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Materials And Hardware > Wood Structures > Flashcards

Wood Structures Flashcards

1
Q

What are the main lengthwise members in a wing called?

A

Spars

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2
Q

What are spars made from?

A

Sitka spruce

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3
Q

What separates the spars?

A

Compression joints (struts)

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4
Q

What are the compression joints usually made out of?

A

Steel or heavy-wall aluminium

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5
Q

Why have compressive ribs strengthened?

A

To take on the compressive loads

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6
Q

What are the wires that cross bay formed by the compression struts called and what do they extend from and to?

A

Drag wires

Extend from the front spar inboard to rear spar outboard

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7
Q

What are the wires that attach from the rear spar inboard to front spar outboard called?

A

Anti-drag wires

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8
Q

What is the use of the anti-drag wires?

A

They oppose any force that tend to move the tip of the wing forward

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9
Q

What do the drag wires do?

A

Oppose the force that tends to drag against the wing and pull it backwards

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10
Q

What are box spars used for?

A

Placed between spars to stiffen the spars so it can withstand all of the bending and torsional loads on the wings during flight

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11
Q

Besides work as an adhesive, what must glue also do to the wood it is applied on?

A

Must also protect the wood

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12
Q

What are some main factors that may cause deterioration to glued structures?

A

Chemical reactions such as moisture, ageing, extreme temperature

Mechanical forces due to timber shrinkage

Development if microbiological growths

Oil percolating from Engine installation

Fuel contamination due to leakage /spills from tank bays

Spillage of water drainage holes

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13
Q

What will natural causes will cause deterioration to fabrics?

A

Inclement weather and strong sunlight as it allows moisture in which will destroy weather proofing qualities

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14
Q

What should you be aware of when surveying a structure?

A

Inspections of panels and covers removed in a dry, well ventilated hangar
Smell of fungus and dampness
Look for warping and misalignment

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15
Q

What is warping?

A

The bending or twisting of a material caused by heat or dampness

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16
Q

What must be done when checking the glue line condition on a structure?

A

All protective coatings of paint should be removed by careful scraping
Use of a magnifying glass, torch and a stipulated feeler gauge to probe the joint

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17
Q

How does glue become defective?

A

If penetration of the joint is possible

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18
Q

What is a good indication of possible moisture ingress or decay on screws?

A

Discolouration on brushings

Corrosion on screws

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19
Q

What are some examples of miscellaneous defects on glued structures?

A 
Shrinkage
Elongated bolt hole
Bruising and crushing of structural members
Compression failure (shakes)
Previous repairs
Dry rot
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20
Q

What does shrinkage do?

A

induces stress on members and causes looseness of attachment

Can cause damage to wood fibres at the edges of the fittings or around the bolt holes

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21
Q

How can shrinkage be detected?

A

Removing any paint or varnish and attempting to insert a thin feeler gauge between the timber and the fitting

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22
Q

How should inspection of elongation bolt holes take place?

A

Bolts should be removed

Check for looseness

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23
Q

What causes bruising and crushing of structural members?

A

Over tightening bolts

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24
Q

How are compression failure defects made?

A

When there is a rupture of wood fibres

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25
Q

How can you test for compression failures?

A

Shining a light parallel to the grain

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26
Q

Why should attention be paid to the previous repairs if inspecting for defects?

A

Must know whether previous repairs were done correctly

If not, more damage may have been made

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27
Q

What do you look for when inspecting for dry rot?

A

When the wood structure begins to crumble away

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28
Q

How can you detect joint failure?

A

Breaking away of the joint and it leaves splinters

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29
Q

If there is joint failure but no splintering, what is likely to be the cause?

A

Glue failure

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30
Q

How could load cause joint failure?

A

Loads can be transmitted to the other end - secondary damage

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31
Q

How is timber ‘seasoned’?

A

After cutting, before shipment timber is stacked for approximately 60 days

32
Q

Why is timber stacked for 60 days before shipment?

A

To allow moisture to evaporate prior to shipment

33
Q

How is timber usually seasoned after shipment?

A

In an air-drying shed for 1 to 3 years or longer

34
Q

What happens when timbers moisture content is the same as the surrounding atmospheres?

A

Protective covering can be applied

35
Q

What does seasoning do?

A

Reduces the moisture content of timber to the point where it is in equilibrium to the surrounding atmospheres and enables protective treatments to be applied more efficiently

36
Q

After timber has been cut and seasoned, what must happen to determine its suitability for use on aircraft?

A

Samples should be cut and tested

37
Q

How much should be cut off the end of a test sample of timber after seasoning and why?

A

Around 6 inches as it may be drier than the rest

38
Q

What are some characteristics of timber that must be tested to determine if it is fit for aircraft use?

A 
Moisture
Density
Brittleness
Splitting
Rate of growth
Test recording
39
Q

What is the ideal moisture content for timber and what is it measured with?

A

15% + or - 2

Measured with a moisture metre

40
Q

What must be checked for density?

A

Density must be checked against the grade of wood being sampled

41
Q

How would you carry out brittleness tests?

A

The izode impact testing or the drop weight testing

42
Q

How would you check splitting for timber?

A

Use a blunt chisel to split the sample and it will reveal the grain direction

43
Q

When should timber samples be rejected?

A

Timber with a growth rate of less than 6 rings per 25mm should be rejected

44
Q

How long should the test recordings be kept?

A

No less than 2 years

45
Q

What are the two types of sawing used for timber?

A

Rift sawing

Tangential sawing

46
Q

Why are the rift and tangential sawing methods used?

A

They produce the best strength and durability

47
Q

What is rift sawing?

A

A method of cutting timber along the radius of the annular rings

48
Q

What is tangential sawing?

A

A method of cutting timber at a tangent to the annular rings

49
Q

What does tangential sawing produce?

A

Flower face

50
Q

What are the 3 main woods used in aircraft maintenance?

A

Spruce
Noble fir
Douglas fir

51
Q

Which out of the three woods used in aircraft is the priority choice?

A

Spruce

52
Q

What are the most common defects of timber?

A 
Dote disease
Decay or rot
Incorrect grain inclination 
Heart shake
Ring shake
Compression shakes
Knots
Pitch holes
Bluestain
53
Q

What is dote disease?

A

The worst of all the defects

An infectious, inherent disease which only occurs in the base of the tree

54
Q

What is the precaution you need to take when cutting a tree with dotes disease?

A

Cut 10ft or more above the ground/base

55
Q

What is decay or rot?

A

Decay happens when the wood is exposed to excessive soaking or partial drying

56
Q

What is the limit of grain inclination for soruce grade A and grade B?

A

Grade A is 1” in 15”

Grade B is 1” in 12”

57
Q

When are mineral streaks acceptable?

A

When there is no sign of decay

58
Q

What type of wood is blue stain found in?

A

Sap wood

59
Q

Why are Synthetic Resin Adhesives extensively used in joints for wooden structures?

A

Avoids localising the stresses and strains in the structure

60
Q

What standards myst the SRA comply with?

A

CAA

61
Q

What does the strength of the joint depend on?

A

The effectiveness of the glued joint

62
Q

What preparation must be made when using SRA on plywood?

A

Light sanding in the direction of the grain to remove loose fibres and all dust should be removed

63
Q

What preparation must be made when using SRA on timber?

A

Checking of the blind joints -> chalking and previous glue must be removed before gluing
Check the moisture levels are within the limits

64
Q

What should you do to prepare when working with adhesives on wooden structures?

A

Make sure all surfaces are clean and free from grease

Make sure all traces of adhesives are removed when working with wood that is being reused

65
Q

What is an adhesives pot life affected by?

A

Temperature

66
Q

What temperature must all wooden joint structures attain?

A

Room temperature

67
Q

What must wooden joints keep clear of during curing?

A

Heating sources

68
Q

What must you remember when applying adhesive?

A 
Apply to both surfaces
Completely cover the surfaces
Should be tacky when pressure is applied
Softer surfaces need a precoat
Avoid high clamping pressure
May require small vent holes on large areas to prevent air process on large glue joints
Temperature affects curing times
69
Q

How many days must you leave the joint until it is at full joint strength?

A

2 days

70
Q

What are two different ways to test adhesive efficiency?

A

Test the samples

Wet tests

71
Q

How would you test the samples?

A

Carry out the test on off cuts of the actual components to be used or use representative test pieces.
The glued sample must be put in a vice and the joint should be broken by leverage exerted on the overhanging member. The fracture faces should show an even distribution of at least 75% of fractured wood fibres

72
Q

What are wet tests?

A

Carried out to test the adhesive efficiency

Joints should be allowed to condition over a 2-3 week period before testing

73
Q

What are glued joints designed to do?

A

Provide maximum strength under shear loading

74
Q

What is the cause if there is a a failure in glued joints without any broken fibres?

A

Caused by the mix or pot life

75
Q

How should adhesives be stored?

A

Kept in controlled environments

Shelf life observed

Materials And Hardware (6 decks)

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