5 - Airframe

Question 1

What is a structural load?

Answer 1

External force placed on structure which causes stress

Question 2

What is stress?

Answer 2

The internal force resisting the tendency of an external force to change its shape

Pressure/Area

Question 3

What is strain?

Answer 3

Deformation caused by stress

Extension/original length

Question 4

What is elasticity?

Answer 4

The capability of a material to be stretched and to return to its original shape and size after strain

Question 5

What is fatigue?

Answer 5

Weakening and eventual fatigue of a metal due to continued reversal, or repeated stress beyond the fatigue limit

Question 6

What is tension?

Answer 6

Stress produced by forces acting along the same line but in different directions

Question 7

What is compression?

Answer 7

Stress produced by forcing acting along the same lines but toward each other

Question 8

Does maximum stress during bending occur in tension or compression?

Answer 8

Tension

Question 9

What stress are the upper skins of the fuselage designed for? What issue may arise?

Answer 9

Tension, fatigue

Question 10

What stress are the lower panels of the fuselage designed for? What issue may arise?

Answer 10

Compression, buckling

Question 11

What stress are the side panels of the fuselage carying?

Answer 11

Shear

Question 12

What is the limit of proportionality? is the elastic limit the same?

Answer 12

The stress beyond which the component will not regain its initial shape after the removal of the load (component will be permanently deformed)

Yes.

Question 13

What are the upper and lower yield point?

Answer 13

Upper - load limit before atomic bond stretch (EL/LP)
Lower - bonds breaking and atomic slip occurring

Question 14

What is the limit load?

Answer 14

maximum load anticipated in normal operating conditions

Question 15

What is the proof load?

Answer 15

Load the structure must be capable of carrying without permanent deformation.

Is the product of limit load and factor of safety.

Question 16

What is the ratio of proof factor to ultimate factor of safety?

Answer 16

2/3 (eg 1.5 ultimate factor of safety, 1 proof factor)

Question 17

What is the ultimate stress point?

Answer 17

Max point on stress/strain curve. Max stress sustained by a structure in tension, if stress applied is maintained fracture will result.

Question 18

What is proof stress? What kind of materials is it used for?

Answer 18

Stress when applied to a tensile stress specimen and removed shall not have resulted in an extension greater than a specified percentage (eg 0.1% or 0.2%)

Al-Alloy (yield point cannot be determined precisely)

Question 19

What is the permissible design stress?

Answer 19

Maximum stress allowed when the ultimate load is applied.

The smaller of;
- Ultimate stress point
- Proof stress x (ratio of ultimate load to proof load)

Question 20

What is the reserve factor? What should it be greater than?

Answer 20

RF = ultimate strength/ultimate load
should be > 1.0

Question 21

What is the margin of safety? What should it be greater than?

Answer 21

MS = ultimate strength/ultimate load (-1)
should be >0 (about 0.5)

Question 22

What is safe life?

Answer 22

Component or airframe removed from service at a specified design life.

Question 23

What is fail safe?

Answer 23

Design of a component such that if failure occurs, its response causes minimal harm to other equipment, the environment, or people. Has redundant elements.

Question 24

What is damage tolerant?

Answer 24

Structure than can sustain cracks/faults until the damage is detected without catastrophic failure.

Question 25

What is a butt line? How it is used?

Answer 25

Vertical reference plane (imaginary line) down the centre of the fuselage, measurements L/R can be made (often on the wing)

Question 26

What is a water line?

Answer 26

Height measurement up and down from a prominent reference point (cabin floor, etc)

Question 27

What is a fuselage station? Which direction measures +ve/-ve?

Answer 27

Measurement fore and aft of a reference datum, usually at or near the nose.

Measurement aft is +ive, fore is -ve.

Question 28

What certification do aircraft need? (4)

Answer 28

Type certificate
Type acceptance certificate
Production certificate
Airworthiness certificate

Question 29

What is a type certificate? is anything else issued with it?

Answer 29

Issued by the applicable authority when an aircraft type is proven to meet safety and airworthiness standards.

A type certificate data sheet is conjunctive with it, containing specifications for the aircraft type (things the ac must conform with to be airworthy)

Question 30

What is a type acceptance certificate?

Answer 30

Issued by the CAA for ac which already have a type certificate which has been issued in another country

Question 31

What is a supplemental type certificate for?

Answer 31

Any changes made to the aircraft which conflict with the type certificate

Question 32

What is a production certificate? production limitation record?

Answer 32

Issued for the manufacturer when they have the sufficient capability, facilities, and quality control procedures to ensure consistency.

The limitation lists the type number and model of every product the production certificate is authorised to manufacture and all interface components they are authorised to manufacture and install

Question 33

What is a airworthiness certificate? when is it invalid?

Answer 33

Confirms the ac conforms with its type certificate and is airworthy condition

When the aircraft is U/S

Question 34

What is a service bulletin?

Answer 34

Document issued by manufacturers of an ac, engine, or component to communicate details of modifications which can be made to the ac

Question 35

What is a airworthiness directive?

Answer 35

A mandatory airworthiness requirement to be implemented by the holder of the CoA for continued safe operation of the ac