Par 7-127 Page 7-316
Examples 12 and 13 show methods for attaching lead seal to protect critical adjustments.
Example 14 shows bolt wired to a right-angle bracket with the wire wrapped around the bracket.
Example 15 shows correct method for wiring adjustable connecting rod.
Example 16 shows correct method for wiring the coupling nut on flexible line to the straight connector brazed on rigid tube.
Fittings incorporating wire lugs shall be wired as shown in Examples 17 and 18. Where no lock- wire lug is provided, wire should be applied as shown in examples 19 and 20 with caution being exerted to ensure that wi re is wrapped tightly around the fitting.
Small size coupling nuts shall be wired by wrapping the wire around the nut and inserting it through the holes as shown.
FIGURE 7-5a. Safety-wiring procedures.
Par 7-126 Page 7-317
Coupling nuts attached to straight connectors shall be wired as, shown, when hex is an integral part of the connector.
Coupling nuts on a tee shall be wired, as shown above, so that tension is always in the tightening direction.
Straight Connector (Bulkhead Type)
Examples 26, 27, and 28 show the proper met hod for wiring various standard fittings with checknut wired independently so that it need not be disturbed when removing the coupling nut.
FIGURE 7-5b. Safety-wiring procedures.
Par 7-140 Page 7-318 SECURING WITH COTTER PINS.
Cotter pins are used to secure such items as bolts, screws, pins, and shafts. Their use is favored because they can be removed and installed quickly. The diameter of the cotter pins selected for any application should be the largest size that will fit consistent with th e diameter of the cotter pin hole and/or the sl ots in the nut. Cotter pins should not be reused on aircraft.
To prevent injury during and after pin installation, the end of the cotter pin can be rolled and tucked.
NOTE: In using the method of cotter pin safetying, as shown in figures 7-6 and 7-7, ensure the prong, bent over the bolt, is seated firmly against the bolt sh ank, and does not exceed bo lt diameter. Also, when the prong is bent over the nut, ensure the bent prong is down and firmly flat against the nut and does not contact the surface of the washer.
Par 7-140 Page 7-319
FIGURE 7-6. Securing with cotter pins.
FIGURE 7-7. Alternate method for securing with cotter pins.
7-128.7-139. [RESERVED.]
Par 7-140 Page 7-320 SECTION 8. INSPECTION AND REPAIR OF CONTROL CABLES
AND TURNBUCKLES
GENERAL. Aircraft control cables are generally fabricated from carbon steel or corrosionresistant steel wire of either flexible or nonflexible-type construction.
CABLE DEFINITIONS. The following cable components are defined in accordance with Military Specifications MIL-W-83420, MIL-C-18375, and MIL-W-87161.
Wire Center. The center of all strands shall be an individual wire and shall be designated as a wire center.
Strand Center or Core. A strand center is a single, straight strand made of preformed wires, similar to the other strands comprising the cable, in arrangement and number of wires.
Independent Wire Rope Center (IWRC) 7 by 7. A 7 by 7 independent wire rope center as specified herein shall consist of a cable or wire rope of six strands of seven wires each, twisted or laid around a strand center or core consisting of seven wires.
FLEXIBLE CABLES. Flexible, preformed, carbon steel, Type I, composition A cables, MIL-W-83420, are manufactured from steel made by the acid-open-hearth, basic-open hearth, or electric-furnace process. The wire used is coated with pure tin or zinc. Flexible, preformed, corrosion-resistant, Type I, composition B cables, MIL-W-87161, MIL-W-83420, and MIL-C-18375 are manufactured from steel made by the electricfurnace process. (See table 7-3 and figure 7-8.)
These cables are of the 3 by 7, 7 by 7, 7 by 19, or 6 by 19 IWRC construction, according to the diameter as specified in table 7-3. The 3 by 7 cable consists of three strands of seven wires each. There is no core in this construction.
The 3 by 7 cable has a length of lay of not more than eight times or less than five times the nominal cable diameter. The 7 by 7 cable consists of six strands, of seven wires each, laid around a center strand of seven wires. The wires are laid so as to develop a cable which has the greatest bending and wearing properties. The 7 by 7 cable has a length of lay of not more than eight times or less than six times the cable diameter. The 7 by 19 cable consists of six strands laid around a center strand in a clockwise direction. The wires composing the seven individual strands are laid around a center wire in two layers. The center core strand consists of a lay of six wires laid around the central wire in a clockwise direction and a layer of 12 wires laid around this in a clockwise direction. The six outer strands of the cable consist of a layer of six wires laid around the center wire in a counterclockwise direction and a layer of 12 wires laid around this in a counterclockwise direction. The 6 by 19 cable consists of six strands of 19 wires each, laid around a 7 by 7.
MIL-C-18375 cable, although not as strong as MIL-W-83420, is equal in corrosion resistance and superior in non-magnetic and coefficient of thermal expansion properties.
NYLON-COATED CABLES.
Nylon-coated cable is made by extruding a flexible nylon coating over corrosion-resistant steel (CRES) cable. The bare CRES cable must conform and be qualified to MIL-W-83420. After coating, the jacketed cable must still conform to MIL-W-83420.
The service life of nylon-coated cable is much greater than the service life of the sa me cable when used bare.
Most cable wear occurs at pulleys where the cable bends. Wear
Par 7-140 Page 7-321 TABLE 7-3. Flexible cable construction and physical properties.
MINIMUM BREAKING STRENGTH (Pounds)
NOMINAL
DIAMETER
OF WIRE ROPE CABLE
CONSTRUCTION
TOLERANCE ON
DIAMETER (PLUS ONLY)
ALLOWABLE
INCREASE OF
DIAMETER AT
CUT END
MIL-W- 83420 COMP A
MIL-W-83420 COMP B (CRES)
MIL-C- 18375 (CRES)
INCHES INCHES INCHES LBS LBS LBS 1/32 3/64 1/16 1/16 3/32 3/32 1/8 5/32 3/16 7/32 1/4 9/32 5/16 11/32 3/8 7/16 1/2 9/16 5/8 3/4 7/8 1 1 - 1/8 1 - 1/4 1 - 3/8 1 - 1/2 3 x 7 7 x 7 7 x 7 7 x 19 7 x 7 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 6 x 19 IWRC 6 x 19 IWRC 6 x 19 IWRC 6 x 19 IWRC 6 x 19 IWRC 6 x 19 IWRC 6 x 19 IWRC 6 x 19 IWRC 6 x 19 IWRC 6 x 19 IWRC 6 x 19 IWRC
0.006
0.008
0.010
0.010
0.012
0.012
0.014
0.016
0.018
0.018
0.018
0.020
0.022
0.024
0.026
0.030
0.033
0.036
0.039
0.045
0.048
0.050
0.054
0.057
0.060
0.062
0.006
0.008
0.009
0.009
0.010
0.010
0.011
0.017
0.019
0.020
0.021
0.023
0.024
0.025
0.027
0.030
0.033
0.036
0.039
0.045
0.048
0.050
0.054
0.057
0.060
0.062 110 270 480 480 920 1,000 2,000 2,800 4,200 5,600 7,000 8,000 9,800 12,500 14,400 17,600 22,800 28,500 35,000 49,600 66,500 85,400 106,400 129,400 153,600 180,500 110 270 480 480 920 920 1,760 2,400 3,700 5,000 6,400 7,800 9,000
12,000 16,300 22,800 28,500 35,000 49,600 66,500 85,400 106,400 129,400 153,600 180,500
1,300 2,000 2,900 3,800 4,900 6,100 7,600
11,000 14,900 19,300 24,300 30,100 42,900 58,000 75,200
is caused by friction between strands and between wires. In bare cable, this is aggravated by dirt and grit working its way into the cable; and the lubricant working its way out leaving dry, dirty wires rubbing against each other. In long, straight runs of cable, vibration workhardens the wires causing the brittle wires to fracture with eventual failure of the cable.
The nylon-jacket protects the cable in a threefold manner. It keeps the lubricant from oozing out and evaporating, it keeps dirt and grit out, and it dampens the vibrations, thereby, greatly reducing their effect on the cable.
NONFLEXIBLE CABLES. (Refer to table 7-4 and figure 7-9.) Nonflexible, preformed, carbon steel cables, MIL-W-87161, composition A, are manufactured by the same processes as MIL-W-83420, composition B, flexible corrosion-resistant steel cables. The nonflexible steel cables are of the 1 by 7 (Type I) or 1 by 19 (Type II) construction according to the diameter as specified in table 7-4. The 1 by 7 cable consists of six
Par 7-144 Page 7-322
FIGURE 7-8. Flexible cable cross section.
TABLE 7-4. Nonflexible cable construction and physical properties.
STRAND TYPE
NOMINAL
DIAMETER OF WIRE STRAND In.
TOLERANCE ON
DIAMETER (Plus Only) In.
ALLOWABLE
INCREASE IN
DIAMETER
AT THE END In.
CONSTRUCTION MIL-W-87161
MINIMUM BREAK
STRENGTH
COMP A & B Lbs.
I I II I II II II II II II II II II II II 1/32 3/64 3/64 1/16 1/16 5/64 3/32 7/64 1/8 5/32 3/16 7/32 1/4 5/16 3/8
0.003
0.005
0.005
0.006
0.006
0.008
0.009
0.009
0.013
0.013
0.013
0.015
0.018
0.022
0.026
0.006
0.008
0.008
0.009
0.009
0.009
0.010
0.010
0.011
0.016
0.019
0.020
0.021
0.024
0.027 1 x 7 1 x 7 1 x 19 1 x 7 1 x 19 1 x 19 1 x 19 1 x 19 1 x 19 1 x 19 1 x 19 1 x 19 1 x 19 1 x 19 1 x 19 185 375 375 500 500 800 1,200 1,600 2,100 3,300 4,700 6,300 8,200 12,500 17,500
FIGURE 7-9. Nonflexible cable cross section.
wires laid around a center wire in a counterclockwise direction. The 1 by 19 cable consists of a layer of six wires laid around a center wire in a clockwise direction plus twelve wires laid around the inner strand in a counterclockwise direction.
CABLE SPECIFICATIONS. Cable diameter and strength data are given in table 7-3 and table 7-4. These values are acceptable for repair and modification of civil aircraft.
CABLE PROOF LOADS. Cable terminals and splices should be tested for proper strength before installation. Gradually apply a test load equal to 60 percent of the cable-breaking strengths given in table 7-3 and
Par 7-144 Page 7-323 table 7-4, for a period of 3 minutes. Place a suitable guard over the cable during the test to prevent injury to personnel in the event of cable failure.
REPLACEMENT OF CABLES. Replace control cables when they become worn, distorted, corroded, or otherwise damaged. If spare cables are not available, prepare exact duplicates of the damaged cable. Use materials of the same size and quality as the original. Standard swaged cable terminals develop the full cable strength and may be substituted for the original terminals wherever practical. However, if facilities and supplies are limited and immediate corrective action is necessary, repairs may be made by using cable bushings, eye splices, and the proper combination of turnbuckles in place of the original installation. (See figure 7-12(c).)
Location of Splices. Locate splices so that no portion of the splice comes closer than 2 inches to any fair-lead or pulley. Locate connections at points where jamming cannot occur during any portion of the travel of either the loaded cable or the sl ack cable in the deflected position.
Cutting and Heating. Cut cables to length by mechanical means. The use of a torch, in any manner, is not permitted. Do not subject wires and cables to excessive temperature. Soldering the bonding braid to the control cable is not permitted.
Ball-and-Socket Type Terminals. Do not use balland-socket type terminals or other types for general replacement that do not positively prevent cable untwisting, except where they were utilized on the original installation by the aircraft manufacturer.
Substitution of Cable. Substitution of cable for hard or streamlined wires will not be acceptable unless specifically approved by a representative of the FAA.
MECHANICALLY-FABRI-CATED CABLE ASSEMBLIES.
Swage-Type Terminals. Swage-type terminals, manufactured in accordance w ith AN, are suitable for use in civil aircraft up to, and including, maximum cable loads. When swag ing tools are used, it is important that all the manufacturers’ instructions, including “go and no-go” dimensions, be followed in detail to avoid defective and inferior swaging.
Observance of all instructions should result in a terminal developing the full-rated strength of the cable.
Critical dimensions, both before and after swaging, are shown in table 7-5.
Terminals. When swaging terminals onto cable ends, observe the following procedures.
Cut the cable to the proper length allowing for growth during swaging. Apply a preservative compound to the cable ends before insertion into the terminal barrel.
NOTE: Never solder cable ends to prevent fraying, since the presence of the solder will greatly increase the tendency of the cable to pull out of the terminal.
Insert the cable into the terminal approximately 1 inch, and bend toward the terminal, then push the cable end entirely into the terminal barrel. The bending action puts a kink or bend in the cable end, and provides enough friction to hold the terminal in place until the swaging operation can be performed. Bending also tends to separate the strands inside the barrel, thereby reducing the strain on them.
Par 7-148 Page 7-324 TABLE 7-5. Straight-shank terminal dimensions. (Cross reference AN to MS: AN-666 to MS 21259, AN-667 to MS 20667, AN-668 to MS 20668, AN-669 to MS 21260.)
Before swaging After swaging
Cable size (inches)
Wire strands
Outside diameter
Bore diameter
Bore length
Swaging length Minimum breaking strength (pounds)
Shank diameter * 1/16 3/32 1/8 5/32 3/16 7/32 1/4 9/32 5/16 3/8 7 x 7 7 x 7 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19
0.160 .218 .250 .297 .359 .427 .494 .563 .635 .703
0.078 .109 .141 .172 .203 .234 .265 .297 .328 .390
1.042
1.261
1.511
1.761
2.011
2.261
2.511
2.761
3.011
3.510
0.969
1.188
1.438
1.688
1.938
2.188
2.438
2.688
2.938
3.438 480 920 2,000 2,800 4,200 5,600 7,000 8,000 9,800 14,400
0.138 .190 .219 .250 .313 .375 .438 .500 .563 .625 *Use gauges in kit for checking diameters.
NOTE: If the terminal is drilled completely through, push the cable into the terminal until it reaches the approximate position shown in figure 7-10. If the hole is not drilled through, insert the cable until the end rests against the bottom of the hole.
FIGURE 7-10. Insertion of cable into terminal.
Accomplish the swaging operation in accordance with the instructions furnished by the manufacturer of the swaging equipment.
Inspect the terminal after swaging to determine that it is free from the die marks and splits, and is not out-of-round. Check for cable slippage in the terminal and for cut or broken wire strands.
Using a “go no-go” gauge or a micrometer, check the terminal shank diameter as shown in figure 7-11 and table 7-5.
FIGURE 7-11. Gauging terminal shank after swaging.
Test the cable by proof-loading it to 60 percent of its rated breaking strength.
Splicing. Completely severed cables, or those badly damaged in a localized area, may be repaired by the use of an eye
Par 7-148 Page 7-325 terminal bolted to a clevis terminal. (See figure 7-12(a).) However, this type of splice can only be used in free lengths of cable which do not pass over pulleys or through fair-leads.
FIGURE 7-12. Typical cable splices.
Swaged ball terminals. On some aircraft cables, swaged ball terminals are used for attaching cables to quadrants and special connections where space is limited. Single shank terminals are generally used at the cable ends, and double shank fittings may be used at either the end or in the center of the cable. Dies are supplied with the swaging machines for attaching these terminals to cables by the following method.
The steel balls and shanks have a hole through the center, and are slipped over the cable and positioned in the desired location.
Perform the swaging operation in accordance with the instructions furnished by the manufacturer of the swaging equipment.
Check the swaged fitting with a “go no-go” gauge to see that the fitting is properly compressed, and inspect the physical condition of the finished terminal. (See figure 7-13.)
FIGURE 7-13. Typical terminal gauge.
Cable slippage in terminal. Ensure that the cable is properly inserted in the terminal after the swaging operation is completed.
Instances have been noted wherein only 1/4 inch of the cable was swaged in the terminal. Observance of the following precautions should minimize this possibility.
Measure the length of the terminal end of the fitting to determine the proper length of cable to be inserted into the barrel of the fitting.
Lay off this length at the end of the cable and mark with masking tape. Since the tape will not slip, it will provide a positive marking during the swaging process.
After swaging, check the tape marker to make certain that the cable did not slip during the swaging operation.
Remove the tape and paint the junction of the swaged fitting and cable with red tape.
At all subsequent service inspections of the swaged fitting, check for a gap in the painted section to see if cable slippage has occurred.
Nicopress Process. A patented process using copper sleeves may be used up to the full rated strength of the cable when the cable is looped around a thimble. This process may also be used in place of the five-tuck splice on
Par 7-148 Page 7-326 cables up to and including 3/8 inch diameter. The use of sleeves that are fabricat ed of materials other than copper will require engineering approval for the specific application by the FAA.
Before undertaking a nicopress splice, determine the proper tool and sleeve for the cable to be used. Refer to table 7-6 and table 7-7 for details on sleeves, tools, and the number of presses required for the various sizes of aircraft cable. The tool must be in good working condition and properly adjusted to ensure a satisfactory splice.
To compress a sleeve, have it well-centered in the tool groove with the major axis of the sleeve at right angles to the tool. If the sleeve appears to be out of line after the press is started, open the tool, re-center the sleeve, and complete the press.
Thimble-Eye Splice. Before undertaking a thimble-eye splice, initially position the cable so the end will extend slightly beyond the sleeve, as the sleeve will elongate somewhat when it is compressed. If the cable end is inside the sleeve, the sp lice may not hold the full strength of the cable. It is desirable that the oval sleeve be placed in close proximity to the thimble points, so that when compressed, the sleeve will contact the thimble as shown in figure 7-14. The sharp ends of the thimble may be cut off before being used; however, make certain the thimble is firmly secured in the cable loop after the splice has been completed. When using a sleeve requiring three compressions, make the center compression first, the compression next to the thimble second, and the one farthest from the thimble last.
Lap Splice. Lap or running splices may also be made with copper oval sleeves. When making such splices, it is usually necessary to use two sleeves to develop the full
FIGURE 7-14. Typical thimble-eye splice.
strength of the cable. The sleeves should be positioned as shown in figure 7-12(b), and the compressions made in the order shown. As in the case of eye splices, it is desirable to have the cable ends extend beyond the sleeves sufficiently to allow for the increased length of the compressed sleeves.
Stop Sleeves. Stop sleeves may be used for special cable end and intermediate fittings. They are installed in the same manner as nicopress oval sleeves.
NOTE: All stop sleeves are plain copper.
Certain sizes are colored for identification.
Terminal Gauge. To make a satisfactory copper sleeve installation, it is important that the amount of sleeve pressure be kept uniform. The completed sleeves should be checked periodically with the proper gauge.
Hold the gauge so that it contacts the major axis of the sleeve. The compressed portion at the center of the sleeve should enter the gauge opening with very little clearance, as shown in figure 7-15. If it does not, the tool must be adjusted accordingly.
Other Applications. The preceding information regarding copper oval sleeves and stop sleeves is based on tests made with flexible aircraft cable. The sleeves may also be
Par 7-148 Page 7-327 TABLE 7-6. Copper oval sleeve data.
Copper oval sleeve stock No.
Cable size
Plain
Plated*
Manual tool No.
Sleeve length before compression (approx.)
(inches) Sleeve length after compression (approx.)
(inches)
Number of presses
Tested strength (pounds)
3/64 18-11-B4 28-11-B4 51-B4-887 3/8 7/16 1 340 1/16 18-1-C 28-1-C 51-C-887 3/8 7/16 1 550 3/32 18-2-G 28-2-G 51-G-887 7/16 1/2 1 1,180 1/8 18-3-M 28-3-M 51-M-850 9/16 3/4 3 2,300 5/32 18-4-P 28-4-P 51-P-850 5/8 7/8 3 3,050 3/16 18-6-X 28-6-X 51-X-850 1 1 1/4 4 4,350 7/32 18-8-F2 28-8-F2 51-F2-850 7/8 1 1/16 4 5,790 1/4 18-10-F6 28-10-F6 3-F6-950 1 1/8 1 1/2 3 7,180 5/16 18-13-G9 28-13-G9 3-G9-950 1 1/4 1 5/8 3 11,130 No. 635 Hydraulic tool dies
3/8 18-23-H5 28-23-H5 Oval H5 1 1/2 1 7/8 1 16,800 7/16 18-24-J8 28-24-J8 Oval J8 1 3/4 2 1/8 2 19,700 1/2 18-25-K8 28-25-K8 Oval K8 1 7/8 2 1/2 2 25,200 9/16 18-27-M1 28-27-M1 Oval M1 2 2 5/8 3 31,025 5/8 18-28-N5 28-28-N5 Oval N5 2 3/8 3 1/8 3 39,200 *Required on stainless cables due to electrolysis caused by different types of metals.
TABLE 7-7. Copper stop sleeve data.
Cable size (inch) Sleeve No. Tool No . Sleeve Sleeve Tested strength (pounds) 3/64 871-12-B4 51-B4-887 7/32 11/64 280 1/16 871-1-C 51-C-887 7/32 13/64 525 3/32 871-17-J (Yellow) 51-MJ 5/16 21/64 600 1/8 S71-18-J (Red) 51-MJ 5/16 21/64 800 5/32 871-19-M 51-MJ 5/16 27/64 1,200 3/16 871-20-M (Black) 51-MJ 5/16 27/64 1,600 7/32 871-22-M 51-MJ 5/8 7/16 2,300 1/4 871-23-F6 3-F6-950 11/16 21/32 3,500 5/16 871-26-F6 3-F6-950 11/16 21/32 3,800 NOTE: All stop sleeves are plain copper. Certain sizes are colored for identification.
used on wire ropes of ot her construction, if each specific type of cable is proof-tested initially. Because of variation in rope strengt hs, grades, construction, and actual diameters, the test is necessary to insure proper selection of materials, the correct pressing procedure, and an adequate margin of safety for the intended use.
FIGURE 7-15. Typical terminal gauge.