11.2 - Airframe Structures - General Concepts Flashcards
Explain the ‘‘Fail Safe’’ design
The fail-safe design principle uses multiple load paths to ensure structural integrity.
If one load path cracks completely through, or sustains accidental damage, the remaining load paths carry the additional load
Explain the Damage Tolerant design?
The damage tolerance principle requires that any aircraft damage is detected and repaired before the strength is below a minimum level.
Will allow for damage to the structure to occur between each scheduled maintenance/inspection
How is cabin pressure maintained where drain valves are employed?
Drain valves are open when the aircraft is unpressurised, but close when the cabin is pressurised to prevent loss of cabin pressure.
(approx 2 psi)
How do you prevent fluid collecting in cavities in the aircraft structure?
A levelling compound is used to prevent fluid collecting in cavities.
The compound directs fluid to the drains
What is primary structure?
The primary structure/construction consists of those parts of the aircraft that bear the loads
Give 3 examples of secondary structure
Dorsal Fin
Nose Radome
Nacelles
wing leading edge
wing trailing edge
stabilisers
Part of the pylon - not all though
Where are body buttock lines measured from?
A body buttock line is measured in the x-z plane,
parallel to the vertical centreline and perpendicular to the floor
right is +, left is -
Where are body water lines measured from?
Body water lines are measured in the x-y plane, parallel to floor.
It is measured up from the ground or even below ground
(How to remember: water is always across horizon/horizontal)
Where are body stations measured?
Body stations are measured in the y-z plane which starts just ahead of the nose.
How are stingers numbered?
From vertical centreline, starting at 12 oclock position
left and right start at 1 and progress
When discussing the aircraft zonal system, the aircraft is divided into 3 planes.
What are they called?
Body water line
Body station line
Body buttock line
List the Major Zones 100-800?
100- Fuselage lower section
200 - Fuselage top section
300 - Stabilisers
400 - Nacelles
500 - Left wing
600 - right wing
700 - landing gear
800 - Doors
How is the left / right side of the aircraft identified using zonal numbers?
the uneven zone number refers to the left-hand zone,
and an even number indicates a right- hand zone.
What is the Empennage?
Empennage = horizontal and vertical stabiliser
(Tailplane)
What type of stress are the upper and lower surfaces of a wing experiencing during flight?
During flight
Upper surface = compressed,
lower surface = tension
…Opposite on ground
There are 2 types of stressed skin construction. What are they?
Monocoque - Bulkheads and formers give it its shape but skins carry all the flight loads
Semi-Monocoque - Bulkheads and formers still provide the shape, and majority of the flight loads are carried in the skin. However, stringers and longerons are installed across the formers to reinforce the skin and prevent/protect against bending forces.
What are the componensts of a monocoque construction?
Bulkheads, formers (shape)
Skins (flight loads)
What are the componensts of a semi-monocoque construction?
Bulkheads, formers, skins, longerons and stringers
(A longeron is the main longitudinal member of the fuselage that runs from front to rear
Longerons are bigger than stringers)
With which type of construction does the skin take most of the loads?
Monocoque
What is the advantage of composite structure over metal?
Every pound of weight saved by replacing metal with composite material adds a pound of payload capacity for each flight and reduces fuel burn.
On some new aircraft how are the stringers, stiffners etc attached?
What are the other 2 structure assembly techniques?
Bonding
Riveting and bolting (other 2 assembly techniques)
What is hoop stress?
Circumferential stress of the fuselage caused by pressurisation.
What methods are employed to protect the aircraft against corrosion?
Different Surface protection methods because variety of materials used
Overall, keep aircraft clean is best way to do it
How are aircraft bolts corrosion protected?
Cadmium plating (aircraft hardware such as bolts)
