The Most Common Aircraft Structure Materials

DALLAS — To ensure the safe, efficient, and economical operation of commercial aircraft during all phases of flight, care is taken to choose the right structural materials during the design, repair, and maintenance of aircraft and their components.

These materials should have the following desirable characteristics: the capacity to resist abrasion and penetration (hardness), the ability to resist deformation (strength), the ability to be bent or twisted without breaking (ductility), the ability to return to its original size and shape after a load is removed (elasticity), the ability to conduct heat or electricity (conductivity), the strength-to-weight ratio, and fatigue resistance.

Different parts of the aircraft must be manufactured and maintained with specific qualities and properties of structural materials because of the amount of load, stress, exposure to various environmental factors like extreme heat and fire, the purpose of the aircraft (subsonic or supersonic), reliability, and many other factors.

Steel alloys, aluminum alloys, composite materials, plastics, rubber, fabrics, and wood are some examples of these materials. The main uses for the material in an aircraft are decided by its properties as follows:

1. Chromium Steel

Chromium Steel is a metal alloy made of iron, carbon, and chromium. It possesses excellent levels of hardness, strength, and corrosion resistance. This alloy, together with nickel, is used to make propeller reduction gears because it provides resistance to corrosion and fatigue.

2. Chrome Nickel

Other names for chrome-nickel include stainless steel and corrosion-resistant alloy steel. Because it contains 18% chromium and 8% nickel, the chrome-nickel steel that is most commonly used to make airplane parts is known as "18-8 steel."

The desired qualities of this alloy allow it to be rolled, drawn, bent, or molded into any shape, thereby making it suitable for aviation springs, tie rods, and control cables.

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3. Chrome-molybdenum Steel

Chrome-molybdenum steel is formed when molybdenum and chromium are added in small amounts, increasing the strength of steel while maintaining its ductility (the ability to be bent or twisted without breaking).

It is robust, more resistant to corrosion and wear, performs well at high temperatures, and, unlike stainless steel, is suited to welding, making it primarily appropriate for welded aircraft structural parts and assemblies.

Because it is nearly four times stronger for the same weight and size as carbon steel, this form of steel has largely substituted carbon steel in the production of fuselage tubings, engine mounts, landing gears, and other structural parts.

4. Wrought Aluminum

One of the most commonly used metals in the production of modern aircraft is aluminum. It is an essential part of the aviation industry due to its strength-to-weight ratio and ease of manufacturing. Aluminum is notable for its light weight, lack of magnetism, and excellent conductivity.

Wrought Aluminum is the most widely used aluminum alloy in aircraft construction, being used for stringers, bulkheads, skin, rivets, and extruded sections.

5. Aluminum - Copper( Al-Cu) Alloys

Al-Cu alloys are primarily recognized for their high strength, high damage tolerance, lightweight, and fracture toughness. They are employed as wing skin due to their increased strength and wide range of applications in fuselage structures due to their exceptional damage tolerance.

Additionally, Al-Cu alloys are employed in lower wing stringers and fuselage skins to create lighter structures with improved corrosion resistance, higher strength, better exfoliation resistance, and better fatigue toughness.

6. Aluminum - Manganese (AlMn) Alloys

AlMn is the name of the aluminum alloy created by adding manganese to aluminum in order to boost strength. Although this alloy has the benefit of being simple to weld, it can only be used for general-purpose, moderate-strength applications that call for good workability, such as cowlings, baffle plating and non-structural pieces.

7. Aluminum - Magnesium ( AlMg) Alloy

AlMg alloy is one of the lightest, most effective, and most widely used alloys in the aerospace industry. When combined with manganese, it produces a moderate to high strength. AlMg alloys have good welding characteristics and good resistance to corrosion in various atmospheres, making them ideal for use in the fabrication of fuel tanks and fluid lines.

8. Aluminum-Zinc (AlZn) Alloy

AlZn is an alloy made of aluminum, zinc, and small amounts of copper, chromium, and magnesium. When anodized, it produces a product with high strength and a high-quality finish.

AlZn is utilized to reinforce aluminum aircraft structures and highly stressed, thick portions of the airframe.

9. Magnesium Alloys

Magnesium is the least dense engineering metal currently in use, weighing only 66% as much as aluminum and having a relative density of 1.7. Magnesium is a weak metal on its own, but it becomes stronger when alloyed with trace amounts of zirconium, aluminum, zinc, and manganese.

Magnesium alloys have a superior strength-to-weight ratio than aluminum alloys despite being weaker than them due to their lower densities.

Wheels for airplanes, gearboxes, valve bodies, turbine engine compressor casings, piston engine crankcases, etc. have all been made with magnesium alloys. When weight reduction is especially crucial, sheets made of magnesium alloy are employed in the frame of various aircraft and helicopters.

10. Nickel Monel

The nickel alloy known as Monel has a composition of roughly 68% nickel, 29% copper, and a small fraction of iron and manganese. It is a good option for aviation engine exhaust systems and gears because of its strength, hardness, and corrosion resistance at high temperatures.

11. Nickel Inconel

Inconel is another nickel alloy that has a composition of 80% nickel, 14% chromium, and minute quantities of other metals. The alloy is commonly used in turbine engines because of its ability to maintain strength and resistance to corrosion in extremely high temperatures.

12. Copper

The reddish-colored metal is one of the most widely distributed metals. It has excellent electrical conductivity raking the

Despite its great weight, copper has some extraordinary characteristics, such as high electrical and heat conductivity, malleability, and ductility, which often outweigh the weight factor.

Therefore, Copper has been used in aircraft's electrical systems for bus bars, bonding, and lock wires.

13. Manganese Bronze

Manganese bronze, a copper-zinc alloy containing aluminum, manganese, iron, and sometimes nickel or tin, is incredibly strong, sturdy, and resistant to corrosion. It is commonly used for brackets and landing gear on airplanes due to its high strength.

14. Titanium

Titanium is a grayish-white metal with a high strength-to-weight ratio. It has a relative density of 4.5, making it 60% heavier than aluminum but twice as strong and 45 % lighter than steel yet equally strong.

Due to the oxide film that forms on titanium, it has a low thermal conductivity, a low coefficient of expansion, and excellent corrosion resistance qualities. It can resist brief exposure to temperatures of 1,650°C and is effective in high-temperature applications like aircraft firewalls.

Additionally, high-strength, corrosion-resistant bolts and fasteners, gas turbine engine compressor discs and blades, hot air pipes, hydraulic pipes, and structural components that need to be strong or function at high temperatures are all made of titanium and its alloys.

Furthermore, it is utilized on the skin of high-performance airplanes when the usage of aluminum is prohibited due to skin heat generated by high speed.

15. Composites

The most cutting-edge materials for building modern aircraft are composites. They consist of two or more materials that differ in composition or form, and when combined, produce an extremely tough, durable, and versatile material.

Composites can be created by "wet laminating" three or more layers of fabric that have been impregnated with resin to create a solid sheet or by employing honeycomb fiber materials sandwiched between matrices that have been carefully developed.

Many components of modern aircraft, such as landing gear doors, flaps, vertical and horizontal tail structures, propellers, internal turbine engine elements, helicopter rotor blades, and flight-control surfaces, are made of composite materials.

They cite several benefits of having a material with a high strength-to-weight ratio and good corrosion and fatigue resistance. Composites are less sensitive to sonic vibrations than conventional sheet-metal structures (they have superior vibration resistance), and they have fewer parts and less expensive assembly expenses. They also feature a lighter design and the capacity to achieve a smooth surface, which lowers aerodynamic and parasitic drag.

16. Plastics

High-performance engineering plastics are lightweight relative to other industrial materials, making them suitable for the aerospace sector. Aerospace-grade plastic sheets are strong, impact- and vibration-resistant, long-lasting, chemically and fire-resistant, and resistant to cleaning agents.

Plastics are used in airplanes to make the cabin interior, aircraft canopies, and glass transparency. Tray tables, armrests, and seatbacks are also made using them.

17. Synthetic Rubber

Synthetic rubber is a polymer that is synthesized from petroleum byproducts and is widely used in the aerospace and aviation industries. Examples of synthetic rubber used in this industry include neoprene, silicone, ethylene propylene diene monomer (EPDM), bunas, and butyls.

These materials are used in thermal insulation, window, and door seals, LED lighting gaskets, instrument panel seals, engine gaskets, hydraulic actuators, bleed air valves and fittings, firewall seals, and vibration dampening.

Synthetic rubber used in the aviation industry must have certain characteristics, such as being resistant to water and heat, being able to withstand wear and tear, having a high endurance threshold under extreme stresses, having high sound and shock absorption, and having a long life span.

18. Woods

Sitka spruce, birch, ash, and Douglas fir are the four types of wood that are most commonly used in aircraft manufacturing. Other woods such as mahogany, balsa, and pine may also be used in specific applications.

These woods must meet certain requirements in order to be certified for use in aircraft construction, including having a moisture content of 12%, having at least 6 annual rings per inch, and having a maximum grain slope of 1 inch per 15 inches.

Woods are chosen for aircraft construction due to their light weight, resistance to splitting and bending, stiffness, substantial strength-to-weight ratio, and long life when properly conserved. These woods are used for the building of various aircraft structures such as propellers, spars, wing tips, and longerons.

19. Fabrics

Metal and composite construction are now the most common types of airplanes, but in the past, fabric-covered airplanes were the most common. Some special-purpose aircraft, such as those used for agricultural purposes or to renovate antique aircraft, still use fabric as one of their structural elements.

Of course, inside the cabin, fabrics are used to make passenger seats.

Cotton, linen, polyester, and glass filament are used to make fabrics that are approved for use on aircraft. Fabrics have the benefit of being lightweight but the drawback of lacking durability and quickly catching fire in airplane structures.

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Featured image: Photo: Michael Rodeback/Airways