AC Systems Flashcards
CS For Airworthiness
CS23 - Small Commuter AC
CS25 - Large Turbine AC 5300kg
Safe Life
To not suffer catastrophic failure in AC expected life cycle
If it does fail there will be no catastrophic damage
Flying hour/Cycles/TO/LD/Pressurisations
Fail Safe
Redundancy alternate component for the load path
+ Backup for critical component
- Costs/POF/Weight
Damage Tolerance Structure
Spreading Load over larger area
Crack arresting features limit spread of cracks
+ eliminates extra structure
CS Standards Focus Points?
Design
Build Materials
Build Quality
Manufacturing standards
Stress
Internal force per unit inside component from external loading (press or stress)
- distorting in skin
- missing rivets
- wrinkles
Strain
Deformation caused by stress
Types of stress
- tension (apart)
- compression (together)
- torsion (twisting)
- sheer (parallel)
Wing in flight
Compression on top of wing
Tension under wing
Excessive compression & tension
Compression - buckling/wrinkling
Tension - pulled rivets
Dynamic load
Quick build up due to flight conditions
Manoeuvring and change in g load.
Severe
Static Load
Constant/slow build up
Weight of wheel on ground on ac wings
Bending Load + relief?
Greatest at wing roots
Weight + dynamic forces by lift
Weight management
Staying within loading g limit
MZFM limit keep wing root within limits
Load alleviation - rigid
Cyclic Loads
Alternating loads at difference phases of flight
Pressurisation
Design limit + design ultimate load
Max load set by designer in service
DLL x 1.5
Wing Spars
Main structural loading
Withstand torsional/bending loads
Fatigue
Failure at a load less than steady applied load.
- weight
- size of loads
- tensions loading
F LIFE - # cycles for metal to fail at certain stress
Corrosion
Disintegration of metals
Oxidation
Electrolytic - dissimilar metals EP contrast
Black oil from rivets = corrosion
Stress Corrosion
Fatigue + corrosion
Corrosive conditions under tensile loads
Delamination
Decrease in composite structure strength
- difficult to detect
- bubbled skin
- hair line cracks
- changes in sound when tapping
Hard time
Removed at intervals
Serial numbers/Part Numbers
Scheduled maintenance
On-Condition
Inspected and monitored
Removed in fails visual inspection
Composite
Two or more materials to give rise to unique structural properties
Matrix - epoxies/polyester
Fibres - glass/carbon/armaid
Matrix spread load between fibres
Advantage/disadvantage of composite
Retain properties at elevated temps
High strength
Stiffness
Costly
Labour intensive
Hard to maintain
Careful electrical bonding required
Delamination
Composite Core
Replaces heavier matrix in some structures
Ideal for:
- thermal acoustic insulation
- high stiffness and strength
Issue:
- water can penetrate
Flight controls
Sound proofing engines
Prepeg Tow
Composite method laying fibre onto of the mould - preferred method
Ratio of the change in size of deformed structure to the non deformed structure is…
Strain
Mercury/Potassium Hydroxide
Produce toxic fumes and rapid corrosion of ac structure
Visual indicator of corrosion
White spots on bare aluminium surfaces
Certification Specifications
Lays down basic requirements for design,material quality, build quality and behavioural characteristics
Rate of corrosion is increased by
Temperature
Humidity
Rainfall
Sulfur dioxide
Air salinity
Indication of corrosion on aluminium
White/grey powder
Corrosion of iron
Red/brown streaks
Metals in combination with saltwater
Yellowish colour
