Gottinger Monograph N

"All volumes of the monographs--Brunswick Monographs were issued and had been translated into English immediately following WWII, except for one: this Volume N about rotary-wing developments made by German scientists between 1939 and 1945. In contrast to a fixed wing aircraft, a rotary-wing aircraft generates its lift not from rigid wings, but rather from large, slowly moving air screws with approximately vertical axis."--