Figure 1-6.  The Junker J-1 all metal construction in 1910. Leading up to World War I (WWI), stronger engines also  allowed designers to develop thicker wings with stronger  spars. Wire wing bracing was no longer needed. Flatter, lower  wing surfaces on high-camber wings created more lift. WWI  expanded the need for large quantities of reliable aircraft.  Used mostly for reconnaissance, stacked-wing tail draggers  with wood and metal truss frames with mostly fabric skin  dominated the wartime sky.  [Figure 1-7]  The Red Baron’s  Fokker DR-1 was typical.  construction of the fuselage.  [Figure 1-9]  The fiberglass  radome was also developed during this period. After WWII, the development of turbine engines led to  higher altitude flight. The need for pressurized aircraft  pervaded aviation. Semimonocoque construction needed  to be made even stronger as a result. Refinements to the  all-metal semimonocoque fuselage structure were made to  increase strength and combat metal fatigue caused by the  pressurization-depressurization cycle. Rounded window  and door openings were developed to avoid weak areas  where cracks could form. Integrally machined copper  alloy aluminum skin resisted cracking and allowed thicker  skin and controlled tapering. Chemical milling of wing  skin structures provided great strength and smooth high- In the 1920s, the use of metal in aircraft construction  increased. Fuselages able to carry cargo and passengers  were developed. The early flying boats with their hull-type  construction from the shipbuilding industry provided the  blueprints for semimonocoque construction of fuselages.  [Figure 1-8]  Truss-type designs faded. A tendency toward  cleaner mono-wing designs prevailed. Into the 1930s, all-metal aircraft accompanied new lighter and  more powerful engines. Larger semimonocoque fuselages  were complimented with stress-skin wing designs. Fewer  truss and fabric aircraft were built. World War II (WWII)  brought about a myriad of aircraft designs using all metal  technology. Deep fuel-carrying wings were the norm, but the  desire for higher flight speeds prompted the development of  thin-winged aircraft in which fuel was carried in the fuselage.  The first composite structure aircraft, the De Havilland  Mosquito, used a balsa wood sandwich material in the  Figure 1-8.  The flying boat hull was an early semimonocoque design  like this Curtiss HS-2L.  Figure 1-7.  World War I aircraft were typically stacked-wing fabric- covered aircraft like this Breguet 14 (circa 1917). 1-4