Characteristics of Aircraft Structures and Materials

Aircraft Flyover very high altitudes. For short-duration flights, the altitude is around 20,000 to 25,000 ft but for long-duration flights, it is around 30,000 to 45,000 ft. Now, one can imagine how less the temperature and pressure are at that height. For imagination let me tell you at 42,000 ft the temperature is around -69.5 degrees Celsius and 0.148 kg/cm2 respectively. And the same at sea level temperature is 25o C and pressure is 1.033 kg/cm2. And the aircraft structure and materials have to withstand such temperatures and high-pressure differences (pressure inside aircraft is sea level pressure, and outside is very low) also that particular aircraft structure has to withstand different loads acting on it (aerodynamic loads, static loads, etc.). Thus, it is designed with such characteristics and phenomena in mind. And therefore, the aviation industry is also called “the riskiest and safest industry”.

Aircraft structures are divided into 5 major parts, namely the fuselage, empennage, wings, landing gears, and Engines. These parts are designed together in conceptual design and quite independently in detail design. And are independently fabricated at various centers spread across the world or country.

Let us discuss all major different structures one by one and of what material they are made.

Fuselage: Aircraft has evolved a lot from its invention era to its modern era. Earlier fuselages were using truss structures made up of wood or steel pipes. The structure of a modern aircraft fuselage is made up of Longerons, Stringers, bulkheads, and skin. There are two epidermal layers of the shell of an aircraft : the inner layer and the outer layer. These sub aircraft structures are embedded in between those layers because passengers and crew do not come in contact with them and this is only opened during maintenance if needed. So, what are these structures inside the two layers of the fuselage?

• Longerons: Long tubes that carry most of the tensile and compressive force of the fuselage. In a fuselage generally, there are four to five longerons.
• Stringers: These are short and thin tubes between bulkheads. To carry minor forces.
• Bulkheads: It is the Layout of the cross-section of the fuselage that gives the fuselage its basic shape. These are thick layers on the edge of which longerons and stringers run.
• Skin: The outermost layer that carries the rest of the tension and compressive force on the fuselage is the skin. Along with covering the entire fuselage it also holds the force. 

The fuselage is also divided into two categories of design. A monocoque and semi-monocoque structure. The one which is very broadly used nowadays is the semi-monocoque aircraft structure. The only difference between them is that semi-monocoque contains longerons and stringers whereas monocoque doesn’t.

Empennage: The empennage consists of the horizontal stabilizer of aircraft, vertical stabilizer of aircraft, and the part of the fuselage that holds both these stabilizers together. The structure of Stabilizers is the same as the structure of the wing, however with a little bit of difference as it does not carry slats and a fuel tank.

Landing Gears: Landing gears are hydraulic force damping devices that hold the aircraft at a distance from the ground and allow it to move to places when in the ground. The landing gear is made up of a heavy sturdy material Steel, as it holds the weight of the entire aircraft. Also, some parts of landing gears are made up of titanium which are vulnerable to high temperatures.

Aircraft Wings: The most and a very important part of an aircraft structure is its wings. Without this, it is impossible for an aircraft to fly. Because it is the wing that generates lift for the entire aircraft.

Similar to the fuselage the structure of aircraft has also evolved a lot such as earlier biplanes were used but nowadays monoplanes are used. There are various types of aircraft wings based on their position on fuselage, profile, and structure. Let us know all of them in short.

• Based on position on the fuselage:

o High Wing: Positioned on top of the fuselage. For example, in most cargo and some trainer aircraft.

o Low Wing: Positioned below of the fuselage. Such as in various commercial aircraft.

o Mid Wing: Positioned at the mid of the fuselage. Such as in combat aircraft and some commercial ones.

o  Dihedral Wing

o  Anhedral Wing

o  Gull Wing

o  Inverted Gull Wing

• Based on Profile:

o   Rectangular wing

o   Elliptical Wing

o   Trapezoidal Wing

o   Delta Wing

Materials Used in Aircraft Construction

In the construction of aircraft and their structures. The most widely used aircraft materials are aluminium and its alloys as one of the best utilities is that it has a very high strength to weight ratio. Steels are used in some parts which bear very high loads such as landing gears and in longerons. Also, another material is used in titanium and its alloys, due to its high melting point. It is used in places such as some parts of landing gears, and mostly in the engine and its components.

Conclusion

Aircraft structure bears different kinds of loads and is thus made very durable and stiff without compromising failure. The structure that holds the maximum load is the fuselage and wings. These aircraft structures are designed to provide very high durability and reliability with very low weight and weight is a very concerning matter in aircraft. And so, such materials are chosen, like aluminium, titanium, steel and their alloys. Also considering that the structure should bear environmental conditions at a very high altitude.