Wood Structures

Question 1

What are the main lengthwise members in a wing called?

Answer 1

Spars

Question 2

What are spars made from?

Answer 2

Sitka spruce

Question 3

What separates the spars?

Answer 3

Compression joints (struts)

Question 4

What are the compression joints usually made out of?

Answer 4

Steel or heavy-wall aluminium

Question 5

Why have compressive ribs strengthened?

Answer 5

To take on the compressive loads

Question 6

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

Answer 6

Drag wires

Extend from the front spar inboard to rear spar outboard

Question 7

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

Answer 7

Anti-drag wires

Question 8

What is the use of the anti-drag wires?

Answer 8

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

Question 9

What do the drag wires do?

Answer 9

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

Question 10

What are box spars used for?

Answer 10

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

Question 11

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

Answer 11

Must also protect the wood

Question 12

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

Answer 12

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

Question 13

What will natural causes will cause deterioration to fabrics?

Answer 13

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

Question 14

What should you be aware of when surveying a structure?

Answer 14

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

Question 15

What is warping?

Answer 15

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

Question 16

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

Answer 16

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

Question 17

How does glue become defective?

Answer 17

If penetration of the joint is possible

Question 18

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

Answer 18

Discolouration on brushings

Corrosion on screws

Question 19

What are some examples of miscellaneous defects on glued structures?

Answer 19

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

Question 20

What does shrinkage do?

Answer 20

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

Question 21

How can shrinkage be detected?

Answer 21

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

Question 22

How should inspection of elongation bolt holes take place?

Answer 22

Bolts should be removed

Check for looseness

Question 23

What causes bruising and crushing of structural members?

Answer 23

Over tightening bolts

Question 24

How are compression failure defects made?

Answer 24

When there is a rupture of wood fibres

Question 25

How can you test for compression failures?

Answer 25

Shining a light parallel to the grain

Question 26

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

Answer 26

Must know whether previous repairs were done correctly | If not, more damage may have been made

Question 27

What do you look for when inspecting for dry rot?

Answer 27

When the wood structure begins to crumble away

Question 28

How can you detect joint failure?

Answer 28

Breaking away of the joint and it leaves splinters

Question 29

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

Answer 29

Glue failure

Question 30

How could load cause joint failure?

Answer 30

Loads can be transmitted to the other end - secondary damage

Question 31

How is timber ‘seasoned’?

Answer 31

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

Question 32

Why is timber stacked for 60 days before shipment?

Answer 32

To allow moisture to evaporate prior to shipment

Question 33

How is timber usually seasoned after shipment?

Answer 33

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

Question 34

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

Answer 34

Protective covering can be applied

Question 35

What does seasoning do?

Answer 35

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

Question 36

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

Answer 36

Samples should be cut and tested

Question 37

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

Answer 37

Around 6 inches as it may be drier than the rest

Question 38

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

Answer 38

``` Moisture Density Brittleness Splitting Rate of growth Test recording ```

Question 39

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

Answer 39

15% + or - 2 Measured with a moisture metre

Question 40

What must be checked for density?

Answer 40

Density must be checked against the grade of wood being sampled

Question 41

How would you carry out brittleness tests?

Answer 41

The izode impact testing or the drop weight testing

Question 42

How would you check splitting for timber?

Answer 42

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

Question 43

When should timber samples be rejected?

Answer 43

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

Question 44

How long should the test recordings be kept?

Answer 44

No less than 2 years

Question 45

What are the two types of sawing used for timber?

Answer 45

Rift sawing | Tangential sawing

Question 46

Why are the rift and tangential sawing methods used?

Answer 46

They produce the best strength and durability

Question 47

What is rift sawing?

Answer 47

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

Question 48

What is tangential sawing?

Answer 48

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

Question 49

What does tangential sawing produce?

Answer 49

Flower face

Question 50

What are the 3 main woods used in aircraft maintenance?

Answer 50

Spruce Noble fir Douglas fir

Question 51

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

Answer 51

Spruce

Question 52

What are the most common defects of timber?

Answer 52

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

Question 53

What is dote disease?

Answer 53

The worst of all the defects | An infectious, inherent disease which only occurs in the base of the tree

Question 54

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

Answer 54

Cut 10ft or more above the ground/base

Question 55

What is decay or rot?

Answer 55

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

Question 56

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

Answer 56

Grade A is 1” in 15” | Grade B is 1” in 12”

Question 57

When are mineral streaks acceptable?

Answer 57

When there is no sign of decay

Question 58

What type of wood is blue stain found in?

Answer 58

Sap wood

Question 59

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

Answer 59

Avoids localising the stresses and strains in the structure

Question 60

What standards myst the SRA comply with?

Answer 60

CAA

Question 61

What does the strength of the joint depend on?

Answer 61

The effectiveness of the glued joint

Question 62

What preparation must be made when using SRA on plywood?

Answer 62

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

Question 63

What preparation must be made when using SRA on timber?

Answer 63

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

Question 64

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

Answer 64

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

Question 65

What is an adhesives pot life affected by?

Answer 65

Temperature

Question 66

What temperature must all wooden joint structures attain?

Answer 66

Room temperature

Question 67

What must wooden joints keep clear of during curing?

Answer 67

Heating sources

Question 68

What must you remember when applying adhesive?

Answer 68

``` 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 ```

Question 69

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

Answer 69

2 days

Question 70

What are two different ways to test adhesive efficiency?

Answer 70

Test the samples | Wet tests

Question 71

How would you test the samples?

Answer 71

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

Question 72

What are wet tests?

Answer 72

Carried out to test the adhesive efficiency | Joints should be allowed to condition over a 2-3 week period before testing

Question 73

What are glued joints designed to do?

Answer 73

Provide maximum strength under shear loading

Question 74

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

Answer 74

Caused by the mix or pot life

Question 75

How should adhesives be stored?

Answer 75

Kept in controlled environments | Shelf life observed