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M6 Mac > 6.3.2 Wooden Structures > Flashcards

6.3.2 Wooden Structures Flashcards

1
Q

What type of structure do fabric covered aircraft have

A

Truss type

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2
Q

What are the main lengthwise members in a wing called

A

Spars

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3
Q

What are wing spars usually made from

A

Sitka spruce

May be solid or laminated

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4
Q

What is the benefit of a laminated spar over a solid spar

A

A laminated spar is much cheaper and just as strong

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5
Q

What are the compression members which separate the spars made from

A

Steel tubing or heavy wall aluminium alloy tubing

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6
Q

What are sometimes used instead of compression members

A

Compression ribs but they must be strengthened to take the loads

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7
Q

What are drag wires

A

Wires that extend from the front spar inboard to the rear spar outboard oppose the forces that tend to drag against the wing and pull it backwards

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8
Q

What are anti drag wires

A

Wires that attach the rear spar inboard and and go to the front spar outboard are called anti drag wires

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

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9
Q

What do most lightweight wing trusses consist of

A
  • Spars
  • Compression members
  • Drag wires
  • Anti drag wires
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10
Q

What type of loads does a built up box spar take

A

Torsional loads and bending loads

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11
Q

What part of a wooden aircraft take majority of the load in flight

A

Spars

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12
Q

What happens if a fabric covered ply structure is subject to excess bad weather and exposure to sunlight over a large amount of time with out maintenance

A

The surface finish will crack allowing moisture to penetrate to the wooden structure resulting in considerable deterioration through water soakage

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13
Q

What should be done before commencing a survey on a wood and fabric aircraft

A

Aircraft should be housed in a dry, well ventilated hangar. With all inspection covers, panels and hatches removed before survey.

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14
Q

What must be done before examining glued joints

A

The aircraft must be completely dried out

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15
Q

What should be the first check done when the inspection panels have been opened

A

A smell check to check for damp

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16
Q

How is NDT testing done on glued wooden joints

A

There is no Non destructive testing available for glued joints which makes it hard to accurately gauge the quality of the joint

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17
Q

How would inspection of a complete aircraft for glue or wood deterioration be carried out

A
  • Checks on trouble spots of the structure
  • Considerable dismantling may be required
  • Must be done in accordance with maintenance manual
  • If a repair that needs to be carried out doesn’t have an approved scheme, the manufacturer must be contacted or approved body
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18
Q

How would access holes be cut

A

Circular in shape and with a sharp trepanning tool to avoid jagged edges

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19
Q

What should be done prior to inspecting a glue line

A
  • All protective paint coatings should be removed
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20
Q

Why must the wood be completely dry before checking a glue line

A

To avoid getting a false impression by wet swollen wood in the glue line

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21
Q

How would checking a glued joint take place

A

After the glued line is sufficiently dried the joint must be inspected with a thin feeler gauge and if penetration is possible the joint must be discarded

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22
Q

How is dry rot indicated

A

Small patches of crumbling wood

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23
Q

How is water penetration indicated

A

Gray streaks or stains running along the grain

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24
Q

If water penetration is suspected what as one main method which is carried out to confirm this

A

Removing a few screws in the area and inspect for corrosion

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25
Q

How would timber shrinkage be indicated

A
  • Stress on glued joints
  • Can cause looseness in metal fittings and bolts
  • If timber shrinkage is suspected all paint and varnishes should be removed and a thin feeler gauge placed between the timber and bolt head
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26
Q

What would be the cause of elongated bolt holes

A

Where bolts secure fittings which take load carrying members or where bolts are subject to landing or shear loads, the bolt holes should be examined for elongation or surface crushing of the wood fibres

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27
Q

What would bruising or crushing of timber be caused by

A

Usually by over tightening bolts

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28
Q

How would you detect a compression failure (compression shakes)

A

By running a torch over the grain to check for ruptured fibres

This would be caused to excess bending during a heavy landing

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29
Q

What type of loads are glued joints designed to take with out the assistance of bolts or screws

A

Shear loads

30
Q

What is done to timber immediately after it has been cut

A

Timber which has been cut from selected trees is stacked prior to shipment for approx 60 days. During this time the timber looses most of its moisture and is ready for shipping

31
Q

Where is timber usually seasoned

A

In air drying sheds ranging from 1 to3 years

It can be artificially dried with a kiln

32
Q

What is the purpose of seasoning

A

To reduce moisture content of timber to a point where it is in equilibrium with the surrounding atmosphere and enables protective treatments to be applied more affectively

33
Q

What should be done to the timber after it has been seasoned to ensure it is suitable to be used on aircraft

A

Samples should be cut and tested

Before this is done approx 6 inches should be cut from the end and discarded as this could be drier than the rest

34
Q

What are the two methods of measuring moisture

A
  • Weighing and drying

- Moisture meter

35
Q

What is the quicker and more effective method of measuring moisture

A

Moisture meter

36
Q

How would density of seasoned timber be measured

A

Weighing and measuring the volume of a sample cut from the plank

37
Q

How would brittleness be detected in wood

A

By using izod impact testing

38
Q

How can the rate of growth be determined

A

The number of rings per 25mm (1 inch)

The timber rate of growth less than 6 rings per 25mm should be discarded

39
Q

How long should test pieces be kept

A

For at least 2 years

40
Q

What is rift sawing

A

The process of cutting timber along the radius of the annular rings is known as rift sawing. Rift sawing and near quarter sawing are much the same

41
Q

What is tangential sawing

A

The process of cutting at a tangent to the annular rings is known as tangential sawing.

Produces what is known as a flower face

42
Q

What is the main advantage of rift sawn timber

A

It shrinks chiefly in one direction only and does not warp very much

43
Q

What is the most economical form of cutting timber

A

Tangential or flat sawing

44
Q

What is the worst form of timber defect

A

Dote disease

45
Q

What is dote disease

A

Worst of all defects does a lot of damage to the wood

Occurs at the base of the living tree only

Dote is contagious and should be burnt

46
Q

How can dote be identified

A

Brownish yellow patches similar to thin mineral oil spots

47
Q

What is decay or rot

A

Usually developed after the tree has been felled due to excessive soaking and partial drying

48
Q

How can decay or rot be identified

A

Brown in colour and and appears as though it has been charred. The timber is rendered soft and dry and will flake off easily

49
Q

What is incorrect grain inclination

A

The limit of grain inclination for spruce is 1 in 15 for grade A and 1 in 12 for grade B. Inclination should be checked to ensure the above limits are not exceeded

50
Q

What is heart shake

A

Usually follows the course of the sap duct longitudinally and visible on the tangential surface

51
Q

What is compression shake

A

Appears on the cross section and usually takes the form of a wavy thin line

52
Q

What is blue stain

A

This defect only occurs in sapwood which should not be used in aircraft parts

53
Q

Why are synthetic wooden adhesives used extensively in wooden structures

A

To avoid localised stresses and strains which may be set up by the use of mechanical methods of attachment

54
Q

What forms do synthetic resin adhesives come in

A

Liquid or powder form

55
Q

What type of synthetic resin adhesive has a longer shelf life

A

Powder resins

56
Q

How are powder resins mixed

A

With water, in accordance with the manufacturers guidance

57
Q

How are liquid resins available to use

A

They are ready for immediate use

58
Q

What type of utensils should be used for mixing synthetic resin adhesives

A

Acid proof utensils and must be very clean

59
Q

What should be done to pry wood structures before gluing

A

They must be sanded to remove surface glazing and loose fibres

60
Q

What should be done to timber before gluing

A

They should be suitably roughened up to form a key for the adhesive

61
Q

Some adhesives contain solvents which must be allowed to evaporate before the joint is made. Why is this

A

If this is not done, bubbles may be created and a weakness caused

62
Q

When gluing large surfaces such as boards of ply, what must be done to prevent air being trapped between the two surfaces

A

The drawing usually specifies the drilling of small vent holes in regular intervals

63
Q

What does the setting time of wood glue depend on

A

Temperature (Increase in temperature will result in a decrease in setting time)

64
Q

How would heat be applied to a glued joint to allow it to set

A

Electrically or steam heated platten

65
Q

How should timber be tested for its characteristics

A

The test samples should be cut from the timber used for the component

66
Q

How can the glue of a glued joint be tested

A

Should be in a vice and broken by leverage exerted on it. The fractured glue faces should show at least 75% of wood fibres evenly distributed over the fractured glued surfaces

67
Q

When should wet tests be carried out

A

Should only be carried out in joints which have been conditioned form2-3 weeks

68
Q

What type of loading are glued joints designed to take

A

Glued joints are designed to provide their maximum strength under shear loading

69
Q

What would be a tell tale sign of a glued joint failing in tension

A

Tension failures appear to strip the glue from one surface leaving bare wood (a fine layer of wood fibres on the glue surface)

70
Q

What temperature should not be exceeded for the storage of adhesives

A

21°c

M6 Mac (11 decks)

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