A Packard Diesel Aircraft Engine

This book excerpt discusses the design and function of the Packard-Diesel engine as compared to earlier gasoline aircraft engine models, including increased fuel economy and reliability.

| January/February 1996

Packard Diesel Aircraft Engine Elevation

Fig. 65. Packard Diesel Aircraft Engine Elevation Partly in Section. Courtesy of Society of Automotive Engineers and Packard Motor Car Co.

Society of Automotive Engineers

Walter Taubeneck of Marysville, Washington thought our readers would be interested in this section of the book, Diesel and Other Internal Combustion Engines by Howard E. Degler, published by the American Technical Society in 1937. 

The Packard-Diesel aircraft engine is of the radial air-cooled type having nine cylinders with a bore of 4-13/16 inches and a stroke of 6 inches. It gives a displacement of approximately 980 cubic inches per minute. The engine is rated at 225 horsepower at 1950 revolutions per minute and weighs 510 pounds.

An inspection of Figs. 65 and 66 (see the Image Gallery) reveals a radical departure from the usual engine in that each cylinder is provided with only one valve, which serves for both inlet and exhaust. The single rocker-arm box, which is slanted in the direction of the spiral of slipstream, contributes considerably to the clean external appearance of the Packard- Diesel engine (Fig. 65), and what is more important, to its low parasitic drag.

Engine Speed and Weight

In the Packard engine, an advance that has been effected over previous Diesel practice consists in the ability to extend the range of engine speeds possible with the Disel  cycle. Heretofore Diesel engines in stationary and marine service have been of the low-speed type, 100 to 500 rpm. Even so-called high-speed Diesels of modern type have been limited to a maximum speed of about 1500 rpm. With this engine the speed has been increased to more than 2000 rpm., which has been attained by an engine design that produces a turbulence never before approached in this type of engine. The engine design and the highly efficient and quick-acting fuel pumps that were developed to go with it are the means that produce the accelerated co-mingling of the fuel and air which brought about this greatly increased engine speed. The fuel pumps give a positive and metered supply of fuel.

The most interesting aspect of the design is undoubtedly a consideration of the features that reduced the weight of the engine to practically the same level as that of gasoline engines of equivalent power. Heretofore (1935), even Diesel engines of the so-called light-weight modern type weighed about 20 pounds per horsepower, whereas this engine weighs but one-tenth as much, i.e., 2.3 pounds per horsepower.

A minimum of weight is essential for any successful aircraft engine; new methods of construction were employed in the Packard-Diesel to reach this desired objective. Important weight economies were secured; first, by the elimination of carburetors and magnetos; and second, by an intensive simplification of design, as shown in Figs. 65 and 66. Evidence of the latter are found in the one-piece crank case construction of extremely light weight and single-valve arrangement which automatically halves the number of parts required for valve operations as used on conventional gasoline engines.