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The first American designed and built turboprop powered commercial aircraft, the Lockheed Electra, will go into airline use in 1958 with the Allison ‘power package’. This consists of the 3750 horsepower 501-D13 turboprop engine and the Aeroproducts ‘606’ turbo-propeller. The changes from the military T56-A-l engine are reviewed and the propeller features, such as the hollow steel ribbed blades and self-contained hydraulic system and regulator, described in some detail. It is disclosed for the first time that the propeller and engine reduction gear and other units as initially delivered will handle a higher rated power section, the -Dl5. In addition the -D13 power sections can be brought up to later ratings at fixed cost during overhaul when the new model goes into production. Control and safety features of the power package insure normal functioning of both engine and propeller in case of complete electrical system failure.

THIS paper recounts, step by step and model by model, the development of the Allison V-1710 aircraft engine - the first liquid-cooled military aircraft engine in production in this country. Since 1930, when the design of this V-type 12-cyl engine was initiated, the powerplant has been stepped up from 650 hp without supercharging to 1000-1500 hp in its supercharged state, and the weight has increased from about 1000 lb to 1320 lb, the author reveals. The following three underlying reasons are given for building the first V-1710 engine: 1. That the V-12 type of construction with its small frontal area could be installed with less drag than any other type of engine. 2. That a liquid-cooled engine could be operated at a higher power output per cubic inch due to the type and uniformity of cooling. 3. That the liquid-cooled engine would be more reliable because it is less sensitive to temporary overloads on account of the heat capacity and limiting temperatures (boiling) of the coolant.

A DISCUSSION is presented of the two-node as well as the single-node characteristics for various crankshaft systems both with regard to frequency and to severity of vibration. The effect of frequency on harmonic torque input, which is a measure of vibration severity, also is discussed. The paper shows that, with a careful selection of the vibration frequency, the harmonic torque input for various vibration orders can be reduced considerably. A method is presented for the selection rather than the determination of vibration frequencies. It shows that, by the careful selection of frequencies, certain harmonic orders both for single-node and two-node vibration can be minimized appreciably and/or eliminated from the normal operating range of the engine. The friction-type and the dynamic-pendulum-type vibration damper are discussed. This paper brings out the fact that a definite restriction on vibration amplitude (degrees) cannot be used to limit the severity of torsional vibration.