Fuselage is responsible for providing space for crew, passengers, cargo, controls and other numerous items along with holding major components together including wings, powerplants, tail-surfaces, and landing gear.
The fuselage thus must have attachment points for the wing, tail-surfaces, landing-gear etc for providing sufficient support whilst inspecting, repairing, and replacing the parts without performing strenuous efforts.
Types of Fuselage
Based on the method by which stresses are transmitted to the structure, the fuselage can be categorized into three principle types namely the Truss, Semimonocoque and Monocoque.
Based on the method by which stresses are transmitted to the structure, the fuselage can be categorized into three principle types namely the Truss, Semimonocoque and Monocoque.
Truss
Trusses can be defined as the framework or an assemblage of members forming a rigid framework which consists of bars, beams, rods, tubes etc.
These trusses can be further classified into two namely the Pratt Truss and Warren Truss.
Trusses can be defined as the framework or an assemblage of members forming a rigid framework which consists of bars, beams, rods, tubes etc.
These trusses can be further classified into two namely the Pratt Truss and Warren Truss.
These trusses are mainly supported by four long beams which in aviation is commonly known as Longerons.
Longerons can be defined as the principle longitudinal member which run through the length of fuselage responsible for carrying and transmitting the loads imposed on the fuselage to various sub-components like frames, stringers, bulkheads etc which are discussed in subsequent paragraphs.
Longerons can be made analogous to the main structural member of the wing running along its span i.e. Spar.
Nevertheless, the only difference between a Pratt truss and a Warren truss is the incorporation of rigid vertical members in Pratt Truss known as struts.
Longerons can be made analogous to the main structural member of the wing running along its span i.e. Spar.
Nevertheless, the only difference between a Pratt truss and a Warren truss is the incorporation of rigid vertical members in Pratt Truss known as struts.
Semimonocoque
Semimonocoque structure includes a framework of vertical and horizontal members covered by a skin that carries a large percentage of stresses imposed.
It is these vertical and horizontal members to which the Longerons transmit the loads acting on the structure namely the frames, bulkheads, stringers etc.
Semimonocoque structure includes a framework of vertical and horizontal members covered by a skin that carries a large percentage of stresses imposed.
It is these vertical and horizontal members to which the Longerons transmit the loads acting on the structure namely the frames, bulkheads, stringers etc.
The Bulkheads are the primary circumferential members whose purpose is to first give a shape to the fuselage just like the ribs in case of wing and secondly disperse concentrated loads and support the whole fuselage structure.
Bulkheads basically are utilized to divide the whole fuselage into sections namely the front fuselage, center fuselage and aft fuselage. Corresponding to that there are 2-3 bulkheads in an a commercial aircraft.
Similar to Bulkheads are the Formers also known as Frames which are placed at regular intervals for refining the shape of the fuselage and maintain its uniformity as well as support the stringers and the skin to which the loads are imposed.
Stringers just like in the wing serve to stiffen the metal skin and prevent it from bulging or buckling under severe stresses.
These are also the longitudinal members but are placed circumferentially at regular intervals as can be seen in the figure and used for transmitting skin loads to body frames.
It is because of these stringers that aircraft designers were able to use aluminum skins as light as 0.020 inch thickness for primary structure on airplanes.
Similar to Bulkheads are the Formers also known as Frames which are placed at regular intervals for refining the shape of the fuselage and maintain its uniformity as well as support the stringers and the skin to which the loads are imposed.
Stringers just like in the wing serve to stiffen the metal skin and prevent it from bulging or buckling under severe stresses.
These are also the longitudinal members but are placed circumferentially at regular intervals as can be seen in the figure and used for transmitting skin loads to body frames.
It is because of these stringers that aircraft designers were able to use aluminum skins as light as 0.020 inch thickness for primary structure on airplanes.
Monocoque
Monocoque structure is one in which the fuselage skin is only responsible for carrying all the structural stresses.
This implies that this structure doesn't possess internal members but involves construction of a tube or cone for giving an adequate shape to the fuselage.
But in some cases, it becomes necessary to incorporate formers for maintaining the shape of fuselage although they do not carry the principle stresses imposed upon the structure.
The monocoque structure is effective and can withstand loads imposed when the diameter of the fuselage is small. As diameter increases, the weight to strength ratio becomes inefficient and it is because of this reason why longitudinal stiffeners, longerons come into picture for bigger airplanes.
Monocoque structure is one in which the fuselage skin is only responsible for carrying all the structural stresses.
This implies that this structure doesn't possess internal members but involves construction of a tube or cone for giving an adequate shape to the fuselage.
But in some cases, it becomes necessary to incorporate formers for maintaining the shape of fuselage although they do not carry the principle stresses imposed upon the structure.
The monocoque structure is effective and can withstand loads imposed when the diameter of the fuselage is small. As diameter increases, the weight to strength ratio becomes inefficient and it is because of this reason why longitudinal stiffeners, longerons come into picture for bigger airplanes.
In earlier airplanes, mechanical fasteners were incorporated for joining various parts of an aircraft.
The issues with mechanical fasteners include:
The issues with mechanical fasteners include:
- While drilling holes, it lead to a number of minor cracks which resulted in stress concentration which in turn proliferated the growth of cracks.
- The fasteners contributed to an increase in drag (parasite drag).
- It fastened the process of corrosion near the circumference of a fastener.
As a result of these complications, Bonded fuselages came into picture where-in adhesives were used for joining parts which allowed distribution of structural loads evenly thereby solving the issue of stress concentration.
Moreover, bonding agents can incorporate corrosion-inhibiting materials in their mixture thus reducing the probability of corrosion occurring.
Nowadays, composites are being extensively used for primary structures of an aircraft owing to high specific strength, excellent corrosion and fatigue resistance, its design flexibility etc.
All these factors make composites ideally suited for numerous primary and secondary structures of an aircraft.
Moreover, bonding agents can incorporate corrosion-inhibiting materials in their mixture thus reducing the probability of corrosion occurring.
Nowadays, composites are being extensively used for primary structures of an aircraft owing to high specific strength, excellent corrosion and fatigue resistance, its design flexibility etc.
All these factors make composites ideally suited for numerous primary and secondary structures of an aircraft.
This post has too many technical terms.
ReplyDeleteI completely agree with you Ananya! Although Aerospace Engineering comes with a sac of technical terms, I'll try my best to explain complicated concepts in facile ways in future! :)
DeleteThanks!
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