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A STUDY of the operation of aircraft gas turbine powerplants under various atmospheric conditions shows that trends in performance will not always be similar to the trends noted with reciprocating engines. High humidity will have a negligible effect on performance, but ingested water will automatically increase power in a turbine engine regulated by speed and combustion-temperature controls without a power-limitation device. Abrasive, erosive, or contaminating matter in the air stream may change blade contours and clearances, decreasing compressor efficiency, engine power, thrust, and overall efficiency. Several inertia-type separators which should be useful in removing foreign material, especially moisture, from the air stream are described.

THIS report on a canvass of a number of engineers concerned with aircraft, aircraft powerplants, and fuels and lubricants indicates that the reciprocating engine will continue to occupy a paramount position among aircraft powerplants for the next 10 years. Turboprops will gradually displace reciprocating engines in some types of airplanes, chiefly air transports and bombers. Turbojets will be common soon in fighters and later in bombers. But small aircraft will still be relying on reciprocating engines in 1957, according to the survey.

THE speed-density carburetion system meters fuel in accordance with engine rpm, intake-manifold temperature, intake-manifold pressure, and exhaust back pressure. The advantage of the system is that these variables can be read and the carburetor settings directly derived or checked during flight. A separate fuel-feed control is provided to govern intake-manifold pressure and temperature - the two main factors affecting detonation.

AN approach to the problem of selecting the optimum compression ratio and spark timing as related to the antiknock qualities of the fuel to be used, has been developed. First it is determined at points throughout the range of engine speeds how far the spark can be advanced before knock appears or power falls off. Then a distributor curve is drawn which is just safely under the curve of maximum permissible spark advance versus engine speed. This information is recorded for each compression ratio under consideration. Finally power output and specific fuel consumption at the spark timing indicated by the distributor curve are compared for the different compression ratios. It has been found that fuels of high sensitivity permit greater spark advance than fuels of low sensitivity.

THE troubles that are experienced when the conventional type of spring suspension is used in commercial vehicles could be eliminated, the author claims, by using the torsion-bar type of suspension. The torsion bar, he says, offers such advantages as weight reduction, reduction of unsprung weight, improvements in riding, stability, and steering.

THIS description of the hydraulic control used with the hydra-matic transmission reveals how the control operates to change ratios under power without direction from the driver. The control's pattern of automatic shifting for ordinary, high-range driving has been selected as the best compromise between top performance and low ratio of engine noise to wind noise. The control's low range shifts gears according to performance dictates alone, furnishing greater power for extreme conditions at low speeds and enabling the driver to use his engine as a brake on steep descents. Heart of the control system is a double hydraulic governor, sensitive both to car speed and throttle opening. THIS paper, as well as the two that follow, one by Messrs. Nutt and Smirl and the other by Mr. Kimberly, make up a symposium on automatic transmission components presented at the 1947 SAE Summer Meeting.