Par 7-142 Page 7-29 FIGURE 7-8. FLEXIBLE CABLE CROSS-SECTION
c. T hese 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.
(1) 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.
(2) 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.
(3) 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.
(4) 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.
7-143. NYLON-COATED CABLES.
a. 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.
b. The service life of nylon-coated cable is much greater than the service life of the same cable when used bare. Most cable wear occurs at pulleys where the cable bends. Wear is caused by friction between strands and between wires. In bare cable, this is aggravated by dirt and grit
Par 7-144 Page 7-30 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 work hardens the wires causing the brittle wires to fracture with eventual failure of the cable.
c. 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.
7-144. NONFLEXIBLE CABLES. (See 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 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.
TABLE 7-4. NONFLEXIBLE CABLE CONSTRUCTION AND PHYSICAL
PROPERTIES STRAND TYPE
NOMINAL
DIAMETER
OF WIRE STRAND Inches
TOLERANCE ON
DIAMETER (Plus Only) Inches
ALLOWABLE
INCREASE IN
DIAMETER
AT THE END Inches
CONSTRUCTION MIL-W-87161
MINIMUM BREAK
STRENGTH
COMP A & B Pounds I 1/32 0.003 0.006 1 x 7 185 I 3/64 0.005 0.008 1 x 7 375 II 3/64 0.005 0.008 1 x 19 375 I 1/16 0.006 0.009 1 x 7 500 II 1/16 0.006 0.009 1 x 19 500 II 5/64 0.008 0.009 1 x 19 800 II 3/32 0.009 0.010 1 x 19 1,200 II 7/64 0.009 0.010 1 x 19 1,600 II 1/8 0.013 0.011 1 x 19 2,100 II 5/32 0.013 0.016 1 x 19 3,300 II 3/16 0.013 0.019 1 x 19 4,700 II 7/32 0.015 0.020 1 x 19 6,300 II 1/4 0.018 0.021 1 x 19 8,200 II 5/16 0.022 0.024 1 x 19 12,500 II 3/8 0.026 0.027 1 x 19 17,500
Par 7-144 Page 7-31 FIGURE 7-9. NONFLEXIBLE CABLE CROSS-SECTION 7-
145. 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.
7-146. 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 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.
7-147. 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, image (c).)
a. 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 slack cable in the deflected position.
b. 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.
c. Ball-and-Socket Type Terminals. Do not use ball-and-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.
d. Substitution of Cable. Substitution of cable for hard or streamlined wires will not be acceptable unless specifically approved by a representative of the FAA.
Par 7-148 Page 7-32
7-148. MECHANICALLY-FABRICATED CABLE ASSEMBLIES.
a. Swage-Type Terminals. Swage-type terminals, manufactured in accordance with AN, are suitable for use in civil aircraft up to, and including, maximum cable loads. When swaging 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.
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 7 x 7 0.160 0.078 1.042 0.969 480 0.138 3/32 7 x 7 .218 .109 1.261 1.188 920 .190 1/8 7 x 19 .250 .141 1.511 1.438 2,000 .219 5/32 7 x 19 .297 .172 1.761 1.688 2,800 .250 3/16 7 x 19 .359 .203 2.011 1.938 4,200 .313 7/32 7 x 19 .427 .234 2.261 2.188 5,600 .375 1/4 7 x 19 .494 .265 2.511 2.438 7,000 .438 9/32 7 x 19 .563 .297 2.761 2.688 8,000 .500 5/16 7 x 19 .635 .328 3.011 2.938 9,800 .563 3/8 7 x 19 .703 .390 3.510 3.438 14,400 .625 *Use gauges in kit for checking diameters.
(1) Terminals. When swaging terminals onto cable ends, observe the following procedures.
(a) 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.
(b) 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
Par 7-148 Page 7-33 swaging operation can be performed. Bending also tends to separate the strands inside the barrel, thereby reducing the strain on them.
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 (
c) Accomplish the swaging operation in accordance with the instructions furnished by the manufacturer of the swaging equipment.
(d) 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.
(e) Using a “go no-go” gauge or a micrometer, check the terminal shank diameter as shown in Figure 7-11 and Table 7-5.
(f) Test the cable by proof-loading it to 60 percent of its rated breaking strength.
Par 7-148 Page 7-34 FIGURE 7-11. GAUGING TERMINAL SHANK AFTER SWAGING (
2) Splicing. Completely severed cables, or those badly damaged in a localized area, may be repaired by the use of an eye terminal bolted to a clevis terminal. (See Figure 7-12, image (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 (
3) 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.
(a) The steel balls and shanks have a hole through the center, and are slipped over the cable and positioned in the desired location.
Par 7-148 Page 7-35
(b) Perform the swaging operation in accordance with the instructions furnished by the manufacturer of the swaging equipment.
(c) 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 (
4) 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.
(a) 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.
(b) 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.
(c) After swaging, check the tape marker to make certain that the cable did not slip during the swaging operation.
(d) Remove the tape and paint the junction of the swaged fitting and cable with red tape.
(e) At all subsequent service inspections of the swaged fitting, check for a gap in the painted section to see if cable slippage has occurred.
b. 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 cables up to and including 3/8-inch diameter. The use of sleeves that are fabricated of materials other than copper will require engineering approval for the specific application by the FAA.
(1) Before undertaking a Nicopress splice, determine the proper tool and sleeve for the cable to be used. See Table 7-6 and Table 7-7 for details on sleeves, tools, and the number of
Par 7-148 Page 7-36 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.
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 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.
Par 7-148 Page 7-37 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.
(2) 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.
c. 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 splice 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.
Par 7-148 Page 7-38 FIGURE 7-14. TYPICAL THIMBLE-EYE SPLICE
d. L ap 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 strength of the cable. The sleeves should be positioned as shown in Figure 7-12, image (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.
e. 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.
f. 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.
FIGURE 7-15. TYPICAL TERMINAL GAUGE
g.
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 used on wire
Par 7-148 Page 7-39 ropes of other construction, if each specific type of cable is proof-tested initially. Because of variation in rope strengths, grades, construction, and actual diameters, the test is necessary to ensure proper selection of materials, the correct pressing procedure, and an adequate margin of safety for the intended use.
7-149. CABLE SYSTEM INSPECTION. Aircraft cable systems are subject to a variety of environmental conditions and deterioration. Wire or strand breakage is easy to visually recognize. Other kinds of deterioration such as wear, corrosion, and/or distortion are not easily seen; therefore, control cables should be removed periodically for a more detailed inspection.
a. At each annual or 100-hour inspection, all control cables must be inspected for broken wires strands. Any cable assembly that has one broken wire strand located in a critical fatigue area must be replaced.
b. A critical fatigue area is defined as the working length of a cable where the cable runs over, under, or around a pulley, sleeve, or through a fair-lead; any section where the cable is flexed, rubbed, or worked in any manner; or any point within 1 foot of a swaged-on fitting.
c. A swaged-on fitting can be an eye, fork, ball, ball and shank, ball and double shank, threaded stud, threaded stud and turnbuckle, compression sleeve, or any hardware used as a termination or end fitting on the cable. These fittings may be attached by various swaging methods such as rotary swaging, roll swaging, hydraulic pressing, and hand swaging tools.
(Refer to MIL-T-781.) The pressures exerted on the fittings during the swaging process sometimes pinch the small wires in the cable. This can cause premature failure of the pinched wires, resulting in broken wires.
d. Close inspection in these critical fatigue areas must be made by passing a cloth over the area to snag on broken wires. This will clean the cable for a visual inspection and detect broken wires if the cloth snags on the cable. Also, a very careful visual inspection must be made since a broken wire will not always protrude or stick out, but may lie in the strand and remain in the position of the helix as it was manufactured. Broken wires of this type may show up as a hairline crack in the wire. If a broken wire of this type is suspected, further inspection with a magnifying glass of 7 power or greater is recommended. Figure 7-16 shows a cable with broken wires that was not detected by wiping, but was found during a visual inspection. The damage became readily apparent when the cable was removed and bent as shown in Figure 7-16.
Par 7-149 Page 7-40 FIGURE 7-16. CABLE INSPECTION TECHNIQUE
e. Kin king of wire cable can be avoided if properly handled and installed. Kinking is caused by the cable taking a spiral shape as the result of unnatural twist. One of the most common causes for this twist is improper unreeling and uncoiling. In a kinked cable, strands and wires are out of position, which creates unequal tension and brings excessive wear at this part of the cable. Even though the kink may be straightened so that the damage appears to be slight, the relative adjustment between the strands has been disturbed so that the cable cannot give maximum service and should be replaced. Inspect cables for a popped core or loose strands.
Replace any cable that has a popped core or loose strands regardless of wear or broken wires.
f. Nylon-jacketed cable with any cracks or necking down in the diameter of the jacket shall be replaced. Usable cable life is over when these conditions begin to appear in the nylon jacket.
g. External wear patterns will extend along the cable equal to the distance the cable moves at that location and may occur on one side of the cable or on its entire circumference.
Replace flexible and nonflexible cables when the individual wires in each strand appear to blend together (outer wires worn 40 to 50 percent) as depicted in Figure 7-17. Actual instances of cable wear beyond the recommended replacement point are shown in Figure 7-18.