13.2 Basic Structures Flashcards
(75 cards)
What are the 4 common certification specifications for aircraft types?
CS–23 (Normal, utility, aerobatics and commuter)
CS–25 (large aeroplanes)
CS–27 (small rotorcraft)
CS–29 (large rotorcraft)
What is the limit load condition?
Maximum loads anticipated during normal operation of the aircraft
How do negative load limits usually compare to positive load limits?
Usually less than
What is the ultimate load?
The load that a component must withstand with a positive margin from the limit load
How long must a structure be able to support ultimate loads without failure?
At least 3 seconds
Which areas of aircraft structure will normally be coloured:
Red
Yellow
Green
Red – Primary structure
Yellow – Secondary structure
Green – Tertiary structure
What conditions will signify when a structure is primary?
Catastrophic structural collapse or loss of control
Power unit failure
Injury to occupants
Unintentional operation of or inability to operate essential equipment or services
What is a Principle Structural Element (PSE) defined by?
Components which contribute significantly to carrying flight, ground and pressurisation loads
Failure could result in catastrophic failure of the aeroplane
What is a fail safe structure described as?
A structure having multiple load paths, providing redundancy
How is the inspection cycle determined in damage tolerance and fail safe?
If a crack of detectable length is missed on first inspection, it will be picked up in the second inspection before it becomes too dangerous
What is ‘notching’ and what is it sometimes referred to as?
Abrupt change in cross–sectional area
stress raiser
Why are additional strengthening frames and doublers often used at fuselage cut–outs such as windows and doorways?
Absorb the stress normally carried by the skin and stringers
Transferred from the door by its hinges and stops
Why is a doubler usually tapered or chamfered?
Doubler is stronger than the original skin
It can transfer loads at its edges greater than the skin was designed to take
What are the three indicators which signify zones?
Major zone
Major sub–zone
Zone
What are the major zones?
100 – Lower half of the fuselage to the rear pressure bulkhead
200 – Upper half of the fuselage to the rear pressure bulkhead
300 – Empennage, including fuselage aft of the rear pressure bulkhead
400 – Power plants and struts or pylons
500 – Left wing
600 – Right wing
700 – Landing gear and landing gear doors
800 – Doors
900 – Reserved for uncommon differences between aircraft types not covered by standard series numbers
What is the difference between the wing buttock lines and the wing station lines?
Stations run perpendicular to the leading edge
Buttock lines run parallel to the Body Buttock Line
What are ties?
Generally, thin solid members used to take tension
What is circumferential stress also known as?
Hoop stress
What is hoop stress?
Fuselage structure subjected to a stress that is caused by the difference in pressure between the inside and outside of the pressurised cabin area
What is the relative proportion between longitudinal stress and hoop stress?
Longitudinal stress is always less than the hoop stress
Hoop stress is the same pressure over a larger surface area
What is cyclic fatigue caused by?
Repeated fluctuating loads
What causes fretting fatigue?
Small scale rubbing movements and abrasion of adjacent parts
What causes thermal fatigue?
Stress fluctuations caused by thermal expansions and contractions
In aviation, how is fatigue testing carried out on aircraft?
Carried out on an aircraft structure taken from the production line
