11.2.a Structures General Flashcards
What philosophy are modern structures developed with?
Stressed skin
What is PSE?
Principle Structural Elements
What are Principle Structural Elements?
The part of the aircraft that contributes significantly to carrying flight, ground, or cabin pressure loads.
What are some of the PSE’s?
Wings
Horizontal Stab
Vertical Stab
Canard
Forward wing
Winglets
Pressurised areas
How are aircraft strength requirements specified?
In terms of the max loads expected in service and max load plus safety factor.
What is a flight load?
The maximum loads expected in service.
What is an ultimate limit load?
Flight limit loads multiplied by a factor of safety.
Where is the criteria found for limit loads of large aircraft?
CS-25
What are the five forces acting on an aircraft?
Torsion
Tension
Shear
Bending
Compression
What is torsion?
Stretch
What is compression?
Squeeze
What is torsion?
Twist
What is shear?
One layer moving opposite to the other.
What is bending?
Combination of tension and compression.
What are the three categories of structure?
Primary
Secondary
Tertiary
What is primary structure?
Any part that should it fail lead to loss of control or catastrophic failures and harm.
What are some examples of primary structure?
Wing spars
Engine Mounts
Fuselage frames
What is an SSI?
Structurally significant item.
What is secondary structure?
Non-primary structural components such as ribs, stringers and segments of skin.
What is secondary structure less prone too?
Weakening without facing failure risks.
What is tertiary structure?
Remaining components of the aircrafts framework.
What kind of stuff comes under tertiary structure?
Fairings
Fillets
Support brackets
What does the document FAA AC 23-13A evaluate?
Fail safe load transfer
Damage tolerance
Fatigue indexing
What is a fail safe design?
Duplication of structural methods to ensure if one fails then the other will take the load.
What is the disadvantage of fail safe designs?
They add weight.
What is the modern version of fail safe?
Damage tolerance.
What is safe life concept?
Prediction of how long a structure can remain in service.
How is the safe life indicated?
As a number of cycles or hours.
What is the safe life given to the structure?
1/3 of the max calculated hours.
What does the damage tolerance concept require?
Evaluation of the structure.
What does damage tolerance testing look like?
Repeated static and dynamic load tests, which demonstrate that the structure can withstand the loads expected in service plus a factor of safety.
What is another type of damage tolerant structure?
Multiple load path concept.
How does multiple load path concept work?
Large, heavy, and highly stressed members are avoided. Small members carry the loads, each supporting only a small percentage of the total.
What are crack limiting joints?
Specially designed structure that will limit the spread of cracks but ensure they can be detected.
What are the five main structural units?
Fuselage
Wings
Stabilisers
Flight Control surfaces
Landing Gears
How are the primary dimensions of an aircraft calculated?
There are defined zones, reference points, lines and planes.