Aircraft Fuselage

In this tutorial, you will learn the basics of the fuselage of an aircraft which includes its definition, classifications, and its working details. You will also learn about the unique differences between
semi-monocoque and monocoque structures and also about the manufacturing processes and its components.

Contents:

  1. What is a Fuselage?
  2. General Construction of Fuselage
  3. Types of Fuselages
  4. Classification of Truss
  5. Semi-monocoque vs Monocoque
  6. How is a Fuselage Manufactured?
  7. Fuselage Components
  8. Passenger Components

What is a Fuselage?

The central portion of an aircraft, which has wings and tails attached to it is called as a fuselage.

  • Fuselages have attachment points for the wings, tail surfaces, and landing gear. It is all arranged and installed so that these parts can be inspected, removed, repaired, and replaced effortlessly. Many aircraft designs, have the wing structures extended throughout the Fuselage.
  • In order to maintain the C.G point of the aircraft, it should have minimum weight and maximum strength criteria. For comparatively large openings within the airframe, it requires more space criteria. In a single-engine type airplane, the engine is mounted in the nose of the fuselage.
  • To withstand the flying and landing loads, the points of attachments of the fuselage must be riveted and bolted strongly. Finally, the fuselage must offer low resistance to the air and also provide good clearance to the pilot.

The general composition of the fuselage is shown in the below diagram:

general composition of the fuselage

The above diagram describes the composition of the fuselage, which includes the passengers, cargo, controls and the crew, the aircraft spaces vary depending upon the size and design of the aircraft.

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General Construction of Fuselages

Generally, the fuselage consists of different kinds of components. The major components of fuselages are made up of metals and semi-monocoque in construction. This is applicable to all small, medium, and large aircrafts.

  • The skin or plating is attached to the internal part of the fuselage. It consists of longerons, frames, bulkheads, stringers and gussets. These are the intercoastal members which is held together to shape the fuselage’s structure.
  • The skin or plating forms the complete unit of the fuselage. According to the fuselage position, the thickness of the skin varies. While designing and analyzing stress, the engineers will determine the required thickness of the material for all the section of the aircraft.
  • The front part of the fuselage usually contains the cockpit and passenger cabin. Based on the specifications and passenger’s capacity, the aircraft’s shape is modified. The rear section is usually circular and rectangular in cross section, that contains the tail cone of the fuselage.

Types of Fuselages

The fuselage is classified into three main types based on the stress transmission method as truss, semi-monocoque & monocoque respectively.

  • Truss: It is comprised of bars, beams, rods, tubes, and wires etc. The truss-type is again classified into Pratt truss and Warren truss. Both Pratt and Warren trusses have four longerons, as a primary strength member.
  • Semi-monocoque: This structure consists of vertical and longitudinal members covered with a structural skin. Frames or bulkheads are the longitudinal member of the tail boom. Formers or rings is attached between the vertical members to create uniform shape.
  • Monocoque: In this structure, there is an outer skeleton to support the stresses and loads applied on it. Fuselage of small diameter can carry loads effectively. The weight to strength ratio is effective in fuselages with smaller diameter that helps to carry loads efficiently.

The following diagram describes the types of fuselages:

types of fuselages

The above diagram shows that, there are three principle types of fuselages, which has its own specifications and varies according to the size and shape of the aircraft. The diagram tells us that, the truss-type is further divided into two major types, and they are Pratt truss and Warren truss.

Classification of Truss

The truss – type is primarily classified into Pratt truss and Warren truss.

  • At every interval, the lateral bracing is placed and it consists of lateral structures such as bulkheads. And the spaces, between two intermediate bulkheads is called as bays.
  • The rigid lateral and vertical members are called as struts, that are connected to the longerons to support the Pratt truss which can carry, either tension or compression eventually. Here, the diagonal is made with strong steel wire to carry only tension but not compression.
  • A Warren truss is only connected to diagonal members unlike Pratt truss. It can also withstand, both tension and compression eventually. when load is applied on one direction, every member carries compression and the alternate member carry tension.
  • Reversal of loading takes place when the load is reversed. The member that carried compression previously, changes to tension and the member that carried tension previously, changes to compression.

Semi-monocoque vs Monocoque

Parameters SEMI – MONOCOQUE MONOCOQUE
Definition Semi-monocoque consists of a vertical and longitudinal member covered with structural skin. Monocoque carries all the structural stresses without internal structural members.
Load carrying capacity It cannot carry loads effectively in fuselages having a small diameter. It can carry loads effectively in fuselages having a small diameter.
Popularity It is the most popular type of structure that is used in aircraft structural designs. It is not the popular design used nowadays.
Internal members It contains internal structural members, like bulkheads, stringers &, etc. It does not contain internal structural members.
Weight ratio It has a good weight -to- strength ratio. It has an inefficient weight-to-strength ratio.
Example Ex: British ARV Super2 and Cessna Model 188 Ex: LFG Roland C.II and Zeppelin D. I

The following table describes the difference between a semi-monocoque and a monocoque.

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How is a Fuselage Manufactured?

The fuselage is usually built by integrating aluminium alloys and composite materials. It is strongly built in order to withstand all kinds of loads and is also designed in such a way, that the fuselage’s shape remains undisturbed.

  • Metallic sheets of desirable measurements are milled, rolled, drilled and riveted, according to the specifications into longitudinal and circumferential stiffening members, to support the internal and external airframe.
  • The fuselage is also designed in a manner to provide interior space for passenger comfort and minimum frontal area contour to drag for maximum performance. Fuselage barrel is built, using a certain number of desirable stiffened panels and the cost is very high along with the flow time.
  • There are two major criteria to design an aircraft:
    • Passenger’s safety in the event of a crash.
    • Attachment of powerplant, wing, landing gear and tail surface loads efficiently.
  • In an Airplane of single-element type, the engine is mounted on the nose of the fuselage. The most prominent feature of the fuselage is the purpose of providing space for the payloads.

Fuselage Components

The main components of fuselages are bulkhead, formers, skin and stringers which are load carrying items. It also includes non-load carrying items such as windows and doors.

  • These components are attached to the areas like wings, landing gears, engines, stabilizers, jack pads and antennas. For making these attachments, the doubler and gusset plates are used.
  • The sheet metals are made as per the requirements of special fittings. The fuselage is further modified internally by using castings and welded assemblies. The top portion of the bulkhead includes the aircraft front spar.
  • The vertical and horizontal members of the bulkhead are attached through casting or by reinforcing and by fastening. So that, they can be removed and replaced easily for maintenance purposes.
  • The vertical and horizontal stabilizers, play a vital role in stabilizing the Airplane. And also, to maintain level flight the aircraft must be properly maintained in order to provide top-notch performance.

The below diagram describes the components of the fuselage:

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components of the fuselage

The above diagram shows that, the component of fuselage is classified based on load which is load carrying and non-load carrying respectively. Former, bulkhead and stringers are the load carrying components, whereas windows and doors are the non-load carrying components.

Passenger Components

Passenger compartments are designed, to give maximum comfort and incredible flying experience to the passenger along with safety.

  • These are sufficiently ventilated, that prevents the presence of fuel fume and other dangerous traces of carbon monoxide gases. This system is also integrated, with the heating and air- conditioning system in order to maintain the cabin pressure.
  • In case the aircraft needs to be pressurized, then the design also includes the pressurization system. The seat belts in the passenger aircraft are securely fastened with aircraft structure for passenger’s safety.
  • Cabin pressurization also plays a vital role, in maintaining the pressure inside the fuselage. And if in case the cabin pressure is not maintained, it can cause severe problems like altitude sickness and even hypoxia.
  • If there is a pressurization failure above 10,000 ft, then the aircraft is in emergency. And in case of emergency, the oxygen masks will be activated automatically for the occupants for passenger’s safety.
  • As per (FAA) Federal Aviation Administration, each seat must be provisioned with a safety belt, in spite of whether or not the safety-belt load is transmitted through the seat and its primary mission is to guarantee the safety of civil aviation.

Key Points to Remember

Here is the list of key points we need to remember about “Fuselage of an aircraft”.

  • The fuselage is the central portion of an aircraft, which has wings & tails attached to it.
  • Fuselage is composed of the crew, passengers, cargo controls etc.
  • The fuselage structure is designed, in order to provide maximum strength with minimum weight criteria and also to maintain the C.G point of the aircraft.
  • The word “fuselage” is derived from the Latin word “fusus” which means spindle.
  • The fuselage is classified into three main types based on the stress transmission method as truss, semi-monocoque & monocoque respectively.
  • The Semi-monocoque structures consists of vertical and longitudinal members covered with a structural skin.
  • In case of a monocoque structure, there is an outer skeleton to support the stresses and loads that is applied on it.
  • The truss – type is primarily classified into Pratt truss and Warren truss.
  • The Fuselage is usually built by integrating aluminium alloy and composite materials.

If you find any mistake above, kindly email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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