PREFACE: This volume has been prepared with a twofold aim: 1. It is designed for a textbook in engineering courses for undergraduate and post-graduate students. 2. It forms a collection of material which is largely new, and which should prove valuable to anyone concerned with design, construction, operation, or maintenance of aircraft engines. This book covers the basic theory and principles of aircraft-engine design and operation, and the authors believe it to be one of three volumes required in a complete course in the design of aircraft engines, the other two being an aircraft-engine design handbook and a textbook on engine dynamics. The authors have attempted to obtain balance in the treatment of the various phases of the subject, and to assemble the material in a serviceable manner which would lend itself readily to amplification and more rigorous development of topics by means of collateral reading and problem work. Opportunities for problems and extension of thought may be discovered, even if they are not suggested, in almost any article in this book. Brevity has been the keynote, although amplification of some phases has been deemed necessary for the sake of greater clarity. Cumbersome introductions, particularly, have been avoided. In attempting to keep this volume from deteriorating into a mere collection of information, which is the most useless and deadly form of textbook, attractive new landmarks have been emphasized and even the old material has been presented differently. All the subject matter is presented in a manner designed to stimulate the forward-looking mind and to develop the spirit of investigation and self-reliance needed for progress in aircraft power plants. The authors have had, between them, varied experiences in the design, construction, operation, maintenance, and testing of internal-combustion engines in different usages.