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.
FIGURE 7-17. CABLE WEAR PATTERNS INDIVIDUAL OUTER WIRES WORN MORE THAN 50% WINT INDIVIDUAL OUTER WIRES WORN 40-50% (NOTE BLENDING OF WORN AREAS) INDIVIDUAL OUTER WIRES WORN LESS THAN 40% (WORN AREAS INDIVIDUALLY DISTINGUISHABLE) Par 7-149 Page 7-41
Par 7-149 Page 7-42 FIGURE 7-18. WORN CABLE (REPLACEMENT NECESSARY)
h. A s wear is taking place on the exterior surface of a cable, the same condition is taking place internally, particularly in the sections of the cable which pass over pulleys and quadrants.
This condition (shown in Figure 7-19) is not easily detected unless the strands of the cable are separated. This type of wear is a result of the relative motion between inner wire surfaces. Under certain conditions, the rate of this type of wear can be greater than that occurring on the surface.
FIGURE 7-19. INTERNAL END VIEW OF CABLE WEAR
Par 7-149 Page 7-43
i. Areas especially conducive to cable corrosion are battery compartments, lavatories, wheel wells, etc. where a concentration of corrosive fumes, vapors, and liquids can accumulate.
Carefully examine any cable for corrosion when it has a broken wire in a section that is not in contact with a wear producing airframe component, such as a pulley, fair-lead, etc. If the surface of the cable is corroded, relieve cable tension and carefully force the cable open by reverse twisting and visually inspect the interior. Corrosion on the interior strands of the cable constitutes failure, and the cable must be replaced. If no internal corrosion is detected, remove loose external rust and corrosion with a clean, dry, coarse-weave rag, or fiber brush. Do not use metallic wool or solvents to clean installed cables. Use of metallic wool will embed dissimilar metal particles in the cables and create further corrosion problems. Solvents will remove internal cable lubricant allowing cable strands to abrade and further corrode. After thorough cleaning, sparingly apply specification MIL-C-16173, grade 4, corrosion-preventive compound to cable.
Do not apply the material so thick that it will interfere with the operation of cables at fair-leads, pulleys, or grooved bellcrank areas.
j. Examine cable runs for incorrect routing, fraying, twisting, or wear at fair-leads, pulleys, anti-abrasion strips, and guards. Look for interference with adjacent structure, equipment, wiring, plumbing, and other controls. Inspect cable systems for binding, full travel, and security of attaching hardware. Check for slack in the cable system by attempting to move the control column and/or pedals while the gust locks are installed on the control surfaces. With the gust locks removed, actuate the controls and check for friction or hard movement. These are indications that excessive cable tension exists.
NOTE: If the control movement is stiff after maintenance is performed on control surfaces, check for parallel cables twisted around each other, or cables connected in reverse.
k. Check swaged terminal reference marks for an indication of cable slippage within the fitting. Inspect the fitting assembly for distortion and/or broken strands at the terminal. Ensure that all bearings and swivel fittings (bolted or pinned) pivot freely to prevent binding and subsequent failure. Check turnbuckles for proper thread exposure and broken or missing safety wires/clips.
l. Inspect pulleys for roughness, sharp edges, and presence of foreign material embedded in the grooves. Examine pulley bearings to ensure proper lubrication, smooth rotation, and freedom from flat spots, dirt, and paint spray. During the inspection, rotate the pulleys, which only turn through a small arc, to provide a new bearing surface for the cable. Maintain pulley alignment to prevent the cable from riding on the flanges and chafing against guards, covers, or adjacent structure. Check all pulley brackets and guards for damage, alignment, and security.
m. Various cable system malfunctions may be detected by analyzing pulley conditions.
These include such discrepancies as too much tension, misalignment, pulley bearing problems, and size mismatches between cables and pulleys. Examples of these condition are shown in Figure 7-20.
Par 7-149 Page 7-44 FIGURE 7-20. PULLEY WEAR PATTERNS
n. In spect fair-leads for wear, breakage, alignment, cleanliness, and security. Examine cable routing at fair-leads to ensure that defection angles are no greater than 3 degrees maximum.
Determine that all guides and anti-abrasion strips are secure and in good condition.
o. Examine pressure seals for wear and/or material deterioration. Seal guards should be positioned to prevent jamming of a pulley in case pressure seal fails and pieces slide along the cable.
7-150. CORROSION AND RUST PREVENTION. To ensure a satisfactory service life for aircraft control cables, use a cable lubricant to reduce internal friction and prevent corrosion.
a. If the cable is made from tinned steel, coat the cable with rust-preventive oil, and wipe off any excess. It should be noted that corrosion-resistant steel cable does not require this treatment for rust prevention.
b. Lubrication and corrosion preventive treatment of carbon steel cables may be affected simultaneously by application of compound MIL-C-16173, grade 4, or MIL-C-11796, Class I. MIL-C-16173 compound should be brushed, sprayed, or wiped on the cable to the extent it penetrates into the strands and adequately covers the cable surfaces. It will dry “tack free” in 24 hours at 77 °F. MIL-C-11796 compound is applied by dipping the cable for 1/2 minute into a tank of compound heated to 77 ° ± 5 °C (170 ° ± 9 °F) for 1/2 minute then removing it and wiping off the excess oil. (An example of cable corrosion, attributable to battery acid, is shown in Figure 7-21.)
Par 7-150 Page 7-45 FIGURE 7-21. CORROSION 7-
151. WIRE SPLICES. Standard manufacturing splices have been mistaken for defects in the cable because individual wire end splices were visible after assembly of a finished cable length.
In some instances, the process of twisting outer strands around the core strand may also slightly flatten individual outer wires, particularly in the area of a wire splice. This flattening is the result of die-sizing the cable and does not affect the strength of the cable. These conditions (as shown in Figure 7-22) are normal and are not a cause for cable rejection.
FIGURE 7-22. MANUFACTURER’S WIRE SPLICE 7-
152. CABLE MAINTENANCE. Frequent inspections and preservation measures, such as rust-prevention treatments for bare carbon steel cable areas, will help to extend cable service life.
Where cables pass through fair-leads, pressure seals, or over pulleys, remove accumulated heavy coatings of corrosion-prevention compound. Provide corrosion protection for these cable sections by lubricating with a light coat of grease or general-purpose, low-temperature oil.
7-153. CABLE TENSION ADJUSTMENT. Carefully adjust control cable tension in accordance with the airframe manufacturer’s recommendations. On large aircraft, take the temperature of the immediate area into consideration when using a tension meter. For long cable
Par 7-153 Page 7-46 sections, use the average of two or three temperature readings to obtain accurate tension values.
If necessary, compensate for extreme surface temperature variations that may be encountered if the aircraft is operated primarily in unusual geographic or climatic conditions such as arctic, arid, or tropic locations. Use rigging pins and gust locks, as necessary, to ensure satisfactory results.
At the completion of rigging operations, check turnbuckle adjustment and safetying in accordance with Section 10 of this chapter.
7-154.–7-164. [RESERVED.]
Par 7-165 Page 7-47 SECTION 9. TURNBUCKLES
7-165. GENERAL. A turnbuckle is a device used in cable systems to provide a means of adjusting tension. Turnbuckles have barrel-shaped sleeves with internal left- and right-hand threads at opposite ends. The cables, with terminals attached, are made to such a length that, when the turnbuckle is adjusted to give the specified cable tension, a sufficient number of threads on the terminal ends are screwed into the barrel to hold the load. The clip-locking turnbuckle and its associated parts are identical to standard AN and MS parts except for a slot grooved on the interior of the barrel and the shanks of the forks, eyes, etc. The clip-locking turnbuckle parts have the following drawing numbers: MS21251, turnbuckle body; MS21252, turnbuckle clevis end; MS21253, turnbuckle clevis end (for bearing); NAS649 and NAS651, turnbuckle clip;
MS21254 and NAS648, turnbuckle eye (for pin); MS21255 and NAS647, turnbuckle eye end (for wire rope); NAS645 and NAS646, turnbuckle fork; MS21256, turnbuckle barrel locking clip; AN130-170, turnbuckle assemblies; and MS21259 and MS21260, terminal, wire rope, stud.
NOTE: Turnbuckles showing signs of thread distortion/bending should be replaced. Turnbuckle ends are designed for providing the specified cable tension on a cable system, and a bent turnbuckle would place undesirable stress on the cable, impairing the function of the turnbuckle.
7-166. TURNBUCKLE INSTALLATION. (See Figure 7-23.) When installing cable system turnbuckles, it is necessary to screw both threaded terminals into the turnbuckle barrel an equal amount. It is essential that turnbuckle terminals be screwed into the barrel so that not more than three threads on the terminal are exposed. (See Figure 7-23, item A.) On initial installation, the turnbuckle terminals should not be screwed inside the turnbuckle barrel more than four threads.
(See Figure 7-23, item B.)