Chp1 P2 Design/Maintenance

Question 1

What measurement used to control the life of structural components?

Answer 1

Flight hours or the number of flights

Question 2

What is the structural useful life

Answer 2

A period in which the structural integrity of an aircraft is ensured

Question 3

What two things are needed to evolve to less restrictive design philosophies

Answer 3

Previous design/engineering experience
The emergence of new technologies

Question 4

What is a safe life

Answer 4

The minimum life during which it is known that no catastrophic damage should occur
(Never 0%)

Question 5

What happens when a structure has elapsed life count or reached max fatigue cycles

Answer 5

It is scrapped and replaced
(It is important to fully scrap certain components to stop them from being resold into the black market)

Question 6

What design philosophy is assured by redundancy

Answer 6

Fail safe

Question 7

What happens when there is a fail safe

Answer 7

The loads are supported redundantly by many components as now there are many load paths

Question 8

What does it mean for the amount of damage occurring if there is a fail safe

Answer 8

If a structure has a fail safe then there can be a crack or single failure in a component without full catastrophic failure
Maintenance isn’t always necessary until the next inspection

Question 9

What is a damage tolerance

Answer 9

There is an allowance for damage to occur

Question 10

What does it mean to have a damage tolerant design

Answer 10

It reduced the amount of components a structure needs so reduces overall weight
It allows damage to exist

Question 11

What needs to be in place for structures to ensure flight safety

Answer 11

A maintenance program to allow for detection of a failure before it occurs

Question 12

What are the three types of maintenance

Answer 12

Hard time maintenance
On condition maintenance
Condition montoring

Question 13

What is hard time maintenance

Answer 13

Intervention at fixed time/periodically

Question 14

What is on condition maintenance

Answer 14

Periodic inspections given at an interval where components are checked and if needed they are replaced
Eg. After 100hrs flying

Question 15

What is condition maintenance

Answer 15

The collection of data from aircraft sensors to best time when to perform maintenance

Question 16

An ideal material would have waht properties

Answer 16

Low density
High strength
High stiffness
Good corrosion resistance
Good fatigue performance
Wide range of temps
Electrical conductivity
Ease of fabrication
Low cost

Question 17

What are some typical metals

Answer 17

Aluminium alloy
Magnesium alloy
Titanium alloy
Steel alloy

Question 18

What would be a typical non metal

Answer 18

Wood
Composites
Fabrics
Plastic

Question 19

What is an alloy

Answer 19

A mix of different metals to get the best characteristics

Question 20

What is a composite

Answer 20

The result of combining two or more materials to get the best characteristics

Question 21

What is FRP

Answer 21

Fibre reinforced plastics
Fibre + filler

Question 22

What are three types of composite materials

Answer 22

Fibre glass - GFRP
Carbon - CFRP
Aramid/kevlar - KFRP

Question 23

What are some advantages of composites

Answer 23

High strength to weight ratio
Capability to tailor strength to direction of load
Stiffness
Corrosion and fatigue resistance

Question 24

What are some disadvantages of composites

Answer 24

Low electrical conductivity
Some damages are difficult to detect during preflight checks as there could be internal damage
Cost

Question 25

What's the purpose of the fuselage

Answer 25

To accommodate people and cargo systems Support other components of the aircraft

Question 26

What are the different shapes of fuselage

Answer 26

Rectangular- easy to manufacture + maximise space Circular- withstands high loads of diff pressure Double bubble - relieves stresses in the shell Oval

Question 27

Why is the fuselage shaped along the longitudinal axis

Answer 27

For improved aerodynamics Visibility And turned up tail prevents strikes during landing and takeoff

Question 28

What are the three parts of the fuselage

Answer 28

Exterior structure Floor Openings (doors and windows)

Question 29

What is a monocoque exterior structure

Answer 29

A type of shell that supports all loads It's shape is achieved by formers It has a shell thickness that is prohibitive

Question 30

What is semi monocoque structure

Answer 30

The load is shared by the skin and other elements acting as stiffeners (frames, bulkheads, stringers, longerons)

Question 31

What is hoop and axial stress

Answer 31

Hoop stress acts around the circumference of a cylinder and axial stress acts along the length of a cylinder

Question 32

How is the thickness of the aircrafts skin determined

Answer 32

By internal pressure and sheer stress, it's normally made out of aluminium alloy or composite

Question 33

What is the purpose of a frame

Answer 33

To stabalise the hull and maintain pressure loads They may also avoid radial buckling and prevent propagation of cracks Aluminium alloy

Question 34

What is the purpose of a bulkhead

Answer 34

It's used to separate different parts of the fuselage that have different pressures and are near the fuel tanks (front pressure bulkhead and after pressure bulkhead) Aluminium alloy or composite

Question 36

What is the purpose of stringers

Answer 36

The longitudinally placed rails increase the skins stiffness and increase its ability to withstand stressses/buckling

Question 37

What is the purpose of longerons

Answer 37

The longditunal beams are more resistant than stringers and are used to withstand bending loads Eg. Floor beams and seat racks

Question 38

What is the purpose of floors in the fuselage

Answer 38

They must support high loads and are small panels supported by a crosshead structure (honeycomb floor tile pattern)

Question 39

What happens if the cargo bay suddenly undergoes depressurisation

Answer 39

It could lead to an entire floor collapse however blow out bungs would be fired to the floor remains intact