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