Ch 2 - Wing Structural Details

Question 1

What are the 4 main structural wing components

Answer 1

Spars, ribs, skin and stiffeners

Question 2

What proportion of a wing is taken up by: main structural box, flaps ailerons & othe rlift control devices, and the slats/services etc?

Answer 2

~40%, ~40%, ~20%

Question 3

What is a stringer?

Answer 3

Spanwise component that runs the length of the wing and transfers aerodynamic loads from the skin to the structure. Positioned between the ribs and the skin.

Question 4

Name 5 considerations that dictate wing structure design.

Answer 4

Strength
Durability
Stiffness
Aerodynamic forces
Subsystems

Question 5

What aerodynamic requirements are there on the wing structure?

Answer 5

To maintain shape under aerodynamic loading

Question 6

What strength requirements are there on wing structure?

Answer 6

Span & chord wise inertial & aerodynamic loads without failure

Question 7

What durability requirements are there on wing structure?

Answer 7

Must be able to endure all operational load cycles with no risk of catastrophic fatigue damage

Question 8

What subsystems requirements are there on wing structure?

Answer 8

Fuel storage, under carriage, flaps and control surfaces, fuselage coupling and supporting engines

Question 9

What stiffness requirements are there on wing structure?

Answer 9

Resist undue deformation (elastic instabilities)

Question 10

What is the main function of a spar?

Answer 10

To carry vertical shear forces and direct bending stresses. They form part of the wing torsion box.

Question 11

What is the main function of ribs?

Answer 11

Hold the skin in the correct shape
Transfer aero forces to spars
Carry shear force, bending moments and in plane tension & compression
Provide support for stringers

Question 12

What is the main function of skin?

Answer 12

Provide smooth aerodynamic shape
Resist pressure / suction without distortion
Resist internal fuel pressure and inertial loads
Carry direct compressive & tensile stresses
Carry shear stresses during wing twist
Resist fatigue failure from cyclic loading

Question 13

Give two examples of the cross section of widely used built up stringers.

Answer 13

Z section
J section (upside down capital J)

Question 14

Give two examples of integral stringer cross section shapes.

Answer 14

Integral Z section

Integral blade section (single upright piece)

Question 15

That is the main function of stiffeners?

Answer 15

Attach spanwise members to the skin
Resist compressive buckling
Ribs supporting stringers increases the buckling load

Question 16

Explain what a doubler is.

Answer 16

A piece of material that overlays an access port or similar, bonding to the skin surrounding the port and to the port itself.

Question 17

Explain what a crank stopper strap / reinforcing flange is.

Answer 17

Strip of material bonded to another component which acts to hold the main component together if a crank attempts to propagate through it. Wing stringers can act and crack stoppers. sometimes fail-safe straps are bonded to the skin between ribs.

Question 18

The 787 Dreamliner is comprised of how much composite material by weight?

Answer 18

50%

Question 19

List 5 advantages of composite materials in aviation. What do these advantages lead to?

Answer 19

• Allow for lighter structures
• Allow for simpler structures
• Easier to visually inspect
• Does not corrode or fatigue
• Damage can be repaired in less than 1 hour
• Resist impacts better
• Reduced scheduled maintenance
• Resists crank propagation

These advantages mean:

• Increased efficiency
• Reduced fuel consumption

Question 20

What do thermoplastic CFRPs offer over theermoset CFRPs?

Answer 20

They can be re-melted for easy recyclability whilst maintaining their composition.

Question 21

Do composites have higher or lower stiffness to weight ratio?

Answer 21

Higher - intrinsically

Question 22

How can composites be tailored to improve aeroelasticity?

Answer 22

Unidirectional laminates can be used in wing construction to stop wing twist, instead the will will bend upward.

Question 23

Disadvantages of composite structures?

Answer 23

Delamination from out f plane loads, compressive loads. This is normally internal so hard to visually inspect.
A detailed understanding of the load path of the structures is required which isnt required for metals.
Imbalance of deformation between composites and metals leads to joint failure.
Drilling holes breaks fibres,