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Technical Paper

AIR FORCES on Radial Air-Cooled Engine Cowling - (as Determined from Pressure Distribution Tests)

1940-01-01
400163
THE purpose of this paper is to discuss some of the factors influencing engine cowl surface pressures; to present and analyze the results of pressure tests on one cowl model in the wind tunnel and on three representative cowl designs in flight; and to suggest methods of applying pressure-distribution data to the stress analysis of other cowls. The flight-test data presented are taken from test reports of the United Aircraft Corp. The structural design of an engine cowl is a matter of considerable importance. Because continued improvement in airplane speeds and the increased severity of tactical maneuvers have increased greatly the aerodynamic forces on the cowling, the need for data from which to calculate these air loads has become increasingly imperative, especially for certain military types which are required to execute terminal velocity dives.
Technical Paper

The PROBLEM of VALVE-STEM and VALVE-HEAD Deposits

1940-01-01
400161
DEPOSITS on valve stems today are causing about 50% of the valve trouble in the automotive field, and slightly more than 50% in the aircraft field, Mr. Colwell reveals. He contends that, although much work has been done on varnish and lacquer deposits, most of it has applied to pistons and rings, with valves receiving only passing interest. Valve deposits are divided into six classifications: those on the valve head; the hard, flint-like deposit from operation; varnish on the stem; deposits under the head and on the stem at the valve-head end of the guide formed by shuttle driving; deposits on intake valves; and deposits on valve seats. The fact that any oil will oxidize or decompose at some temperature found along the valve stem makes a complete solution of the build-up problem most difficult, Mr. Colwell points out. It has been definitely proved, he continues, that oils with good oxidation resistance at high temperatures cause the least trouble.
Technical Paper

Economic Aspects of LIGHT AIRPLANE ENGINES …

1940-01-01
400152
THIS paper discusses the parallel design and development work of two air-cooled engines with widely different applications, although the basic design of both engines is quite similar. Instead of following the usual aircraft practice in any detail, the author points out the advisability of using automotive practice and thus bringing about a simplicity in design which is impossible when following the normal aircraft practice. The cylinder design of the two engines is discussed and points of similarity shown. A description is given of an 80-hp, 176 cu in. aircraft engine, and the reasons why the design for this particular engine was selected over five other types which were designed, are given. It is pointed out that the use of large-production automotive equipment such as starters and generators in light plane engines effects economies which can never be expected by using the more specialized apparatus which is available for airplane engines only.
Technical Paper

Progress in Light Aircraft Engines

1940-01-01
400147
IF the gains in production of light aircraft made in recent years are continued at the same rate, the light plane and engine industry can be expected to at least double 1939 volume, Mr. Bachle points out graphically. Present trends are toward two types of light airplanes, he announces: those in the 50-hp class intended for student training and three-place or higher-performance types for private owner usage, requiring up to 90 hp. He tells how the output of one engine originally developed for a 50-hp unit had been increased to 80 hp, to put it into the latter type. Developments and refinements made to boost the output are described, covering cylinder-head design, exhaust valves and seats, pistons and rings, valve mechanisms, and fuel injection. The introduction of fuel injection (replacing carburetion) in light aircraft engines has been a major development of the year, Mr. Bachle asserts, and gives a detailed description of the injection equipment adopted.
Technical Paper

Engine Deposits-and the Effect of Some Fuel Additives

1940-01-01
400148
THE authors report equipment used and procedure followed in determining ratings of fuels and of engines in so far as they affect or are affected by fuel deposits. In other words, this paper is a discussion of fuel-residue ratings. Their study, they report, indicates that the combustion chamber of any internal-combustion engine, operating under any given set of conditions or under varying sets of conditions, is constantly attempting to attain and maintain an overall equilibrium which is composed of, and is being constantly balanced between, many definitely interrelated and interdependent equilibriums - mechanical, thermal, and chemical. The disturbing of any one of these equilibriums, they add, must be balanced or offset by compensating changes of one or more of the rest of the equilibriums.
Technical Paper

Piston-Ring Coatings and Their Effect on Ring and Bore Wear

1940-01-01
400143
PISTON-ring scuffing occurs most frequently during the break-in period and has been a problem to both the automobile and ring producers, for some time. Ring coatings have been under development for several years and their general adoption by nearly all automobile companies indicates both the need for them and their effectiveness. The coatings fall into two general classes, chemical and metallic. The chemical are: Ferrox, an iron oxide; Granoseal, an iron-manganese phosphate; Graphitox and Grafotox, a zinc-iron phosphate with colloidal graphite; and Surfide, ferrous sulphide. The metallic coating is of electrolytically deposited tin. Careful tests under accelerated wear or scuffing conditions on newly finished surfaces showed that untreated rings produced twice the wear that occurred on the coated rings when only the compression rings were coated. The difference in wear was even greater when both compression and oil rings were coated properly.
Technical Paper

Performance of Aircraft Spark-Ignition Engines with Fuel Injection

1940-01-01
400137
FUEL injection offers two main advantages over the carburetor: Low volatile fuels (safety fuel), which reduce the fire hazard, can be used; and the combustion chamber can be scavenged without the loss of fuel by the use of large valve overlap. Other advantages are improved starting, acceleration, maneuverability, and distribution of fuel, as well as freedom from icing. The National Advisory Committee for Aeronautics has investigated the factors influencing the injection of fuel into the engine cylinder. This investigation included the time of start of injection, the length of the injection period, the location of the fuel-injection valve in the cylinder, the rate of fuel injection, the type of fuel spray, and the maximum injection pressure. Tests were conducted on cylinders with two and four valves having pent-roof, disc, and spherical combustion-chamber forms.
Technical Paper

The Wear of Crankshafts with “Lead-Bronze” Bearings

1940-01-01
400131
CASE-HARDENING is a satisfactory means of reducing crankpin wear with “lead-bronze” or copper-lead bearings, the authors reveal. They report the results of tests to determine the relative wearing properties of various crankshaft materials when running against a typical copper-lead alloy bearing at a temperature of 212 F. In general and contrary to what was observed with the softer crankpin materials, bearing wear occurred more rapidly than crankpin wear, they divulge, this result being due largely to high initial wear of the bearings during the early part of the tests. Variations in composition-percentage of lead and tin, and hardness-of the copper-lead bearings did not have a marked effect on the wear obtained, they find.
Technical Paper

Processes in Injection Systems of Oil Engines

1940-01-01
400134
AFTER stating the general conditions affecting injection systems and, in particular, the difficulties of small cylinder size, the authors treat simple systems analytically, and demonstrate experimentally the validity of their treatment, limited, in the first instance, to open nozzles. The variables investigated include pipe length, engine speed, nozzle dimensions, throttle position, and also the viscosity, elasticity, and density of fuels. Conclusions are summarized. The authors next state the general conditions in the more usual systems embodying spring-loaded nozzle valves, piping, and special pump delivery valves, and gave a general mathematical treatment of these factors. They also investigate these systems experimentally, and here discuss the effects of variables: speed, throttle opening, pump delivery valve design, nozzle conditions. They conclude with deductions of value to engine designers.
Technical Paper

High-Output Aircraft Engines

1940-01-01
400133
INDIRECT or liquid-cooled aircraft engines fit into the picture of future aircraft types better than do the direct or air-cooled engines, the authors contend. As reasons for their belief they draw attention to the small frontal area of this type; the heat capacity of the liquid in equalizing temperatures; and greater freedom in cylinder design because large heat-transfer surfaces are unnecessary. Rolls-Royce has been producing liquid-cooled aero engines for 23 yr, they announce, and has concentrated a large staff on installation problems. One of the results of this work, they report, has been the development of the interchangeable powerplant in which the engine-mounting auxiliaries and bulkhead form a complete detachable unit. These units, the authors explain, are interchangeable within 48 hr, and provide interchangeability between air-cooled and liquid-cooled engines.
Technical Paper

Engine Combustion and Pressure Development - Effects of Mixture Ratio, Spark Position, and Throttle Opening on Flame Pictures and Pressure Cards

1940-01-01
400127
HIGH-SPEED motion pictures of the flames in a gasoline engine have been photographed, together with pressure records of the same explosions. These records of flame motion and pressure development have been examined to determine the effects of changing the mixture ratio, the spark position, and the throttle opening. Also, some quantitative relationships between the fraction of charge burned and the pressure developed at any time during the explosion have been tested with the experimental data observed while operating the engine under several sets of conditions. It is shown that, by means of these relationships, both the fractional volume and fractional mass of charge inflamed at any time may be calculated from the pressure cards with an accuracy comparable with the accuracy of the present experimental observations.
Technical Paper

Design Problems in the Quantity Production of Aircraft Engines

1940-01-01
400126
THE aircraft engine producer faces three unique conditions which make quantity production a complex problem: first, intensely rapid development; second, great pressure for perfection in reliability; and third, an unusually large number of variables in the product. The author points out that these special conditions all tend to emphasize the importance of quality in the design engineering, with particular reference to simplicity. The oil-circulating system of the aircraft engine is described as an example of one source of production and service troubles. Design improvements which have overcome these troubles are explained, including a new steel crankcase, the end-sealed master rod bearing, the “uniflow” piston, and a self-cleaning oil filter.
Technical Paper

SEVERE DUTY ENGINE CONDITIONS AS RELATED TO OIL AND FUEL

1940-01-01
400088
Engine performance (availability and operating costs), maintenance (parts affected) and life (general overhaul period) are today a problem of severe duty engine conditions. Severe conditions, generally, are measured in terms of high power output (horsepower per cubic inch of piston displacement or BMEP). Such operations have brought about high piston ring groove and valve guide temperatures, which greatly increase ring and valve sticking tendencies. In the case of some passenger car engines at high speed and some truck and bus engines overloaded, ring sticking is not a problem but high crankcase oil temperatures cause excessive oxidation resulting in varnish on piston skirts and overhead valve mechanism. Time between crankcase drains, alloy type bearings and blowby contamination all relate to the severity of engine conditions.
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