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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.

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.

It is stated that in cases where cylinder distortion produces exhaust valve leakage, the problem of valve burning becomes one of considerable difficulty. A flexible exhaust valve seat, which apparently conforms to the valve and produces a tight seat even though the cylinder head be distorted, has been designed and tested. Apparently complete sealing of the valve was secured in a cylinder known to be subject to exhaust valve seat distortion. This result indicates that heat dissipation through the seat is not of major importance when a tight seal of the valve is secured. The use of flexible inserts may remove some present limitations on cylinder design.

THE great increase during the last 20 years in the knowledge of fuel behavior in piston engines the author attributes largely to the use of full-scale engines for fuels testing and engine development work, the use of pure compounds as reference standards, and the standardizing of laboratory knock-test methods. He sees preignition, fuel-air mixture distribution, and stability of stored fuels as engine-fuel problems which may have to be tackled in the next few years if development of the piston aircraft engine continues. Mr. Heron presented this lecture after receiving the Horning Memorial Award for 1945.

THIS paper is an elementary nonmathematical discussion of the essential thermal processes of gas turbines with emphasis on turbine types suitable for use in vehicles. A brief history is followed by discussion of the limitations imposed by strength of materials. The effects of pressure ratio, compressor and turbine efficiency, turbine inlet temperature, and atmospheric temperature upon output and thermal efficiency, are discussed., The effects of regeneration upon thermal efficiency at full and part load, with particular emphasis upon the latter, are discussed, and the regenerator is stated to be essential to obtain acceptable fuel mileage in vehicle use. The probable performance parameters of a vehicle turbine of about 200 rated hp are explored.

OIL cooling of aircraft powerplants is increasingly difficult. The weight and drag of the oil coolers necessary with the present maximum “Oil-in” temperature of 185 deg. fahr. (85 deg. cent.) are both decidedly objectionable. It appears possible to increase the “oil-in” temperature to about 220 deg. fahr. (104 deg. cent.) with oils which can be produced by the newer refining methods. The use of an “oil-in” temperature of 220 deg. fahr. would render possible a material reduction in weight, size and drag of oil coolers in comparison with present practice. Oils suitable for use at 220 deg. fahr. “oil-in” temperature would not be likely to cause a material increase of engine-starting difficulty, as they would only be used in summer when the shearing resistance of the oil has slight influence on engine starting. The approximate temperature cycle encountered by the oil in its passage through a modern aircraft-engine is discussed.

A STUDY has been made of materials available and suitable for the construction of transparent windows employed for observation inside the combustion-chamber. Materials that can be used include quartz, spinel, sapphire, periclase, and fluorite. The transparency of these materials in the infrared region increases in the order just mentioned. Mechanical strength varies greatly, being highest for sapphire and lowest for fluorite. Resistance to the chemical action of the combustion products varies widely. Sapphire is not attacked by any products of combustion, including the lead oxide present when leaded fuels are used. The choice of a suitable material for a given investigation will be based on a judicious balance of the four chief characteristics: mechanical resistance, chemical resistance, transparency, and cost.