The Sikorsky plant in Bridgeport, Connecticut, is the base of operations for Mr. Lent (whose other non-fiction, for late pre-teens and up, has made his name a standby in the market) who gives us a pretty full description of helicopters. Starting with a brief note on their history and the inventors who pioneered to make the first successful ones, Mr. Lent moves quickly into the most important part of his book- how the modern helicopter is built, works and flies. Its components and controls, the tests made at the plant, the theory of its suspension and flight in various altitudes, the work of the machine shop and the assembly line, are all satisfyingly described and accounted for in this introduction to these machines. To our knowledge it is the first juvenile to deal this extensively with the inner workings of the helicopter.