One of the most important branches of aeronautical engineering is that dealing with powerplant design, construction, installation and repair and aeronautical engineers may be divided into two main groups, "plane" men and "engine" men. The division of the engine men is in three main classes; designers, builders or production men and ﬁeld men who are concerned with installation, maintenance and repair. Specialists in any of the subdivisions find that it takes all their time to become familiar with the many phases of the subject they are interested in. While the author has had a broader experience than many of the specialists, it is only because he has been identiﬁed with aviation since its inception and because of particularly fortunate circumstances while serving on the Staff of the Chief of the Air Corps during the World War, which offered unexcelled opportunities to obtain experience on a larger scale than normal peace time activities permitted.
Regardless of this experience, the author has found it desirable and even necessary to consult other authorities and specialists in order to check up on his own opinions and experience and every effort has been made in this treatise to present both sides of every controversial subject. The reader may select the line of reasoning that best applies to the case under consideration and no matter what he ﬁnally accepts, he will ﬁnd ample authority as a basis for his line of thought. In preparing this work the author has made references to the authority responsible for the opinions or information presented and in every case due acknowledgment is made in the text to the expert quoted, when the opinions are not those of the author.
There are many sources of aeronautical data at the present time besides the manufacturers of airplanes, engines and auxiliary apparatus. Government documents and publications of the Engineering Division, U. S. Army Air Corps, with laboratory facilities at Wilbur Wright Field, Dayton, Ohio; and also those of the National Advisory Committee for Aeronautics, Washington, D. C.; have been consulted freely and brief excerpts and abstracts from these public documents have been used to bring out points in the text that were considered in greater detail in reports of experts and specialists. The United States Bureau of Standards, and the United States Department of Commerce, Washington, D. C., have also published much valuable data in the form of reports issued in co-operation with the Government agencies previously mentioned.
The membership of the Society of Automotive Engineers, Inc., includes many aeronautical experts and specialists and much valuable data has been published in the S.A.E. Journal on aviation and kindred subjects. The publications Aviation and Aero Digest of New York City were also of great value and references to editorial opinions and descriptions of aircraft engines, have also been included to justify and support some of the opinions of the author. Such leaders in the industry as the Goodyear-Zeppelin Co.,