ACM-125 WOOD STRUC - (GENERAL QUESTIONS) Flashcards
(98 cards)
1
Q
Why was wood used for the first airplanes?
A
Due to its favorable strength-to-weight ratio
Wood construction has largely been replaced by all-metal designs due to the cost of additional hand labor.
2
Q
What is the primary wood used for aircraft structures?
A
Sitka spruce
Sitka spruce is chosen for its uniformity, strength, and excellent shock-resistance qualities.
3
Q
What are the specifications for ‘Aircraft Sitka Spruce’ grade?
A
- Kiln-dried to AN-W-2 specification
- Specific gravity not less than .36
- Slope of the grain not steeper than 1 to 15
- Sawn vertical-grain
- No fewer than six annular rings per inch
4
Q
What is the maximum slope of the grain for aviation-grade lumber?
A
1:15
5
Q
What is the significance of the number of growth rings in wood?
A
Minimum grain count for softwoods is six rings per inch
Exceptions include Port Oxford white cedar and Douglas fir, which require a minimum of eight rings per inch.
6
Q
What are laminated wood and plywood?
A
- Laminated wood: layers of solid wood bonded with grains parallel
- Plywood: layers bonded with grains at 90° angles
7
Q
What is the primary defect associated with brown rot in wood?
A
Produces a light to dark brown, easily crumbled residue
8
Q
What is a compression failure in wood?
A
Buckling of fibers that appear as streaks on the surface at right angles to the grain
9
Q
What is the acceptable size for hard knots in aviation-grade wood?
A
Up to 3/8 inch in diameter
They must be in the center third of the beam and not closer than 20 inches to another defect.
10
Q
List some non-acceptable wood defects.
A
- Excessive cross grain
- Wavy, curly, and interlocked grain beyond specified limits
- Hard knots that do not meet specified conditions
11
Q
What is the purpose of AC 43.13-1B?
A
Outlines information regarding acceptable wood species substitutions
12
Q
Fill in the blank: The minimum grain count for softwoods is _______.
A
six rings per inch
13
Q
True or False: Laminated wood is more flexible than solid wood.
A
False
14
Q
What is the primary purpose of the inspection and repair of wood structures in aircraft?
A
To ensure that the structure is as strong as the original
15
Q
What types of wood are commonly used for structural aircraft-grade plywood?
A
- African mahogany
- American birch
- Basswood
16
Q
What is a pitch pocket in wood?
A
Lens-shaped opening extending parallel to the annual growth rings
17
Q
What is the significance of quarter-sawing wood?
A
Reduces the amount of shrinkage over the life of the component
18
Q
What is the appearance of compression wood?
A
High specific gravity with little or no contrast in color between springwood and summerwood
19
Q
What are the acceptable defects in aviation-grade lumber?
A
- Cross grain within specified limits
- Wavy, curly, and interlocked grain within specified limits
- Small clusters of pin knots
20
Q
What are non-acceptable defects in wooden aircraft structures?
A
The following defects are non-acceptable:
1. Cross grain
2. Wavy, curly, and interlocked grain
3. Hard knots
4. Pin knot clusters
5. Spike knots
6. Pitch pockets
7. Mineral streaks
8. Checks, shakes, and splits
9. Compression wood
10.Compression failures
11. Decay
These defects increase the chance of future structural failure.
21
Q
What is the significance of the adhesive used in aircraft structural repair?
A
The adhesive plays a critical role in the overall finished strength of the structure and must meet performance requirements for aircraft use.
22
Q
What type of glue was commonly used in older airplanes?
A
Casein glue, which is a powdered glue made from milk.
23
Q
Why is casein glue considered obsolete for aircraft repairs?
A
Casein glue deteriorates over time when exposed to moisture and temperature variations, and it is incompatible with many modern adhesives.
24
Q
What is plastic resin glue?
A
A urea-formaldehyde resin that is water-, insect-, and mold-proof, typically coming in powdered form.
25
What are the limitations of plastic resin glue in aircraft repairs?
It rapidly deteriorates in hot, moist environments and under cyclic stresses, making it obsolete for structural repairs.
26
What is resorcinol glue?
A two-part synthetic resin glue consisting of a resin and a hardener, known for meeting FAA strength and durability requirements.
27
What type of glue is most commonly used in manufacturing aircraft-grade plywood?
Phenol-formaldehyde glue.
28
What is the bonding process critical for?
The structural strength of an aircraft wooden structure.
29
What are the three most important requirements for a strong and durable structural bond?
The requirements are:
1. Preparation of the wood surface before applying adhesive
2. Use of a good quality aircraft-standard adhesive
3. Following the manufacturer's instructions during the bonding process.
30
Fill in the blank: The wood surface must be _______ before applying any adhesive.
clean, dry, and free of oil, grease, or wax.
31
What is pot life in the context of adhesives?
The usable life of the glue from the time it is mixed until it must be used.
32
What is open-assembly time?
The allowable time between the application of the glue and the assembly of the joint.
33
What is closed-assembly time?
The allowable length of time between the assembling of the joint and the application of clamping pressure.
34
What is pressing time?
The period during which the parts are pressed or clamped together, essentially the adhesive curing period.
35
What can cause splitting or cracking in wood members?
Varying shrinkage rates of bonded wood members or outside forces applied to the structure.
36
What is wood decay?
Damage resulting from the attack and growth of fungus on wood, indicated by softness, swelling when wet, excessive shrinkage when dry, cracking, and discoloration.
37
What is the recommended clamping pressure for soft-woods when using resorcinol glue?
Between 125 and 150 psi.
38
What method can be used to apply pressure when bonding wood?
Methods include:
* Hand nailing
* Screw clamps or 'C' clamps
* Hydraulic presses.
39
True or False: Sanding the wood surface is recommended before applying adhesive to create a smooth surface.
False.
40
What should be done if wood surfaces cannot be freshly machined before bonding?
Lightly sand them using a very fine grit such as 220.
41
What precautions should be taken when using hand nailing as a clamping method?
Use nailing strips to spread pressure and place waxed paper between the strip and the structure to prevent sticking.
42
What should be done with nails used for clamping pressure after the adhesive has cured?
They may or may not be removed, but they are not intended to hold the structure together for strength purposes.
43
What indicates wood decay in wooden products?
Softness, swelling when wet, excessive shrinkage when dry, cracking, discoloration, musty or moldy odors
## Footnote
These signs are critical for identifying compromised wood integrity.
44
What causes wood splitting when different types of woods are bonded together?
Differential shrinkage rates leading to induced stress exceeding cross-grain strength
## Footnote
For example, bonding mahogany plywood to spruce can result in splits due to their differing shrinkage rates.
45
What are the common causes of bond failure in wood joints?
Improper bonding process, prolonged exposure to moisture, wrong type of glue, inadequate wood preparation
## Footnote
Following manufacturer's bonding procedures is crucial to prevent bond failures.
46
What leads to finish failure in wood structures?
Long-term exposure to water, wood splitting, ultraviolet light, surface abrasion
## Footnote
Protective finishes are essential to prevent decay and maintain wood integrity.
47
What is stress damage in wood structures caused by?
Excessive impact, mechanical loads, aerodynamic loads, over-tightening of fittings
## Footnote
Use of steel bushings can prevent wood crush and add bearing strength.
48
What is the first step in inspecting a wooden aircraft structure?
Move the aircraft into a dry, well-ventilated hangar
## Footnote
This facilitates drying and prepares the structure for inspection.
49
What tool is used to determine the moisture content of wood?
Moisture meter
## Footnote
It's essential for assessing the structural integrity of wooden members.
50
What sound should tapping a solid wood structure produce?
A sharp, solid noise
## Footnote
Hollow sounds indicate potential issues that require further inspection.
51
What should you do if soft, hollow wood is found during inspection?
Probe the area with a sharp metal tool
## Footnote
This helps determine if the wood is solid or rotted.
52
How can prying help in inspecting wood joints?
It checks for signs of separation between bonded joints
## Footnote
Light prying helps confirm bond integrity without causing damage.
53
What does a musty or moldy odor indicate during inspection?
Possible wood deterioration or moisture presence
## Footnote
Odor is a key indicator of potential decay.
54
What should be visually inspected on the external wood structure of an aircraft?
Fabric covering for tears or looseness, signs of internal damage, bulging panels
## Footnote
Damage to the fabric can signify underlying structural issues.
55
Where is wood deterioration most likely to begin in an aircraft?
The lowest point inside the structure
## Footnote
Moisture and dirt accumulation at these points can lead to rot.
56
What should be done if glue failure or wood rot is suspected?
Open and examine the internal structure
## Footnote
This may include creating inspection openings or removing part of the skin.
57
What indicates a glue line failure?
Separation between the glue line and the wood, presence of stains
## Footnote
Inspecting glue lines with a magnifying glass is recommended.
58
What is the basic criterion for repairing an aircraft's wooden structure?
The repaired structure must be as strong and rigid as the original
## Footnote
Equivalent aerodynamic shape is also essential.
59
What types of wooden spars are commonly encountered in aircraft construction?
Solid spars, laminated spars, externally routed spars, built-up box spars, built-up I-beam spars
## Footnote
Each type requires specific repair procedures as outlined in the manufacturer's manual.
60
What is a solid wood rectangular spar?
A type of wooden spar with a simple rectangular cross-section
## Footnote
It is one of the basic designs found in aircraft structures.
61
Identify a type of spar that is designed to reduce weight while maintaining strength.
Routed I-beam spar
## Footnote
This type of spar is routed for weight reduction while meeting strength requirements.
62
What is critical to inspect in wood spars during maintenance?
Reinforcement plates, glue lines, and signs of separation
## Footnote
These components are vital for maintaining structural integrity.
63
How should a longitudinal crack in a solid wood spar be repaired?
Carefully scrape away the finish on both sides and glue reinforcing plates of spruce or plywood on each side.
## Footnote
Reinforcing plates should be one-fourth as thick as the spar and extend beyond each end of the crack for at least three times the thickness of the spar.
64
What is the recommended taper for beveling the ends of reinforcing plates?
5:1 taper to within 1/8-inch of the thickness of the plate.
65
Why should nails not be used in spar repairs?
Nails compromise the structure and produce moisture collection points, increasing the chance of wood decay.
66
Where can a wing spar be spliced or reinforced?
At any point except under the attachment fittings for the wing root, landing gear, engine-mount, lift, or inter-plane struts.
67
What is the maximum number of splices allowed on a single spar?
No more than two splices.
68
What are the restrictions for attachments passing through a spar splice?
Reinforcement plates must not interfere with the proper attachment or alignment of fittings.
69
What depth limit is set for cleaning out damaged material in a spar?
No more than one-fourth of the spar thickness.
70
What is the taper slope required for the ends of a repaired edge in a solid wood spar?
5:1 slope.
71
What type of splice is used for solid or rectangular wood spars?
A scarf repair that requires a taper of 1:10 or 1:12.
72
What is crucial for ensuring a strong scarf joint?
Making sure the bevel cuts match precisely.
73
What should not be used to smooth the surface of a scarf joint?
Sandpaper.
74
What is the purpose of using a back-up board when clamping scarfed spar pieces?
To provide solid support for the spar.
75
What should be done after the glue has cured on a scarf joint?
Inspect the glue line and carefully cut away any excess glue.
76
What type of reinforcement plates are used for routed I-beam spars?
Plates must be one-half the thickness of the spar web and contoured to fit into the routed portion.
77
What is the required taper for a built-up I-beam spar repair?
10:1 to 12:1 scarf joint.
78
What are filler blocks used for in built-up box spar repairs?
To provide added support between the spar flanges.
79
What is the critical aspect of built-up box spar repairs?
Requires the use of approved drawings as proper guidelines.
80
What is the cross-section size of wood strips typically used for wing ribs?
Approximately 1/4 to 5/16-inch.
81
What should be done to cap strips before bending them over a form?
Soften them with steam.
82
What is the taper required for a broken cap strip repair?
10 to 12 times its thickness.
83
What should be done if damage is located above an upright member in a cap strip?
Cut the cap strip with a 10:1 to 12:1 taper over the upright member and splice in a new piece.
84
What should be used to cover the splice of a cap strip?
Splice plates of thin plywood on each side of the splice.
85
What is the correct taper when cutting cap strips over a spar?
10:1 to 12:1 taper.
86
What taper should be used when cap strips are cut over a spar?
10:1 to 12:1 taper
## Footnote
This taper helps to ensure a strong splice when repairing cap strips.
87
What is the purpose of drainage grommets in wing ribs?
To drain accumulated moisture and ventilate the compartment
## Footnote
This prevents condensation and decay of wood structures.
88
What should be done if the trailing edge of a wing shows movement when flexed?
Cut away the trailing edge fabric and examine the edge structure
## Footnote
This allows for inspection and repair of potential rot.
89
How should a damaged trailing edge rib be repaired?
Cut a spruce block to fit the removed rib section and glue reinforcing plates of plywood
## Footnote
Fasten new trailing edge finishing materials to the repaired rib.
90
What type of joint should be used to repair wooden compression members?
10:1 to 12:1 scarf joint
## Footnote
This method provides a strong connection for the repair.
91
What material should reinforcing plates be made from when repairing wooden compression members?
The same material as the strip being repaired
## Footnote
The plates should be 12 times the thickness of the strip.
92
What is required for plywood skin repairs according to FAA guidelines?
Repairs must be made according to the manufacturer's recommendations or Advisory Circular 43.13-1B
## Footnote
This ensures FAA approval for the repair.
93
What type of patch is recommended for small holes in thin plywood skin?
Splayed patch
## Footnote
This patch is used if the skin is less than or equal to 1/10-inch thick.
94
When fabricating a splayed patch, what is the maximum diameter for the hole to be repaired?
No more than 15 thicknesses (15T)
## Footnote
This ensures the patch fits properly and maintains structural integrity.
95
What is the process for creating a splayed patch?
Tape a scrap plywood piece over the damage, draw circles for the patch size, cut the patch to fit, and apply glue
## Footnote
Align the face grain of the patch with that of the skin.
96
What is a surface patch used for in plywood skin repair?
To cover damaged plywood skin with aircraft fabric and finish it to match the airplane
## Footnote
This is a simple and economical repair method.
97
What is a plug patch?
A patch that is trimmed to a round or oval shape and glued to a doubler for support
## Footnote
This creates a flush finish on the damaged area.
98
Why is a scarfed patch preferred for stressed wood skin repairs?
It makes the least change in skin thickness or rigidity
## Footnote
This helps maintain the structural integrity of the skin.
