Figure 5-8. Typical structural corrosion5-18
Figure 5-9. Magnetic field disrupted5-20
Figure 5-10. Crack detection by magnetic particle inspection5-20
Figure 5-11. Circular magnetization5-26
Figure 5-12. Longitudinal magnetization5-27
Figure 5-13. Penetrant and developer action5-33
Figure 5-14. Radiography5-40
Figure 5-15. Ultrasound5-43
Figure 5-16. Pulse-echo and through-transmission ultrasonic inspection techniques5-44
Figure 5-17. Typical portable ultrasonic inspection instrument5-45
Figure 5-18. Example of position fixture and shoe5-46
Figure 5-19. Example of the use of a transducer positioning fixture5-46
Figure 5-20. Example of a typical reference standard5-47
Figure 5-21. Examples of bonded structure configurations and
suggested inspection coverage5-50
Figure 5-22. Sample of special tap hammer5-55
Figure 6-1. Simplified corrosion cell showing conditions which must exist for
electrochemical corrosion6-1
Figure 6-2. Elimination of corrosion by application of
an organic film to metal surface6-2
Figure 6-3. Corrosion attack6-5
Figure 6-4. General surface corrosion6-5
Figure 6-5a. Pitting corrosion (external view)6-6
Figure 6-5b. Pitting corrosion (magnified cross-section)6-6
Figure 6-6. Concentration cell corrosion6-7
Figure 6-7. Active-passive cell6-8
Figure 6-8. Filiform corrosion6-8
Figure 6-9. Intergranular corrosion of 7075-T6 aluminum adjacent
to steel fastener6-9
Figure 6-10. Exfoliation corrosion6-10
Figure 6-11. Galvanic corrosion of magnesium adjacent to steel fastener6-10
Figure 6-12. Stress corrosion cracking6-11
Figure 6-13. Fretting corrosion6-13
Figure 6-14. Typical example of acceptable cleanup of corrosion pits6-26
Figure 6-15. Blendout of corrosion as a single depression6-27
Figure 6-16. Blendout of multiple pits in a corroded area6-28
Figure 7-1. Typical aircraft bolt markings7-6
Figure 7-2. Torque wrench with various adapters7-8
Figure 7-3. Securing screws, nuts, bolts, and snaprings7-19
Figure 7-3a. Wire twisting by hand7-19
Figure 7-4. Use of a typical wire twister7-21
Figure 7-4a. Securing oil caps, drain cocks, and valves7-22
Figure 7-5. Safety-wiring procedures7-23
Figure 7-5a. Safety-wiring procedures7-24
Figure 7-5b. Safety-wiring procedures7-25
Figure 7-6. Securing with cotter pins7-26
Figure 7-7. Alternate method for securing with cotter pins7-26
Figure 7-8. Flexible cable cross-section7-29
Figure 7-9. Nonflexible cable cross-section7-31
Figure 7-10. Insertion of cable into terminal7-33
Figure 7-11. Gauging terminal shank after swaging7-34
Figure 7-12. Typical cable splices7-34
Figure 7-13. Typical terminal gauge7-35
Figure 7-14. Typical thimble-eye splice7-38
Figure 7-15. Typical terminal gauge7-38
Figure 7-16. Cable inspection technique7-40
Figure 7-17. Cable wear patterns7-41
Figure 7-18. Worn cable (replacement necessary)7-42
Figure 7-19. Internal end view of cable wear7-42
Figure 7-20. Pulley wear patterns7-44
Figure 7-21. Corrosion7-45
Figure 7-22. Manufacturer’s wire splice7-45
Figure 7-23. Turnbuckle thread tolerance7-47
Figure 7-24. Safetying turnbuckles7-49
Figure 7-25. Securing turnbuckles7-51
Figure 7-26. Clip-type locking device7-52
Figure 7-27. Assembling and securing clip-locking turnbuckles7-53
Figure 8-1. Schematic of differential pressure compression tester8-9
Figure 8-2. Chart of spark plug temperature ranges8-11
Figure 8-3. Hot and cold spark plugs8-12
Figure 8-4. Spark plug reach8-13
Figure 8-5. Method of checking spark plug gap8-13
Figure 8-6. Typical carbon-fouled spark plug8-15
Figure 8-6a. Typical lead-fouled spark plug8-15
Figure 8-6b. Typical oil-fouled spark plug8-16
Figure 8-6c. Typical spark plug with cracked core nose8-17
Figure 8-6d. Typical worn out spark plug8-17
Figure 8-6e. Typical spark plug with bridged electrodes8-18
Figure 8-7. Spark plug well flashover8-19
Figure 8-8. Typical method of clamping leads8-20
Figure 8-9. Normal contact point8-21
Figure 8-10. Point with minor irregularities8-21
Figure 8-11. Point with well-defined mound8-21
Figure 8-12. Location of clamps at tube bends8-24
Figure 8-13. Typical muffler wall fatigue failure at exhaust outlet. (A. Complete muffler
assembly with heat shroud removed; B. Detail view of failure)8-28
Figure 8-14. Typical muffler wall failure. (A. Complete muffler assembly with heat shroud removed; B. Detail view of failure; C. Cross-section of
failed muffler)8-29
Figure 8-15. Typical muffler wall fatigue failure. (A. Complete muffler assembly
with heat shroud partially removed; B. Detailed view of failure)8-30
Figure 8-16. Typical fatigue failure of muffler end plate at stack inlet8-30
Figure 8-17. Section of a muffler showing typical internal baffle failure8-31
Figure 8-18. Loose pieces of a failed internal baffle8-31
Figure 8-19. Failed internal baffle partially obstructing the muffler outlet8-32
Figure 8-20 Failed internal baffle completely obstructing the muffler outlet8-32
Figure 8-21a. Example of exhaust outlet guard8-33
Figure 8-21b. Example of exhaust outlet guard installed8-33
Figure 8-22. Effect of improperly positioned exhaust pipe/muffler clamp8-34
Figure 8-23. Primary inspection areas8-35
Figure 8-24. Method of repairing surface scratches, nicks, etc., on
aluminum-alloy propellers8-38
Figure 8-25. Correct and incorrect method of reworking leading edge of
aluminum-alloy propellers8-38
Figure 8-26. Method of repairing damaged tip of aluminum-alloy propellers8-39
Figure 8-27. Example 1: Determine the repair width limits8-40
Figure 8-28. Example 2: Determine the repair thickness limits8-41
Figure 8-29. Repair of fixed-pitch hub and propeller with elongated or
damaged bolt holes8-43
Figure 8-30. Propeller tracking (wood block or cowling fixture shown)8-50
Figure 9-1. A typical ski installation9-7
Figure 9-2. Typical bolt cracks9-9
Figure 9-3. Typical cracks near bolt holes9-10
Figure 9-4. Typical bolt hole cracks9-10
Figure 9-5. Typical rod-end cracks9-10
Figure 9-6. Typical torque tube bolt hole elongation9-11
Figure 9-7. Examples of tread wear indicating overinflation and underinflation9-13
Figure 9-8. Hose assembly instructions (can be used for low-pressure hydraulic fluid,
and oil line applications)9-25
Figure 9-9. Proper hose installations9-28
Figure 9-10. Minimum bend radii9-29
Figure 9-11. Suggested handling of preformed hose9-31
Figure 9-12. Minimum bend radii–Teflon hose9-32
Figure 9-13. Inflation valve9-37
Figure 9-14. Repair dimensions9-43
Figure 9-15. Oxygen cylinder damage9-49
Figure 9-16. Cylinder brackets and clamps9-50
Figure 10-1. Typical datum locations10-2
Figure 10-2. Illustration of arm (or moment arm)10-3
Figure 10-3. Example of moment computation10-3
Figure 10-4. Empty weight center of gravity formulas10-4
Figure 10-5. Empty weight and empty weight center of gravity tailwheel type aircraft10-5
Figure 10-6. Empty weight and empty weight center of gravity
nosewheel type aircraft10-6
Figure 10-7. Operating center of gravity range10-7
Figure 10-8. Weighing point center line10-8
Figure 10-9. Empty weight and empty weight center of gravity when
aircraft is weighed with oil10-11
Figure 10-10. Example of check of most forward weight and balance extreme10-14
Figure 10-11. Example of check of most rearward weight and balance extreme10-15
Figure 10-12. Loading conditions: determination of the number of passengers and
baggage permissible with full fuel10-17
Figure 10-13. Loading conditions: determination of the fuel and baggage permissible
with maximum passengers10-18
Figure 10-14. Loading conditions: determination of the fuel and the number and
location of passengers permissible with maximum baggage10-19
Figure 10-15. Effects of the addition of equipment items on balance10-20
Figure 10-16. Example of moment and weight changes resulting from
equipment changes10-21
Figure 10-17. Sample weight and balance report to determine
empty weight center of gravity10-22
Figure 10-18. Sample weight and balance report including an equipment change
for aircraft fully loaded10-23
Figure 10-19. Permanent ballast computation formula10-24
Figure 11-1. Battery ventilating systems11-11
Figure 11-2. Conductor chart, continuous flow11-35
Figure 11-3. Conductor chart, intermittent flow11-36
Figure 11-4a. Single copper wire in free air11-37
Figure 11-4b. Single copper wire in free air11-38
Figure 11-5. Bundle derating curves11-39
Figure 11-6. Altitude derating curve11-40
Figure 11-7. Group and bundle ties11-58
Figure 11-8. Comb for straightening wires in bundles11-59
Figure 11-9a. Slack between supports11-60
Figure 11-9b. Drainage hole in low point of tubing11-61
Figure 11-10. Separation of wires from plumbing lines11-63
Figure 11-11. Safe angle for cable clamps11-67
Figure 11-12. Typical mounting hardware for AS21919 cable clamps11-67
Figure 11-13. Installing cable clamp to structure11-68
Figure 11-14. Clamping at a bulkhead hole11-69
Figure 11-15. Single cord lacing11-72
Figure 11-16. Double cord lacing11-73
Figure 11-17. Making ties11-74
Figure 11-18. Staggered splices in wire bundle11-75
Figure 11-19. Millivolt drop test11-83
Figure 11-20. Copper jumper connector to tubular structure11-88
Figure 11-21. Bonding conduit to structure11-88
Figure 11-22. Aluminum jumper connection to tubular structure11-88
Figure 11-23. Spacing of printed identification marks (direct marking)11-93
Figure 11-24. Spacing of printed identification marks (indirect marking)11-93
Figure 11-25. Identification of wire bundles and harnesses11-97
Figure 11-26. Standard sleeves (135 ºC)11-97
Figure 11-27. Installation of heat-shrinkable insulation sleeves11-98
Figure 11-28. Cable markers11-99
Figure 11-29. Tie-down strap installation11-99
Figure 11-30. Tie-down strap installation tool11-102
Figure 11-31. Completed installation11-103
Figure 11-32. Temporary wire identification marker11-103
Figure 11-33. Inserting wire into marker11-104
Figure 11-34. Shrinking marker on wire11-104
Figure 11-35. Connector information example11-107
Figure 11-36. Different types of connectors11-108
Figure 11-37. Coax cable connectors11-109
Figure 11-38. Spare wires for potting connector11-114
Figure 11-39. Stub wire installation11-119
Figure 11-40. Sealing unused contact cavities—unpressurized areas (cut-away view)11-120
Figure 12-1. Venturi system for providing airflow through gyro instruments12-15
Figure 12-2. Instrument vacuum system using a wet-type vacuum pump12-16
Figure 12-3. Instrument vacuum system using a dry-type air pump12-18
Figure 12-4. Instrument pressure system using a dry-type air pump12-18
Figure 12-5. Pitot/static system for a small aircraft12-19
Figure 12-6. Pitot/static tube head12-20
Figure 13-1. Personal minimums checklist13-2
LIST OF TABLES
Table 1-1. Selection and properties of aircraft wood1-2
Table 1-2. Minimum recommended bend radii for aircraft plywood1-29
Table 2-1. Cotton and linen fabrics2-2
Table 2-2. Cotton and linen, tapes and threads2-4
Table 2-3. Safety tips for dope/paint2-28
Table 2-4. Tips for doping2-28
Table 3-1. Typical temperatures for forming acrylic sheets3-23
Table 4-1. Ferrous (iron) alloy materials4-1
Table 4-2. Numerical system for steel identification4-2
Table 4-3. Examples of stainless and heat-resistant steels
nominal composition (percent)4-3
Table 4-4. Basic temper designations and subdivisions from aluminum alloys4-4
Table 4-5. Hardness values for aluminum alloys4-7
Table 4-6. Recommended radii for 90-degree bends in aluminum alloys4-17
Table 4-7. K-chart for determining setback for bends other than 90 degrees4-18
Table 4-8. Aircraft rivet identification4-22
Table 4-9. Number of rivets required for splices (single-lap joint) in bare 2014-T6, 2024-T3, 2024-T36, and 7075-T6 sheet, clad 2014-T6, 2024-T3, 2024-T36, and 7075-T6 sheet, 2024-T4, and 7075-T6 plate, bar, rod,
tube, and extrusions, 2014-T6 extrusions4-41
Table 4-10. Number of rivets required for splices (single-lap joint) in 2017,
1017 alclad, 2024-T3 alclad sheet, plate, bar, rod, tube, and extrusions4-42
Table 4-11. Number of rivets required for splices (single-lap joint)
in 5052 (all hardnesses) sheet4-48
Table 4-12. Current and polarity selection for inert gas welding4-64
Table 4-13. Torch tip sizes4-66
Table 4-14. Calculated allowable strength of base metal4-72
Table 4-15. Chart showing welding filler rod selection4-76
Table 5-1. Advantages and disadvantages of NDI methods5-7
Table 5-2. Listing of commonly accepted standards and specifications
for magnetic particle inspection5-23
Table 5-3. Classification of penetrant inspection materials covered by
MIL-I-25135E5-34
Table 5-4. Fluorescent and visible penetrant inspection general processing
procedures flowsheet5-35
Table 5-5. Pre-cleaning methods for penetrant inspection5-36
Table 5-6. Listing of commonly accepted standards and specifications for
penetrant inspection5-38
Table 5-7. Acceptable ultrasonic inspection methods associated with
the example bonded structure configurations shown in Figure 5-215-51
Table 5-8. Ultrasonic inspection methods for bonded structures5-52
Table 6-1. Abrasives for corrosion removal6-25
Table 7-1. Recommended torque values (inch-pounds)7-9
Table 7-2. Minimum prevailing torque values for reused self-locking nuts7-13
Table 7-3. Flexible cable construction and physical properties7-27
Table 7-4. Nonflexible cable construction and physical properties7-30
Table 7-5. Straight-shank terminal dimensions7-32
Table 7-6. Copper oval sleeve data7-36
Table 7-7. Copper stop sleeve data7-37
Table 7-8. Turnbuckle safetying guide7-51
Table 7-9. Locking-clip application7-53
Table 7-10. Table of rivets7-54
Table 7-11. Table of screws7-56
Table 7-12. Table of bolts7-64
Table 7-13. Table of nuts7-71
Table 7-14. Table of washers7-78
Table 7-15. Table of pins7-81
Table 8-1. Current engine and maximum permissible cylinder barrel oversize8-6
Table 8-2. Sample manufacturer’s propeller inspection checklist8-45
Table 9-1. Bungee cord color codes9-2
Table 9-2. Tube data9-23
Table 9-3. Aircraft hose specifications9-26
Table 9-4. Ball diameters for testing hose restrictions or kinking9-30
Table 9-5. Table of filling pressures9-55
Table 11-1. ASTM consensus standards11-3
Table 11-2. Lead-acid battery electrolyte freezing points11-6
Table 11-3. Sulfuric acid temperature correction11-7
Table 11-4. DC wire and circuit protector chart11-17
Table 11-5. Switch derating factors11-19
Table 11-6. Selection of contact material11-20
Table 11-7. Tabulation chart (allowab le voltage drop between bus and
utilization equipment ground)11-24
Table 11-8. Examples of determining required tin-plated copper wire size and
checking voltage drop using Figure 11-211-25
Table 11-9. Examples of determining maximum tin-plated copper wire length and
checking voltage drop using Figure 11-211-25
Table 11-10. Current carrying capacity and resistance of copper wire11-27
Table 11-11. Current carrying capacity and resistance of aluminum wire11-28
Table 11-12. Comparable proper ties of wire insulation systems11-43
Table 11-13. Open w iring11-44
Table 11-14. Protected wiring11-46
Table 11-15. Allowable nicked or broken strands11-71
Table 11-16. Stud bonding or grounding to flat surface11-85
Table 11-17. Plate nut bonding or grounding to flat surface11-86
Table 11-18. Bolt and nut bonding or grounding to flat surface11-87
Table 11-19. Recommended size of identification sleeving11-96
Table 11-20. Selection table for standard sleeves11-100
Table 11-21. Selection table for thin-wall sleeves11-100
Table 11-22. Selection table for high-temperature sleeves11-101
Table 11-23. Selection table for cable markers11-101
Table 11-24. Plastic tie-down straps (MS3367, Type I, Class 1)11-102
Table 11-25. Bend radii for rigid conduit11-116
Table 11-26. Minimum bending radii for flexible aluminum or brass conduit11-117
Table 11-2 7. Contact cavity sealing-quick reference11-118
Table 11-28. Sealing rod dimensions11-120
Table 11-29. Electronic/electrical symbols11-121
Table 12-1. Color codes for pitot- static systems12-24
Par 1-1 Page 1-1 CHAPTER 1. WOOD STRUCTURE SECTION 1. MATERIALS AND PRACTICES
1-1. GENERAL. Wood aircraft construction dates back to the early days of certificated aircraft.
Today only a limited number of wood aircraft structures are produced. However, many of the older airframes remain in service. With proper care, airframes from the 1930s through the 1950s have held up remarkably well considering the state of technology and long-term experience available at that time. It is the responsibility of the mechanic to carefully inspect such structures for deterioration and continuing airworthiness.
1-2. WOODS.
a. Quality of Wood. All wood and plywood used in the repair of aircraft structures should be of aircraft quality (refer to Air Force Navy Commerce Department Bulletin ANC-19, Wood Aircraft Inspection and Fabrication). Table 1-1 lists some permissible variations in characteristics and properties of aircraft wood. However, selection and approval of woodstock for aircraft structural use are specialized skills and should be done by personnel who are thoroughly familiar with inspection criteria and methods.
b. Substitution of Original Wood. The wood species used to repair a part should be the same as that of the original whenever possible; however, some permissible substitutes are given in Table 1-1. Obtain approval from the airframe manufacturer or the Federal Aviation Administration (FAA) for the replacement of modified woods or other nonwood products with a substitute material.
Par 1-2 Page 1-2 TABLE 1-1. SELECTION AND PROPERTIES OF AIRCRAFT WOOD (See notes following table) Species of Wood Strength properties as compared to spruce Maximum permissible grain deviation (slope of grain) Remarks
1. 2. 3. 4.
Spruce (Picea) Sitka (P. Sitchensis) Red (P. Rubra) White (P. Glauca).
100% 1:15 Excellent for all uses.
Considered as standard for this table.
Douglas Fir (Pseudotsuga Taxifolia). Exceeds spruce. 1:15 May be used as substitute for spruce in same sizes or in slightly reduced sizes providing reductions are substantiated.
Difficult to work with hand tools. Some tendency to split and splinter during fabrication and considerable more care in manufacture is necessary. Large solid pieces should be avoided due to inspection difficulties.
Gluing satisfactory.
Noble Fir (Abies Nobiles).
Slightly exceeds spruce except 8% deficient in shear.
1:15 Satisfactory characteristics with respect to workability, warping, and splitting. May be used as direct substitute for spruce in same sizes providing shear does not become critical. Hardness somewhat less than spruce.
Gluing satisfactory.
Western Hemlock (Tsuga Heterpphylla).
Slightly exceeds spruce. 1:15 Less uniform in texture than spruce. May be used as direct substitute for spruce. Upland growth superior to lowland growth. Gluing satisfactory.
Pine, Northern White (Pinus Strobus).
Properties between 85% and 96% those of spruce.
1:15 Excellent working qualities and uniform in properties, but somewhat low in hardness and shock-resisting capacity.
Cannot be used as substitute for spruce without increase in sizes to compensate for lesser strength. Gluing satisfactory.
Par 1-2 Page 1-3 Species of Wood Strength properties as compared to spruce Maximum permissible grain deviation (slope of grain) Remarks White Cedar, Port Orford (Charaecyparis Lawsoniana).
Exceeds spruce. 1:15 May be used as substitute for spruce in same sizes or in slightly reduced sizes providing reductions are substantiated.
Easy to work with hand tools.
Gluing difficult, but satisfactory joints can be obtained if suitable precautions are taken.
Poplar, Yellow (Liriodendrow Tulipifera).
Slightly less than spruce except in compression (crushing) and shear.
1:15 Excellent working qualities.
Should not be used as a direct substitute for spruce without carefully accounting for slightly reduced strength properties.
Somewhat low in shock-resisting capacity.
Gluing satisfactory.
Notes for Table 1-1
1. Defects Permitted.
a. Cross grain. Spiral grain, diagonal grain, or a combination of the two is acceptable providing the grain does not diverge from the longitudinal axis of the material more than specified in column 3. A check of all four faces of the board is necessary to determine the amount of divergence. The direction of free-flowing ink will frequently assist in determining grain direction.
b. Wavy, curly, and interlocked grain. Acceptable, if local irregularities do not exceed limitations specified for spiral and diagonal grain.
c. H ard knots. Sound, hard knots up to 3/8 inch in maximum diameter are acceptable providing:
(1) they are not projecting portions of I-beams, along the edges of rectangular or beveled unrouted beams, or along the edges of flanges of box beams (except in lowly stressed portions); (2) they do not cause grain divergence at the edges of the board or in the flanges of a beam more than specified in column 3; and (3) they are in the center third of the beam and are not closer than 20 inches to another knot or other defect (pertains to 3/8 inch knots—smaller knots may be proportionately closer). Knots greater than 1/4 inch must be used with caution.
d. Pin knot clusters. Small clusters are acceptable providing they produce only a small effect on grain direction.
e. Pitch pockets. Acceptable in center portion of a beam providing they are at least 14 inches apart when they lie in the same growth ring and do not exceed 1-1/2 inches length by 1/8 inch width by 1/8 inch depth, and providing they are not along the projecting portions of I-beams, along the edges of rectangular or beveled unrouted beams, or along the edges of the flanges of box beams.
f. Mineral streaks. Acceptable, providing careful inspection fails to reveal any decay.
2. Defects Not Permitted.
a. Cross grain. Not acceptable, unless within limitations noted in 1a.
b. Wavy, curly, and interlocked grain. Not acceptable, unless within limitations noted in 1b.
c. Hard knots. Not acceptable, unless within limitations noted in 1c.
d. Pin knot clusters. Not acceptable, if they produce large effect on grain direction.
e. Spike knots. These are knots running completely through the depth of a beam perpendicular to the annual rings and appear most frequently in quarter-sawed lumber. Reject wood containing this defect.
Par 1-2 Page 1-4
f. Pitch pockets. Not acceptable, unless within limitations noted in 1e.
g. Mineral streaks. Not acceptable, if accompanied by decay (see 1f).
h. Checks, shakes, and splits. Checks are longitudinal cracks extending, in general, across the annual rings. Shakes are longitudinal cracks usually between two annual rings. Splits are longitudinal cracks induced by artificially induced stress. Reject wood containing these defects.
i. Compression wood. This defect is very detrimental to strength and is difficult to recognize readily.
It is characterized by high specific gravity, has the appearance of an excessive growth of summer wood, and in most species shows little contrast in color between spring wood and summer wood. In doubtful cases reject the material, or subject samples to toughness machine test to establish the quality of the wood. Reject all material containing compression wood.
j. Compression failures. This defect is caused from the wood being overstressed in compression due to natural forces during the growth of the tree, felling trees on rough or irregular ground, or rough handling of logs or lumber. 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, and vary from pronounced failures to very fine hairlines that require close inspection to detect. Reject wood containing obvious failures. In doubtful cases reject the wood, or make a further inspection in the form of microscopic examination or toughness test, the latter means being the more reliable.
k. Decay. Examine all stains and discoloration carefully to determine whether or not they are harmless, or in a stage of preliminary or advanced decay. All pieces must be free from rot, dote, red heart, purple heart, and all other forms of decay.
c. Effects of Shrinkage. When the moisture content of a wooden part is lowered, the part shrinks. Since the shrinkage is not equal in all directions, the mechanic should consider the effect that the repair may have on the completed structure. The shrinkage is greatest in a tangential direction (across the fibers and parallel to the growth rings), somewhat less in a radial direction (across the fibers and perpendicular to the growth rings), and is negligible in a longitudinal direction (parallel to the fibers). Figure 1-1 illustrates the different grain directions and the effects of shrinkage on the shape of a part. These dimensional changes can have several detrimental effects upon a wood structure, such as loosening of fittings and wire bracing and checking or splitting of wood members. A few suggestions for minimizing these shrinkage effects are:
(1) Use bushings that are slightly short so that when the wood member shrinks the bushings do not protrude and the fittings may be tightened firmly against the member.
(2) Gradually drop off plywood faceplates by feathering as shown in Figure 1-2.
(3) Thoroughly seal all wood surfaces, particularly end grain and bolt holes, with varnish, epoxy, or other acceptable sealer to slow or prevent moisture changes in the member.
(See Section 5, Finishing Wood Structures.)
Par 1-2 Page 1-5 FIGURE 1-1. RELATIVE SHRINKAGE OF WOOD MEMBERS DUE TO DRYING F IGURE 1-2. TAPERING OF FACEPLATE 1 -3. MODIFIED WOOD PRODUCTS. The most common forms of modified woods found in aircraft construction are plywood. Although not a wood product, Phenolic parts are sometimes incorporated into structures. These products are used whenever the manufacturer requires specialized strength or durability characteristics.
1-4. ADHESIVES. Because of the critical role played by adhesives in aircraft structure, the mechanic must employ only those types of adhesives that meet all of the performance requirements necessary for use in certificated civil aircraft. Use each product strictly in accordance with the aircraft and adhesive manufacturer’s instructions.
a. Adhesives acceptable to the FAA can be identified in the following ways:
(1) Refer to the aircraft maintenance or repair manual for specific instructions on acceptable adhesive selection for use on that type aircraft.
(2) Adhesives meeting the requirements of a Military Specification (MIL-SPEC), Aerospace Material Specification (AMS), or Technical Standard Order (TSO) for wooden aircraft structures are satisfactory providing they are found to be compatible with existing structural materials in the aircraft and the fabrication methods to be used in the repair.