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CAT B- Mod 6 Materials and Hardware > 6.3.2 Wooden Structures > Flashcards

6.3.2 Wooden Structures Flashcards

1
Q

Till when was wood the preferred material for aircraft?

A

1940’s

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2
Q

What did the early types of wooden aircraft feature?

A

Truss type wing and fabric covering

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3
Q

In truss type design what are the main lengthwise members?

A

Spars

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4
Q

What is between the spars?

A

Compression members

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5
Q

How is the truss held together?

A

High strength steel wires that cross the bays

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6
Q

What are drag wires?

A

The wires that go from front spar to rear spar.

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7
Q

What do drag wires do?

A

Oppose the forces that drag against the wing

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8
Q

Where do anti drag wires connect too?

A

Rear spar inboard to front spar outboard

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9
Q

What was an adaptation of the truss type?

A

Box spar

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10
Q

What is the most common type of wood used?

A

Sitka spruce

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11
Q

Why is sitka spruce preferred?

A

Relatively free from defects.

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12
Q

Where does sitka spruce come from?

A

British columbia and alaska

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13
Q

What are the grade specs for sitka?

A

Kiln dried
SG more than 0.36
Grain slope 1 to 15

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14
Q

How must sitka be sawn?

A

Edge grained

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15
Q

How many rings must sitka spruce have?

A

Six annular rings per inch

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16
Q

What other woods are used?

A

Douglas fir
Noble fir
Port orford white cedar

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17
Q

How is the wood normally cut?

A

Quartered to reduce shrinkage

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18
Q

What must wood preservatives do?

A

Be toxic to fungi, pests and marine organisms
Not have corrosive properties

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19
Q

How are wood structures kept clean?

A

Wiped with a soft and slightly damp cloth. The a good quality polish is rubbed in.

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20
Q

What is the primary job of exterior wood protection?

A

Protect the wood against weathering and provide a smooth surface

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21
Q

Once a repair is finished how should interior wood be protected?

A

One half coat and and two full coats

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22
Q

At 50 degrees C how much strength does wood lose?

A

25%

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23
Q

If surfaces are to be doped or lacquered what should be used to seal the end grains?

A

Dope proof sealer or epoxy sealer.

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24
Q

What is grain slope?

A

The amount the grain rises over the grain length

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25
Q

Are knots in the wood acceptable?

A

No

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26
Q

What is a pitch pocket?

A

Small openings in the wood which fill with resin and weaken the wood

27
Q

What is compression wood?

A

If the tree grows on a lean the rings are eccentric, this wood is denser and weaker and cannot be used?

28
Q

What causes a split?

A

Poor drying process

29
Q

What is a check?

A

A crack that runs across the rings and occurs during seasoning

30
Q

What is a shake?

A

A crack that occurs when two rings separate along the boundary

31
Q

How can dry rot be prevented?

A

Using only kiln dried wood with moisture content of 20% or less.

32
Q

What are some of the common adhesives?

A

Casein glue
Plastic resin glue
Resorcinol glue
Epoxy adhesives

33
Q

How is casein glue made?

A

Made from milk, it has a alkaline nature that stops it working with any fresh glue

34
Q

What is plastic resin glue also known as?

A

Urea-formaldehyde adhesive

35
Q

What is the benefit of resorcinol glue?

A

It is the most water resistant.

36
Q

What are the three important requirements when bonding wood joints?

A

Preparation
Utilisation
Good technique

37
Q

How must the woods surface be prepared?

A

Clean
Dry
Free of oil, grease, wax or old glue.

38
Q

How long must the wood be kept at a constant pressure when bonding?

A

24 hours

39
Q

What is the recommended clamping pressure for soft wood?

A

125psi-150psi

40
Q

What is the recommended clamping pressure for hard wood?

A

150-200psi

41
Q

How are freshly bonded joints tested?

A

Off cuts with the same resin must be tested, there must be 75% coverage as a minimum.

42
Q

What happens if a drain hole is clogged?

A

Causes a build-up of moisture and condensation which leads to deterioration of the wood.

43
Q

How can delaminated wood be identified?

A

Tap testing

44
Q

What can help identify the level of moisture in wood when visually inspecting?

A

Moisture meter
Removing screws

45
Q

What does it mean if you shake the wing and there is looseness?

A

Possible elongation of boltholes.

46
Q

What are some of the most common wood spars?

A

Box beam
I Beam
C section
Plain
Routed

47
Q

What should you do if you find a longitudinal crack in a solid wood spar?

A

Carefully remove the finish on both sides and apply reinforcing plates.

48
Q

What dimensions must the reinforcing plates have?

A

1/4 thick as the spar
Extend beyond the crack 3x times the thickness

49
Q

How must reinforcing plates attached?

A

Glue

50
Q

Where are splice repairs not permitted?

A

Under the attachment fittings for the wing root.
Landing gear
Engine mount
Lift struts or inter-plane struts.

51
Q

What is the max number of splices on one spar?

A

Two

52
Q

What is a cap strip?

A

The part of the rib that forms the upper and lower surface that attach to the supporting web.

53
Q

If a cap strip is broken between two upright members what should the strip be cut too?

A

12 times its thickness.

54
Q

What are the most common methods of plywood skin repair?

A

Fabric patch
Splayed patch
Surface Patch
Plug patch
Scarf Patch

55
Q

What is the maximum hole size for a fabric patch repair on plywood skin?

A

2.5cm

56
Q

What are the best shears for a fabric patch?

A

Pinking shears

57
Q

What is the maximum dimensions for a splayed patch repair?

A

16 times the thickness of the skin and the skin is not more than 0.25cm thick

58
Q

What are Plywood skins not over 0.3 cm (1⁄8 in) thick that are damaged between or along framing members can be repaired with?

A

Surface or overlay patch

59
Q

What percentage aft of the chord line are surface patch repairs permissable?

A

10%

60
Q

What size holes can surface patches be used to repair?

A

Up to 125cm, an area that can be as large as one frame or rib.

61
Q

What shape must the damaged area be trimmed too for a surface patch repair?

A

Rectangle or triangular shape with rounded corners.

62
Q

What is the requirements for doublers on surface patch repairs?

A

Must extend from one framing member to another and be strengthened at the ends by saddle gussets.

63
Q

What is the best repair for damaged plywood?

A

Scarf patch

CAT B- Mod 6 Materials and Hardware (14 decks)

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