M11.2 Flashcards
What’s is PSE and examples?
Principle Structural Elements
A principal structural element (PSE) is a part of the aircraft that contributes significantly to carrying flight, ground, or cabin pressurisation loads, and whose integrity is essential in maintaining the overall structural integrity of the aircraft.
Examples of PSE’s are:
Wings.
Horizontal stabiliser.
Vertical Stabiliser (fin).
Canard.
Forward wing.
Winglets/tip fins.
Pressurised areas
What is a flight limit load and ultimate limit loads?
Aircraft designers must consider the strength requirements which are specified in terms of flight limit loads and ultimate limit loads.
Flight limit loads are those which are the maximum loads expected in service.
Ultimate limit loads are those which are flight limit loads multiplied by a factor of safety.
Where can the criteria for structural standards on large aircraft be found?
Cs-25
What are the 5 stresses on aircraft?
Tension
Compression
Torsion (Twisting)
Shear
Bending
In most cases structural members are designed to carry what loads?
designed to carry end loads rather than side loads. They are designed to be subjected to tension or compression rather than bending.
What are the 3 classification of aircraft structures?
Primary structure
Secondary structure
Tertiary structure
What is a primary structure?
Primary structure encompasses any part of the aircraft’s framework that, should it fail either during flight or while grounded, could lead to
Loss of control over the aircraft.
Catastrophic structural collapse.
Harm to occupants.
Failure of the power unit.
Unintended operation.
Incapability to perform a service.
What are some examples of primary structure?
Wing spars
Engine mounts
Fuselarge frames
primary structural members of the main floor.
Also compartments referred as PSE
Also can be know as SSI (structurally significant item)
What is SSI?
Structurally Significant Item (SSI), listed in a supplementary structural inspection document. Due to their critical role in the aircraft’s integrity, these elements might necessitate special inspections and possess specific repair constraints.
What is secondary structure?
all non-primary structural components of the aircraft that possess intrinsic structural significance and exhibit strength surpassing design requisites.
These structures are less prone to weakening without facing failure risks as seen in primary structures
examples of secondary structure comprise wing ribs, fuselage stringers, and designated segments of the aircraft’s skin.
What is a tertiary structure?
Tertiary structure refers to the non primary and secondary components of the aircraft’s framework.
Tertiary structures consist of lightly stressed elements added to the aircraft for diverse purposes.
Fairings, fillets, various support brackets, and similar items fall under the category of tertiary structure.
What is the fail-safe concepts?
The fail-safe method relies upon duplication of certain structural members to ensure that if one member fails, the other would assume the load of the failed member.
What is the disadvantages of the fail safe concept?
When a structure fails it is no longer fail safe and relies on a human to inspect.
The disadvantage of the fail-safe concept is that it adds additional weight. This concept is now outdated, and the preferred concept is that of damage tolerance.
What is the safe life concept?
based on a prediction of how long a structure can remain in service before reaching the point of fatigue damage.
a test airframe is subjected to repeated static, dynamic load, and fatigue testing, where the airframe is taken to the point of fatigue damage and then on to catastrophic failure.
How is a safe life calculated?
calculated as a number of cycles or operating hours. The safe-life allotted to the structure is around one-third of the maximum calculated cycles or operating hours calculated during testing. Individual components may be given separate life and may be scheduled for inspection, repair, or replacement long before their expected failure.
What are the disadvantages of the safe life concept?
the ‘safe-life’ is a calculation and does not account for the role that an aircraft may be assigned.
For example, an aircraft doing short-haul island hops may be subjected to many more flight cycles in a corrosive environment shortening the life of the component.
Each ‘lifed’ component must be monitored through an appropriate aircraft maintenance programme.
What is the damage tolerance concepts?
The damage tolerance design concept requires an evaluation of the structure.
This includes repeated static and dynamic load tests, which demonstrate that the structure can withstand the loads expected in service plus a factor of safety.
if considerable damage occurs, i.e., cracking or partial failure, it remains within the operational life of the aircraft.
What are the main 5 structural units?
The fuselage
The wings
The stabilisers
The flight control surfaces
The landing gears
What are the numbers of the major zones?
ATA
100 Lower half of the fuselage
200 Upper half of the fuselage
300 Empennage which covers the aft fuselage and the horizontal and vertical stabilisers
400 Power plants and the struts
500 Left wing
600 Right wing
700 Landing gear and the landing gear doors
800 Doors
What is a sub major zone
The sub-major zones are identified by the second digit of the number code.
The second digit is a number from one to six for smaller aircraft or one to nine for larger aircraft.
right-hand side of the aircraft have even numbers and the sub-major zones on the left-hand side have odd numbers.
What are zones identified by?
Zones are identified by the third digit of the number code.
Usually, they are numbered from forward to aft, from inboard to outboard, and from bottom to top.
What are the major types of stress?
Tension
Compression
Torsion
Shear
Stress
Bending
Hoop stress
Strain
Fatigue
What is hoop stress?
When pressurised, the cabin experiences two types of stress. One that acts axially on the forward and rear pressure bulkheads and one that acts circumferentially on the skin exerting a tensile force on the skin panels and longitudinal joints.
This circumferential tensile stress is called hoop stress. For any given pressure, the hoop stress will be twice the value of the longitudinal stress.
