Ch 1 - Structural Design Intro

Question 1

What is the limit load?

Answer 1

The anticipated maximum real load on a structure / part during its operational lifetime (FL).

Question 2

What was the main driver of innovation in early aviation?

Answer 2

Speed

Question 3

What is the proof load?

Answer 3

Yield stress is difficult to define, so proof load (Fp) is the limit load (FL) multiplied by proofing factor (μp or αp) where the proofing factor is usually ~1-1.25 to ensure elastic deformation a small fraction above normal operation load.

Question 4

What is the ultimate load?

Answer 4

Not to be confused with the breaking load. 
Ultimate load (Fu) is typically 1.5 times limit load (μu or αu * FL). Fu is used for certification, to show that under 1.5 times FL the structure will not break.

Question 5

Define reserve factor.

Answer 5

Reserve factor (Rf) = Maximum or breaking load over ultimate load (Ff/Fu). This must be greater than 1.

Question 6

Define margin of safety.

Answer 6

Margin of safety is the reserve factor minus 1. This must be greater than 0.

Question 7

Draw a picture to represent the different certification loads defined against a stress strain graph.

Answer 7

See lecture 1.2

Question 8

Complete question from end of lecture 1.2 and find reserve factor and safety margin.
Would this pass certification?

Answer 8

Diameter:
Ultimate load: 2.72mm
Proof load: 2.78mm

Reserve factor: 1.21

Safety margin: 0.21 so yes it would pass. (SM>0)

Question 9

Which loads do stringers help with?

Answer 9

Tension and compression

Question 10

What is the UK Airworthiness Authority?

Answer 10

CAA

Question 11

What is the USA Airworthiness Authority?

Answer 11

FAA

Question 12

What is the main aircraft certification system in the United States?

Answer 12

FAR 25 (Federal Aviation Regulations)

Question 13

What is the main aircraft certification system in the European Union?

Answer 13

JAR 25 (Joint Aviation Requirements)

Question 14

What 3 main things should an aircraft structure be designed to be?

Answer 14

Strong, Stiff, Durable

Question 15

Give 4 examples of static structural tests that would be carried out on a new jet liner.

Answer 15

• Max wing bending at limit load (FL)
• Ailerons and spoilers functioning test at max wing bend
• Fuselage pressure test
• Fatigue and flight cycles simulation tests

Question 16

Which 4 stages are flight cycles split into for testing?

Answer 16

Taxiing, Take-off, Cruising, Landing

Question 17

How many more flight cycles was the A380 tested to survive than its designed service life?

Answer 17

2.5

Question 18

A structure must survive proof load without…….?

Answer 18

Permanent deformation

Question 19

A structure must survive the ultimate load without………?

Answer 19

Failure

Question 20

Aircraft structure must be able to safely respond to what?

Answer 20

Gusts, Aeroelasticity demands, Manoeuvres