Materials Used in Aircraft Construction

Most people at some point wonder how airplanes can fly, but have you ever wondered what they are made of? The materials used in the construction of airplanes, wings and fuselages make a big difference in terms of strength, lightness and reliability, and are key to aircraft construction.

What are airplanes made of?

Most aircraft are made of titanium, steel, aluminum and many other materials, including composites. Composites can include a variety of different materials, often including polymers, carbon fiber and more.

These metals are hard and strong as well as corrosion resistant and lightweight. They are excellent materials for making airplanes of all kinds.

Importance of Aluminum in Aircraft Construction?

While steel is a very important and necessary material in aircraft construction, it has been partially, if not completely, replaced by aluminum in recent years due to its high specific gravity. Since steel is too heavy to be used alone, some aircraft, including the 787 Dreamliner produced by Boeing, use twice as much aluminum as steel.

Some manufacturers add materials such as aluminum to titanium and other alloys because these materials can be too expensive to use on their own.

For example, the Airbus A350 jetliner uses an aluminum-lithium alloy extensively, and many of Boeing's airframes are made from materials containing various polymers.

The Rise of Composite Materials

Composite materials are widely used in aerospace due to their wide range of physical, mechanical and chemical characteristics, as well as the ability to change their properties through structural modification. In this sense, the most important reason for the increase in the use of composite materials is the high strength-to-weight ratio. 

Reducing the weight of the material used in the construction of aircrafts enables the transportation of more cargo, fuel and passengers in civil aircraft, and more ammunition, cargo, fuel and longer ranges in military aircraft. 

Polymer matrix composite materials (plastic composites) are as strong as metal materials and lighter than them. Another advantage of composite materials is that they can easily take geometric shapes with complex and aerodynamic profiles. With the use of composite materials, the number of parts and fasteners that make up the structure is reduced. Thus, aircraft construction becomes simpler and costs are reduced. 

Since composites have a highly flexible, vibration-resistant structure, they can be designed in such a way that the material fatigue seen in metal structures does not occur. They also do not corrode like metals. High surface resistance is another advantage of composites. Composites can easily stretch without the formation of stress cracks seen in metals.

When we look at the materials used in aircraft construction, it is seen that for many years, aluminum has been predominantly used. Today, important parts such as important wing structural elements are still produced with this material. However, the proportion of aluminum used in today's aircraft has decreased, and instead, composite materials such as thermoset, thermoplastic, ceramic, etc. with fibers; hybrid materials formed by combining more than one material such as composite-composite or metal-composite, or alloys such as aluminum-lithium alloy are now used. 

For example, while Boeing 757s manufactured in the 1990s used 78% Al (aluminum) and 3% composite, a new passenger aircraft design that entered service in 2010 used 65% composite and 11% Al.

The rate of increase in the use of composite materials in aircraft could be even higher, but there are two major reasons why this is not the case: certification difficulties and cost. 

Composites are materials consisting of two or more elements with volumetrically different shapes and properties, where the boundary between these elements can be easily seen, and where the positive properties of these elements are combined. The main elements of composite materials are matrix and reinforcement materials. The main reinforcing elements are fibers, flakes, grains, particles and plates, while the matrices can be polymer, metallic and ceramic based materials. 

Composite Materials Used in Aircraft Construction

Today, studies in the field of composite materials are carried out in three main categories. These are; fiber reinforced, grain reinforced, and particle reinforced composite materials. Regardless of the material, the composite consists of a matrix with a low modulus of elasticity and a reinforcing element with strength and toughness values 10-1000 times higher than the matrix.

The modulus of elasticity of conventional materials has been reached in composite materials developed with great advances in resin and fiber technology in the last 30 years. Therefore, composite materials have found applications in coatings, control surfaces of reinforcing parts and flaps. Aircraft are generally designed to meet specific performance requirements such as freight, distance, cruising speed, altitude as well as airframe weight control, long service life, system design outline and cost characteristics. All other things being equal, the design criterion that minimizes weight will be the most appropriate design criterion. Accordingly, lightweight materials with appropriate properties will provide the best characteristics. There are two important elements in composite material design. The first of these is the orientation direction of the fiber in the matrix. The second is the necessity to consider aerodynamic conditions in material design. When these conditions are met, the suitability of composite materials for manufacturing, low maintenance cost and good mechanical properties provide a great advantage in aircraft design.

All Materials Have Pros and Cons

Since each material has its own advantages and disadvantages, many airplanes are actually built using many aircraft materials.

For example, most Airbus and Boeing airplanes are made of a minimum of 50% composite materials, while Rolls Royce PLC, which makes aircraft engines, uses composite materials such as ceramics and plastics.

Different materials have different strengths and weaknesses. In practice, this means that an airplane will be made of many different materials for parts such as wings, fuselage, body and skin.

As you can see, airplanes don't have to be built with one type of material, because there are many materials that can be used, so the important thing is a safe and easy-to-fly airplane that is also reliable.

Saving Weight is Top Priority

Of course, the aircraft materials normally used are made up of both light and heavy components, mainly because the aircraft has to fly and therefore cannot be made of super heavy metals. In particular, the weight of the body must be kept to a minimum.

The first passenger plane, the Ford Tri-Motor, was made of aluminum in the late 1920s, just like today's Boeing 747. The fastest jet-powered airplane, the Lockheed SR71 Blackbird, was made of titanium.

Still, here are other reasons for adding titanium to steel in aircraft construction:

It is almost as strong as steel.

It is heat resistant.

It is resistant to corrosion.

It is a medium-weight metal.

Design Priorities Depend on the Purpose of the Aircraft

The purpose of an airplane is very influential in the manufacturers' decision to use a particular type of material, especially metal, metal-composite and plastic-composite for the airframe.

The size, purpose and other aspects of the aircraft help them determine which materials to use because this is the only way to guarantee that the aircraft will be well built and reliable.

Conclusion:

The strength, lightness and cost of the material used in aircraft construction are of great importance. As the technology and industry advances to find and produce new materials that are both lightweight, strong and cost-effective, the new types of materials that this advancement will create will continue to play a primary role in the construction of air platforms.