Wood Structures

Question 0

What is the basic difference between plywood and laminated wood?

Answer 0

The grain in each layer of laminated wood runs in the same direction. The grain in the layers of plywood runs at 90 degrees or 45 degrees to each other.

Question 1

Which species of wood is considered to be the standard when comparing other woods for use in aircraft structure?

Answer 1

Sitka spruce.

Question 2

What kind of glue is recommended for making repairs to a wooden aircraft structure?

Answer 2

Synthetic resin or resorcinol glue.

Question 3

What types of glue are used in aircraft structures?

Answer 3

Casein and resin.

Note; Glue joint to be under pressure for 7 hours.

Question 4

How is aircraft plywood prepared for making a compound bend?

Answer 4

The wood is soaked in hot water until it is pliable.

Question 5

How is pressure applied to the glued joint when splicing a wooden aircraft spar?

Answer 5

With cabinetmakers parallel clamps.

Question 6

How much pressure must be applied to a glue joint in a piece of softwood to produce a strong joint?

Answer 6

125 to 150 pounds per square inch.

Question 7

What is the correct repair to a wooden aircraft wing spar if the wing-attach bolt holes in the spar are elongated?

Answer 7

Splice in a new section of the spar and drill new holes.

Question 8

What kind of repair is recommended for a hole in the plywood skin of an aircraft wing?

Answer 8

A scarf patch.

Question 9

What is the recommended taper for a splayed patch in a plywood aircraft skin?

Answer 9

5 to 1.

Question 10

What is the recommended taper for a scarf patch in a plywood aircraft skin?

Answer 10

12 to 1.

Question 11

Why should sandpaper never be used when preparing a scarf joint in a wing spar for splicing?

Answer 11

The dust caused by sanding will plug the pores of the wood so the glue cannot get in to form a good bond.

Question 12

What is the largest hole in a plywood wing skin that can be repaired with a fabric patch?

Answer 12

One inch in diameter.

Question 13

Why are light steel bushings often used in bolt holes in a wooden wing spar?

Answer 13

The bushing keeps the spar from being crushed when the nut on the attachment bolt is tightened.

Question 14

How long should a glue joint be kept under pressure when splicing a wooden aircraft wing spar?

Answer 14

For at least seven hours.

Question 15

Are mineral streaks in a piece of structural aircraft wood reason for rejecting the wood?

Answer 15

No, if there is no evidence of decay in the wood.

Question 16

Which area of a wooden aircraft wing spar must not contain any splice?

Answer 16

There must be no splice under wing-attach fittings, landing gear fittings, engine mount fittings, or lift and interplane strut fittings.

Question 17

How is compression wood identified?

Answer 17

It has a high specific gravity, it appears to have an excessive growth of summer wood, and little contrast between the spring wood and the summer wood.

Question 18

What is done to a splice in a wooden aircraft wing spar to strengthen the splice?

Answer 18

Reinforcing plates are glued to both sides of the splice.

Question 19

Why must abrupt changes in the cross-sectional area of a wooden structural member be avoided?

Answer 19

Abrupt changes in the cross-sectional area of a structural member concentrate stresses and can cause failure.

Question 20

What effect does moisture have on a wood aircraft structure?

Answer 20

Moisture causes the wood to swell and crack as it dries out. It allows fungus to develop in the wood and cause it to decay.

Question 21

Can northern white pine be used as a substitute for spruce?

Answer 21

Yes, but it must be increased in size to compensate for its lower strength.

Question 22

Which wood is more inclined to warp, flat grain or vertical grain?

Answer 22

Flat grain.

Question 23

How do you detect decay in a wood structure?

Answer 23

Stick a sharp-pointed knife blade in the suspect area and pry the wood up. If the wood is good, it will come up as a long splinter; if it is decayed it will come up as a long splinter.

Question 24

Is a hard knot, 1/2-inch in diameter allowed if it is in the web of a wing spar?

Answer 24

No, 3/8-inch diameter is the maximum allowable knot, and it must meet severe restrictions.

Question 25

Are pin knot clusters allowable in aircraft structural wood?

Answer 25

Yes, if they cause only a small effect on grain direction.

Question 26

What reference material may be used for acceptable repairs to wood aircraft structure?

Answer 26

AC 43.13-1B, Chapter 1.

Question 27

How is a scarf splice on a wing spar reinforced?

Answer 27

Solid spruce or birch plywood reinforcing plates are glued to each side of the spar, centered at each end of the scarf.

Question 28

What is the minimum taper to use when repairing a wood wing rib cap strip?

Answer 28

12 times the thickness recommended, 10 times is minimum.

Question 29

What effects does temperature have on glue?

Answer 29

Cure time and joint strength.

Question 30

What are results of low glue pressure?

Answer 30

Thick and weak joint.

Question 31

Why does the strength of a beveled scarf depend on the accuracy of cut?

Answer 31

Glue area is reduced if bevels are not the same.

Question 32

Always splice and reinforce plywood with?

Answer 32

The same type of plywood.

Question 33

What is laminated wood?

Answer 33

Laminated wood is constructed of two or more layers of solid wood that are bonded together.