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High Strength Components of an Aircraft

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Benjamin Epi

on 23 January 2015

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Transcript of High Strength Components of an Aircraft

Their section usually comprises an approximately plane annular main part extending along a direction approximately perpendicular to the axis of the fuselage and two secondary heel- or sole-shaped parts attached to the inner and outer peripheral edges of the main part.
Airplane Weight
Shell Cutouts
Frame and stringer intersection
Basic fuselage design requirements
The design of a fuselage will be impacted by its functional as well as
its basic strength, stiffness and life requirements.
Functional systems such as passenger accommodations, and cargo containment interact with the basic design features of the fuselage structure.
Accommodate the interface requirements of the nose landing gear, the wing carry-through structure, and the flight station and empennage.
Basic fuselage design requirements
conventional semi-monocoque
structure fabricated using aluminum alloy materials
circular cross section
This constant section, the flight station and a smell section, where the fuselage begins to taper at the aft end form the fuselage pressure shell.
This pressure shell must be designed for the pressure differential attained with an 2.44 km altitude cabin pressure at an airplane altitude
Structure considerations
Airplane weight
Large weight savings are being forecast.

Comprehensive design studies on large composite components are required to validate weight equations.
Minimum skin thickness
Based on manufacturing,
Damage tolerance
fail-safe consideration
Provide strength and rigidity
Able to sustain the load and environment imposed during operation
Effectively unlimited life
passengers safety
Define the possible types of damage that can be inflicted on the aircraft
Capable of withstanding damage without lowering structural integrity
An improved resin system would improve durability aspects of current materials
Fire resistance
Impact damage tolerance,
Repair ability
Ease of manufacturing
Shapes and assemblies
Moisture and temperature capabilities
Strength after exposure
Compatibility with metallic.
Basic composite material system
Shell cutout and holes
Allow for the same types of penetration of the basic shell
The location and size of these doors and windows will affect the geometry
and spacing of the frame and stringer design
a conventional aluminum design
Reinforcement members must be provided around these cutouts to avoid any needless discontinuities
Strain compatibility with the adjacent composite structure must be
Ensure fatigue and life requirements are met.
Requires a large number of longitudinal and girth joints for assembly of the fuselage
Only close tolerance fasteners are used
Fasteners are selected for their corrosion resistance
no unsupported splice joints are permitted
The effects of deflection ,moisture induced expansion, and thermal expansion of adjacent connected structure are considered in the design
Frame and stringers intersection
Provide the necessary strength and rigidity.

Maintain the appropriate pressurization loads and basic body-bending loads.

Incorporate shells of skin/stringer configuration with internal frame for reinforcement.
1) Creates discontinuity forces at the juncture of the shell and frame when the cabin is pressurized.
2) Cause the shell to pillow out between frames. (pillowing effect).
3) This effect dictates the method of attachment and design of the frame/shell interface.

The interface forces at the shell frame juncture have more stringent requirement.

Skin shear ties and stringer clips are most likely required in area of high compression and/or shear loading on the pressurized cabin

The use of mechanical fastener and other attachment methods, such as stitching.
structure interface requirement
Major components like nose landing gears support structure and pressure deck pose structural requirements.
Impose high concentrated forces on the fuselage structure, which
requires reinforcement members (e.g., bulkheads, doublers, etc.) and thicker
skin to redistribute these loads into the shell.
Structural interface Requirements
Minimum skin thickness
Material properties
Damage tolerance requirements
Three basic cross-sectional shapes
Circular cross section

Oval or double bubble fuselage

Flattened bottom fuselage
Circular cross section
provides a deep space under the cabin floor suitable for low wing aircraft
By eliminating corners, the flow will not separate at moderate angles of attack or side slip.
When the fuselage is pressurized, a circular fuselage can resist the loads with tension stresses, rather than the more severe bending loads that arise on non-circular shape.

Oval or double bubble fuselage
Sometimes, substantial amounts of space would be be wasted a circular fuselage when specific arrangements of passenger seats and cargo containers fuselage must be accommodated.

Provide more space and better shape for freight compartment
Flattened bottom fuselage
Provide easier loading as fuselage is near to the ground

Suitable for high wing aircraft where the landing gears are fitted to the fuselage


Nowadays, the fuselage of all modern aircraft are of the semi-monocoque structure where the load are carried by the stressed skin and the internal support structure of formers and stringers.
Airplane accidents
United Airlines Flight 811
Incident report summary
reasons for the failure
United Airlines Flight 811
The Boeing 747-122 was set to fly to Auckland, New Zealand from hawai's Honolulu International Airport during the climb the plane detoured off their original flight path to avoid flying through the thunderclouds the forward cargo doors dislodged and slammed into the side of the fuselage causing a large blowout in the fuselage.
this caused a decompression leaving the cabin unpressurized and also causing engine 3 and 4 severely damaged due to debris from the damanaged fuselage.
the plane ended landing with majority of its flight control damanged.
Circumferential member that is spaced at regular intervals along the fuselage.
Usually oval in shaped
There are various types of bulkhead and the most common type is a curved channel formed from sheet stock with stiffeners added
o Provides the fuselage its cross-sectional shape
o Usually are attached to longeron to support the skin
o Prevents it from buckling under bending loads.
o Prevents instability

Main lengthwise member of the fuselage structure
Normally it extends to the entire fuselage length
Creates attachment points for other structural support including the skin of the aircraft.
It holds the bulkhead and the frames/formers to form a rigid fuselage framework with the help of stringers
Attached to frames/formers and ribs
Longerons are also found in the wings
o Responsible for transferring aerodynamic loads created at the skin onto the frames/formers.
o Longerons found in the wings also transfer loads but not from the skin the frames/formers but from the wings to the ribs and spar.

Longitudinal members that are spaced around the fuselage circumference, which also extends to the full length along the fuselage similar to longerons.
It is smaller and lighter compared to longerons and it behaves similar to longerons.
o Helps the longerons transfer skin loads to internal structure such as frames/formers.
o Support the skin under compression load and torsion load and also prevent bulging and buckling.
Fabrication methods
Material such as aluminum alloy wit high strength are put through a stage known as hot plastic stage, where materials are placed under pressure in dies to provide a uniform cross section of a “T”, “U”, “V”, “L” and other different shapes to be use as reinforcing stiffeners and stringers.
o Sheet material are often re-rolled to form constant “Z”, “S” or hot sections that are to be used as skin stiffening stringers. This process is called roll forming.
o Processed material are then bent and formed into circular shapes making frames/formers for the fuselage.
Fabrication Methods
Repair Methods
Formed sections:
Extruded sections
Cause of damage
Fatigue and stress cracks around the fasteners
Repair Method: Riveting (Flush repair)
1. Stop drill crack
2. Fabricate doubler of the same material, has to be at least twice the thickness of the original material.
3. Calculate the amount of rivet required and plan a layout.
4. Select the appropriate rivets to be used.
5. Attach doubler to the part with clamps and drill holes
6. Install rivets

Cause of incident
Bad design of cargo
- inward plunged door
Poor design of locking system
- ease to open due to latch system.
Poor oversight of materials
- aluminum was too thin for the latch clam to withstand the pressure at high altitudes
Aloha Airlines Flight 243
incident report summary

reason for failure
Aloha Airlines Flight 243
The plane was flight was between Hilo and Honolulu in Hawaii. Everything was clear and until the plane reached the altitude of 7,300 m above sea level as one of the airplane plane of the fuselage broke off from the structure over time due to decompression majority of the planes roof was torn off leaving the pilot flying a (sun roof plane convertible) after then plane roof was torn apart the pilot skillfully made an emergency landing on maui island.
Longeron one of the earliest components as it dates back to the truss, one of the very first fuselage structure.
Materials like wood, carbon fiber, and metal can be used in constructing a longeron.
Older aircraft such as the de Havilland DH.98 Mosquito were almost entirely made up of wood, however, with the improving technology, aircraft today are made from stronger material to provide strength and flexibility.
Cause of damage:
Fatigue and stress cracks around the fasterners
Corrosion between the skin and the longeron
Repair methods
• As longerons are comparatively heavier to stringers, heavier rivets are to be used.
• In some occasions, bolts are preferred to repair longerons are it has higher accuracy. The cons of using bolts is it longer installation time.
Eddy Current Testing
Detection method
Eddy current testing
• Used to detect small cracks in and near the surface of the material
• The surface requires minimal preparation
• Able to detect corrosion and cracking
Corrosion Detection
Cracking Detection
Material Requirement
High strength
Small grain size
Good resistance to stress corrosion cracking
Very high degree of workability
Aluminium base alloy
AA7072 alloy
AA7072 alloy
• A typical material used for components such as aircraft stringers and also has a widespread use on aircraft field.
All in all, stringers, longerones and frames are essential to form a semi-monocoque fuselage. This presentation has covered the background knowledge and examples of those components, design considerations of fuselage, construction of stringers , longerones and frames and a case study of airplane incident
• Preparation process:
1. AA7072 alloy ingot is heated evenly at approximately 460° C for 16 to 24 hours.
2. Hot rolled at 400° C to about 4m to 8mm thick sheets.
3. Cold working can also be carried out to strengthen the material.
Stringers are made in different shapes and sizes, repair methods can differ.
As longeron and stringer have similar characteristics, their repair methods are similar
Causes of damage to stringers by:
Vibration during flight
Collison during grounded activities
Evolution of High Strength Components
Repair methods
By patching
By insertion
Case Studies
Design Considerations
Basic fuselage design requirements
Structure considerations
Types of Fuselage layout
1. Determine the extent of damage
2. Remove rivets surrounding the area of damage
3. Carefully remove the damaged area using tools such as hacksaw, keyhole saw, drill, or file.
4. Stringer repair requires the use of insert and splice angle. Consult the applicable structural repair manual when locating the splice angle.
5. Bend allowance and sight lines should be taken into consideration when marking the layout and bends for these formed parts. For repairs to curved stringers, make the repair parts fit the original contour of the aircraft.
By patching
Only used when the damage does not exceed two-thirds of the width of one section and is not more than 12-inch long.
Repair Methods
Airplane truss structure are first invented in 1903, by the Wright brothers and it includes longerons, vertical and diagonal web members.
Circumferential frames with a base plate which is attached directly to the inner face of the self-stiffened skin, in which case the frames have notches where the stringers are to pass
Types of Truss design:
Pratt truss
Warren truss
Configurations the stringers are interposed between the circumferential frames and the self-stiffened skin (the frames thus pass above the stringers), and angle pieces, commonly called “clips”, are positioned between the stringers, and connect the circumferential frames to the self-stiffened skin.
- Structural frames are approximately circular in shape, for example annular or oval, or they may have two or three lobes or they may be any other shape of the same type.
The Wright Brothers
In the 1911, a Swiss marine engineer Eugene Ruchonnet discovered and invented the monocoque structure, which includes skin, former and bulkhead.
Eugene Ruchonnet
After a period of time, the monocoque structure have evolved into the semi-monocoque structure, which includes longerons, skin, bulkhead and stringers.
Content Page
Introduction to High Strength Components
Design Consideration
Construction of High Strength Components
Significant incidents/accidents related to High Strength Components
Group Reflection
Introduction to High Strength Components
High Strength Components
In aircraft construction, a longeron is a thin strip of wood or metal, to which the skin of the aircraft is fastened. longerons are attached to formers, in the case of the fuselage, or ribs in the case of a wing, or empennage.
In very early aircraft, a fabric covering was sewn to the longerons, and then stretched tight by painting it with "dope", which would make the fabric shrink, and become stiff. Longerons are sometimes called "stringers".
Fatigue cracking plus with bad maintenance precautions cause one of the tile to dislodged over time.

Over flying of the plane way above the planes designed limits.

Due to cyclic loading from the constant compressing and decompressing of the plane the fuselage.
Cause of incident
Group Reflection
Jia Jun
Zhi Mao
Done by:
Zhi mao
Jia jun












High Strength Components
I was in-charged of doing the design consideration of the and different layouts of the fuselage. I was amazed at number the criteria that corespondent in-order to construct/assemble a fuselage. I realized the requirements imposed were stringent, this tremendously increase the safety of the passengers. Since there are massive amount of components inside a fuselage, that was why our group decided to focus on stringers, longerones and frames. All in all, this project increase my awareness of past case studies and the components' functions and construction.
I did the research on the construction of the high strength components, repair methods and helped in the introduction. From this project, i have learnt that every component in the fuselage has an important part to play in maintaining the fuselage shape together without falling apart. Althought there are many components in a fuselage, we have decided to only focus on a few main components. Prior to this project, my knowledge on the fuselage and its repair methods were only as much as what was taught in our lecture notes. Also, i applied my knowledge taught through lectures and practical lessons into this project with the aid of researched points. Through this project, i found out that human flight has a rich history dating a long time back and how technology has aided us and improved the way we travel today.
In this project, I did the introduction to high strength components and i discovered the history of the aircraft like who built the first aircraft and when did he built it. I was also surprised to discover that even for a small part like stringers, the construction is very precise and complicated and its not an easy thing to do. Among so many variations of design of high strength components, engineers could picked out the perfect size and type of component to use for an aircraft. After knowing the history of aircraft components through my research, i am truly aspired to be an aircraft engineer by the people who discovered aircraft.
After completing this project how important the design of the fuselage is although it is just use to carry loads there are many safety factors going into the design of the plane including the decision for the choice material that goes into every component that makes up the planes fuselage.

I did the part on the research of accidents/incidents caused by the fuselage although there aren't many accidents. we as engineers to be should learn from the mistakes help improve on our already impressive tract record.
For this project I researched on the construction of the high strength components and repair methods. During this project, I understand more about the fuselage structure, type of material use for different parts of the fuselage and ways to repair different structure. For this project our main objective is focus on longeron, stringer and frame, as they are all under high strength components. Through this project, I read many reports, articles and books which related to high strength components. This project helps me with my coming exam for ASAS, I used some of the ideas which had taught through lectures and practical. As for the repair part I can apply it to my coming internship. Through this project, I had gain a lot of new knowledge which related to aircraft.
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