6.3.2 Wooden Structures

Question 1

Till when was wood the preferred material for aircraft?

Answer 1

1940’s

Question 2

What did the early types of wooden aircraft feature?

Answer 2

Truss type wing and fabric covering

Question 3

In truss type design what are the main lengthwise members?

Answer 3

Spars

Question 4

What is between the spars?

Answer 4

Compression members

Question 5

How is the truss held together?

Answer 5

High strength steel wires that cross the bays

Question 6

What are drag wires?

Answer 6

The wires that go from front spar to rear spar.

Question 7

What do drag wires do?

Answer 7

Oppose the forces that drag against the wing

Question 8

Where do anti drag wires connect too?

Answer 8

Rear spar inboard to front spar outboard

Question 9

What was an adaptation of the truss type?

Answer 9

Box spar

Question 10

What is the most common type of wood used?

Answer 10

Sitka spruce

Question 11

Why is sitka spruce preferred?

Answer 11

Relatively free from defects.

Question 12

Where does sitka spruce come from?

Answer 12

British columbia and alaska

Question 13

What are the grade specs for sitka?

Answer 13

Kiln dried
SG more than 0.36
Grain slope 1 to 15

Question 14

How must sitka be sawn?

Answer 14

Edge grained

Question 15

How many rings must sitka spruce have?

Answer 15

Six annular rings per inch

Question 16

What other woods are used?

Answer 16

Douglas fir
Noble fir
Port orford white cedar

Question 17

How is the wood normally cut?

Answer 17

Quartered to reduce shrinkage

Question 18

What must wood preservatives do?

Answer 18

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

Question 19

How are wood structures kept clean?

Answer 19

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

Question 20

What is the primary job of exterior wood protection?

Answer 20

Protect the wood against weathering and provide a smooth surface

Question 21

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

Answer 21

One half coat and and two full coats

Question 22

At 50 degrees C how much strength does wood lose?

Answer 22

25%

Question 23

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

Answer 23

Dope proof sealer or epoxy sealer.

Question 24

What is grain slope?

Answer 24

The amount the grain rises over the grain length

Question 25

Are knots in the wood acceptable?

Answer 25

No

Question 26

What is a pitch pocket?

Answer 26

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

Question 27

What is compression wood?

Answer 27

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

Question 28

What causes a split?

Answer 28

Poor drying process

Question 29

What is a check?

Answer 29

A crack that runs across the rings and occurs during seasoning

Question 30

What is a shake?

Answer 30

A crack that occurs when two rings separate along the boundary

Question 31

How can dry rot be prevented?

Answer 31

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

Question 32

What are some of the common adhesives?

Answer 32

Casein glue Plastic resin glue Resorcinol glue Epoxy adhesives

Question 33

How is casein glue made?

Answer 33

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

Question 34

What is plastic resin glue also known as?

Answer 34

Urea-formaldehyde adhesive

Question 35

What is the benefit of resorcinol glue?

Answer 35

It is the most water resistant.

Question 36

What are the three important requirements when bonding wood joints?

Answer 36

Preparation Utilisation Good technique

Question 37

How must the woods surface be prepared?

Answer 37

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

Question 38

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

Answer 38

24 hours

Question 39

What is the recommended clamping pressure for soft wood?

Answer 39

125psi-150psi

Question 40

What is the recommended clamping pressure for hard wood?

Answer 40

150-200psi

Question 41

How are freshly bonded joints tested?

Answer 41

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

Question 42

What happens if a drain hole is clogged?

Answer 42

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

Question 43

How can delaminated wood be identified?

Answer 43

Tap testing

Question 44

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

Answer 44

Moisture meter Removing screws

Question 45

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

Answer 45

Possible elongation of boltholes.

Question 46

What are some of the most common wood spars?

Answer 46

Box beam I Beam C section Plain Routed

Question 47

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

Answer 47

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

Question 48

What dimensions must the reinforcing plates have?

Answer 48

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

Question 49

How must reinforcing plates attached?

Answer 49

Glue

Question 50

Where are splice repairs not permitted?

Answer 50

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

Question 51

What is the max number of splices on one spar?

Answer 51

Two

Question 52

What is a cap strip?

Answer 52

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

Question 53

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

Answer 53

12 times its thickness.

Question 54

What are the most common methods of plywood skin repair?

Answer 54

Fabric patch Splayed patch Surface Patch Plug patch Scarf Patch

Question 55

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

Answer 55

2.5cm

Question 56

What are the best shears for a fabric patch?

Answer 56

Pinking shears

Question 57

What is the maximum dimensions for a splayed patch repair?

Answer 57

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

Question 58

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?

Answer 58

Surface or overlay patch

Question 59

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

Answer 59

10%

Question 60

What size holes can surface patches be used to repair?

Answer 60

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

Question 61

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

Answer 61

Rectangle or triangular shape with rounded corners.

Question 62

What is the requirements for doublers on surface patch repairs?

Answer 62

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

Question 63

What is the best repair for damaged plywood?

Answer 63

Scarf patch