Great changes in materials from wood to composite aircraft manufacturing

What is aircraft material?
Aircraft materials range from body materials (both structural and non-structural materials) to engine materials and coatings. The most important of these are the structural materials of the body and the engine materials. In general, non-structural materials include: transparent materials, cabin facilities and decorative materials, accessories and piping materials for systems such as hydraulics and air conditioners, radomes and electromagnetic materials, and tire materials. Non-structural materials are used in small quantities, but they are very diverse, including glass, plastics, textiles, rubber, aluminum alloys, magnesium alloys, copper alloys, and stainless steel.
The structural material should have as high a specific strength and specific stiffness as possible to reduce the structural weight of the aircraft. The reduction in structural weight can improve flight performance and improve economic efficiency or operational effectiveness. At the same time, the structural material should also have good processability to facilitate the fabrication of the required parts, which in turn involves process issues.
Wood-framed aircraft have been popular since the 1930s. Even Boeing’s founder, William Boeing, was originally a timber merchant in Seattle. According to Wikipedia, the first powered material developed by the Wright brothers, "Flighter 1", was made from spruce. Among the materials used, wood accounts for 47%, steel accounts for 35%, and cloth accounts for 18%. The propeller is also wooden and the entire aircraft has no designed seats.
In the more than 100-year history of aviation manufacturing development, the upgrading of aircraft materials presents a state of high-speed change and transformation. Throughout the history of human aviation, materials and aircraft have been continuously developed and improved under mutual promotion.

The era of wooden fabric
At the beginning of the last century, the world’s first manned aircraft was in heaven. The material used by the inventor Wright brothers was dominated by wood, accounting for 47%, followed by steel (35%) and cloth (18%). Of course, the flight time of this aircraft is only 16 kilometers. The early planes only flew off the ground with brave explorers. At that time, the designer was the driver. Because the simple structure of the body is very unreliable, ordinary people are afraid to take risks.
In the early days, the aircraft used wooden strips and wooden plywood to make the girders and skeletons, and linen was used as the wing surface of the wing. This is called the aircraft wooden cloth structure. Between the wood and the laminate, it is usually spliced ​​with bolts. The wings are covered with varnished linen, which is sewn together with the ribbed frame, while the varnish ensures the stiffness of the airfoil, its geometry and strength. This material structure has been used until the end of the First World War, but the aerodynamic shape and internal structure of the aircraft are more reasonable and perfect.
Since the 1920s, semi-rigid fuselage and wing with airfoil space have been designed, and the performance of the aircraft has been greatly improved, and new requirements have been placed on aircraft materials. In parts where local forces are applied, such as engine mounts and fairings, metal parts are used more, but the airfoil, the rudder surface and the rear fuselage are still partially covered with cloth. This is called the aircraft semi-metal structure.

The rise of metal materials
In 1906, German metallurgists invented the hard-aluminum that can be aged, also known as Dura aluminum, making it possible to manufacture aircraft with all-metal structures. In the 1920s, very few aircraft began to try harder hard aluminum alloys. Hard aluminum alloys replaced the original wooden skeletons and ribs, and also replaced a large fabric wing skin. However, the non-bearing components on the aircraft still used a low-cost wooden fabric.
At that time, there were designers in the Soviet Union and other countries who tried to use "unfinished" steel to make airplanes, even small passenger planes. Steel has a higher specific gravity than aluminum, so it is certainly not a good idea for an aircraft designer who is "to fight for every gram of structural weight." Heavy metals are not part of the aircraft, and their use will seriously impair the flight performance or performance of the aircraft. In the end, it is also expected that the weird "steel plane" will be abandoned.
After 1925, many countries gradually replaced steel with steel pipes to make fuselage skeletons, and used aluminum panels to make skins to create all-metal aircraft. The all-metal structure aircraft increases structural strength, improves aerodynamic shape, and improves aircraft performance. By the 1940s, the speed of all-metal structures had exceeded 600 kilometers per hour.
However, there are also many people who have made hard aluminum sheets extremely extreme. As an advanced aviation country at the time, Germany and the United States tried to use a thin aluminum plate pressed into a fine corrugated shape to make the surface of the aircraft surface in the late 1930s. Such a shape can additionally increase its longitudinal strength. The world's first passenger aircraft designed for passenger aircraft, the Junker F13 and other series of passenger aircraft or transport aircraft of the Junker, Fogg and Ford brands have successfully used this external material. It is important to note that until now, hard aluminum is still the main material for aircraft worldwide.
By the early 1940s, many countries had an urgent need for non-ferrous metals, especially aviation aluminum, due to war. Some factories have also become a retro dream of "wood planes." As the most successful example, the Royal Air Force's "mosquito" fighter-bomber was the most prestigious model at the time. "Wood Plane" uses a large number of glue-bonded structural parts, which are not only sturdy and durable, but also have good combat performance.
After entering the 1950s, humans entered the era of supersonics. Aircraft materials are particularly focused on high temperature resistance, and humans are beginning to look for new high-strength heat-resistant materials. As a result, a solid and heat-resistant titanium alloy and stainless steel for aviation have emerged. Among them, the successful development and application of titanium alloys have played a major role in solving the thermal barrier problem of wing skins. However, it should be pointed out that they are particularly difficult to process, and because of the large specific gravity, they are usually used only in special parts, internal skeletons and landing gear pillars. As a special case, these special steels have also been used on a very large number of special aircraft. For example, in the 1960s, the all-titanium spy plane SR-71, which could fly at 3 times the speed of 30,000 meters, appeared.

Composite materials came into being
With the advancement of materials science, since the 1970s, a new generation of aviation materials - composite materials - came into being. It is equivalent to a "plastic" incorporated into the reinforcing fibers, such as a glass fiber blended in an epoxy resin. The composite material has the characteristics of high specific strength, high rigidity and light weight, and has a series of advantages such as anti-fatigue, vibration reduction, high temperature resistance and design. It allows the aircraft to reduce weight while maintaining the original strength, or at the same weight, with higher strength. The economic and military benefits created by composite materials are imaginable. The most extreme example is the emergence of the world's first "all-plastic" aircraft AVTEK400 in the 1980s.
Since the advent of the first generation of composite glass fiber reinforced plastics with glass fiber and organic resin, ceramic fiber and boron fiber reinforced composite materials have been successfully developed, and the performance has been continuously improved, which makes the field of composite materials appear a life. However, in most cases, composite materials still cannot completely replace traditional aluminum-based metal materials, and most of them are only used on non-main bearing components, such as rudder skins, equipment flaps, small aircraft fuselage and wings. Skinned and so on.
In addition, the aircraft's airborne radar is generally made of glass fiber reinforced plastic head cones, which are covered to transmit electromagnetic waves. The cockpit cover and windshield of the cockpit are made of acrylate transparent plastic (plexiglass), while the main landing gear of the aircraft must use ultra-high-strength structural steel with good impact toughness.
With the advancement of aerospace technology, a new generation of composite materials is available, the best of which is carbon fiber composites. It features: high strength (5 times that of steel), excellent heat resistance (can withstand temperatures above 2000 degrees Celsius), excellent thermal shock resistance, low coefficient of thermal expansion, low heat capacity (energy saving), low specific gravity (It is 1/5 of steel), excellent corrosion resistance and radiation performance. Since the 1970s, more and more aircraft have adopted new composite materials reinforced with boron fiber or carbon fiber. Aluminum, titanium, steel and composite materials have become the basic structural materials for modern aircraft.
In the 21st century, advanced aircraft have become more and more popular with carbon fiber composite materials, and even its proportion in the total weight of aircraft structures is used as a hard indicator for measuring a country's aircraft manufacturing technology, and is used for mains such as wings and even front fuselage. The direction of bearing components is developing.
The advancement and development of aviation technology has played a positive role in promoting the development of aviation materials. At the same time, the development of materials science and engineering, the emergence of new materials, the advancement of manufacturing processes and physical and chemical testing technologies, and the provision of important material and technical foundations for the design and manufacture of new aviation products, thus playing a role in the development of the aviation industry. Effective promotion.
From a material science perspective, the Boeing 787 is a revolutionary leap in manufacturing history. The Boeing 787 uses composite materials over a large area of ​​the fuselage and main structure, which not only reduces the weight of the aircraft, but also reduces the maintenance burden on the airline. Boeing's data shows that composites account for 50% of the Boeing 787's structural weight (80% of volume), aluminum accounts for 20%, titanium accounts for 15%, steel accounts for 10%, and other materials account for 5%.

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