Aircraft Cables
Aircraft cables (also called “wire ropes” by their manufacturers are stranded wires used in a wide variety of applications on or around the aircraft including flight control surfaces and tie-downs or other purposes. In contrast to the commercial cables, aircraft contrl cables undergo extensive testing and are lubricated providing substantially better fatigue life.The term "wire rope" is commonly used when the cable diameter is larger than 3/8 inch (9.52 mm), with smaller gauges designated as cables or cords. In terms of their construction, they are specified by a number (bundle) of strands times and a number of wires in each strand. For example, “7x19” means the cable has seven (7) strands, with 19 wires in each strand.
The smaller diameter wires allow the wire to bend without putting as much compression or tension strain on the individual wire. On a large diameter wire the large volume of material being compressed and pulled simultaneously during a bend causes it to fatigue and break. Smaller diameter wires do not have as much steel to be compressed or stretched during a bend, so the strain on the steel is not as great.
Cables with low number of strands like 1 x 7 or 1 x 19 cables don’t bend well around pulleys, and they are called “non-flexible” in contrast to most common aircraft types 7 x 7 or 7 x 19 termed as flexible or extra flexible cables. The 1 X 19 cable has one strand of 19 wires. It has more metallic area than 7 x 7 or 7 x 19 constructions which makes it the strongest but also the least flexible. The 1 x 19 cable is generally used for bracing purposes, drag and anti-drag wires. It is often used with swage type terminals.The 7 X 7 flexible control cable is used for control purposes where extreme flexibility is not required but where abrasion is a factor. The 7 X 19 type cable is the most flexible aircraft cable construction, approximately twice as flexible as 7x7 construction. Its greater metallic area makes it stronger than 7 X 7 cable. Because of its fine wires the best service is obtained where abrasion is not too severe. These same wires, however, make it flexible to meet severe bending.
In terms of materials used in the manufacturing of flight control cables, galvanized carbon steel or corrosion resistant (stainless steel) are typically used. The non-corrosion steel cable is made from regular carbon steel and hot dipped or electroplated with either zinc or tin over zinc to provide some measure of corrosion protection for the strands.
Galvanized carbon steel and stainless cables are soaked in a Mil-SPEC rust preventative and lubricating compound. The advantages of galvanized steel cables are their wear resistance and cost. Galvanized cables resist abrasion wear four or five times longer than those of stainless steel. Their use is recommended except in coastal geographical areas, agricultural aircraft, float planes, and other applications where the cable is exposed directly to water. In these cases stainless steel cables should be preferred. Stainless steel cables are high in nickel and much softer than those of carbon steel. They will show signs of wire wear at pulleys and fairleads much quicker than the galvanized carbon steel wires. In addition, stainless steel cables cost about 30% more than galvanized steel cables.
All cables used in certificated aircraft should conform to MIL SPEC standards MIL-C-18375 and MIL-DTL-83420 (formerly MIL-W-83420) covering the requirements for flexible wire ropes. In addition, some aircraft control cables are QPL certified.
The Qualified Products List (QPL) is mandated by the United States’ Department of Defense. Qualified Products Lists are generally used by the military, local governments, state departments, and federal agencies.The QPL list identifies products that have been pre-tested and proven to follow required specifications before procurement. Before obtaining QPL Approval, a supplier must submit a sample product for testing. Typically, the QPL includes essential details such as product/material type, product identification, and test/qualification reference number. It also includes the name and plant address of the manufacturer and distributor, as applicable. QPL products are commonly used in industries such as aerospace, defense, telecommunications, electronics, and other sectors, where product reliability & performance and adherence to strict standards are crucial. Non-QPL products are often less expensive than their QPL counterparts but QPL approval offers buyers additional assurance of the quality of wires or cables for use in their applications, also eliminating the need for any additional testing or documentation after the product is purchased.
Aircraft cables may come with a nylon coating helping protection of the strands from contamination. When exposed to the environment cables often pick up contamination like dirt while they are also susceptible to internal corrosion as humidity, rain, or salt-laden air penetrates the bundles. Dirt acts as an abrasive in cables as they bend around pulleys, wearing on the individual strands if not protected by the nylon coating. Coated cables are considered to have a greater life span than their uncoated (bare) counterparts. For aircraft in relatively clean conditions, the life of a bare cable may be sufficient. For aircraft operating in harsh environments (such as sandy or salty conditions) the nylon-coated wire may be necessary.
Two important requirements to be observed during the manufacturing of aircraft control cables are those of lubrication and endurance testing. Lubrication is also required after installation for their proper maintainance.
Lubrication of aircraft cables allows the individual strands to slide against each other as they bend around a pulley. Without the lubricant, the strands tend to wear quickly and the cable can fail from the inside of the bundle outward. Typically the most wear on cable strands occurs inside the cable bundles.
An endurance test is a MIL SPEC requirement. This involves placing the cable in a test rig under a load to examine the cable endures how long it takes for the cable strands to begin breaking and the tension the cable must hold at the conclusion of the test. The endurance test ensures that the cable will bend a minimum number of times before strands begin to break.
Αircraft cables are sourced by leading manufacturers such as CONTINENTAL CABLE or CENTRAL WIRE Group of Companies (CWI) like LOOS & CO. or STRAND CORE. They are offered with or without coating (jacket) in different constructions, materials (such as galvanized carbon steel or stainless steel), diameters in inches and pre-cut or cut-to-order lengths in feet. Many of the offered aircraft cables are also included in U.S. DoD Qualified Products List (QPL). Different flight control cables, cable assemblies and related parts are also offered from various manufacturers either as OEM or FAA-PMA approved parts like those from TEXTRON AVIATION for use on Cessna, Beechcraft and Hawker aircraft or FAA-PMA approved cables and parts from McFARLANE® AVIATION, one of a few DOD QML-6117 certified manufacturers of aircraft cable assemblies with over 4,500 cable assemblies and chains in stock. Their flight control cables meet the highest standards possible and exceed the military specifications governing the respective cables. McFARLANE® AVIATION cables are FAA-PMA approved and offered in corrosion resistant stainless or high strength galvanized steel for most 100 and 200 series Cessna aircraft, PA28, PA32, and PA34 series Piper aircraft and G-164 series Ag-Cat aircraft. The company also stocks cables for single engine piston and many turbine and twin engine Beechcraft, and stabilator adjust cables for Piper J3, PA11, PA12, PA14, PA16, PA18, PA18A, PA20 and PA22 aircraft. McFARLANE® AVIATION cables are sold separately or in kits for convenience and economy. Flight control cable and trim chain kits are available for most single engine aircraft from the Cessna model 120 through model 210 and cable kits for most Beechcraft and Piper single engine airplanes.
Industrial Cables
Those for industrial applications can be used when no compliance to MIL specifications is required. They include a diversified range of coated and non-coated steel galvanized and stainless steel cables/wire ropes for general engineering, crane, mining, lift & elevator, pilling, shipping, fishing, rotation resistance, and other applications. Competitively priced they are available in different Fibre/IWRC /WSC cores (*), tensile strengths, metric diameters ( 9 -12mm for cables, 5-52 mm for ropes) and cut to order lengths in meters. Supplied with or without fittings. For additional information and quotation please contact us.
(*) Fibre Cores can be either Natural (Jute, Sisal, Manila) or Manmade (Polyolefin, Polyethene, Polypropylene etc.). They are tested for various parameters such as its lay, diameter, lubrication, breaking strength etc., as per IS-1804:2004. Steel Cores (SC or WSC) / Independent Wire Rope Cores (IWRC). Core wires are selected as per the tensile, not exceeding the main wire. IWRC (7X7) or Strand cores (1X7, 1X19, 1x36, 1X37) are constructed as per BIS.9 specifications.
