Göttinger monograph N: German research and development on rotary wing aircraft (1939 1945) 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.