WHILE virtually all aircraft builders agree in placing reliability as the most important factor in gaging engine performance, from there on agreement is lacking. The author believes that all factors exclusive of reliability can be evaluated so as to provide a good basis for choosing an engine. These factors include durability, which despite the opinion of some aeronautic engineers is not synonymous with reliability; weight per horsepower of the complete powerplant, including radiators and cowling; head resistance; fuel consumption; and first cost. The effect of changes in engine weight on operating cost are discussed, the text being supplemented by tables showing the effect of increased engine-weight, operating cost and the operation-expense items that are affected.
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.
CAUSES of troubles and expense to air-transport companies in their airplanes are dealt with comprehensively by the operations manager and a division superintendent of the National Air Transport. Commercial operation is asserted to be the proving ground for the products of both airplane and airplane-engine manufacturers, and four reasons given for this are (a) lack of understanding between the manufacturer and the purchaser as to precisely what is required of the airplane purchased, (b) inability of the manufacturer to deliver a product equal to his anticipation, (c) inability of the operator properly to use and care for the equipment furnished, and (d) the varied and opposed uses to which different operators must put their equipment. Detailed and valuable information is given regarding the parts that give trouble and what should be done to avoid it.
THE TRACTIVE ability of a motor-vehicle, as stated by the author, is the measure of its power to overcome outside resistances to its translation, based on the tangential force exerted by the driving wheels at their points of contact with the road. The propelling force is derived from the engine. To compute the “tangential force” of the foregoing definition it is engine torque that interests us rather than the horsepower, he states. If the horsepower is given, it can be converted into torque. After analyzing this point mathematically, the author discusses typical tractive-factors of modern motor-trucks so that he is enabled to develop an economic factor mathematically and thus be prepared to discuss tractive resistance as opposed to tractive effort. Air resistance is considered in detail as a particularly important factor concerning motorcoaches, and the author's points are backed up by diagrams and charts as well as by numerous tables of statistical and computed data.
THE AUTHORS say in part that although it has been recognized for many years that electrical ignition systems on airplane powerplants are a prolific source of disturbances tending to prevent the successful reception of radio signals, the serious and intensive development of methods of suppressing such interference is a comparatively recent undertaking. This arises from the fact that only in recent years has special significance been attached to radio operations with limited collecting structures or antennas, over such distances that the signaling waves intercepted by these antennas are relatively weak. They then outline the systems in which interference is present and discuss how it can be suppressed.
THE PAPER urges united cooperation instead of the present division of responsibility between the engine designer and the airplane designer in the installation of aircraft engines. The tubular rings upon which engines are commonly mounted are usually supported by structural members that are welded to the ring and attached to the fuselage at the four longitudinals. Inaccuracy is common in these structures, and many of them lack sufficient stiffness. Gravity gasoline-feed is recommended for its simplicity, provided the pressure head required by the carbureter can be secured, but the author reports having seen an installation in which the engine would operate so long as the airplane had its tail on the ground, yet the engine would die as soon as the tail was raised during a take-off. The use of gasoline-resisting rubber-hose with metal liners and the avoidance of sharp bends are recommended for the gasoline connections.
COMPARATIVELY large rake and clear angles required for best results leave a relatively thin cutting-edge on a cutting tool for aluminum. One difficulty encountered is that tools of such form are not always available or suitable, for various reasons, for instance, small tools of various types are available only with cutting edges suitable for steel and bronze, and the desirable amount of top rake cannot well be provided on circular form-tools. Tool bits of various sorts can be reground to the desired angle. A simple round form of tip that is shown can be utilized in tools for various purposes, including use as inserted teeth in a face-milling cutter. High-speed-steel tools are suitable for most aluminum alloys, but alloys containing a high percentage of silicon can be machined to advantage only by using cemented tungsten-carbide. Machine-tools should be suitable for high speed.
CYLINDER-BLOCKS, with their hollow form and complicated arrangement of water-jackets, valve passages, pockets and bearings, are difficult to cast, and require a large quantity of cores. These have generally been baked or dry-sand cores, but the author's organization has met with success in making the more bulky cores, those for the cylinder-barrels and crankcase, in green sand. Descriptions and copious photographs and drawings are given of two methods of molding one six-cylinder block in green sand, and the possibilities of the system are indicated by illustrations of cylinders and details of cylinders that have been molded or that are suitable for molding in green sand. Cooperation between designer and foundryman is essential in realizing the economy possible with this method of molding, a large part of which results from the great saving in cost of sand.
MAINTENANCE is a part of automotive production and as such is destined to adopt production standards. While passenger-car manufacturers have fostered the application of these standards to maintain a parity between factory production and maintenance, commercial-vehicle operators have established standards and methods in response to an economic demand to obtain low-cost maintenance. How this has been done in Philadelphia is the subject of the paper. Scheduling vehicles through the shop in accordance with the seasonal requirements of transportation enables a centralized shop having 120,000 sq. ft. of floor space to service a fleet of 450 motorcoaches, 1500 taxicabs and approximately 150 pieces of various utility equipment with practically no fluctuations in the working force and the minimum number of spare units. Major overhauling of motorcoaches is done in the winter months when the demand is relatively light, while the taxicabs receive attention in the summer.