S Airframe Design and Materials

Question 1

What causes a high rate of repeated stress?

Answer 1

High flight cycle rate

Question 2

What does repeated stressing cause?

Answer 2

Metal fatigue

Question 3

What is the certification standard for turbine powered large aircraft?

Answer 3

CS25

Question 4

What types of aircraft does CS23 cover?

Answer 4

• Normal
• Utility
• Aerobatic
• Commuter

Question 5

What does CS25 deem permissible for minor failures?

Answer 5

Probable

Question 6

What does CS25 deem permissible for major failures?

Answer 6

Remote

Question 7

What does CS25 deem permissible for hazardous failures?

Answer 7

Extremely remote

Question 8

What does CS25 deem permissible for catastrophic failures?

Answer 8

Extremely improbable

Question 9

What is the safe life concept?

Answer 9

A part which can comfortably sustain safe operations within its designed life span

Question 10

Will a safe life component fail?

Answer 10

It can fail, but it will not lead to catastrophic structural damage during normal operation

Question 11

What is the fail safe concept?

Answer 11

Critical areas are built with multiple load paths so if one fails an alternate path can carry the load

Question 12

What should happen if the primary load path fails?

Answer 12

Inspection should capture the fault before the alternate also fails

Question 13

What is the damage tolerance concept?

Answer 13

Structures have crack-arresting features which limit the extent to which cracks can speed

Question 14

What is redundancy?

Answer 14

The duplication/triplication of vital systems for use in the event of a failure

Question 15

What is load?

Answer 15

An external force that causes stress

Question 16

What is stress?

Answer 16

Internal force per unit area inside the component

Question 17

What is strain?

Answer 17

Deformation of a component

Question 18

4 types of stress?

Answer 18

• Tension
• Compression
• Torsion
• Shear

Question 19

What is bending?

Answer 19

A material experiences multiple stresses simultaneously. Compression inside the bend, tension outside the bend and shear along the component centreline

Question 20

What is a dynamic load?

Answer 20

Load imposed by manoeuvring, can change quickly, rapid buildup can impose severe stress

Question 21

What is a static load?

Answer 21

Build up slowly or remain constant e.g when the aircraft is parked

Question 22

What is a cyclic load?

Answer 22

The change of loads during flight, components experience changes from compression to tension

Question 23

What can cyclic loads lead to?

Answer 23

Metal fatigue

Question 24

What can lead to structural failure?

Answer 24

Undetected overstress

Question 25

What must a flight crew do if overstress is suspected?

Answer 25

Instigate an investigation

Question 26

Where is the greatest bending force experienced?

Answer 26

Wing root

Question 27

When does maximum stress occur?

Answer 27

Empty wing tanks and a loaded aircraft

Question 28

What are signs of stress?

Answer 28

Deterioration, distortion, loose or missing rivets, ripples, bubbles, dents, creases, waves, cracked paint and black oxide near a rivet

Question 29

What is the ultimate load limit?

Answer 29

Any stress within this limit will be elastic deformation and return to original condition, not leading to structural failure

Question 30

What is fatigue?

Answer 30

Multiple applications of stress

Question 31

At what stress does a component fail?

Answer 31

Ultimate stress

Question 32

What is fatigue strength?

Answer 32

Stress at which failure occurs for a given number of cycles

Question 33

What is fatigue life?

Answer 33

The number of cycles required for a metal to fail at a certain stress

Question 34

What is max ramp mass?

Answer 34

Max mass authorized for maneuvering (taxiing or towing) aircraft on ground

Question 35

What is max take-off mass?

Answer 35

Maximum mass at which the pilot of the aircraft is allowed to take-off

Question 36

What is max zero fuel mass?

Answer 36

Mass of airplane and all its contents (including unusable fuel), but excluding the total weight of the usable fuel on board

Question 37

What is max landing mass?

Answer 37

Maximum mass at which an aircraft is permitted to land

Question 38

3 ways to reduce fatigue?

Answer 38

1. Avoid coarse manoeuvring 2. Avoid turbulence 3. Not flying with excess load (fuel or payload)

Question 39

How does corrosion effect fatigue life?

Answer 39

Provides a natural starting point for fatigue cracks

Question 40

What is elasticity?

Answer 40

Material will return to original shape

Question 41

What is plasticity?

Answer 41

Material will permanently deform

Question 42

What are composite materials?

Answer 42

Materials made form 2 or more constituent materials

Question 43

6 key benefits of composite materials?

Answer 43

``` Fibres can be aligned to provide best load qualities Lighter Make complex structures High strength High stiffness Resistant to corrosion ```

Question 44

Where would glass fibre reinforced be used?

Answer 44

Non-load bearing ducts and panels

Question 45

What is a matrix in a composite structure?

Answer 45

Material that support the fibres and bonds them together

Question 46

Disadvantages of composite materials?

Answer 46

``` Hard to inspect for flaws May absorb moisture which can freeze and cause delamination Less damage tolerant Requires immediate repair Does not conduct electricity ```

Question 47

Which materials are more damaged by lightning strikes?

Answer 47

Composite

Question 48

3 ways to check composite structure delamination?

Answer 48

Bubbles Hair-line cracks Changes in sound when tapping the surface

Question 49

What is corrosion?

Answer 49

Disintegration of a engineered material into its constituent atoms

Question 50

What is oxidisation?

Answer 50

Chemical reaction between metal and air causing a breakdown of the metals surface

Question 51

What is electrolytic corrosion?

Answer 51

Corrosion resulting between 2 metals coupled with fluid between them

Question 52

What is stress corrosion?

Answer 52

Interaction of fatigue and corrosion

Question 53

What is delamination?

Answer 53

When overstressed composite layers begin to separate and significantly reduce the strength of a structure

Question 54

What is hard time maintenance?

Answer 54

Planned maintenance of a component based on a predetermined parameter (landings, hours, cycles etc)

Question 55

What is on condition maintenance?

Answer 55

Based on the physical condition of a component in a given instant, components that fail checks must be replaced

Question 56

What is condition monitoring?

Answer 56

Monitoring a components condition based on predetermined parameters to identify changes that may be indicative of a fault