Page xil AC 43.13-1 197 LIST OF ILLUSTRATIONS- Continued Figure Page
2.27 Application of Typical Flange Splices and Reinforcement 68
2.28 Number of Rivets Required for Splices (Single-Lap Joint) in Bare 2014-T6, 8024-18, 2024-T86, and 7075-T6 Sheet, Clad 2014-T6, 2024-T8, 2024-T96 and 7075-T6 Sheet, 2024-T4, and 7075-T6 Plate, Bar, Rod, Tube, and Extrusions, 2014-T6 Extrusions 64
2.29 Number of Rivete Required for Splices (Single-Lap Joint) in 2017, 2017 Alclad, 2024-T86 and 2024-T86 Alclad Sheet, Plate, Bar, Rod, Tube, and Extrusions - 65
2.80 Number of Rivets Required for Splices (Single-Lap Joint) in 5052 (All Hardnesses) Sheet 66
2.81 Example of Splice of Intermediate Frame (Material 2017 AL Alloy) 67
2.82 Typical Methods of Repalring Cracked Leading and Trailing Edges and Rib Intersections - 68
2.88 Typical Methods of Replacing Cracked Members at Fittinga 69
2.84 Typical Methods of Repairing Cracked Frame and Stiffener Combinations 70
2.85 Typical Repairs to Rudder and to Fuselage at Tail Post 71
2.86 Typical Methods of Repairing Elongated or Worn Bolt Holes 72
2.87 Typical Laminate (Facing) Repair 74 2,88 Typical Core and Facing Repair - 75
2.89 Typical Stepped Joint Repair 75
2.40 Typical Scarfed Joint Repair 78
2.41 Typical One Side Blind Repair 76
2.42 Typical Metal Facing Patch
2.48 Typical Types of Core Replacement 78
2.44 Typical Undercut Core Material Cavity 78
8.1 Textile Fabric Used in Aircraft Covering 88
3.2 Miscellaneous Textile Materials 84
8.8 Typical Methods of Attaching Fabric 85
3.4 Standard Knot for Rib Lacing and Terminating a Sewed Seam (Modified Seine Knot) 86
8.6 Splice Knot 87
3.6 Starting Stitch for Rib Stitching 88
8.7 Standard Double Loop Lacing 89
8.8 Standard Knot for Double Loop Lacing 90
8.9 Fabric Attachment Spacing 91
3.10 Repair of Tears in Fabric 95
4.1 Cable Cross Section 99
4.2 Strength of Steel Cable 100
4.8 Straight-Shank Terminal Dimensiona 101
4.4 Insertion of Cable into Terminal 101
4.5 Gauging Terminal Shank After Swaging 101
4.6 Typical Cable Splices 102
4.7 Typical Terminal Gauge 102
4.8 Copper Oval Sleeve Data 108
4.9 Typical Thimble-Eye Splice 108
4.10 Copper Stop Sleeve Data 104
4.11 Typical Terminal Gauge 104
4.12 Preparation of a Woven Cable Splice 106
4.18 Preparation of a Wrapped Soldered Terminal 108
4.14 Cable Inspection Technique 107
4.15 Cable Wear Patterns .- 107
4.16 Worn Cable (Replacement Necessary) 108
4.17 Worn Cable (Replacement Recommended) 108
4.18 Internal Cable Wear 108
4.19 Corrosion 109
4.20 Manufacturer's Wire Splice 109
4.21 Pulley Wear Patterns 110
AC 43.13-1A Page xill 1972 LIST OF ILLUSTRATIONS- Continued Figure Page 4,22 Turnbuckle Safetying Guide 112
4.28 Safetying Turnbuckles 118
4.24 Clip Type Locking Device 114
5.1 Bolt Indentification 116
5.2 Recommended Torque Values For Nut-Bolt Combinations-(without lubrication) . 118
5.8 Torque Wrench With Various Adapters 119
7.1 Numerical System for Steel Identification 129
7.2 Basic Temper Designationa and Subdivisions for Aluminum Alloys 180
7.8 Rockwell C Scale Steel Hardneas Numbers Comparison Table 188 7,4 Hardness Values for Aluminum Alloys 182
7.5 Maximum Recommended X-Ray Kilovolts 188
8.1 Typical Bolt Cracks 141
8.2 Typical Cracke Near Boltholes 142
8.8 Typical Bolthole Cracka 142
8.4 Typical Rod-End Cracks 142
8.5 Typical Torque Tube Bolthole Elongation 142 8,6 Aircraft Tire Types and Ratings 146
8.7 Oxygen Cylinder Damage 155
8.8 Cylinder Brackets and Clamps 156
9.1 Stop-Drilling Cracks 160
9.2 Surface Patches 160
9.8 Plug Patch Repair 161
10.1 Tube Data 165
10.2 Hose Assembly Instructions 167
10.8 Aircraft Hose Specificationa 168
10.4 Proper Hose Installations 169
10.5 Minimum Bend Radif 170
10.6 Ball Diameters for Testing Hose Restrictions or Kinking 171
10.7 Suggested Handling of Preformed Hose 171
10.8 Minimum Bend Radil-Teflon Hose 172
11.1 Wire and Circuit Protector Chart 177
11.2 Switch Derating Factors 177
11.8 Examples Determining Voltage Drop from Electric Wire Chart (Fig. 11.7) 179
11.4 Examples Determining Voltage Drop from Electric Wire Chart (Fig. 11.7) 179
11.5 Copper Electric Wire Current Carrying Capacity 180
11.8 Aluminum Electric Wire Current Carrying Capacity 180
11.7 Electric Wire Chart 182
11.78 Wire Used in Aircraft Installations 188
11.8 Staggered Splices in Wire Bundle 186
11.9 Cable Clamp at Bulkhead Hole 187
11.10 Cable Clamp and Grommet at Bulkhead Hole 187
11.11 Allowable Nicked or Broken Strands .. 188
11.12 Stud Bonding or Grounding to Flat Surface 189
11.18 Plate Nut Bonding or Grounding to Flat Surface 190
11.14 Bolt and Nut Bonding or Grounding to Flat Surface 191
11.15 Copper Jumper Connection to Tubular Structure 192
11.16 Bonding Conduit to Structure 192
11.17 Aluminum Jumper Connection to Tubular Structure 192
11.18 Sizes of Identification Sleeving 104
11.19 Identification of Wire Bundles and Harnesses 195
11.20 AN Connectors 107
11.21 Classes of AN Connectors 187
11.22 AN Connector Marking .. 198
11.28 Spare Wires for Potting Connector 199
11.24 Bend Radil for Rigid Conduit 201
Page xiv AC 43.19-1 197 LIST OF ILLUSTRATIONS- Continued Pioure Page
11.25 Minimum Bending Radii for Flexible Aluminum or Brass Conduit 202
11.26 Group and Bundle Ties 208
11.27 Comb for Straightening Wires in Bundles 208
11.28 Slack Between Supports 204
11.29 Drainage Hole in Low Point of Tubing 204
11.80 Separation of Wires from Plumbing Lines 205
11.81 Safe Angle for Cable Clamps .. 206
11.82 Typical Mounting Hardware for MS-21919 Cable Clamps 206
11.88 Installing Cable Clamp to Structure - 207
11.84 Installing Cable Clamps to Tubular Structure 207
11.85 Single Cord Lacing 208
11.86 Double Cord Lacing 209
11.87 Making Ties.. 209
11.88 Lead-Acid Battery Electrolyte Freezing Points 210
11.89 Sulfuric Acid Temperature Correction 211
12.1 Propeller Repair by Addition of Small Inlay 217
12.2 Method of Repairing Surface Cracks, Nicks, etc., on Aluminum Alloy Propellers 224
12.8 Correct and Incorrect Method of Reworking Leading Edge of Aluminum Alloy Propellers 225
12.4 Repair Limits to Blade Section Width and Thickness for Aluminum Alloy Propellers 226
12.5 Method of Repairing Damaged Tip of Aluminum Alloy Propellers 227
12.6 Protractor and Method of Measuring Angle of Bend in Aluminum Alloy Propellers 228
12.7 Repair of Fixed-Pitch Hub and Propeller With Elongated or Damaged Boltholes 281
12.8 Blade Leading Edge and Trim Tab 287
12.9 Blade Bonding and Crack Location 288
12.10 Blade Damage Location 288
12.11 Blade Cross-Section 289
12.12 Blade Retention and Link Attach Points 240
18.1 Typical Datum Locations 244
18.2 Illustration of Arm (or Moment Arm) 245
18.8 Example of Moment Computation . 246
18.4 Empty Weight Center-of-Gravity Formulas 247
18.5 Empty Welght and Empty Weight Center-of-Gravity-Tail-Wheel Type Aircraft - 248 18,6 Empty Weight and Empty Weight Center-of-Gravity--Nose-Wheel Type Aircraft 249
18.7 Operating Center-of-Gravity Range 250
18.8 Weighing Point Centerline 251
18.9 Empty Weight and Empty Weight Center-of-Gravity When Aircraft is Weighed With Oil 252
18.10 Example of Check of Most Forward Weight and Balance Extreme 254
18.11 Example of Check of Most Rearward Weight and Balance Extreme 255
18.12 Loading Conditions: Determination of the Number of Passengers and Baggage Permissible with Full Fuel 256
18.18 Loading Conditions: Determination of the Fuel and Baggage Permissible with Maximum Passengers 258
18.14 Loading Conditions: Determination of the Fuel and the Number and Location of Passengers Permissible with Maximum Baggage 259
18.15 Effects of the Addition of Equipment Items on Balance 260
18.16 Example of Moment and Weight Changes Resulting from Equipment Changes 261
18.17 Sample Welght and Balance Report To Determine Empty Weight Center-of-Gravity 262
C 43.13-14 Page xY 973 LIST OF ILLUSTRATIONS- Continued Pinurs Page
18.18 Sample Weight and Balance Report Including an Equipment Change for Aircraft Fully Loaded 268
13.19 Permanent Ballast Computation Formula 264
14.1 Schematic of Typical Differential Pressure Compression Tester 278
14.2 Spark Plug Heat Ranges 214
14.8 Spark Plug Reach 275
14.4 Method of Checking Spark Plug Gap . 275
14.58 Typical Carbon Fouled Spark Plug . 276
14.5b Typical Lead Fouled Spark Plug 276
14.бе Typical Oil Fouled Spark Plug 276
14.6а Typical Eroded Spark Plug 277
14.6b Typical Spark Plug With Copper Runout 277
14.7 Typical Spark Plug With Bridged Electrodes 277
14.8 Spark Plug Well Flashover 278
14.9 Typical Method of Clamping Leads 278
14.10 Normal Contact Point -- 279
18.11 Point With Minor Irregularities 279
14.12 Point With Well-Defined Mound 279
14.18 Location of Clamps at Tube Bends 281
14.14 Typical Muffler Wall Fatigue Failure at Exhaust Outlet 285
14.15 Typical Muffer Wall Failure .. 286
14.16 Typical Muffler Wall Fatigue Failure 286
14.17 Typical Fatigue Failure of Muffler End Plate at Stack Inlet 287
14.18 Section of Muffler Showing Typical Internal Baffle Fallure 287
14.19 Loose Pieces of Failed Internal Baffle .. 287 14,20 Failed Internal Baffle Partially Obstructing Muffler Outlet 288
14.21 Failed Internal Baffle Completely Obstructing Muffer Outlet 288
14.22a Example of Exhaust Outlet Guard ... 288
14.22b Example of Exhaust Outlet Guard Installed 289
14.28 Effect of Improperly Positioned Exhaust Pipe/Muffler Clamp 289
14.24 Primary Inspection Areas 290
AC 43.13-1A Page 1 1972 Chapter 1. AIRCRAFT WOOD STRUCTURES Section 1. MATERIALS AND PRACTICES
1. MATERIALS. Three forms of wood are commonly used in aircraft: solid wood, plywood, and laminated wood. Although several kinds of modified wood are sometimes used for special purposes, these three forms constitute the bulk of all wood aircraft construction materials.
a. Quality of Wood. All wood and plywood used in the repair of aircraft structures should be of aircraft quality. Figure 1.2 fists the permissible variations in characteristics and properties of aircraft wood.
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 face plates either by feathering or by shaping as shown in figure 1.1.
b. Species Substitution. The species used to repair a part should be the same as that of the original whenever possible; however, permissible substitutes are given in figure 1.2.
c. Effects of Shrinkage. When the moisture content of wood is lowered, its dimensions decrease. The dimensional change 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). These dimensional changes can have several detrimental effects upon a wood structure, such as loosening of fittings and wire
2. REPLACEMENT OF DRAINHOLES AND SKIN STIF- FENERS. Whenever repairs are made that require replacing a portion that includes drainholes, skin stiffeners, or any other items, the repaired portion must be provided with similar drainholes, skin stiffeners, or items of the same dimensions in the same location. Reinforcing, under skin repairs, that interferes with the flow of water from some source, such as inspection holes, is to be provided with drainholes at the lowest points.
3. CONTROL SURFACE FLUTTER PRECAUTIONS.
When repairing control surfaces, especially on high-performance airplanes, care must be exer-
FEATHERED END/ SPADED END- FIGURE 1.1.-Tapering of face plates.
Chap 1 Par 1
Page 2 AC 43.13-1A 1972 FIGURE 1.2.—Selection and properties of aircraft wood.
Maximum utrength permisaible Species of wood properties as compared to ation (alope Frain devi- Remarks spruce of grain) Spruce (Picea) Sitka (P. Bit- 100% 1:15 Excellent for all us. Considered as standchensle) Red (P. Bubra) ard for this table.
White (P. Glauce).
Douglas Fir (Paeudotsuga Taxi- Exceeds spruce 1:16 May be need as substitute for spruce in same folia). sizes or in alightly 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 pleces should be avoided due to Inspection difficulties. Gluing satisfactory.
Noble Fir (Ables Noblies) - Slightly exceede spruce 1:15 Satlafactory characteristics with respect to except 8 percent workability, warping, and splitting. May be deficient in shear. used as direct substitute for spruce In same sizes providing shear does not become critical.
Hardness somewbat less then spruce. Gluing satisfactory.
Western Hemlock (Truga Het- Slightly exceeds spruce 1:15 Less uniform in texture than spruce. Afay be eropbylia). used as direct substitute for spruce. Upland growth superior to lowland growth. Gluing satisfactory.
Pine, Northern White (Pinus Properties hetween 85 1:15 Excellent working qualities and uniform in Strobus). percent and 96 per- propertles but somewhat low in hardness and cent those of spruce. abock-resisting capacity. Cannot be used as substitute for spruce without increase in sizes to compensate for lesser strength. Gluing satisfactory.
White Cedar, Port Oxford Exceeds spruce - (Charaecyparla Lawsoniana).
1:15 Nay be used as substitute for spruce In same sizes or in slightly reduced sizes proriding reductione are substantiated. Easy to work with band toola. Gluing difficult but satistactory joints can be obtained if suitable precau tlone are taken.
Poplar, Yellow (Lirlodendron Slightly leas than 1:15 Excellent working qualities. Should not be Tulipifera). spruce except in used as a direct aubstitute for spruce without compression (crush- carefully accounting for slightly reduced ing) and shear. strength properties. Somewhat low in shockresisting capacity. Gluing satisfactory.
(Bee notes follosoing table.)
Notes for Agure 1.2.
1. Defeots Permitted.
a. Oross grain. Spiral grain, diagonal grain, or a combination of the two is acceptable providing the grain does Par 3
AC 43.13-1A Page 3 1972 not diverge from the longitudinal axis of the material more than specifed in column 8. 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. Wacy, ourly, and interlocked grain. Acceptable, if local irregularities do not exceed limitations specifed for spiral and diagonal grain.
c. Eard knots. Sound bard knots up to ¼-inch In maximum diameter are acceptable prorlding: (1) they are not in projecting portions of I-beams, niong the edges of rectangular or beveled unrouted beams, or along the edges of manges of box beams (except in lowly stressed portions); (2) they do not cause grain divergence at the edges of the board or in the fanges of a beam more than specifed in column 8; and (B) they are in the center third of the beam and are not closer than 20 inches to another knot or other defect (pertains to %-inch knots-smaller knots may be proportionately closer). Knote greater than ¾-inch must be used with caution.
d. Pin knot olusters. Small clusters are acceptable providing they produce only a small effect on grain direction.
e. Pitoh pookots. 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 1½ inch length by %-inch width by ⅛-inch depth and providing they are not along the projecting portions of I-beams, along the edges of rectangular or beveled unronted beams, or along the edges of the flanges of box beams.
f. Afineral streaks. Acceptable, providing careful inspection falls to reveal any decay.
2. Defects Not Permitted.
a. Cross grain. Not acceptable, unless within limitations noted in 1a.
D. Wavy, curly, and interlocked grain. Not acceptable, unless within limitatlons noted in 1b.
c. Hard knots. Not acceptable, unless within limitations noted in 1c.
d. Pin knot oluaters. 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 ringe and appear most frequently in quartersawed lumber. Reject wood containing this defect.
1. Pitch pockets. Not acceptable, unless within limitations noted in le.
g. fineral streaks. Not acceptable. If accompanied by decay (see 1f).
b. Checks, shakes, and aplits. Checks are longitudinal cracks extending, in general, across the annunl rings.
Shakes are longitudinal cracks usually between two annual rings. Splits are longitudinal cracks induced by artificially induced stress. Reject wood containing these defects.
1. Compression cood. This defect is very detrimental to strength and is difficult to recognize readily. It la characterized by high specific gravits; has the appenrance of an excessive growth of summer wood; and in inost species shows but little contrast in color between epring wood and summer wood. In doubtful cases reject the material, or subject samples to a tonghness machine test to establish the quality of the wood. Reject all materlal containing compression mood.
j. Compressio» failures. This defect ia caused from the wood belng overstressed in compresslon due to natural forces during the growth of the tree, felling trees on rough or irregular ground, or rough handling of logs or lnmber.
Compression failures are choracterized by a buckling of the fbers that appear as streaks on the surface of the piece substantially at right angles to the grain, and rary from pronounced fallures 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 rellable.
k. Decay. Examine all stains and discolorations carefully to determine whether or not ther are harmless, or in a stage of preliminary or advanced decay. All pleces must he free from rot, dote, red heart, purple heart, and all other cised that the repairs do not involve the addition of weight aft of the hinge line. Such a procedure may adversely disturb the dynamic and static balance of the surface to a degree which would induce flutter. As a general rule, it will be necessary to repair control surfaces in such a manner that the structure is identical to the original so that the weight distribution and resulting mass balance are not affected in any way.
4. GLUING PRECAUTIONS. Satisfactory glue Chap 1 joints in aircraft will develop the full strength of wood under all conditions of stress. To produce this result, the gluing operation must be carefully controlled so as to obtain a continuous, thin, uniform film of solid glue in the joint with adequate adhesion to both surfaces of the wood. Some of the more important conditions involve:
o. Properly prepared wood surfaces.
b. Glue of good quality, properly prepared.
c. Good gluing technique.
Par 3
Pago 4
5. PREPARATION OF WOOD SURFACES FOR So more than GLUING, It is recommended that no more than 8 hours be permitted to elapse between final surfacing and gluing. The gluing surfaces should be machined smooth and true with planers, jointers, or special miter saws. Planer marks, chipped or loosened grain, and other surface irregularities will not be permitted. Sandpaper must never be used to smooth softwood surfaces that are to be glued. Sawed surfaces must approach well-planed surfaces in uniformity, smoothness, and freedom from crushed fibers.
a. Tooth-planing, or other means of roughening smooth well-planed surfaces of normal wood before gluing is not recommended. Such treatment of well-planed wood surfaces may result in local irregularities and objectionable rounding of edges. While sanding of planed surfaces is not recommended for softwoods, sanding is a valuable aid in improving the gluing characteristics of some hard plywood surfaces, wood that has been compressed through exposure to high pressure and temperatures, resin-impregnated wood (impreg and compreg), and laminated paper plastic (papreg).
b. Wood surfaces for gluing should be free from oil, wax, varnish, shellac, lacquer, enamel, dope, sealers, paint, dust, dirt, oil, glue, crayon marks, and other extraneous materials.
c. Wetting tests are useful as a means of detecting the presence of wax. Drops of water placed on the surface of wax-coated wood do not spread or wet the wood. At present, preliminary gluing tests appear to be the only positive meana of actually determining the gluing characteristics of plywood surfaces.
6. GLUES. Glues used in aircraft repair fall into two general groups: casein glues and resin glues. Any glue that meets the performance requirements of applicable United States military specifications or has previously been accepted by the FAA is satisfactory for use in certificated civil aircraft. In all cases, glues are to be used strictly in accordance with the glue manufacturer's recommendations.
Par 5 AC 43,13-1A 1972
a. Caseln Glues. Casein glues have been widely used in wood aircraft repair work. The forms, characteristics, and properties of water-resistant casein glues have remained substantially the same for many years, except for the addition of preservatives. Casein glues for use in aircraft should contain suitable preservatives such as the chlorinated phenols and their sodium salts to increase their resistance to organic deterioration under high-humidity exposures. Most casein glues are sold in powder form ready to be mixed with water at ordinary room temperatures.
b. Synthetic Resin Glues. Synthetic resin glues for wood are outstanding in that they retain their strength and durability under moist conditions and after exposure to water. The best known and most commonly used synthetic resin glues are the phenol-formaldehyde, resorcinolformaldehyde, and urea-formaldehyde types.
The resorcinol-formaldehyde type glue is recommended for wood aircraft applications. Materials, such as walnut-shell flour, are often added by the glue manufacturer to the resin glues to give better working characteristics and joint-forming properties. The suitable curing temperatures for both urea-formaldehyde and resorcinol glues are from 70° F. up. At the 70° F. minimum temperature it may take as long as 1 week for the glueline in a spar splice to cure to full strength. Thinner pieces of wood and/or higher curing temperatures shorten curing time considerably. The strength of a joint cannot be depended upon if assembled and cured at temperatures below 70° F.
7. MIXING OF RESIN GLUES. Liquid resin glues may come ready for use or in a form which requires only the addition of a hardener. In all cases, the mixing, glue consistency, assembly time, etc., should comply with the glue manufacturers' recommendations and instructions.
Cold-setting synthetic-resin glue, when prepared for use, is limited in working life, and care should be taken to discard the glue and clean the equipment before the end of the working life period. In very warm weather it may be found advisable to keep the gluepot in a bath of cool water, approximately 70° F., to prolong the working life of the mixture.
Chap 1
AC 43.13-1A Page 7 1972 1 6A RECOMMENDED •-
DA MINIMUM ‡
- 12 A RECOMMENDED- 6A RECOMMENDEO 10A MINIMUM 5A MINIMUM
NO FITTINGS WITHIN THESE LIMITS 1/4 A +
DIRECTION OF GRAIN IF SPRUCE
OR OUTER FACE GRAIN IF PLYWOOD REINFORCEMENT PLATES TO BE SPRUCE OR PLYWOOD AND SHALL BE GLUED ONLY.
SOLID SPARS MAY BE REPLAGED WITH LAMINATED ONES OR VICE VERSA, PROVIDED THE MATERIAL IS OF THE SAME HIGH QUALITY.
FIoURE 1.4.-Method of splicing solid or laminated rectangular spars.
but not necessarily, at a bolthole or cutout and spread in each direction until, in most cases, they extend a short distance beyond the ends of the plates where the resistance to spar shrinkage disappears. Other factors which have been found conducive to the formation of cracks, due to spar shrinkage in the region of plywood plates, are poor protective finishes, large cutouts, and metal fittings which utilize two lines of large diameter bolts.
The presence of cracks does not necessarily mean that the spar must be discarded. If the crack is not too long or too close to either edge and can be reinforced properly, it will probably be more economical and satisfactory to effect a repair than to install a new spar or section. However, a generally acceptable proce dure suitable for all airplane models cannot be Chap 1 described here. It is recommended the manufacturer or the Federal Aviation Administration be contacted for specific instructions before making repairs not in accordance with the manufacturer's approved instructions or the recommendations of this advisory circular, because of the possibility of strength deficiencies.
16. ELONGATED HOLES IN SPARS. In cases of elongated boltholes in a spar or cracks in the vicinity of boltholes, splice in a new section of spar, or replace the spar entirely, unless the method of repair is specifically approved by a representative of the HAA. In many cases, it has been found advantageous to laminate the new section of the spar (using aircraft plywood for the outer faces, particularly if the spar roots are being replaced.
Par 15
Page 8 АС 43.13-1А 1972 IF SPLICE IS MADE WHERE ROUTIN 18 FEATHERED TO FULL
WIDTH OF SPAR, TAPERED PLATES OONFORMING TO THE CONTOUR OF THE ROUTINS, SHOULD FIRST BE ADDED.
OTHERWISE THE SPLICE N THE SAME AS SHOWN.
БА
- 6А - • 6А
- 12A RECOMMENDED -
IDA MINIMUM
NO FITTING WITHIN THESE LIMITS
DIRECTION OF GRAIN
REINFORCEMENT PLATES MAY BE OF PLYWOOD, THE SAME MATERIAL AS THE SPAR, OR MATERIAL OF EQUAL OR HIGHER QUALITY AND SHALL BE GLUED ONLY.
FIGURE 1.5.-Method of splicing solid "I spars.
17. RIB REPAIRS. Make replacement ribs from & manufacturer's approved drawing, or from a drawing made by the repair agency, and certified by the manufacturer as correct. The original rib may be used as a pattern in making the new rib if it is not too seriously damaged to permit comparison. Wood ribs should not be attached to wood spars by nails driven through the rib capstrips, as this weakens the rib materially. The attachment should be by means of glue with cement-coated, barbed, or spiraled nails driven through the vertical rib members on each side of the spar. The drawing or pattern should be retained by the repair agency for use by the FAA inspector when making his inspection. (Acceptable methods of repairing damaged ribs are shown in figure 1.10.)
a. Compression Ribs. Acceptable methods of repairing damaged compression ribs are shown in figure 1.11. (A) illustrates the repair of a compression rib of the "I" section type; i.e., wide, shallow capstrips, a center plywood web with a rectangular compression member on Par 17 each side of the web. The rib is assumed to be cracked through capstrips, web member, and compression member. Cut the compression member as shown in (D), remove and replace the shortest section, adding the reinforcement blocks as also shown in figure 1.11(D). Cut and replace the aft portion of the capstrips and reinforce as shown in figure 1.10 excep that the reinforcement blocks are split in the vertical direction to straddle the center web.
The plywood sideplates, as indicated in figure
1.11(A), are glued on. These plates are added to reinforce the damaged web. (B) illustrates a compression rib of the type that is basically a standard rib with rectangular compression members added to one side and plywood web to the other side. The method used in this repair is essentially the same as in (A) except that the plywood reinforcement plate shown in solid black in section B-B is continued the full distance between spars. (C) illustrates a com pression rib of the "I" type with a rectangular vertical member each side of the web. Th Chap
I€ 43.13-1A Page 9 972 10 д
NO FITTING WITHIN THESE LIMITS
- DIRECTION OF GRAIN IN - 1/28
PLYWOOD REINFORCEMENT
PLATES TO BE SAME AS ORIGINAL WEB.
PLYWOOD
A-SOLID WOOD FILLER BLOOKS
SECTION A-A FIGURE 1.6.-Repairs to built-up "I spar.
method of repair is essentially the same as in (A) except the plywood reinforcement plates on each side shown in solid black in section -C are continued, as in (C), the full distance between spars.
18. PLYWOOD SKIN REPAIR. Make extensive repairs to damaged stressed skin plywood structures in accordance with apecific recommendations from the manufacturer. It is recommended hat repairs be made by replacing the entire panel from one structural member to the hext, if damage is very extensive. When damaged plywood skin is repaired, carefully inspect the adjacent internal structure for possible hidden damage. Repair any defective frame members prior to making skin repairs.
a. Types of Patches. Four types of patcheshe surface or overlay patch, the splayed atch, the plug patch, and the scarf patch-are acceptable for repairing plywood skins. Surface patches should not be used on skins over 1/8 inch thick. Splayed patches should not be used on skins over 1/10 inch thick. There are no skin thickness limitations for the use of scarf patches and plug patches.
b. Determination of Single or Double Curvature, Much of the outside surface of plywood aircraft is curved. On such areas, plywood used for repairs to the skin must be similarly curved. Curved skins are either of single curvature or of double (compound) curvature. A simple test to determine which type of curvature exists may be made by laying a sheet of heavy paper on the surface in question. If the sheet can be made to fit the surface without wrinkling, the surface is either flat or has single curvature. If, however, the sheet cannot be made to fit the surface without wrinkling, the surface is of double curvature.
op 1 Par 17
Page 10 AC 43.13-1A 1972
ANGLE OF FACE GRAIN SAME AS IN ORIGINAL WEB
NEW WEB STAGGER WEB SPLICES (See Fig. 1.8 for method of splicing plywood webs).
• 10 B C
FOR CLARITY IOA - 6A- NEW WEB NOT INOLUDED IN THIS VIEW.
- SPRUCE REINFORCEMENT PLATES. A, 8,0, D = ORIGINAL DIMENSIONS.
FoURs 1.7.-Method of splicing box-spar flanges (plate method).
19. REPAIRS TO SINGLE CURVATURE PLYWOOD SKIN. Repairs to skins of single curvature may usually be formed from flat plywood, either by bending it dry or after soaking it in hot water.
The degree of curvature to which a piece of plywood can be bent will depend upon the direction of the grain and the thickness. Figure
1.12 is presented as a guide in determining which process of bending should be used for the curvature being considered. Plywood, after softening, may be bent on a cold ventilated form, or it may be bent over the leading edge near the part being patched if space permits.
In either method it should be allowed to dry completely on the form. When bending plywood over a leading edge, drying may be hastened by laying a piece of coarse burlap over the leading edge before using it as a bending form.
A fan to circulate the air over the bent piece will speed the drying. In bending pieces of small radii, or to speed up the bending of a large number of parts of the same curvature, it Par 19 may be necessary to use a heated bending form. The surface temperature of this form may be as high as 149° C. (800° F.), if necessary, without danger of damage to the ply.
wood. The plywood should be left on the form, however, only long enough to dry to room conditions.
20. REPAIRS TO DOUBLE CURVATURE PLYWOOD SKIN. The molded plywood necessary for a repair to a damaged plywood skin of double curvature cannot be made from flat plywood unless the area to be repaired is very small, or is of exceedingly slight double curvature; there fore, molded plywood of the proper curvature must be on hand before the repair can be made.
If molded plywood of the proper curvature is available, the repair may be made following the recommended procedures.
21. SPLAYED PATCH. Small holes with largest dimensions not over 15 times the skin thickness in skins not more than 1/10 inch in thickness Chop