products, livestock, produce, vegetables and fruit. These are followed by the use of the motor-truck in local and long-distance general hauling, retail delivery service of dry-goods and chain-store supplies, the oil industry and for the transportation of express matter. A section follows on the use made of this form of transportation by public utilities and municipalities.

THE AMERICAN public demands that, in safety, comfort, appearance, speed, acceleration and deceleration, motorcoaches shall compare favorably with the present-day automobile, according to the author. These demands have resulted in a substantial increase in weight that has required the use of much larger engines, and this has brought about a tremendous increase in fuel consumption. Since fuel costs represent a large percentage of the total cost of operation, the possibility of decreasing these expenditures is receiving considerable attention. In addition, and apart from the increase in fuel usage resulting, taxation is causing grave concern. The author describes the fuel issue as it now exists in the United States. Data are submitted showing the tax situation, costs and refining operations, the potential saving assuming the employment of the less volatile fuels, their possible method of employment, advantages, disadvantages and the like.

TWO distinct phases of the subject are the physical and the economic, both of which are included in the conclusions stated in the paper, based on investigations made by the Bureau of Public Roads. It is as pertinent to inquire what effect the highways have on the motor-vehicle as to inquire what effect the motor-vehicle has on the highways. Mutual adjustment must be made if real economy is to result. Two general conclusions that may be drawn from the observations presented are that the six-wheel vehicle offers a desirable and effective answer to (a) the problem of the load in excess of the normal desirable limit of weight for the four-wheel truck, and (b) the problem of the load equal to the heavier four-wheel truck in areas where road conditions do not permit the maximum wheel-load concentration.

RIGID six-wheel vehicles and semi-trailer combinations are classified and described as to load distribution, application of power, arrangement of spring suspension and of tires. Consideration is given to the desirability of a conventional differential between the two driving axles, and the advantages to be gained by substituting a differential in which the action is limited. The semi-trailer is said to be useful for specialized services and to compete rarely with the rigid six-wheeler. The automotive industry is said to be following in the steps of railway engineers in providing more wheels for greater loads. At the close of the paper is given a bibliography of S.A.E papers and general periodical literature referring to six-wheel vehicles.

INCREASE in the amount of night flying with the advent of airplanes into the commercial field makes more acute the need for proper lighting facilities, not only of airports and airways, but of the airplanes themselves. As only about one-half of the regularly used airways in this Country are lighted for night flying, and few airports are equipped with lighting facilities for night landings, it is necessary for airplanes to be provided with lighting equipment for flying and for emergency landing at night. Besides the high-intensity lighting needed for following unlighted airways and for landing, airplanes need navigation lights and illumination for the instruments and the cabin. Immediate study and direction should be given to the problems of meeting each of these requirements most effectively and economically before it becomes too difficult to standardize methods and equipment.

FOLLOWING a brief outline of the development of aircraft propellers and a statement of the most important fundamentals of propeller design, the authors discuss the problem of propellers for use on geared-down engines, this being the installation of reduction gearing between the crankshaft of the engine and the propeller hub when the increase of airplane-performance characteristics more than offsets the added complication of the installation. The advantages and the disadvantages of using reduction gearing are considered. Concerning the installation of reduction gears, the authors state that the decision whether to use gears or not must result from a compromise between the gains and the losses involved and the amount of net gain depends largely upon the particular engine and airplane combination and its designed performance.

ALUMINUM and magnesium, being the lightest commercial metals and therefore the most suitable for aircraft construction, are discussed in their pure and alloyed states. Physical properties of the pure metals and their alloys are given and the effects of adding small quantities of alloying elements are shown. Heat-treating as a means of increasing the strength per unit weight of the alloys is discussed at length, together with the effects of natural aging and artificial aging at elevated temperatures and of quenching in hot and in cold water after heat-treating. The several types of corrosion are considered and resistance to corrosion of the metals and their various alloys are discussed. Protection afforded to aluminum alloy by a surface coating of pure aluminum is described, and other methods are mentioned.

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.

WHILE much experimental work has been done on the controllable-pitch propeller, complexity of existing devices has prevented their being placed on the market. After reviewing briefly the difficulties encountered, due to propeller and engine characteristics, the author discusses the effect of camber ratio and of angle of attack on the speed at which burble occurs, following this with comments on the efficiency of propellers as static-thrust producers, the use of the method of momentum to compute thrust and the application of adjustable-pitch propellers to supercharged engines. The causes of the forces required to operate the control adjustments are given as (a) friction, (b) twisting moments produced by centrifugal force and (c) twisting moments produced by air pressure.

QUOTING a comparison of the radial engine with a star fish, the author compares the frontal areas of radial and V-type engines and shows how air can be applied to the cylinders of in-line engines to secure efficient cooling with minimum parasite drag. Advantages of upright and inverted engines are contrasted in various respects; and engine-mountings, cylinder design and valve gears are discussed. Difficulties that have been encountered in gearing in-line engines having less than 12 cylinders are mentioned, and a simple method of gearing is proposed in which the elasticity of a relatively long propellershaft is utilized. The paper concludes with a comparison of the production problems of radial and in-line aircraft engines.

NEARLY all the aircraft propellers used by both the Army and the Navy are of the detachable-blade type. The Navy has found it necessary to make its own designs and to furnish the propeller manufacturers with finished detail drawings. The author lists the sources from which data can be obtained and shows a chart from which can be found a diameter and setting of a pair of detachable blades that will give reasonably good performance for nearly any horsepower, revolutions per minute and airspeed commonly used with the direct-drive type of propeller. Discrepancies between model tests and wind-tunnel tests are cited, and the author then considers the subject theoretically. Substitute propellers are next considered, and also the strength of propellers.

ATTAINMENT of the full potentialities of airships as carriers is dependent upon and will be greatly expedited by the solution of mooring and ground-handling problems. It is felt that the fundamental solutions have been found, and trials of newly designed equipment are virtually at hand. Communities that desire to erect mooring masts and provide servicing facilities are advised to await patiently the further trial of experimental equipment designed by the engineers stationed at the Naval Air Station at Lakehurst, N. J. This equipment is now under construction on contract. Evolution of the mooring mast, a British post-war device, and the present methods of mooring an airship to the mast are described to show the trend of development.

COMPARISON by the author shows that the cost of aeronautic powerplants per horsepower is materially lower than that of ship powerplants, and that airplane reliability compares well with the safety of other modes of travel. Some of the advantages of radial air-cooled aeronautic engines are given, followed by a brief outline of their development, which was necessarily slow because of the novel mechanical problems involved in the connecting-rods, valve mechanism and lubrication. The supercharger drive and the recently developed propeller reduction-gears of the Wasp engine are described, and the paper concludes with an outline of procedure in developing a new model of engine. In the absence of Mr. Mead, the paper was presented by E. A. Rider, who answered the many questions propounded in the discussion. These have to do chiefly with supercharging, cooling problems, engine operation in flying upside down, and the use of a double ignition system.

NOTABLE developments in 1928 that have greatly increased interest in lighter-than-air craft were the transatlantic flight of the Graf Zeppelin as an experiment in commercial transoceanic air-service, the ordering by the United States Navy Department of the construction in this Country of two rigid airships larger than any yet built or under construction, the development and construction of two British airships for long-distance passenger and mail transportation, the starting of erection of the world's largest airship factory and dock at Akron, Ohio, and the construction and operation in this Country of a number of non-rigid airships to be used for commercial purposes. Each of these developments is dealt with in order. General dimensions, major characteristics, and unique features of the Graf Zeppelin, the new Navy airships, and the projected large transoceanic commercial airships are given.

WHAT can be done to increase safety, efficiency and comfort in flight of aircraft now in use? In answer, the author describes several devices designed to bring about this result and supplements this with the results of wind-tunnel research. Detailed descriptions of the particular devices mentioned are not included, the object of this paper being to show the great possibilities of their use and the resulting improvement in performance.

THE causes and nature of the spinning of an airplane, and measures for the prevention of and recovery from a spin, are discussed. Tests and analysis are said to have shown that spinning is a stable motion of rotation, and that the real dangers are in its instability. Recovery from a spin is held to be more important than prevention, as complete knowledge of means of recovery will lead to mastery of the whole phenomenon. The spinning motion is a combination and balance of aerodynamic and purely dynamic forces and couples, asserts the author. Full-scale experiments prove beyond doubt that side-slip may be very pronounced in a spin, which changes considerably the rate of roll of the simple autorotational kind. The rolling of the wings leads to the establishing of a yawning couple which may become dangerous, tending to keep the craft in a spin because of the increased shielding of the tail surfaces.