Airframe Structures: Wood Structures 🔊

Question 1

What species of wood is used as a standard for strength properties of other species of wood used in aircraft structures?

Answer 1

Spruce

Question 2

Is northern white pine an acceptable substitute for spruce?

Answer 2

Yes, but only if its larger in size to make up for the lower strength

Question 3

Are knots allowed in aircraft wood?

Answer 3

Yes, within limitations (type, location, spacing, and number)

Question 4

What type of wood quality must be used in the repair of aircraft structures?

Answer 4

Must be aircraft quality and equivalent to its original strength or greater

Question 5

What is the difference between laminated wood and plywood?

Answer 5

Both consist of two or more layers of wood which have been glued together. Laminated wood has the grain of all layers approximately parallel. Plywood grain runs 90° with adjacent ply.

Question 6

What are two types of glue used for aircraft wood structure repair?

Answer 6

Casein and synthetic resin glue

Question 7

What method is used to prepare plywood for bending?

Answer 7

The wood is soaked in hot water then placed in a form until completely dry

Question 8

What are the results of using insufficient gluing pressure when making a wood joint?

Answer 8

Thick glue lines which indicate a weak joint

Question 9

What is the recommended clamping pressure for a glued joint?

Answer 9

125 to 150 psi

Question 10

How long should a wood glue joint be kept under pressure before removing the clamps?

Answer 10

Time will vary depending on the temperature of the room. Higher temperature cures glue faster. (85° for at least 7 hours; full joint strength after two days)

Question 11

What are some of the various methods used to apply pressure to joints in aircraft gluing operations?

Answer 11

Brads, nails, screws, clamps, or hydraulic and electric power presses

Question 12

Why does the strength of a scarf joint depend upon the accuracy of the two beveled surfaces?

Answer 12

An inaccurate bevel will reduce the amount of effective glue area

Question 13

Why is sanding unacceptable when preparing a joint for slicing?

Answer 13

The dust created from sanding will clog the pores of the wood, preventing the proper penetration of glue.

Question 14

What type of patch is preferred for repair of stressed plywood skin and why?

Answer 14

Scarf patch; Scarfed patches are 12 to 1 slope and it uses reinforcements under the patch where the glue joints occur.

Question 15

Are mineral streaks acceptable in aircraft wood?

Answer 15

Yes

Question 16

How do you inspect for decay/rot in wood?

Answer 16

Visual, odor, tapping, probe, or prying

Question 17

How can the moisture content of wood be determined?

Answer 17

A moisture meter or more accurately take a sample, weigh it, then dry it in an oven at 100°C to 105°C, and reweigh it.

Question 18

What area of the wood spar may not be spliced?

Answer 18

Under wing attachment fittings, landing gear fittings, engine mount fittings, or lift-and-interplane strut fittings

Question 19

What type of joint is generally used in splicing structural members in aircraft?

Answer 19

A scarf joint

Question 20

What is compression wood and why is it not acceptable for aircraft structures?

Answer 20

It is characterized by high specific gravity and has the appearance of an excessive growth of summer wood. This defect is difficult to recognize and is very detrimental to strength.

Question 21

What are three forms of wood?

Answer 21

Solid, ply, and laminated.

Question 22

What are two forms of wood that are acceptable for the repair of wooden aircraft skin?

Answer 22

Plywood or laminated woods

Question 23

What would be the greatest number of splices placed into one spar?

Answer 23

Two

Question 24

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

Answer 24

1 inch