Stating that most of the copying of aircraft practice in post-war car-design has proved a failure because the fundamental difference in duty has not been realized, the author proposes to show wherein the automobile designer and the engine builder can profit by the use of practice developed for air-cooled aircraft engines and, after generalizing on the main considerations involved, discourses on the simplicity of layout of the efficient air-cooled cylinder as a preface to a somewhat detailed discussion regarding cylinder design and performance, inclusive of valve location, type of finning and form of cylinder-head.
Cylinder material, cooling surface, port arrangement for in-line engines, and the camshaft and valve-gear arrangement most desirable are subjects treated at length and illustrated, the thought then passing to a consideration of sleeve-valve types, temperature and exhaust-valve cooling, in such detail as to include many enlightening data; and similar treatment is accorded the subjects of air supply, a cooling system for in-line engines, air-blast direction and the necessary quantity of air. Desirable types of fan, spark-plug, piston and fuel are commented upon somewhat briefly. The author concludes (a) that scaling-down of design in internal-combustion-engine cylinders is a safe process, while scaling-up is decidedly unsound; (b) that, since thermal troubles have been the greatest cause of difficulty with air-cooled cars, a consideration of the designs capable of continuous full-throttle operation is likely to demonstrate the ease with which the relatively mild thermal difficulties of an air-cooled car can be overcome.
Appendix 1, by C. Fayette Taylor, treats the subject of the experimental development of air-cooled engine-cylinders specifically; it reviews briefly the methods used by the Engineering Division in developing and testing cylinder units for both air and water-cooled engines, and discusses some of the results obtained with several of the air-cooled cylinders mentioned in the paper proper. Performance investigations of experimental cylinders are described and commented upon, inclusive of illustrations and tabular data that are given rather lengthy attention. Laboratory experience in regard to exhaust-valve cooling is related, together with mention of the experimental results with internally cooled valves. Subsequently, many air and water-cooled-type comparisons are made, the conclusion being that there will be a rapid and healthy growth of the air-cooled type of powerplant for automotive vehicles.
Appendix 2, by E. H. Dix, Jr., has as its subject the foundry production of air-cooled cylinders with the fins cast integrally and first describes the experience of the Engineering Division foundry in casting aluminum-alloy cylinder-heads, numerous illustrations of castings being included. The suitable gating for aluminum-alloy casting is discussed, supplementary illustrations being presented, and the conclusion is reached that the experience related tends to show that air-cooled cylinder-head castings of the types illustrated are far from being bad production propositions.