WOOD STRUCTURES

Question 1

How would you inspect wood for rot (decay)?

Answer 1

Inspect for a dark discoloration of the wood surface or gray stains along the grain.

Question 2

What three forms of wood are used in aircraft?

Answer 2

Solid, Laminated and Plywood.

Question 3

What is a laminated wood assembly?

Answer 3

Two or more Layers glued together with the grain of all layers approximately parallel.

Question 4

How is aircraft plywood constructed?

Answer 4

Made of an odd number of thin plies, and grains of each layer placed 90° with adjacent ply or plies.

Question 5

What species of wood is used as a standard for strength?

Answer 5

Spruce.

Question 6

Are hard knots acceptable?

Answer 6

Yes, within specified limits.

Question 7

Why is compression wood NOT acceptable?

Answer 7

It is very prejudicial to strength.

Question 8

When are mineral streaks acceptable?

Answer 8

If the inspection fails to reveal any decay.

Question 9

Why is it necessary to examine all stains and discoloration?

Answer 9

To determine if the stains are harmless, preliminar or advanced decay.

Question 10

What types of glue are used in aircraft wood structure repair?

Answer 10

Casein, Epoxies, Phenol-formaldehyde, resorcinol Glue.

Question 11

What type of glue may have been used in OLDER AIRCRAFT construction that requires careful inspection to detect deterioration?

Answer 11

Casein Glue.

Question 12

What types of glues are used in MODERN AIRCRAFT wood structure repair?

Answer 12

Resorcinol glu, Phenol-formaldehyde glue and Epoxy resin glue.

Question 13

What is the minimum °F for curing wood joints with resin repair?

Answer 13

70°F or as specified by glue manufacturer.

Question 14

Why is it important to consider the open-assembly time when gluing wooden structures?

Answer 14

Because if the maximum open-assembly time is exceeded the joint may fail since the glue may begin setting up before the joint is assembled.

Question 15

Why is it important to apply the proper clamping pressure to a glue joint?

Answer 15

Clamping forces the air out, brings the wood surfaces together evenly and in part responsible for the strength of the glue line.

Question 16

Describe the acceptable methods used to repair elongated bolt holes found in a wooden wing spar:

Answer 16

Remove the damaged section and splice in a new section or replace the entire spar.

Question 17

Describe the characteristics of a scarf joint:

Answer 17

The pieces to be joint are tapered or beveled on a slope of 1 to 10 or 1 to 12.

Question 18

What are the results of insufficient gluing pressure?

Answer 18

Thick glue and a weak joint.

Question 19

What methods are used to apply pressure to wood glue joints?

Answer 19

Clamps, Braids, Nails, Elastic Straps, Weight, Vacuum Bags, Screws, Electric and Hydraulic power presses.

Question 20

What type of joint is used in splicing structural members?

Answer 20

A scarf joint.

Question 21

What areas of a wood spar may NOT be spliced.

Answer 21

Under a wing attachment, landing gear, engine mount and lift strut fittings.

Question 22

What are the two primary uses for plywood skin repair?

Answer 22

Gusset plates and Aircraft skin.

Question 23

Provide examples of at least three types of plywood skin repair:

Answer 23

Scarf, surface, plug, splayed and scarfed patches.

Question 24

What type of patch should be used to repair small holes in thin plywood skin if the skin is less than 1/10 inch thick?

Answer 24

A splayed patch.

Question 25

Why must the bevel cut be accurate on both pieces of wood being repaired with a scarfed joint?

Answer 25

The pieces must match exactly to ensure a tight glue joint.

Question 26

Name at least three different types of defects found in wood:

Answer 26

Knots, checks, decay, splits, pitch pockets, curly grain, cross grain, dry rot.

Question 27

Why should the various pieces of wood be kept in a room for at least 24 hours prior to joining?

Answer 27

To allow the moisture content to equalize, minimizing dimensional changes in the wood.

Question 28

The maximum number of splices that should be made to any one spar?

Answer 28

Two.

Question 29

Always splice and reinforce plywood webs with what type of wood?

Answer 29

The same type of plywood as the original.

Question 30

Why are light steel brushing sometimes used in wooden structures?

Answer 30

To prevent crushing the wood when the bolts are tightened.

Question 31

What is the purpose of large surface area washers when used in wooden structures?

Answer 31

To provide additional bearing area for hardware to help preclude damage to the wood when the hardware is tightened.

Question 32

What method will prevent a patch and a plywood pressure plate from adhering together due to extruding glue form the patch?

Answer 32

The use of waxed paper or vinyl plastic between the patch and pressure plate.

Question 33

Name several facings and core material used in bonded honeycomb structures intended for special applications:

Answer 33

Stainless steel, titanium, magnesium, plywood, glass, nylon and Cotton cloth.

Question 34

Describe the construction of a bonded honeycomb structure:

Answer 34

It is a laminated structure that has a solid facing bonded to either side of a core consisting of open six-sided cells.

Question 35

What must be done with a damaged area in a bonded honeycomb structure prior to beginning repairs?

Answer 35

Inspect the area, determine the damage prior removing the affected area.

Question 36

A drill bit used for drilling composites should operate at approximately what speed?

Answer 36

20,000 rpm.

Question 37

What are most common causes for delamination of a composite structure?

Answer 37

Sonic vibration, expansion of internal moisture, liquid leakage and manufacturing error.

Question 38

What type of defect in, or damage to, a bonded honeycomb structure can be repaired using the potted repair method?

Answer 38

Filling the hole.

Question 39

Name some of the factors that cause crazing in transparent plastic windows and windshields:

Answer 39

Exposure to UV, stress, improper solvents and improper handling.

Question 40

How should a hole be drilled in plexiglass to avoid damage to the hole when the drill breaks through to the underside?

Answer 40

Backup the plastic with a piece of wood and feed the drill slowly.

Question 41

What should be done to twist drills that are to be used for drilling completely through plexiglass?

Answer 41

Drill free of burrs, drill angle of 150°, feed the drill slowly.