11.2 Flashcards
What’s a primary structural element
A part of the aircraft which contributes significantly to carrying flight, ground or pressurisation loads and is essential to maintaining ac structural integrity
What are flight limit loads
Max loads that are expected in service
What’s ultimate limit loads
Loads in which flight limit loads are multiplied by a factor of safety
What two forces are a combination to make bending forces
Compression and tension
Are structural member primarily designed to carry end loads or side loads
End loads
Whats primary structure
Any structure of the aircraft that can cause
Loss of control over the aircraft.
Catastrophic structural collapse.
Harm to occupants.
Failure of the power unit.
Unintended operation.
Incapability to perform a service.
What’s secondary structure
Secondary structure encompasses all non-primary structural components of the aircraft that possess intrinsic structural significance and exhibit strength surpassing design requisites.
Eg. Wing ribs, fuselage stringers, certain parts of ac skin
Less prone to weakening without Facing failure risks as seen in primary structure
Whats tertiary structure
Lightly stressed elements added to ac for diverse purposes
What’s fail safe
A method where there’s duplications of structurall members to ensure if one fails then the other can take over
Disadvantage of fail safe
Added weight
What’s safe life concept
A prediction of how long a structure can remain in service before Reaching the point of fatigue damage
Once testing is done the parts or components are given specific safe cycles of safe hours in service
Once testing is done the parts or components are given specific safe cycles of safe hours in service
Test limits are tested and the safe life is usually one third of the max amount of cycles of testing to ensure it’s safe
What’s damage tolerance concept
The structure is designed to be allowed to take damage and that damage is monitored until it exceeds limits and then it must be replaced
What’s zone 100
Lower fuselage
What’s zone 200
Upper fuselage
What’s zone 300
Empyenage
What’s zone 400
Power plants and struts
What’s zone 500
Left wing
What’s zone 600
Right wing
What’s zone 700
Landing gear AND LAMDING GEAR DOORS
What’s zone 800
Doors
Are sub major stations on the left hand odd or even numbers
Odd
Right is even
One larger aircraft whats the range that the second number can be
1-9
Smaller is 1-6
What’s a body station
A vertical plane at a right angle o the body centreline
Body stations are Measured from nose
What’s a buttock line
Vertical planes parralell to the body centreline
Button line 0 is the centreline
What’s water lines
Horizontal planes at a right angle to body station and body buttock lines
Body waterline 0 is sometimes below fuselage in landing gear or sometimes under landing gear
What chapter can the numbering of aircraft stations be found
6 AMM
What are wing stations measured in and where from
Inches or mm
From a butt line reference point or from wing rib one
How are component stations numbered
Have own numbering system from inbrd to outbrd
Hows stress calculated
Force / cross sectional area
What’s the relationship between longitudinal and hoop stress
Hoop is always double what longitudinal is
What’s hoop stress
Circumferential stress exerting tensile forces on skin
What helps to direct the water to the drainage holes
A system of longitudinal and cross drain paths through stringers and the frame
How are the drain holes held open and when are they open
Spring
When ac depressurised
What do highly susceptible areas have as well as ventilation points
Ram air inlets and exit points to enable a full flow of fresh air
What’s advantages of have dedicated or general purpose computers grouped and secured in sections of aircraft
Max security
Accessibility
Environmental conditions
What’s the ac basic form of lightning strike protection
All metal structure
Or for composites…
Metallic paint or conductive mesh
What’s direct and indirect lightning strike damage
Direct is damage such as burn, melt or distortion of metal surface
Indirect is damage to electrical systems on the aircraft
What size is the burn mark of a high intensity lightning strike
6mm
What’s the normal size of a burn caused by a lightning strike
3mm
Where’s the most common areas for lightning strikes
Nose, trailing edge, and extremities of wings and stabs
What can happen to metal structures after a lightning strike
They can become magnetised
What’s the difference between grounding and bonding
Grounding- the process of electrically connecting conductive objects to either a conductive structure or so,e other conductive return path to safely complete a normal or fault circuit
Bonding- done by connecting all two electrical conductors
What’s the reasons for bonding
To minimise radio and radar interference.
To eliminate fire hazards by preventing a spark between two metallic components at different potentials.
To minimise the damage to the aircraft and its passengers from lightning strikes.
To provide a low-resistance return path for single-wire electrical systems.
To aid in the effectiveness of the shielding.
What conditions must apply when installing grounds
Grounds must be seperated
There must be no more than 4 terminals on one stud
Dual grounds must be installed in fuel vapour areas
How’s a ground plate installed in a aircraft
By bonding an aluminium wire mesh into the composite structure
What’s direct and indirect bonding
Direct- achieved by exposing the mesh and mounting the equipment directly onto the conductive path
Indirect- achieved by exposing the mesh and installing a bonding wire and connector
If binding done correctly what should the values be
No higher than 0.025 ohms
Where are the heaviest vertical frames/ formers located
Located at intervals where heavy loads need to be carried like wings and power plants
What shape are frames
Circular
Disadvantage if monocoque construction
Maintaining strength while not exceeding weight limits
What supplements longerons
Stringers
What’s the main longitudinal member of a fuselage or nacelle
Longerons
What part of the structure takes the primary bending loads
Longerons
What are stringers for
Serve as stiffners for along the skin
Have some rigidity but are used for shaping and attaching skin.
What do the clips/ cleats in aircraft structures do
Help attached the skin to the frame and help with transferring the pressure loads from the skin
What holds the bulkheads formers and stringers together
Heavy strong longerons
What holds the bulkheads formers and stringers together
Heavy strong longerons
What are doublers
Additional sections of material on the skin where extra strength is required
Found around apertures, doors, Windows
What are crack stoppers
They are types of doublers that and are placed at a right angle to the path of a anticipated crack to limit crack propergation
What’s added around doors as well as doublers and why
Kick plate as they prone to damage for being kicked or loading luggage
What type of loads do struts usually take
Compression forces
What are struts for and what are they made of
Long slender members that are used for transferring loads from one part of the fuselage to the other
Made of aluminium as it’s light but strong
What type of forces do ties take
Tension
What are the purpose of ties
Used to maintain structural integrity of various parts of fuselage to prevent excessive deformation under external loads
What are ties made of
Steel or titanium
What are the floor boards made off
Honeycomb composite structure and screwed into the ALLUMINIUM FLOOR BEAMS
What loads do floor beams carry
Tension under pressurisation
What’s under the floorboards
Foam to prevent fretting
What’s different about floor boards in wet areas (galley and lavatories)
They’re sealed to prevent corrosion
What’s the longitudinal members called in wings
What’s the main span wise member
Spars
Ribs
What type of constructions used for wings
Semi monocoque
What’s the primary purpose of ribs
Maintaining the correct contour of the wing covering and also a stress bearer
What’s a truss type aircraft construction
Rigid framework made up of beams, struts and bars
Made of aluminium and rivets
What carry’s the primary stresses in a monocoque construction
Skin
What’s the semi monocoque structure also known as
The stressed skin structure
What material is semi monocoque fuselage primarily made up of
Aluminium but in some high temp areas steel and titanium
What’s the main advantage of semi monocoque structures
Another advantage
An withstand damage and still be strong enough to hold together
The structure of the bulk heads frames stringers and longerons facilitate the construction of a streamline fuselage
Doesn’t depend on a few structural member for strength and rigidity due to stressed skin
What’s important to remember when making an aircraft with carbon fibre and alluminium
Care must be taken to avoid contact with each other as it will cause galvanic or electro chemical corrosion ( painting, anodising, seals Ra can be used to prevent this )
Strength to weight ratio
What are common ways to protect structure from corrosion
Sacrificial layer (cladding or plating)
Sealant
Anodising
Painting
Why’s there sometimes a third false spar in a wing
Adds an additional strong attachment point for landing gear
What suppports the wing box
Keel beam and heavy frames
What’s the wing box for
Attached to wings and provides support and rigidity
Absorbs impacts
What’s the strongest point of the fuselage
Wing box
What type of construction is the vertical stab
Semi monocoque
What shape are nacelles and why
Round or epicyclic to reduce aerodynamic drag
What’s the nacelle house
The engine and accessories like the mounts, firewalls, skin, cowling and structural members
When are bolts used
In areas where high strength is required
What’s the advantages of combining adhesive bonds and rivets
Weight saving, strength, durability
What’s the most effective method assembly method
Adhesive bonding
What’s the main uses for adhesives on ac
Bonding of stringers to skin fat fuselage and wings
And for honey comb structures for ailerons, elevators and tabs
What does the type of surface protection depend on
The material
Function of the material
Location of the material
What external areas are acceptable to not have surface protection
Leading edge of slats, wing tips and fences
Leading edge or engine intake cowls
External surfaces of pylon made of corrosion resistant metals
Scuff plates on doors
Equipment like a of a sensors and static ports
What’s chromating
Pre treatment process that produces a protective oxide film and has a yellow appearance
What’s the most common form of chromating
immerse the part in a potassium dichromate solution.
What negative does paint have
Added weight
What negative does paint have
Added weight
What’s the two sections paint coatings can be divided into and what are they
Primer- gives the anti corrosion properties
Topcoat- protects the primer layers and gives a good appearance
What are the two types of special coatings
Type 1- water repellent coating made of silicone free materials
Type 2- heavy duty corrosion preventive compound (can be soft or hard forming)
How often do ac need to be washed
Prescribed maintenance periods
What are the three main ways to clean an aircraft
How’s it decided which one will be used
Wet wash
Dry wash
Polishing
Depending I;the type and extent of the soil
What type of wash would be used when the ac is greasy and oily
Wet wash
What type of wash would be used on ac when there’s dust, small accumulations of dirt and soil
Dry
What type of wash would be done on ac when wanting to restore brightness or colour to unpainted surfaces
Polish
Why’s it important to use the appropriate cleaning agents when washing the ac
Can cause undesirable affects like hydrogen embrittlement in steel
What type of solvents shouldn’t be used in the hangar due to toxic fumes
Chlorinated solvents
Why’s it important to dilute washing solvents before washing windows
Can cause crazing
What are some cases where aircraft symmetry and alignment checks should be carried out
Any major structural repair
The aircraft that has been subjected to severe conditions, such as a heavy landing, extreme turbulence, overspeeding, or violent manoeuvres
The flight crew reports unusual flight characteristics
Wrinkling or buckling of structural skins
Loose or sheared fasteners
Areas of badly fitting access and inspection panels
What are some cases where aircraft symmetry and alignment checks should be carried out
Any major structural repair
The aircraft that has been subjected to severe conditions, such as a heavy landing, extreme turbulence, overspeeding, or violent manoeuvres
The flight crew reports unusual flight characteristics
Wrinkling or buckling of structural skins
Loose or sheared fasteners
Areas of badly fitting access and inspection panels
What should be done before checking angle or position of components in alignment and symmetry checks
Jacked and levelled
What alignment checks Are usually specified to be checked
Wing dihedral angle
Angle of incidence of wing and horizontal stab
Verticality of the wing
Engine alignment
Symmetry
When checking the incidence of the wing what’s done to ensure that the wing is not twisted
It’s measured at 2 points
What effects can happen as a result of misalignment
Dramatically change flight characteristics and impare the safe control of the aircraft as intended by the designer
