Par 4-57 Page 4-117 TABLE 4-6. Recommended radii for 90-degree bends in aluminum alloys.
Alloy and Approximate sheet thickness (t) (inch) t e m p e r
0.
0 1 6
0.
0 3 2
0.
0 6 4
0.
1 2 8
0.
1 8 2
0.
2 5 8 2024-01 0 0-1t 0-1t 0-1t 0-1t0-1t 0-1t 2024-T31, 2 1½t-3t 2t-4t 3t-5t 4t-6t 4t-6t 5t-7t 2024-T61 2t-4t 3t-5t 3t-5t 4t-6t 5t-7t 6t-10t 5052-0 0 0 0-1t 0-1t 0-1t 0-1t 5052-H32 0 0 ½t-1t ½t-1½t ½t-1½t ½t-1½t 5052-H34 0 0 ½t-1½t 1½t-2½t 1½t-2½t 2t-3t 5052-H36 0-1t ½t-1½t 1t-2t 1½t-3t 2t-4t 2t-4t 5052-H38 ½t-1½t 1t-2t 1½t-3t 2t-4t 3t-5t 4t-6t 6061-0 0 0-1t 0-1t 0-1t 0-1t 0-1t 6061-T4 0-1t 0-1t ½t-1½t 1t-2t 1½t-3t 2½t-4t 6061-T6 0-1t ½t-1½t 1t-2t 1½t-3t 2t-4t 3t-4t 7075-0 0 0-1t 0-1t ½t-1½t 1t-2t 1½t-3t 7075-T61 2t-4t 3t-5t 4t-6t 5t-7t 5t-7t 6t-10t 1 Alclad sheet may be bent over slightly smaller radii than the corresponding tempers of uncoated alloy.
2 Immediately after quenching, this alloy may be formed over appreciably smaller radii.
To determine setback for a bend of more or less than 90 degrees, a correction known as a K-factor must be applied to find the setback.
Table 4-7 shows a chart of K-factors. To find the setback for any degree of bend, multiply the sum of the bend radius and metal thickness by the K-value for the angle through which the metal is bent.
Figure 4-3 shows an example of a piece of
0.064 inch sheet metal bent through 45 degrees to form an open angle of 135 degrees. For 45 degrees, the K-factor is 0.41421. The setback, or the distance from the mold point to the bend tangent line, is:
Setback = K(BR + MT) = 0.41421 (0.25 + 0.064) = 0.130 inches
If a closed angle of 45 degrees is formed, the metal must be bent through 135 degrees. The K-factor for 135 de-grees is 2.4142, so the setback, or distance from the mold point to the bend tangent line, is 0.758 inch.
RIVETING.
The two major types of rivets used in aircraft are the common solid shank rivet, which must be driven using an air-driven rivet gun and bucking bar; and special (blind) rivets, which are installed with special installation tools. Design allowables for riveted assemblies are specified in MIL-HDBK-5.
Solid shank rivets are used widely during assembly and repair work. They are identified by the material of which they are made, the head type, size of shank, and temper condition.
Par 4-57 Page 4-118 TABLE 4-7. K-chart for determining setback for bends other than 90 degrees.
Deg. K Deg.
K Deg. K Deg.
K Deg:
K 1 0.0087 37 0.3346 73 0.7399 109 1.401 145 3.171 2 0.0174 38 0.3443 74 0.7535 110 1,428 146 3.270 3 0.0261 39 0.3541 75 0.7673 111 1.455 147 3.375 4 0.0349 40 0.3639 76 0.7812 112 1.482 148 3.487 5 0.0436 41 0.3738 77 0.7954 113 1.510 149 3.605 6 0.0524 42 0.3838 78 0.8097 114 1.539 150 3.732 7 0.0611 43 0.3939 79 0.8243 115 1.569 151 3.866 8 0.0699 44 0.4040 80 0.8391 116 1.600 152 4.010 9 0.0787 45 0.4142 81 0.8540 117 1.631 153 4.165 10 0.0874 46 0.4244 82 0.8692 118 1.664 154 4.331 11 0.0963 47 0.4348 83 0.8847 119 1.697 155 4.510 12 0.1051 48 0.4452 84 0.9004 120 1.732 156 4.704 13 0.1139 49 0.4557 85 0.9163 121 1.767 157 4.915 14 0.1228 50 0.4663 86 0.9324 122 1.804 158 5.144 15 0.1316 51 0.4769 87 0.9489 123 1.841 159 5.399 16 0.1405 52 0.4877 88 0.9656 124 1.880 160 5.671 17 0.1494 53 0.4985 89 0.9827 125 1.921 161 5.975 18 0.1583 54 0.5095 90 1.000 126 1.962 162 6.313 19 0.1673 55 0.5205 91 1.017 127 2.005 163 6.691 20 0.1763 56 0.5317 92 1.035 128 2.050 164 7.115 21 0.1853 57 0.5429 93 1.053 129 2.096 165 7.595 22 0.1943 58 0.5543 94 1.072 130 2.144 166 8.144 23 0.2034 59 0.5657 95 1.091 131 2.194 167 8.776 24 0.2125 60 0.5773 96 1.110 132 2.246 168 9.514 25 0.2216 61 0.5890 97 1-130 133 2.299 169 10.38 26 0.2308 62 0.6008 98 1.150 134 2.355 170 11.43 27 0.2400 63 0.6128 99 1.170 135 2.414 171 12.70 28 0.2493 64 0.6248 100 1.191 136 2.475 172 14.30 29 0.2586 65 0.6370 101 1.213 137 2.538 173 16.35 30 0.2679 66 0.6494 102 1.234 138 2.605 174 19.08 31 0.2773 67 0.6618 103 1.257 139 2.674 175 22.90 32 0.2867 68 0.6745 104 1.279 140 2.747 176 26.63 33 0.2962 69 0.6872 105 1.303 141 2.823 177 38.18 34 0.3057 70 0.7002 106 1.327 142 2.904 178 57.29 35 0.3153 71 0.7132 107 1.351 143 2.988 179 114.59 36 0.3249 72 0.7265 108 1.376 144 3.077 180 Inf.
The material used for the majority of solid shank rivets is aluminum alloy. The strength and temper conditions of aluminum alloy rivets are identified by digits and letters similar to those used to identify sheet stock. The 1100, 2017-T, 2024-T, 2117-T, and 5056 rivets are the six grades usually available. AN-type aircraft solid rivets can be identified by code markings on the rivet heads. A rivet made of 1100 material is designated as an “A” rivet, and has no head marking. The 2017-T alloy rivet is designated as a “D” rivet and has a raised teat on the head. Two dashes on a rivet head indicate a 2024-T alloy designated as a “DD” rivet. The 2117-T rivet is designated as an “AD” rivet, and has a dimple on the head. A “B” designation is given to a rivet of 5056 material and is marked with a raised cross on the rivet head. Each type of rivet is identified by a part number to allow the user to select the correct rivet. The numbers are in series and each series represents a particular type of head. (See figure 4-4 and table 4-8.)
An example of identification marking of rivet follows.
MS 20470AD3-5 Complete part number MS Military standard number 20470 Universal head rivet AD 2117-T aluminum alloy 3 3/32nds in diameter 5 5/16ths in length
RIVET IDENTIFICATION T = 0.064" The material can be identified by the head marking Material R = 0.250 Rivet Code Head Marking Material SETBACK PLAIN (Dyed) 1100 ° (- AD DIMPLED 2117
- SETBACK D RAISED DOT 2017T This is a 90-degree angle.
Setback = BR + MT DD TWO RAISED DASHES 2024 = 0.250 + 0.064 = 0.314" B RAISED CROSS (Dyed) 5056 T = 0.064" RAISED CIRCLE 7050 M TWO DOTS Monel R = 0.250
PART NUMBER BREAKDOWN
• MS20470 AD 4-7
SETBACK This is a 135-degree open angle. The metal has only been bent 45°.
SB = (BR + MT)K • MS20470 •• AD = (0.250 + 0.064) 0.4121 = 0.130" Type Head Material Diameter Length Code Measured Measured T = 0.064 in 32nds in 16ths of an inch of an inch Length is measured from the SETBACK Length top of the flush head and the R = 0.250 underside of the universal head.
SETBACK This is a 45-degree closed angle.
Setback = (BR + MT)K = (0.250 + 0.064)2.4142 = 0.758" FIGURE 4-3. Methods of determining setback for bends other than 90 degree.
Countersunk head rivets (MS20426 supersedes AN426 100-degree) are used where a smooth finish is desired. The 100-degree countersunk head has been adopted as the standard in the United States.
The universal head rivet (AN470 superseded by MS20470) has been adopted as the standard for protruding-head rivets, and may be used as a replacement for the roundhead, flathead, and brazier head rivet. These rivets can also be purchased in half sizes by designating a "0.5" after the main length (i.e., MS20470 AD4-3.5).
FIGURE 4-4. Rivet identification and part number breakdown.
Replace rivets with those of the same size and strength whenever possible. If the rivet hole becomes enlarged, deformed, or otherwise damaged; drill or ream the hole for the next larger size rivet. However, make sure that the edge distance and spacing is not less than minimums listed in the next paragraph. Rivets may not be replaced by a type having lower strength properties, unless the lower strength is adequately compensated by an increase in size or a greater number of rivets. It is acceptable to replace 2017 rivets of 3/16 inch diameter or less, and 2024 rivets of 5/32 inch diameter or less with 2117 rivets for general repairs, provided the replacement rivets are 1/32 inch greater in diameter than the rivets they replace.
Par 4-57 Page 4-119
Par 4-57 Page 4-120 TABLE 4-8. Aircraft rivet identification.
Material 1100 2117T 2017T 2017T-HD 2024T 5056T 7075-T73 Head Marking Plain Dimpled Raised Dot Raised Dot Raised Double Dash Raised Cross Three Raised Dashes
AN Material Code
A AD D D DD B AN425 78º Counter- Sunk Head
X X X X X X
AN426 100º Counter- Sunk Head MS20426
X X X X X X X
AN427 100º Counter- Sunk Head MS20427
AN430 Round Head MS20470
X X X X X X X AN435 Round Head MS20613 MS20615
AN 441 Flat Head
AN 442 Flat Head MS20470
X X X X X X X
AN 455 Brazier Head MS20470
X X X X X X X
AN 456 Brazier Head MS20470
X X X X X X X
AN 470 Universal Head MS20470
X X X X X X X Heat Treat Before Using No No Yes No Yes No No Shear Strength psi 10000 30000 34000 38000 41000 27000 Bearing Strength psi 25000 100000 113000 126000 136000 90000
Par 4-57 Page 4-121 TABLE 4-8. Aircraft rivet identification. (continued) Material Carbon Steel Corrosion- Resistant Steel Copper Monel Monel Nickel- Copper Alloy Brass Titanium Head Marking Recessed Triangle Recessed Dash Plain Plain Recessed Double Dots Plain Recessed Large and Small Dot
AN Material Code
F C M C AN425 78º Counter- Sunk Head
AN426 100º Counter- Sunk Head MS20426 MS 20426 AN427 100º Counter- Sunk Head MS20427
X X X X AN430 Round Head MS20470
AN435 Round Head MS20613 MS20615 X MS20613 X MS20613 X X MS20615 X MS20615
AN 441 Flat Head
X X X X AN 442 Flat Head MS20470
AN 455 Brazier Head MS20470
AN 456 Brazier Head MS20470
AN 470 Universal Head MS20470
Heat Treat Before Using No No No No No No No Shear Strength psi 35000 65000 23000 49000 49000 95000 Bearing Strength psi 90000 90000
Par 4-57 Page 4-122 Rivet edge distance is defined as the distance from the center of the rivet hole to the nearest edge of the sheet.
Rivet spacing is the distance from the center of the rivet hole to the center of the ad jacent rivet hole. Unless structural deficiencies ar e suspected, the rivet spacing and edge distance should duplicate those of the original aircraft structure. If st ructural deficiencies are suspected, the following may be used in determining minimum edge distance and rivet spacing.
For single row rivets, the edge distance should not be less than 2 times the diameter of the rivet and spacing should not be less than 3 times the diameter of the rivet.
For double row rivets, the edge distance and spacing should not be less than the minimums shown in figure 4-5.
For triple or multiple row rivets, the edge distance and spacing should not be less than the minimums shown in figure 4-5.
The 2117 rivets may be driven in the condition received, but 2017 rivets above 3/16 inch in diameter and all 2024 rivets are to be kept packed in dry ice or refrigerated in the “quenched” condition until driven, or be reheat treated just prior to driving, as they would otherwise be too hard for satisfactory riveting.
Dimensions for formed rivet heads are shown in figure 4-6(a), together with commonly found rivet imperfections.
When solid shank rivets are impractical to use, then special fasteners are used. Special fastening systems used for aircraft construction and repair are divided into two types, special and blind fa steners. Special fasteners are sometimes designed for a specific purpose in an aircraft structure. The name “special fasteners” refers to its job requirement and the tooling needed for in stallation. Use of special fasteners may require an FAA field approval.
Blind rivets are used when there is access to only one side of the structure. Typically, the locking characteristics of a blind rivet is not as good as a driven rivet. Therefore, blind rivets are usually not used when driven rivets can be installed.
CAUTION: Blind rivets should not be used on floats or amphibian hulls below the water line.
Self plugging friction-lock cherry rivets. This patented rivet may be installed when there is access to only one side of the structure. The blind head is formed by pulling the tapered stem into the hollow shank. This swells the shank and clamps the skins tightly together.
When the shank is fully upset, the stem pulls in two. The stem does not fracture flush with the rivet head and must be trimmed and filed flush for the installation to be complete.
Because of the friction-locking stem, these rivets are very sensitive to vibrations.
Inspection is visual, with a loose rivet standing out in the standard “smoking rivet” pattern.
Removal consists of punching out the frictionlocked stem and then treating it like any other rivet. (See figure 4-7.)
Mechanical-lock rivets have a device on the puller or rivet head which locks the center stem into place when installed. Many frictionlock rivet center stems fall out due to vibrations; this in turn, greatly reduces its shear strength. The mechanical-lock rivet was developed to prevent that problem.
Various manufacturers make mechanical-lock fasterners such as: Bulbed Cherrylock, CherryMax, Olympic-Loks, and Huck-Loks.
STRENGTH THROUGH THIS SECTION IS 75% OF SHEET WITHOUT HOLES.
D = DIAMETER OF 40 RIVET (PREFER- ABLY ABOUT 3x
THICKNESS OF
THICKER SHEET) 2D →4Dx - 20 (A) DOUBLE ROW
CAN DO TA SA NOTES WITHOUT HOLES..
6D 30 20-→ * 20 (B) TRIPLE OR MULTIPLE ROWS FIGURE 4-5. Rivet hole spacing and edge distance for single-lap sheet splices.
Par 4-57 Page 4-123
(a) DIMENSIONS FOR FORMED RIVET HEADS.
-1ž0 65D (ID MIN.) (MIN.) (=D MIN.)
(b) RIVETING TOOLS
CORRECT
INCORRECT SHAPE FOR
RIVET SNAP OR SET.
BUCKING BAR OR DOLLY.
(C) RIVET IMPERFECTIONS.
RIVET DRIVEN AT SLANT, RIVET DRIVEN RIVET FLAT ON ONE
CORRECTLY, DOLLY SIDE OR DOLLY HELD HEAD AT SLANT. FLAT.
BODY OF RIVET TOO SHORT. CLOSING HEAD RIVET NOT PULLED TIGHT, CLINCHES BULGED ON ACCOUNT RIVET TIGHT, PLATES SHAPED TOO MUCH BETWEEN PLATES, OF POOR FIT.
WITH SNAP DIE. CLOSING HEAD TOO FLAT.
RIVETED TOO MUCH. RIVET BODY CLINCHED TOO MUCH, HEAD CRACKED.
PLATES CLINCHED AT RIVET MATERIAL TOO AND DRIVEN APART. HARD WHEN RIVETING TOOL FORMED.
DAMAGED PLATE FIGURE 4-6. Riveting practice and rivet imperfections.
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FIGURE 4-7. Self plugging friction-lock Cherry rivets.
Bulbed Cherrylock Rivets. One of the earlier types of mechanical-lock rivets developed were Bulbed Cherrylock blind rivets. These blind rivets have as their main advantage the ability to replace a solid shank rivet size for size. (See figure 4-8.)
A Bulbed Cherrylock consists of three parts;
a rivet shell, a puller, and a lockring. The puller or stem has five features which are activated during installation; a header, shank expanding section, lockring indent, weak or stem fracture point, and a serrated pulling stem. Carried on the pulling stem, near the manufactured head, is the stem lockring. When the rivet is pulled the action of the moving stem clamps together the sheets of metal and swells the shank to fill the drilled hole. When the stem reaches its preset limit of travel, the upper stem breaks away (just above the lockring) as the lockring snaps into the recess on the locking stem. The rough end of the retained stem in the center on the manufactured head must never be filed smooth, because it will weaken the strength of the lockring and the center stem could fall out. (See figure 4-8.)
The Bulbed Cherrylock rivets are available in two head styles: universal and 100° countersunk. Their lengths are measured in increments of 1/16 inch. It is important to select a rivet with a length related to the grip length of the metal being joined.
The Bulbed Cherrylock rivet can be installed using a G35 cherry rivet hand puller or a pneumatic Bulbed Cherrylock pulling tool.
The CherryMax (see figure 4-9) rivet uses one tool to install three standard rivet diameters and their oversize counterparts. This makes the use of CherryMax rivets very popular with many small general aviation repair shops.
CherryMax rivets are available in four nominal diameters 1/8, 5/32, 3/16, and 1/4 inch and three oversized diameters. CherryMax rivets are manufactured with two head styles, universal and countersunk. The CherryMax rivets consists of five parts; bulbed blind header, hollow rivet shell, locking (foil) collar, driving anvil, and pulling stem. The blind bulbed header takes up the extended shank and forms the bucktail on a CherryMax rivet stem. Rivet sleeves are made from 5056 aluminum, monel, and INCO 600. The stems are made from alloy steel, CRES, and INCO X-750 stem. CherryMax rivets have an ultimate shear strength ranging from 50 KSI to 75 KSI.
An Olympic-Lok (see figure 4-10) rivet is a light three-piece mechanically locked, spindle-type blind rivet. It carries its stem lock integral to the manufactured head. While installing, the lockring is pressed into a groove on the pulling stem just as the rivet completes drawing the metal together. After installation is completed, never file the stem of an Olympic-Lok rivet, because it will weaken the lockring attachment. The Olympic-Lok fastener is available in three head styles:
- STEM
STEM IS PULLED
COLLAR LOCKING BEFORE PULLING INTO RIVET SLEEVE AND STARTS TO FORM BULB BLIND HEAD BEGINS RIVET HEAD SHEET GAP > CLAMP-UP AND
HOLE FILL
ACTION BEGIN SHEAR RING
FORMATION OF BLIND
CLAMP-UP COMPLETED HEAD AND HOLE FILLING
AS STEM CONTINUES TO ARE COMPLETED
BULB OUT BLIND HEAD
SHEAR RING NOW SHEARS
FROM STEM CONE TO ALLOW
STEM TO PULL FURTHER INTO
RIVET HEAD RIVET
FIRMLY SEATED
BLIND SIDE BULB HEAD
- IS FORMED BELOW SHEAR RING GUARANTEES
MINIMUM GRIP BLIND SIDE BULBED HEAD (IN MINIMUM GRIP SHEAR
RING MAY NOT SHEAR)
SHEAR RING HAS MOVED
DOWN STEM CONE UNTIL
PULLING HEAD AUTOMATICALLY STOPS STEM BREAK NOTCH COMPLETELY INSTALLED BULBED CHERRYLOCK
FLUSH WITH TOP OF
RIVET HEAD
PULLING HEAD HAS
LOCKING COLLAR IS NOV INSERTED LOCKING
READY TO BE INSERTED COLLAR AND STEM
HAS FRACTURED FLUSH
WITH RIVET HEAD (MAXIMUM GRIP
BLIND SIDE ILLUSTRATED)
BULBED HEAD FIGURE 4-8. Mechanical-lock (Bulbed Cherrylock) Cherry rivet.
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F IGURE 4-9. CherryMax rivet.
universal protruding, 100-degree flush countersink, and 100-degree flush shear; and three diameters 1/8, 5/32, and 3/16 inch. The three di ameters are available in eight different alloy combinations of 2017-T4, A-286, 5056, and monel. Olympic-Lok lock spindles are made from the same material as the sleeves.
Huck rivets (see figure 4-11) are available in two head styles, protruding and flush. They are available in four diameters 1/8, 5/32, 3/16, and 1/4 inch. Their diameters are measured in increments of 1/32 inch and lengths are measured in 1/16 inch increments. They are manufactured in three different combinations of alloys: 5056 aluminum sleeve with 2024 aluminum alloy pin, A-286 corrosion-resistant steel sleeve with an A-286 pin, and a monel 400 sleeve with an A-286 pin. The Huck fastener has the ability to tightly draw-up two or more sheets of metal together while being installed. After the take-up of the Huck fastener is completed, the lockring is squeezed into a groove on the pulling stem. The anvil or footer (of the installation tool) packs the ring into the groove of the pulling stem by bearing against the lockring.
Common pull-type Pop rivets, produced for nonaircraft related applications, are not approved for use on certificated aircraft structures or components.
Design a new or revised rivet pattern for strength required in accordance with one of the following:
The aircraft manufacturer’s maintenance manuals.
The techniques found in structural text books and using the mechanical properties found in MIL-HDBK-5.
The specific instructions in paragraphs 4-58g through 4-58n. When following the instruction in paragraphs 4-58g through 4-58n, the general rule for the diameter of the rivets used to join aluminum sheets is to use a diameter approximately three times the thickness of the thicker sheet. Do not use rivets where they would be placed in tension, tending to pull the heads off; and backup a lap joint of thin sheets with a stiffener section.
SLEEVE REDUCED INTERNAL DIAMETER TO DOUBLE
PRECISELY ALIGN THE LOCKING GROOVE TAPER DESIGN
FULLY SERRATED STEM CONTINUOUS INTEGRAL
FOR INCREMENTAL PULL-UP LOCKING COLLAR RV 1201 SERIES
COUNTERSUNK
HEAD STYLE 1/16 INCH GRIP VARIATION CAPABILITY
DESIGNED INTO FASTENER
LARGER SECOND SHANK RV 1200 SERIES FLUSH BREAKING STEM DIAMETER FOR EXTRA
PROTRUDING SLEEVE EXPANSION AND
HEAD STYLE GREAT BLIND-SIDE
BEARING AREA
GREATER LOCKING COLLAR VOLUME PROTRUDING HEAD
DRIVEN INTO LOCKING GROOVE UNDERCUT ELIMINATES
DEBURRING When the stem travel is Continued pulling breaks Olympic-Lok blind rivet is Tool jaws grip the stem and stopped by the sleeve's inter- the stem flush to the fasteninserted into a prepared pull it into the sleeve, closing nal step, the integral locking er head. Flushness is hole. Note the clearance the sheet gap, expanding the collar shears free and is assured by the positioning between the rivet and the sleeve to fill the hole, and forced into the stem locking of the break-groove when sides of the hole and the forming a consistently larger groove. This forms a stem travel is stopped by gap between the sheets. blind side bearing area. permanent mechanical lock. the sleeve's internal step.
FIGURE 4-10. Olympic-Lok rivet.
REPAIR METHODS AND PRECAUTIONS FOR ALUMINUM STRUCTURE. Carefully examine all adjacent rivets outside of the repair area to ascertain that they have not been harmed by operations in adjacent areas. Drill rivet holes round, straight, and free from cracks. Deburr the hole with an oversize drill or deburring tool.
The rivet-set used in driving the rivets must be cupped slightly flatter than the rivet head. (See figure 4-6.) Rivets are to be driven straight and tight, but not overdriven or driven while too hard, since the finished rivet must be free from cracks. Information on special methods of riveting, such as flush riveting, usually may be obtained from manufacturer's service manuals.
Splicing of Tubes. Round or streamline aluminum alloy tubular members may be repaired by splicing (See figure 4-12.) Splices in struts that overlap fittings are not acceptable. When solid rivets go completely through hollow tubes, their diameter must be at least one-eighth of the outside diameter of the outer tube.
Rivets which are loaded in shear should be hammered only enough to form a small head and no attempt made to form the standard roundhead. The amount of hammering required to form the standard roundhead often causes the rivet to buckle inside the tube. (Correct and incorrect examples of this type of rivet application are incorporated in figure 4-12.)
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