11.2 AIRFRAME STRUCTURES Flashcards
What are the 3 structural classifications
- primary structure
- secondary structure
- tertiary structure
Explain secondary structure
- non-primary structural components
- less prone to weakening
- e.g. fuselage stringers
Explain primary structure
- If structure fails, can lead to a very bad consequence
- e.g. engine mounts
Explain tertiary structure
- lightly stressed components
- e.g. fairings, support brackets etc
What does it mean by fail-safe
- back-up protection despite failure
- once failure occurs it is no longer ‘fail safe’
- will require frequent inspections
What does it mean by safe-life
- Prevent catastrophic failure
- structure is serviceable approx 1/3 of max calculated operating hours
What does it mean by damage tolerance
- repeated static + dynamic load tests
- ensures that even with damage it remains within the operational life
- reliant on visual inspection to find damage
What is included in the zonal identification system
- major zones
- sub-major zones
- zones
100
Lower half of fuselage
200
Upper half of fuselage
300
Empennage (aft fuselage and horizontal and vertical stabilisers)
400
Power plants and the struts
500
Left wing
600
Right wing
700
Landing gear and LG doors
800
Doors
For smaller aircraft the 2nd digit in the sub-major zones is between
1-6
For larger aircraft the 2nd digit in the sub-major zones is between
1-9
Usually the sub-major zones on the right hand side are even or odd
Even
Usually the sub-major zones on the left hand side are even or odd
Odd
What digit is the zone and how are they numbered
- 3rd digit
- FWD to AFT, INBOARD to OUTBOARD, BOTTOM to TOP
Explain body stations or fuselage stations
- vertical plane at right angle to body centreline
- distance measured from a point in front of nose
Explain buttock lines
Vertical planes parallel to body centre line (longitudinal)
Explain waterlines
-horizontal planes, right angle to body buttock lines (horizontal)
What is tension
Resists forces which pull it apart
What is compression
- shorten/squeeze
What is torsion
- stress causes twisting
What is shear
-resists one layer of material to slide over adjacent layer
What is the stress calculation
- Force/cross-sectional area
What is bending
Combination of compression and tension
Explain Hoop stress
- pressure exerted circumferentially on skin
- hoop stress = 2(axial axis)
(twice value of longitudinal stress)
Where are drain holes located
- various positions of aircraft’s lower fuselage
What are ‘bilge-like’ valves
- Prevent loss of air during aircraft pressurisation
Valve open = depressurised
Valve closed = pressurised
When interior cabin is depressurised is the spring loaded ‘bilge like’ valve open or closed
Open
What must be ensured when flammable vapour or water is present
Ventilation
What does easy access to locate system components result in
- saves time and lowers maintenance cost
What are installed securely but with ease of removal in mind
Cockpit indicators
What does lightning strike caused by direct damage look like
- burned surface/melted
What does lightning strike caused by indirect damage look like
- damage to the electrical system and equipment
A lightning strike usually causes small damage approximately —mm in diameter
3mm
What is the hole diameter of a high intensity lightning strike
6mm
Most common area for lightning strikes?
- nose
- trailing edges
What is bonding
Same electrical current potential (low resistance path)
What is grounding
To maintain a constant electrical potential between aircraft and ground
How do you prevent the build up of static charges
Bonding
What does the frames do in the airframe construction
- give cross-sectional shape (often circular)
- give shape and provide strong attachment points
What are bulkheads and what is its function
- give shape to fuselage
- pressure bulkheads used to contain pressure
- fireproof bulkheads used to seal and isolate fires
Main difference between bulkheads and grommet
Bulkheads- cannot put hand through
Grommet - can put hand through
What are Longerons
Main longitudinal member of fuselage/nacelle
Primary bending loads are taken by
- stringers
- longerons
- bulkhead
Longerons
What are Longerons supplemented by
Stringers
Explain stringers
-smaller and lighter than longerons
- carry loads along their length
- used for skin attachment
What is the function of clips/cleats?
Help transfer the pressure loads from the skin
What is the clips/cleats attached to
Skin to frame and stringer
Explain doublers
-reinforced skin that requires extra strength
- often found around doors or windows
What are some types of doublers known as
Crack stoppers
What are struts
-load bearing components that primarily hand compression forces
- transmit loads from one part of fuselage to another
What are struts made out of
- lightweight materials such as aluminium or composite material
Explain ties
- handle tension forces
- typically made from high strength materials like steel or titanium
What construction are floorboards
- honeycomb composite
What usually carries tension loads during pressurisation
Floor beams
What are the 2 types of fuselage construction
- truss type
- monocoque type
Explain truss type
Carries both tension and compression loads
Explain true monocoque construction
- Frame assemblies and bulkheads give fuselage shape
- skin carries primary stress
Explain semi-monocoque construction
- loads shared between skin and framework
- ‘known as stressed skin structure’
What is the wing box supported by
Heavy frames and a ‘keel beam’
Aircraft’s empennage contains vertical and horizontal stabilisers (T or F)
T
What is type 1 for special coatings
Water repellent coating
What is type 2 for special coatings
Heavy duty corrosion preventive compound
What are the 3 aircraft cleaning methods
- wet washing
- dry washing
- polishing
What type of wash removes oil, grease, dirt, carbon deposits etc
Wet washing
What type of wash removes dirt and small accumulation of dirt
Dry wash
Explain polishing
- removes oxidisation and corrosion
- restore colour and make brighter
How are acrylic windows cleaned
- windows must be washed with warm water and soap
- polish with cloth
