Answers - Aircraft Wood and Structural Repair

Fill in the Blanks

1. 8‐12%, 20%
2. decay, musty, moldy
3. temperature, humidity, deterioration
4. shear
5. decay, rot, decay
6. water penetration
7. compression
8. sharp or solid
9. spruce
10. plywood
11. softwoods
12. grain direction
13. mineral streaks
14. cracks
15. compression
16. casein glue, plastic resin glue, resorcinol glue, epoxy
17. wetting tests
18. full strength, stress
19. scarf joints
20. wing attachment, landing gear, engine mount fittings.

True or False

1. true: a certificated mechanic may not perform work unless he has performed the work concerned at an earlier date.
2. false: ideal range is 8‐12%.
3. true
4. false: Shear loads
5. true
6. false: The condition of the fabric provides an useful indication of the condition of the wood underneath.
7. true
8. true: A soft and mushy area is an indication of rotting.
9. false: Spruce is the preferred choice.
10. false: softwoods
11. true
12. false: Hard knots are acceptable under certain conditions.
13. false
14. true
15. true
16. false: Surfaces should be prepared with a planer or joiner.
17. true
18. false: any point except at wing attachment fittings, landing gear , engine mount, or lift and interplace strut fittings.
19. true
20. true

Knowledge Application

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

2. It is usually made of an odd number of thin plies with the grain of each layer at 45 or 90 degrees to the adjacent ply or plies. Laminated wood all grain are parallel.

3. Spruce

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

5. Casein (obsolete), plastic resin glue, resorcinol glue, and epoxy resin.

6. Curing time as well as joint strength. Curing time will be shorter and the joint strength will increase.

7. If inspection fails to reveal any decay.

8. Yes, hard knots up to ¾ inch in diameter are acceptable under certain conditions.

9. It is detrimental to strength and is difficult to recognize, compression wood is characterized by high specific gravity.

10. To determine whether or not they are harmless, or preliminary, or advanced decay.

11. prevent crushing the wood when the bolts are tightened.

12. weak and strong areas in the same joint.

13. Clamps, elastic straps, weight, vacuum bags, brads, nails, screws, and electric and hydraulic presses.

14. A scarf joint.

15. The effective glue area will be reduced if both beveled cuts are not the same.

16. The same type of plywood as the original.

17. The use of waxed paper or release films between the patch and pressure plate.

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

19. To provide additional bearing surface.

20. 70 F.

Multiple Choices

1. c
Solid spruce spars may be replaced with laminated ones or vice versa, provided the material is of the same high quality.

2. b
When a wood splice is made, the bond between the two pieces of wood consists only of a layer of glue. How strong the joint will be depends on how well the gluing operation was performed.

3. c
The species used to repair a part should be the same as that of the original whenever possible; however, permissible substitutes are given in EA-43.13-1B.

4. b
In cases of elongated boltholes in a spar, or cracks in the vicinity of boltholes, a new spar section should be spliced in, or the spar should be replaced.

5. a
Compression failures are characterized by a buckling of the fibers that appear as streaks on the surface of the piece, substantially at right angles to the grain.

6. c
Decay. All pieces must be free from rot, dote, red heart, purple heart, and all other forms of decay.

7. b
Mineral streaks are not acceptable in wood if they are accompanied by any decay.

8. a
I-beam spars are externally routed on both sides to reduce weight while retaining adequate strength.

9. b
Pin knot clusters. Small clusters are acceptable, provided they produce only a small effect on grain direction.

10. b
A cantilever wing is one that uses no external bracing.

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