History of Airframes

Recognized as the mechanical skeletal structure of an aircraft, airframes encompass the fuselage, undercarriage, empennage, and wings. Airframes are designed with a combination of aerodynamic, materials technology, and manufacturing methods that place a major focus on weight, strength, aerodynamic drag, reliability, and cost. To better understand the complexity of these structures, this blog will outline their long history and importance.

The modern airframe has a long history that can be traced to Orville and Wilbur Wright’s 1903 wood biplane that revealed the potential of fixed-wing designs. It was not until 1912, however, that the Deperdussin Monocoque became the first strong and streamlined monocoque fuselage formed of thin plywood layers over a circular frame. Like most developments in the aviation industry, many fuselage designs can be pinpointed to military needs.

During WWI, Dutch designer Anthony Fokker devised combat aircraft for the German Imperial Army, US Curtiss flying boats, and German/Austrian Taube monoplanes, all of which featured hybrid wood and metal structures. By 1915, the German Luft-Fahrzeug-Gesellschaft (LFG) aircraft manufacturer designed a fully monocoque all-wood structure with only a skeletal internal frame, utilizing strips of plywood that took advantage of a wrapped-body construction known as Wickelrumpf.

By 1916, German biplane fighters were made with semi-monocoque fuselages with load-bearing plywood skin panels affixed to longitudinal longerons and bulkheads. Since then, this design has been replaced by the popular stressed skin structural configuration as metal began taking over wooden designs. Just a year before, German engineer Hugo Junkers carried out a test flight for the first all-metal airframe with entirely metal cantilever wings and a stressed-skin monoplane made of steel.

A few years later in 1919, 300 all-metal aircraft were built, alongside the first four-engine, all-metal passenger aircraft, the Zeppelin-Staaken E-4/20. Going into the 1920s and 1930s, aircraft development began to focus on monplanes using radial engines, one notable model including the Spirit of St. Louis that was flown across the Atlantic by Charles Lindbergh in 1927. Just two years later in 1929, the Hall Aluminum Company’s XFH naval fighter prototype was flown, serving as the first aircraft with a riveted metal fuselage. This fuselage type consists of an aluminum skin placed over steel tubing using rivets.

By the second world war, military needs drove the need for more complex airframe designs, of which the US C-47 Skytrain, B-17 Flying Fortress, B-25 Mitchell, P-38 Lightning, and British Vickers Wellington using a geodesic construction method were born. However, due to the wartime scarcity of aluminum, many subsequent models were built from wood. Toward the end of the war, commercial airframe design focused on airliners, turboprop engines, and jet engines. With the higher speeds and tensile stresses of turboprops and jets, newly developed aluminum alloys with copper, magnesium, and zinc were employed in such aircraft.

Over time, with the need to meet rigid weight requirements and safety regulations, boron fiber composites and other carbon fiber reinforced polymers were preferred for their reduced weight and cost. By the end of the 20th century, major manufacturers like Airbus, Boeing, ATR, Bombardier, and others were taking great strides to improve airframes even further. For instance, the vertical stabilizer of the Airbus A310-300 flown in 1985 was the first carbon-fiber primary structure utilized in a commercial aircraft. In 1998, the Cirrus SR20 served as the first widely produced general aviation aircraft made of an all-composite construction. The following years proved that composites were definitely here to stay, oftentimes in combination with metals for added durability.

In 2009, the Boeing 787 was the first commercial aircraft where 50% of its structure was made from carbon fiber composites, aluminum accounted for 20%, and titanium made up another 15%. This combination of materials allowed for lower drag, a higher wing aspect ratio, and higher cabin pressurization. Serving as a worthy competitor, the Airbus A350 that was flown in 2013 was made of 53% carbon-fiber. By 2016, the first certified light jet composed entirely of carbon-fiber composites was introduced. Since then, technology has continually advanced, meaning that the aviation industry will see even more changes to airframe structures, making air travel safer and more efficient.

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