Airframe  The mechanical structure of an aircraft is known as the airframe. This structure is typically considered to include the fuselage, undercarriage, empennage and wings, and exclude the propulsion system. Airframe design is a field of aerospace engineering that combines aerodynamics, materials technology and manufacturing methods with a focus on weight, strength and aerodynamic drag, as well as reliability and cost. Modern airframe history began in the United States when a 1903 wood biplane made by Orville and Wilbur Wright showed the potential of fixed-wing designs. In 1912 the Deperdussin Monocoque pioneered the light, strong and streamlined monocoque fuselage formed of thin plywood layers over a circular frame, achieving . Many early developments were spurred by military needs during World War I. Well known aircraft from that era include the Dutch designer Anthony Fokker's combat aircraft for the German Empire's "Luftstreitkräfte", and U.S. Curtiss flying boats and the German/Austrian Taube monoplanes. These used hybrid wood and metal structures. By the 1915/16 timeframe, the German Luft-Fahrzeug-Gesellschaft firm had devised a fully monocoque all-wood structure with only a skeletal internal frame, using strips of plywood laboriously "wrapped" in a diagonal fashion in up to four layers, around concrete male molds in "left" and "right" halves, known as "Wickelrumpf" (wrapped-body) construction - this first appeared on the 1916 LFG Roland C.II, and would later be licensed to Pfalz Flugzeugwerke for its D-series biplane fighters. In 1916 the German Albatros D.III biplane fighters featured semi-monocoque fuselages with load-bearing plywood skin panels glued to longitudinal longerons and bulkheads; it was replaced by the prevalent stressed skin structural configuration as metal replaced wood. Similar methods to the Albatros firm's concept were used by both Hannoversche Waggonfabrik for their light two-seat CL.II through CL.V designs, and by Siemens-Schuckert for their later Siemens-Schuckert D.III and higher-performance D.IV biplane fighter designs. The Albatros D.III construction was of much less complexity than the patented LFG "Wickelrumpf" concept for their outer skinning.