Airplanes are high-tech vehicles designed with complex engineering principles and operating with many critical components working together. These structural components are vital for the aircraft to perform its function safely, stably, and functionally. The structural components of aircraft are listed as follows:

1. Fuselage
2. Engines
3. Wings
4. Landing Gear
5. Empennage

 

_{Main structure of airplanes (credit: grc.nasa.gov)}

Fuselage

It is one of the most essential parts for passenger aircraft. The fuselage is a section where passengers,and baggage are carried. It also ensures that other parts of the aircraft are connected to the fuselage to form a whole. The fuselage generally consists of two sections: Main Deck, Lower Deck.

 

^{Aircraft fuselage (Credit: istock)}

Main Deck

It is generally referred to as the interior of the cabin where passengers travel.

 

^{Fuselage sections (Credit: Wong Kim Chuan)}

Lower Deck

These are the areas where baggage, mail, and cargo are generally carried. It is divided into five sections;

1. Hold: The lower part of the aircraft is divided into aft and forward hold.
2. Compartment: Compartments are the sections of the holds located in the front and rear.
3. Section: Refers to the separation of compartments by means of nets.
4. Bay: These are the sections used in ULD (loading with containers) loading, where containers are secured with certain locking mechanisms to prevent them from shifting.
5. Position: These are areas with locking mechanisms used in ULD loading.

 

The reason for the division into sections is the application of two different loading types to aircraft (ULD and BULK), as well as the carriage of live animals, funerals, special cargo, and baggage with priority service, has created certain procedures during aircraft loading and unloading. The need for compartmentalization has arisen to ensure that these procedures are carried out without interruption.

 

 

^{Cargo (lower deck) section of different passenger aircraft. (Credit: Telair and Infinite Flight)}

Engines

Engines provide thrust, one of the main forces acting on aircraft. The general operating principle is to draw air into the engine through the rotation of the PALs. Compressors are located inside the engine; these compressors heat and compress the air, making it easier to burn. Then, the heated and compressed air proceeds to the combustion chamber. Fuel is sprayed into the combustion chamber via fuel injectors, meeting the heated and compressed air to cause combustion. The resulting effect of this combustion is expelled through the exhaust, creating thrust. In addition, engines have many functions beyond simply generating thrust, such as providing the necessary energy for the aircraft's avionics systems and providing the compressed air necessary for the rotation of the PALs.

 

Boeing B737-800 Passenger Aircraft Turbofan Engine (Credit: Independent Aviators)

Wings

Wings are one of the main parts that provide lift in aircraft. Generally, from the moment aircraft take off, a continuous airflow occurs around the wings. This airflow moves faster on the upper part of the aircraft wing and slower on the lower part. The pressure will be higher in the area where the airflow is slow, meaning that since the pressure on the underside of the wings is higher than the pressure on the upper side, this high-pressure air will create lift by keeping the aircraft in the air. Another function is the ability to carry fuel with fuel tanks located in the aircraft wings. The main reasons for this function are to make the wings structurally strong and to save space from the storage area inside the aircraft.

 

The inside of the wings is divided into sections called ribs (or profiles). Ribs are divided into sections to regulate the passage of fuel within the wing and to control the fuel flow. Wings also help to attach the necessary control surfaces for aircraft to maneuver. The main ones of these control levels are flaps, slats, spoilers, and ailerons.

 

Rib (Profile): Nerve. They are structural parts parallel to the spar axis (perpendicular to the spar) on wings, tail, and other aerodynamic surfaces. They both shape the wing and tail surfaces, and carry the loads caused by the airflow and pressure during the movement of the coverings of these main aircraft parts to the spars.

Example of wing rib structure (Credit: cfinotebook.net)

Lift depiction on wings (Credit: shutterstock.com)

Landing Gear

Landing gear is the main structural element that carries the weight of aircraft when they are on the ground. The number of landing gears can vary depending on the weight and specific characteristics of the aircraft. Besides, the landing gear located at the front of the aircraft is called the nose landing gear, while the landing gears located at the rear are called the main landing gear. During landing, the main landing gears touch the ground first, followed by the nose landing gear. During takeoff, it is the opposite; the nose landing gear breaks contact with the ground first, followed by the main landing gear. In passenger aircraft, the landing gear is usually attached to the underside of the wings. In addition, in some aircraft, parts such as floats and skids replace the landing gear. Helicopters generally use skids, and aircraft that take off and land on water generally use floats as landing gear. The landing gear does not have the function of steering the aircraft in the air.

 

^{Landing gears (Credit: Aviation for Everyone)}

Empennage

The empennage is the most important element that provides balance to aircraft. It provides stability to aircraft, ensuring that the aircraft returns to its flight axis if it deviates from it. The empennage generally consists of two parts;

1. Vertical stabilizer: The rudder, one of the primary control surfaces, is attached.
2. Horizontal stabilizer: The elevator, one of the primary control surfaces, is attached. The horizontal stabilizer also moves up and down, helping the aircraft maintain stable flight. The movement of the stabilizer is carried out according to the trim setting given by the pilot from the cockpit. Also, as with the wings, fuel can be stored inside the horizontal stabilizer, but this is more common in extra-long-range aircraft.

 

^{Empennage (Credit: Science Young TÜBİTAK)}