11.2 Airframe Structures - General Flashcards
What must be done if a defect is found on an aircraft
It must be noted in the logbook so it can be rectified with an approved drawing
What type of loads do structural members usually carry
End loads rather than side loads
Tension or compression rather than bending
Rather than taking structural loads what qualities are required from fairings and cowlings
They need to have a neat appearance and streamlined shape
Every part of the aircraft must be planned to take the load to be imposed on it what is this process called
Stress analasys
To ensure the aircraft structure is capable of taking all of the stresses it will experience in flight what is done in the initial design phase
Fail safe load transfer, damage tolerance and fatigue indexing
What does the fail safe method rely on
Duplication of certain structural members. If one fails the other will take the load
What is the damage tolerance method
Requires an assessment to see if the damage sustained will lead in failure
This method is old and outdated
What is a further method of damage tolerance
By using crack limited joints. The joints will limit the spread of cracks
What is fatigue known as
Fracturing after a series of cyclic loads, may be much less than the ultimate load
What are the 3 categories of aircraft structure
- Primary structure
- Secondary structure
- Tertiary structure
What are the characteristics of the primary structure
Critical load baring structure. Requires immediate repair if damaged as it can affect the structural integrity of the aircraft
What are the characteristics of the secondary structure
Not load baring and the failure of a secondary structure would not affect the structural integrity of the aircraft
These consist of things like access panels and require repair as soon as possible
What are the characteristics of a tertiary structure
Not load baring and do not make up an integral part of the airframe. They consist of things like wing root fairings and landing gear fairings
What are the 5 main structural units of an aircraft
- The fuselage
- The wings
- The stabilisers
- Flight control surfaces
- The landing gears
What main structural members make up an aircrafts structure
Stringers, frames, bulkheads, ribs, skin and other members
How are structural members fixed together
With brackets, rivets, bolts, screws and nuts which add strength to the fuselage
What are structural members designed to do
Carry a load or resist stress
How is stress created
By the internal force of a substance which opposes or resists deformation
What are the 6 major types of stress that can effect aircraft structure
- Tension
- Compression
- Torsion
- Shear
- Bending
- Hoop stress
Give the definition of tension
Stress that resits the forces trying to pull it apart
How do you calculate tensile strength
Divide the load (in pounds) with by the cross sectional area
The result is PSI
What is the definition of compression
Stress that resists a crushing force. Causes aircraft parts to be squeezed together
Usually measured in PSI
What type of stress is torsion
A twisting stress. For example when the rudder is deflected
What is shear stress
Unaligned forces pushing one part of a body in one direction and another part in the opposite direction
What is bending stress
A combination between compression and tension.
When an aircraft is pressurised what type of load is it under
Differential loading
What are the two side effects of differential loading
One causes the compartment to stretch longitudinally and the other causes the circumference of the compartment to expand
This is known as hoop stress
What are the zones of the aircraft
Primary areas of aircraft such as the fuselage, wings and engines
In what units do Boeing measure their zones
Imperial in inches
What are the reference lines called on Boeing aircraft
Body stations, body buttock lines and body water lines
Where is the body station
- A vertical plane at right angle to the body centreline
- Measured from a point in front of the aircraft (jig)
What is the abbreviation of body station
BS
What are the body buttock lines
Vertical planes parallel to the fuselage centreline
Body buttock line 0 is the body centreline
What is the abbreviation of Body Buttock line
BBL
For right - R BBL
For left - L BBL
What are the body water lines
Water lines are horizontal planes at right angles to the body stations and body buttock lines
Body waterline 0 is bellow the fuselage
Where is the reference line used for installation on components and equipment used by the manufacturer
Along the top surface of the floor beams
On Boeing aircraft what are the wing coordinates used
- The wing reference plane
- Wing buttock lines
- Wing stations
On Boeing aircraft what are nacelle coordinates divided in to
- Nacelle stations
- Nacelle buttock lines
- Nacelle water lines
Where is nacelle station 0 on Boeing aircraft
In front of each forward engine mount
On Boeing aircraft what are the horizontal stabiliser coordinates
- The stabiliser chord plane
- Buttock lines stations
- Leading edge stations
- Elevator stations
What is the horizontal stabiliser reference plane
The plane through the leading edge and trailing edges of the stabiliser aerofoil
On Boeing aircraft what coordinates is the vertical stabiliser split in to
- Fin stations
- Waterlines
- Leading edge stations
- Rudder stations
How are the vertical and horizontal stabiliser stations identified on Airbus
They are called horizontal stab stations and vertical stab stations
What zone is 100
Bottom of the fuselage
What zone is 200
Top half of fuselage
What zone is 300
Vertical and horizontal stabiliser
What zone is 400
Power plant and struts
What zone is 500
Left wing
What zone is 600
Right wing
What zone is 700
Landing gear and landing gear doors
What zone is 800
Doors
What is done to make a more accurate description of an object rather than just zone number
Major zones are broken down in to sub major zones for more precise location
If two or more access panels are in the same zone what is done to identify each one
A letter is used after zone numbers
How is the lower half of the pressurised fuselage drained
By using a system of valved drain holes
How are fluids directed to the drain holes in the lower pressurised fuselage
Through a system of longitudinal and cross-drain paths through the stringers and frame shear clips
What is used to prevent the loss of pressure through drain holes
Bilge- like valves are fitted
They are spring loaded
What is the most basic form of lightning protection
The exterior almost all metal structure. It acts as a shield protecting internal areas from lightning and electrical systems from electromagnetic interference
What must be done after a lightning strike has happened
- General walk around and find out damaged area and discharge
- If damage is found a detailed inspection is required and must be documented
What two types of damage do lightning strikes usually result in
Direct damage - Surface is burned or melted or shows signs of metalic distortion at two or more points
Indirect damage - Large electrical transients on the wiring which may cause damage to the electrical systems equipment
What type and size of mark will a lightning strike usually cause
A small circular melt mark approx 1/8 inch diameter
What might other signs of lightning strike be
Burned or discoloured skin or rivets
What are the lightning strike conditional inspection examines these areas
- External surfaces
- Static discharges
- Fuel system valves
What are the most likely places for lightning strikes to occur
Fuselage nose section and the aerofoil trailing edge tips
What components could a high intensity lightning strike damage
- Fuel valves
- Generators
- Power feeds
- Electrical distribution systems
Why are aircraft bonded
- To minimise radio and radar interference
- To eliminate fire hazard by preventing spark between two metallic components at different potentials
- To minimise damage from lightning strikes
- To provide a low resistance return path for single wire electrical systems
- To aid effectiveness of shielding
As long as protective coatings have been removed from components which bonding leads are attached what should the resistance not exceed when checked
A resistance no greater than 0.025 Ohms
What conditions apply when installing grounds
- Grounds must be separated AC, DC shields
- There must be no more than 4 terminals on 1 stud
- In a fuel vapour area dual grounds must be installed
What is grounding
Grounding is the process of connecting systems and the shields of shielded cables to the aircraft metallic structure at pre-designated points
What is a longeron
Main longitudinal member of a fuselage or nacelle
What is a tie rod (tension rod)
Member taking a tensile load
What is a strut
A member taking a compression load
What is a spar
The main spanwise member of an aerofoil. Frequently consists of an upper and lower boom separated by a web
What is a stringer
A stiffener which assists with sheet materials to carry loads along their length.
With integral construction they are machined or etched out of the skin panel
What is ‘safe life’
The period in which It is considered that a failure of a component is extremely unlikely.
What is a crack stopper
A reinforcing member usually placed at right angles to the path of an anticipated crack which will reduce the rate of further propagation
What is static loading
Loads imposed on an aircraft when stationary
What are the two types of fuselage construction
- Truss Type
- Monocoque type
What is truss type
Rigid framework made up from members such as beams, struts and bars to resist deformation by applied loads.
Usually light aircraft covered in fabric. Tubular fame welded
What is the biggest problem with monocoque constructions
Since no bracing members are present the skin has to be strong enough to take all of the stress.
Strength the weight is the issue
What is the main advantage of the semi monocoque construction
The structure can take a lot of stress or damage and still maintain enough strength to hold together
What are floorboards constructed from
A honeycomb composite construction
What is the empennage attachment
Similar to the wing box but for the horizontal and vertical stabilisers
What is the purpose of engine nacelles
The contain the engine components and provide a streamlined enclosure
When are bolts most commonly used on aircraft
When high strength is needed. If high strength is not needed then screws are used as a replacement
What are the 3 main types of surface protection
- Pretreatment
- Paint coatings
- Special coatings
What would a pretreatment consist of
- Increase corrosion resistance of the metal by chemical or electrochemical procedures
- Give a good surface for paint coatings
What would paint coatings consist of
- Primer: Increases corrosion resistance
- Top coat: Adds to the surface protection and then provides good finishing qualities
Why are special coatings used and what are used
They are used on materials or places that require extra or more intensive corrosion resistance
- Type 1: Water repellant coating usually made from silicone free materials
- Type 2: Heavy duty corrosion preventative compound, i.e. Greases available in various grades
What is the purpose of surface cleaning
To remove dirt or oil for inspection and maintenance purposes
