Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft.It has two major and overlapping branches: Aeronautical engineering and Astronautical Engineering. Avionics engineering is similar, but deals with the electronics side of aerospace engineering. Early knowledge of aeronautical engineering was largely empirical with some concepts and skills imported from other branches of engineering. Scientists understood some key elements of aerospace engineering, like fluid dynamics, in the 18th century. Many years later after the successful flights by the Wright brothers, the 1910s saw the development of aeronautical engineering through the design of World War I military aircraft.