types: the H615 (figure 5-61) and H640 (figure Cherrylock mechanical pulling heads are of two DIAMETER PULLING HEAD NUMBER DIMENSIONS 5-62) series. They differ only in their method of 3/32" H681-3€ / Universal Head .188 346 attachment to the riveter. The H615 series is for H681-4C / Universal Hea ( Countersunk Heat .163 .331 _359 the smaller screw-on type tools and the H640 is for H681-B166-4 Uni-Sink Head I Countersunk Hea 250 install bulbed and wiredraw Cherrylock rivets. the larger clip-on type. Both pulling heads will 5/38" H681-B166-5 Uni-Sink Head +68)-SC {Countersunk Hea rUnwersal Hea 313 .313 .269 M681-5C 1 Countersunk Head Universal Head 375 .415 3716" 335 H681-8166-6 Uni-Sink Head 375 .419 1/9 MGB1-BC Countersunt Head .458 .500 452 398 FICURE 5-63. H681 Series pulling head tool.
RIVET Cherrylock Hydroshift Tooling DIAMETER PULLING HEAD NUMBER The hydroshift tooling system is an advanced 1/8' H615-4C | Countersunk Hea Universal Head design in which the sequence of operations neces- sary to install the rivet is accomplished hydraulic- H615-4S Uni-Sink Head ally within the hydroshift tool rather than by means 5/32' H615-5C% Countersunk Hea ¿ Universal Head of a mechanical pulling head Cherrylock hydroshift pulling heads are of one H615-5S Uni-Sink Head type only, the H681 (figure 5-63).
3/16" 1615-6C1 Countersunk Heal Universal Head stall each diameter Cherrylock rivet. A separate H681 pulling head is required to in- Separate H615-6S Uni-Sink Head pulling heads are recommended for universal and countersunk head rivets but countersunk pulling FIGURE 5-61. H615 Series pulling head tool. heads may be used for both styles.
A separate pulling head is required to install each diameter Cherrylock rivet. Separate pulling heads are recommended for universal and countersunk head rivets but countersunk pulling heads may be used, for both styles.
Hydroshift riveters are factory adjusted to break the rivet stem flush and set the collar properly. Fine adjustments to the shift point setting can be made by the operator. This adjustment determines the flushness of the break of the rivet stem (figures 5-64 and 5-65).
Installation Procedures Procedures for installing self-plugging (mechanical lock) rivets are basically the same as those used for installing the friction lock type of rivets. Precautions to be observed are:
(1) Be sure the correct grip range is selected.
DIAMETER RIVET PULLING HEAD NUMBER 1/8" 1640-4CL Countersunk Hea universal neat H640-4S Uni-Sink Head 5/32' H640-5C1 Countersunk Head • Universal Head H640-5S Uni-Sink Head 3/16" 1640-5C1 Countersunk Hea nonversa, Heat Adjuster Knob H640-6S Uni-Sink Head 1/4" H640-8C1 Countersunk Hear Universal Head Limit Pin FIGURE 5-62. H640 Series pulling head tool. FIGURE 5-64. H681 pulling head adjuster.
1 File a small flat on rivet head Note Do steps 1, 2, and 3 only if rivet is in a thin or resilient material.
2 Centerpunch flat 3 Drill off tapered portion of pin which forms the lock 4 Shear lock by driving out pin FIGURE 5-65. Hydroshift pulling tool.
(2) Always use the correct nose assembly or pulling tool for the diameter rivet selected.
(For the CKL rivet, check the tool air 5 Pry out remainder pressure for the correct setting.) of locking collar
(3) When inserting the rivet in the tool and the material, hold a slight pressure against the head of the rivet.
(4) Determine that the rivet is completely driven before lifting the tool from the 6 Drill almost rivet head. (The stem should snap.) through rivet head
(5) Check each rivet after the driving sequence has been completed for proper 7 Pry off stem breakage. (The rivet stem should rivet head snap off even with the head of the rivet.)
Inspection Visual inspection of the seating of the pin in the.
manufactured head is the most reliable and simplest means of inspection for mechanical lock rivets. If the proper grip range has been used and the locking collar and broken end of the stem are approximately flush with the manufactured head, the rivet 8 Tap shank out with pin has been properly upset and the lock formed. Insufficient grip length is indicated by the stem breaking below the surface of the manufactured head. Excessive grip length is indicated by the stem breaking FIcURE 5-66. Rivet removal.
off well above the manufactured head. In either case, the locking collar might not be seated properly, thus forming an unsatisfactory lock.
Removal Procodures The mechanical lock rivet can easily be removed by following the procedures illustrated in figure
5-66.
PULL-THRU RIVETS squeezed, and the mandrel crank is turned clockwise after each stroke. Continue squeezing the handle and turning the mandrel crank of the heading tool until you feel a solid resistance, indicating that the rivet is set.
Mandrel crank This type of blind mechanically expanded rivet is used as a tacking rivet to attach assemblies to hollow tubes, and as a grommet. It differs from the two previously discussed rivets in that the stem pulls completely through the sleeve of the rivet during installation. Pull-thru rivets are structurally weak Movable because of the hollow center after installation is handle completed. Methods and procedures for installation, inspection, and removal are not discussed here because of the limited use for this type rivet in the airframe field. Figure 5-67 illustrates a typical pull-thru rivet before and after installation.
Threaded mandrel FIGURE 5-68. Rivnut heading tool.
Before installation After installation FIGURE 5-67. Pull-thru rivet.
RIVNUTS Rivnut is the trade name of a hollow blind rivet made of 6053 aluminum alloy, counterbored and threaded on the inside. Rivnuts are installed by one person using a special tool which heads the rivet on the blind side of the material (figure 5-68). The Rivnut is threaded on the mandrel of the heading tool and inserted in the rivet hole. The heading tool is held at right angles to the material; the handle is All Rivnuts, except the thin head (0.048 in.)
countersunk type, are available with or without small projections (keys) attached to the head to keep the Rivnut from turning. Keyed Rivnuts are used for service as a nut plate, whereas those without keys are used for straight blind riveting repairs where no torque loads are imposed. A keyway cutter is needed when installing Rivnuts which have keys (figure 5-69).
Tools used in the installation of Rivnuts include the hand-operated heading tools, the pneumatic power Rivnut driver, and the keyway cutter. All heading tools have a threaded mandrel onto which the Rivnut is threaded until the head of the Rivnut is against the anvil of the heading tool.
Hand-operated heading tools are made in three types: (1) Straight, (2) 45°, and (3) 90°. The pneumatic power driving tools are made in two types: (1) Lever throttle and (2) offset handle.
With the power tool, the threading, upsetting, and withdrawal or unthreading, are accomplished by compressed air through the manipulation of finger- 184
Radial dash marks Keyed Rivnut FIGURE 5-69. Keyed Rivnut and keyway cutter.
tip controls. The keyway cutter is for cutting keyways only. In some instances, the keyway cutter cannot be used because the material may be too thick. If such is the case, use a small round file to form the keyway.
The important factors to be considered in selecting Rivnuts are grip range, style of head, condition of Rivnut end, and the presence or absence of a key.
Proper grip length is the most important of these conditions. The grip range of a Rivnut can be determined from its number. For example, a 6-45 has a maximum grip of 0.45 in. Note the procedure to follow when determining the grip range. The total thickness of the sheets shown in figure 5-70 is
0.052 in. By referring to the Rivnut data chart in figure 5-70, we see that 6-75 is the grip length to choose since the maximum grip length of the preceding size (6-45) is only 0.045 in. and would be too short. The grip length of the 6-75 Rivnut actually ranges from 0.045 in., the maximum length of the preceding size (6-45), to 0.075 in., which is the maximum grip length of the 6-75 Rivnut.
The objective when installing this. type of rivet is to produce an ideal bulge on the blind side of the work without distorting any of the threads inside the Rivnut. In other words, be sure the bulge takes place between the first thread of the rivet and the lower edge of the riveted material. The space between the ideal bulge and the upper thread, where the gripping takes place, is considered the grip range.
When selecting head style, apply the same rules as for solid shank rivet application. Select key-type Rivnuts whenever screws are to be inserted, and use closed-end Rivnuts only in special places, such as sealed compartments of floats or pressurized compartments.
Drilling the holes for Rivnuts requires the same precision as for solid shank rivets. The shank of the Rivnut must fit snugly in the hole. To obtain the best results for a flathead installation, first drill a pilot hole smaller than the shank diameter of the Rivnut and then ream it to the correct size.
If keyed Rivnuts are used, cut the keyway after the hole has been reamed. In cutting the keyway, hold the keyway cutter so that it makes a 90° angle with the work. Also, cut the keyway on the side of the hole away from the edge of the sheet, especially when the Rivnut is used on the outside row. Operate the keyway cutter by inserting it in the hole and squeezing the handles.
The use of flush Rivnuts is limited. For metal which has a thickness greater than the mimum grip length of the first rivet of a series, use the machine countersink; for metal thinner than the minimum grip length of the first rivet, use the dimpling process. Do not use the countersunk Rivnut unless the metal is thick enough for machine countersinking, or unless the underside is accessible for the dimpling operation.
For a countersunk Rivnut the sheets to be joined can usually be machine countersunk. This method is preferred because the bearing surface in a dimpled hole in one sheet of average gage will normally occupy the entire gripping surface of the Rivnut, thus limiting its grip range to that of an anchored nut only.
When installing Rivnuts, among the things to check is the threaded mandrel of the heading tool to see that it is free from burrs and chips from the previous installation. Then screw the Rivnut on the mandrel until the head touches the anvil. Insert the Rivnut in the hole (with the key positioned in the keyway, if a key is used) and hold the heading tool at right angles to the work. Press the head of the 185
Flat 0.32 Head Thickness 6-45 6-75 5-10 8-45 8-75 8-10 10-45 10-75 10-100 6845 6875 68100 8B45 8B75 88100 10845 10875 10B100 6K45 6K75 6K100 8K45 8K75 8K100 10K45 1.0K75 10K100 6KB45 6KB75 6KB100 .052 10KB45 8KBA5 10KB75 8KB75 10KB100 8KB100
1.075 Max. 100°-0.48 Head Thickness 6-91 6-121 6-146 8-91 8-121 8-146 ..045 Min. 10-91 6891 10-121 68121 10-146 68146 8891 8B121 8B146 10891 108121 108146 100°-0.63 Head Thickness 6-106 6-136 6-167 8-106 8-136 8-761 10-106 10-136 10-161 68106 6B136 68161 88106 8B136 88161 108106 108136 108161 6K106 6K136 6K161 8K106 8K136 8K167 10K106 10K136 10K16!
6KB106 6KB136 6KB161 8KB106 8KB136 8KB167 10KB106 10KB136 10K8161 FIcURE 5-70. Determining Rivnut grip length.
Rivnut tightly against the sheet while slowly squeezing the handles of the heading tool together until the Rivnut starts to head over. Then release the handle, and screw the stud further into the rivnut.
This prevents stripping the threads of the Rivnut before it is properly headed. Again squeeze the handles together until the Rivnut heading is complete. Now remove the stud of the heading tool from the Rivnut by turning the crank counterclockwise.
The action of the heading tool draws the Rivnut against the anvil, causing a bulge to form in the counterbored portion of the Rivnut on the inaccessible side of the work. This bulge is comparable to the shop head on an ordinary solid shank rivet. The amount of squeeze required to head the Rivnut properly is best determined by practice. Avoid stripping the thread in the Rivnut.
The installation of a Rivnut is incomplete unless it is plugged either with one of the plugs designed for that purpose or with a screw used for attaching purposes. A Rivnut does not develop its full strength when left hollow.
Three types of screw plugs can be used: (1) The 100° countersunk screw plug, (2) the headless screw plug, and (3) the thin ovalhead screw plug.
The 100° countersunk and the headless screw plugs have either a Phillips or a Reed and Prince recess.
The oval head either has a common screwdriver slot, a Phillips, or a Reed and Prince recess. All screw plugs are made of high tensile strength SAE steel and are cadmium plated.
The same tools are used for installation of the splined Rivnut as for installation of the standard types, but the pullup stud of the heading tool must be adjusted to accommodate the longer shank.
DILL LOK-SKRUS AND LOK-RIVETS Dill Lok-Skru and Lok-Rivet are trade names for internally threaded rivets (two piece). They are used for blind attachment of such accessories as fairings, fillets, access door covers, door and window frames, floor panels, and the like. Lok-Skrus and Lok-Rivets are similar to the Rivnut in appearance and application. Lok-Skrus and Lok-Rivets, however, come in three parts and require more clearance on the blind side than the Rivnut to accommodate the barrel.
Special hand- and air-operated power tools are required for installation of Lok-Skrus. An interchangeable barrel blade fits into the blade handle and is held in place by a set screw. The barrel 186
blade has a flattened portion which fits into a slot in the end of the Lok-Skru barrel. The head driver has projections which fit into recesses in the Lok- Skru head. Head drivers and blades are interchangeable for use with various sizes and styles of Lok-Skrus.
The drilling procedure for Lok-Skrus is identical to that for common solid shank rivets. To install the Lok-Skru, insert the Lok-Skru tool so that the blade extends through the barrel slot and the driver sets firmly in the head slot. Insert the fastener in the drilled hole. Fit the ratchet handle assembly together and adjust the pawl lever for proper ratchet direction. Hold the ratchet handle stationary and turn the barrel blade handle to the left until the barrel is drawn firmly against the sheet on the opposite side. Press the tool firmly against the Lok- Skru to hold the tool blade and driver in the slots.
Stop turning the barrel handle when the Lok- Skru barrel has been drawn against the sheet. Finally, tighten by an additional quarter turn or less on the ratchet handle, drawing the head into the sheet. This time, hold the blade handle stationary while turning the ratchet handle. Test the tightness of the installation with an ordinary 8-in. screwdriver which has been ground round on the end.
Attachments are made by using the attaching screw and a regular screwdriver.
DEUTSCH RIVETS The Deutsch rivet is a high-strength blind rivet with a minimum shear strength of 75,000 p.s.i. and can be installed by one man. This rivet consists of two parts, a stainless steel sleeve and a hardened steel drive pin. The pin and sleeve are coated with a lubricant and a corrosion inhibitor.
A Deutsch rivet may be driven with an ordinary hammer or a pneumatic rivet gun and a flathead set.
Seat the rivet in the previously drilled hole and then drive the pin into the sleeve. If the Deutsch rivet is driven into a tight hole, a hollow drift punch should be used to seat the rivet against the material. The punch should clear the drive pin and rest against the head of the rivet to prevent premature expansion of the sleeve and head.
The driving action causes the pin to exert pressure against the sleeve and forces the sides of the sleeve out. This stretching forms a shop head on the end of the rivet and provides a positive fastening action for the fastener. The ridge on the top of the rivet head locks the pin into the rivet as the last few blows are struck.
The head of the Deutsch rivet should never be shaved or milled. Milling or shaving will destroy the locking action of the ring on top of the rivet head.
Another feature of the Deutsch rivet is that it can be installed without going all the way through the second piece of material. However, this type of installation is not recommended unless the second piece is very thick.
One of the main restrictions to the use of the Deutsch rivet is that no bucking tool is used to take up the shock of driving. The structure where installation is made must be heavy and solid enough to support the driving forces.
If a Deutsch rivet that extends through the material is to be removed, use the same procedures used to remove a solid shank rivet. The head can be drilled off, and the pin can be driven out with a drift punch slightly smaller than the diameter of the drive pin. To drive the sleeve out of the material, use a drive punch slightly smaller than the diameter of the sleeve.
If the rivet does not extend through the material, drill out the drive pin to approximately one-half its depth. Then tap the hole and finish drilling out the remainder of the pin. Next, insert a screw through a spacer and tighten the screw into the sleeve. Continue tightening the screw until the sleeve is removed.
HI-SHEAR RIVETS Hi-Shear pin rivets are essentially threadless bolts. The pin is headed at one end and is grooved about the circumference at the other. A metal collar is swaged onto the grooved end, effecting a firm tight fit.
The proper length rivet may be determined by part number or by trial. Part numbers for pin rivets can be interpreted to give the diameter and grip length of the individual rivets. A typical part number and an explanation of the terms are discussed in Chapter 6, Hardware, Materials, and Processes, in the Airframe and Powerplant Mechanics General Handbook, AC 65-9A.
To determine correct grip length by trial, insert the correct diameter rivet in the hole. The straight portion of the shank should not extend more than 16 in. through the material, insert the correct diameter rivet in the hole. The straight portion of the shank should not extend more than 16 in. through the material. Place a collar over the grooved end of the rivet. Check the position of the collar.
The collar should be positioned so that the shearing edge of the pin groove is just below the top of the collar. It is permissible to add a 0.032-in. (approximately) steel washer between the collar and the material to bring the collar to the desired location.
The washer may be positioned on the rivet head side of the material when using a flathead rivet.
Hi-Shear rivets are installed with standard bucking bars and pneumatic riveting hammers. They require the use of a special gun set that incorporates collar swaging and trimming and a discharge port through which excess collar material is discharged. A separate size set is required for each shank diameter.
Prepare holes for pin rivets with the same care as for other close tolerance rivets or bolts. At times, it may be necessary to spot-face the area under the head of the pin so that the head of the rivet can fit tightly against the material. The spot-faced area should be 1e in. larger in diameter than the head diameter.
Pin rivets may be driven from either end. Procedures for driving a pin rivet from the collar end are:
(1) Insert the rivet in the hole.
(2) Place a bucking bar against the rivet head.
(3) Slip the collar over the protruding rivet end.
(4) Place previously selected rivet set and gun over the collar. Align the gun so that it is perpendicular to the material.
(5) Depress the trigger on the gun, applying pressure to the rivet collar. This action will cause the rivet collar to swage into the groove on the rivet end.
(6) Continue the driving action until the collar is properly formed and excess collar material is trimmed off. (See figure 5-71.)
Procedures for driving a pin rivet from the head end are:
(1) Insert the rivet in the hole.
(2) Slip the collar over the protruding end of rivet.
(3) Insert the correct size gun rivet set in a bucking bar and place the set against the collar of the rivet.
(4) Apply pressure against the rivet head with a flush rivet set and pneumatic riveting hammer.
(5) Continue applying pressure until the Hi-Shear rivet set insert stud and place bar against head.
Slip collar over stud and place gun set against collar.
Apply pressure (collar begins to deform).
Apply pressure until collar is trimmed.
Remove bar and set.
FIcURE 5-71. Using pin rivet set.
collar is formed in the groove and excess collar material is trimmed off.
inspection Pin rivets should be inspected on both sides of the material. The head of the rivet should not be marred and should fit tightly against the material.
Figure 5-72 illustrates acceptable and unacceptable rivets.
Removal of Pin Rivets The conventional method of removing rivets by drilling off the head may be utilized on either end of the pin rivet (figure 5-73). Center punching is recommended prior to applying drilling pressure. In some cases alternate methods may be more desirable for particular instances.
Grind a chisel edge on a small pin punch to a blade width of ⅛ in. Place this tool at right angles to the collar and drive with a hammer to split the collar down one side. Repeat the operation on the opposite side. Then, with the chisel blade, pry the collar from the rivet. Tap the rivet out of the hole.
Use a special hollow punch having one or more 188
Acceptable rivets Protective shoulder Broken edge 1/32-inch maximum resisting overdrive Normal Slightly overdriven Occurs in maximum grip Unacceptable rivets Drive until collar trims More than 1/32-inch Underdriven collar - Do not remove, but continue driving until collar trims, Overdriven collar - Remove.
Pin too long - Remove Pin too short - Remove.
FICURE 5-72. Pin rivet inspection.
blades placed to split the collar. Pry the collar from the groove and tap out the rivet.
Grind a pair of nippers so that cutting blades will cut the collar in two pieces, or use nippers at right angles to the rivet and cut through the small neck.
A hollow-mill collar cutter can be used in a power hand drill to cut away enough collar material to permit the rivet to be tapped out of the work.
SPECIFIC REPAIR TYPES Before discussing any type of a specific repair that could be made on an aircraft, remember that the methods, procedures, and materials mentioned in the following paragraphs are only typical and should not be used as the authority for the repair.
When repairing a damaged component or part, consult the applicable section of the manufacturer's structural repair manual for the aircraft, Normally, a similar repair will be illustrated, and the types of material, rivets, and rivet spacing and the methods and procedures to be used will be listed. Any addi- 189
* Line of stress 1 Drill off head or collar.
•- Trimmed hole 2 Tap rivet out with punch.
Removing from head end Draw parallel lines 1 Split coLar with 1/8-1nch chisel and pry collar off.
2-1/2 D
2. Tap rivet out with hammer Locate lines Effective Effective area area B. Removing from collar end FICURE 5-73. Removal of pin rivets.
tional knowledge needed to make a repair will also - P be detailed.
If the necessary information is not found in the structural repair manual, attempt to find a similar repair or assembly installed by the manufacturer of Locate rivets the aircraft.
2-1/2 D Smooth Skin Repair Added rivet radius Minor damage to the outside skin of an aircraft can be repaired by applying a patch to the inside of the damaged sheet. A filler plug must be installed in the hole made by the removal of the damaged skin area. It plugs the hole and forms a smooth outside surface necessary for aerodynamic smoothness of modern day aircraft.
The size and shape of the patch is determined in general by the number of rivets required in the repair. If not otherwise specified, calculate the required number of rivets by using the rivet formula.
Make the patch plate of the same material as the Draw outline of patch original skin and of the same thickness or of the next greater thickness. FIGURE 5-74. Elongated patch.
Elongated Octagonal Patch Whenever possible, use an elongated octagonal patch for repairing the smooth skin. This type of patch provides a good concentration of rivets within the critical stress area, eliminates dangerous stress concentrations, and is very simple to lay out.
This patch may vary in length according to the condition of the repair.
Follow the steps shown in the paper layout of this patch (figure 5-74). First, draw the outline of the trimmed-out damage. Then, using a spacing of three to four diameters of the rivet to be used, draw lines running parallel to the line of stress. Locate the lines for perpendicular rows two and one-half rivet diameters from each side of the cutout, and space the remaining lines three-fourths of the rivet pitch apart.
Locate the rivet spots on alternate lines perpendicular to the stress lines to produce a stagger between the rows and to establish a distance between rivets (in the same row) of about six to eight rivet diameters. After locating the proper number of rivets on each side of the cutout, add a few more if necessary so that the rivet distribution will be uniform. At each of the eight corners, swing an arc of two and one-half rivet diameters from each corner rivet. This locates the edge of the patch. Using straight lines, connect these arcs to complete the layout.
Round Patch Use the round patch for flush repairs of small holes in smooth sheet sections. The uniform distribution of rivets around its circumference makes it an ideal patch for places where the direction of the stress is unknown or where it is known to change frequently.
If a two-row round patch is used (figure 5-75), first draw the outline of the trimmed area on paper.
Draw two circles, one with a radius equal to the radius of the trimmed area plus the edge distance, and the other with a radius ¾-in. larger. Determine the number of rivets to be used and space twothirds of them equally along the outer row. Using any two adjacent rivet marks as centers, draw intersecting arcs; then draw a line from the point of intersection of the arcs to the center of the patch.
Do the same with each of the other pairs of rivet marks. This will give half as many lines as there are rivets in the outer row. Locate rivets where these ines intersect the inner circle. Then transfer the layout to the patch material, adding regular outer Approx 3/4" transverse -2-1/2 D pitch FIGURE 5-75, Layout of a two-row round patch.
edge material of two and one-half rivet diameters to the patch.
Use a three-row round patch (figure 5-76) if the total number of rivets is large enough to cause a pitch distance smaller than the minimum for a tworow patch. Draw the outline of the area on paper;
then draw a circle with a radius equal to that of the trimmed area plus the edge distance. Equally space one-third of the required number of rivets in this row. Using each of these rivet locations as a center, draw arcs having a ¾-in. radius. Where they intersect, locate the second row rivets. Locate the third row in a similar manner. Then allow extra material of two and one-half rivet diameters around the outside rivet row. Transfer the layout to the patch material.
-Approx 3/4" transverse pitch
• 2-1/2 D FIGURE 5-76. Layout of a three-row round patch.
After laying out and cutting the patch, remove the burrs from all edges. Chamfer the edges of all external patches to a 45° angle and turn them 191
slightly downward so that they will fit close to the of a panel between adjacent stringers and bulksurface (figure 5-77). heads. Where a section of skin is damaged to such an extent that it is impossible to install a standard skin repair, a special type of repair is necessary.
The particular type of repair required depends on whether the damage is reparable outside the mem- Approx 1/64" ber, inside the member, or to the edges of the panel.
Damage which, after being trimmed, has less than eight and one-half manufacturer's rivet diameters of material inside the members requires a patch which extends over the members, plus an extra row of rivets along the outside of the members. For dam- 1-1/4 D age which, after being trimmed, has eight and onehalf rivet diameters or more of material, extend the patch to include the manufacturer's row of rivets 2-1/2 D and add an extra row inside the members. Damage FIGURE 5-77. Chamfering and turning edge. which extends to the edge of a panel requires only one row of rivets along the panel edge, unless the Panel Repair manufacturer used more than one row, The repair In aircraft construction, a panel is any single procedure for the other edges of the damage follows sheet of metal covering. A panel section is the part the previously explained methods.
Repair seam same as strongest parallel adjacent seam Damage Repair seam same as strongest parallel adjacent seam.
Use original holes & add as needed. Trimmed Hole Additional Rivets Radiused Corners Rivet Symbols
• 3/16"
• 5/32"
• 1/8" FIcURE 5-78. Panel skin patch.
The procedures for making all three types of panel repairs are similar. Trim out the damaged portion to the allowances mentioned in the preceding paragraph. For relief of stresses at the corners of the trim-out, round them to a minimum radius of ½ in. Lay out the new rivet row with a transverse pitch of approximately five rivet diameters and stagger the rivets with those put in by the manufacturer. See figure 5-78.
Cut the patch plate from material of the same thickness as the original or the next greater thickness, allowing an edge distance of two and one-half rivet diameters. At the corners, strike arcs having the radius equal to the edge distance. Chamfer the edges of the patch plate for a 45° angle and form the plate to fit the contour of the original structure.
Turn the edges downward slightly so that the edges fit closely.
Place the patch plate in its correct position, drill one rivet hole, and temporarily fasten the plate in place with a fastener. Using a hole finder, locate the position of a second hole, drill it, and insert a second fastener. Then, from the back side and through the original holes, locate and drill the remaining holes. Remove the burrs from the rivet holes and apply corrosion protective material to the contacting surfaces before riveting the patch into place.
Stringer Repair The fuselage stringers extend from the nose of the aircraft to the tail, and the wing stringers extend from the fuselage to the wing tip. Surface control stringers usually extend the length of the control surface. The skin of the fuselage, wing, or control surface is riveted to stringers.
Stringers may be damaged by vibration, corrosion, or collision. Damages are classified as negligible, damage reparable by patching, and damage necessitating replacement of parts. Usually the damage involves the skin and sometimes the bulkhead or formers. Such damage requires a combination of repairs involving each damaged member.
Because stringers are made in many different shapes repair procedures differ. The repair may require the use of preformed or extruded repair material, or it may require material formed by the airframe mechanic. Some repairs may need both kinds of repair material.
When repairing a stringer, first determine the extent of the damage and remove the rivets from the surrounding area. Then remove the damaged area by using a hacksaw, keyhole saw, drill, or file.
In most cases, a stringer repair will require the use of an insert and splice angle. When locating the splice angle on the stringer during repair, be sure to consult the applicable structural repair manual for the repair piece's position. Some stringers are repaired by placing the splice angle on the inside, whereas others are repaired by placing it on the outside.
Extrusions and preformed materials are commonly used to repair angles and insertions or fillers.
If repair angles and fillers must be formed from flat sheet stock, use the brake. It may be necessary to use bend allowance and sight lines when making the layout and bends for these formed parts. For repairs to curved stringers, make the repair parts so that they will fit the original contour.
When calculating the number of rivets to be used in the repair, first determine the length of the break. In bulb-angle stringers, the length of the break is equal to the cross sectional length plus three times the thickness of the material in the standing leg (to allow for the bulb), plus the actual cross sectional length for the formed stringers and straight angles.
Substitute the value obtained, using the procedure above as the length of the break in the rivet formula, and calculate the number of rivets required. The rivet pitch should be the same as that used by the manufacturer for attaching the skin to the stringer. In case this pitch exceeds the maximum of 10 rivet diameters, locate additional rivets between the original rivets. Never make the spacing less than four rivet diameters.
When laying out this spacing, allow two and one-half rivet diameters for edge distance on each side of the break until all required rivets are located. At least five rivets must be inserted on each end of the splice section. If the stringer damage requires the use of an insertion or filler of a length great enough to justify more than 10 rivets, two splice angles should usually be used.
If the stringer damage occurs close to a bulkhead, cut the damaged stringer so that only the filler extends through the opening in the bulkhead The bulkhead is weakened if the opening is enlarged to accommodate both the stringer and the splice angle. Two splice angles must be used to make such a repair.