Building Basics: Control Cables
Transcription
Building Basics: Control Cables
Nuts & Bolts Building Basics MATERIALS USED TO ailerons, has seven build airplanes seem strands that wrap to have contradicaround each other, tory qualities. Take and each strand is Connecting a pilot's actions to the airplane's reactions control cable. It has composed of 19 fine wires. For a smaller to be flexible and strong. A length of cable such as the TO/ H.G. FRAUTSCHY i:-:-.• • > : 1/8-inch diameter, •'•-' 3/32-inch diameter variety, you can imagine just how 7x19 galvanized cable has a breaking Specs & Strands strength of 2,000 pounds—that's Military specifications standardize fine each of the 19 wires must be. enough to sustain the weight of a the manufacture of the three major Coated with a permanent lubricant, fully loaded Piper Cub, with a pretty types used in aircraft. They define the fine wires give the cable excepgood margin left over. the cable's three common uses and tional flexibility, making it ideal for Control cable is wire rope. First distinguish aircraft quality cable control cables that use a pulley or created in the 19th century, it ranges from the stuff you can get at the fairlead to change direction. The second cable specification defrom the cables used in suspension hardware store. All three are made of bridges to the finer strands that give galvanized carbon steel stainless fines 7x7 control cable (seven shape to the brims of ladies hats. steel, and the strength differences be- strands of seven wires each), used Control cable has been a staple since tween the two materials are minimal. where extra flexibility isn't required, Its number of wires and strands but abrasion is a problem. The third aviation's earliest days because it's light, reliable, cost-efficient, and classifies cable. For example, 7x19 cable specification is the strongest does so many things well, like trans- cable, which measures 1/8-inch in but least flexible, and used with mitting a control input around a diameter and is most often used to swage-type terminals. 1x19 cable's corner or bracing a wooden wing. actuate rudders, elevators, and most common use is general inter- Control Cables STANDARD NICOPRESS TERMINALSPUCE 1 STRAND OF 19 WIRES 1X 19 NONFLEXIBLE USED FOR BRACING STRUCTURES 7 STRANDS OF 7 WIRES 7 X 7 FLEXIBLE WHERE EXTREME FLEXIBILITY IS NOT A FACTOR RESISTS ABRASION 88 AUGUST 2000 7X19 EXTRA FLEXIBLE 7 STRANDS OF 19 WIRES TOLERATES SEVERE BENDS IN CONTRO SYSTEMS. SUSCEPTIBLE TO ABRASION DAMAGE Tir'l.Oj nal bracing and the external drag and anti-drag wires that brace a wing. In most cases, round and streamlined solid wires with threads on each end have replaced 1x19 for external bracing. Cable Maintenance ...Get DUATS* Free! Don't let dirt and grime build up in the spaces between the cable's fine wires. The grime wears on the wires as it flexes, causing fraying over time. Never clean cable by soaking it in a solvent. This removes the lubricant that aids the cable's flexibility. Instead, wipe it with a clean rag. During preflight inspections and routine maintenance, inspect for fraying or broken strands visually and by running a gloved hand along the cable. A broken wire or two is not cause for immediate alarm; it means the cable is under stress, and you should check it frequently for signs of additional deterioration. 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Those with nautical blood laboriously weave a five-tuck Navy splice. (About the only time you'll see this splice today is on an accurately restored antique airplane.) Others wrap the end of the cable with soft steel wire and then dip it in solder. On homebuilt and production aircraft, the most common cable terminal is the Nicopress sleeve, an oval-shaped, soft-metal sleeve invented and produced by the National Telephone Supply Company. Builders use a special tool to compress the sleeve, forcing the soft metal sleeve around the cable to grip it tightly. Builders compress the Nicopress fitting three times. In order, they compress it in the sleeve's center, then next to the thimble or bushing installed when making the cable, and, finally, at the outer end. At each compression, builders check the sleeve with a go/no-go gauge to ensure the compression has com- Dua....__._ Inputs All/Crew/ISO mall 2.5" x 1" Easy Retrofit for SPA-400/600 5-Year Warranty FULL SERVICE WEB SITE!!! isigtronics.com/sa • Full Product Line • Technical Information • Accessories • Installation Instructions Fast E-mail Response Full Flex Boom Noise Cancelling Mio 5-Year Warranty ~S)igtronics .when it counts! 949 N. Cataract Avenue # D • San Dimas, California 91773 (909) 305-9399 • FAX (909) 305-9499 • www.sigtronics.com/sa For more information, visit SPORT AVIATION on the Web at www.eaa.org Building Basics Resources pletely squashed the fitting into a circular cross section, resulting in a tight, strong cable end. A thimble or bushing is always part of a finished cable end because it transmits the load on the cable to all the strands of wire equally without damaging individual strands. While the cable itself is strong, each tiny wire is susceptible to damage due to kinks or abrasion. Often, a shackle or turnbuckle rod end may be installed as the terminal end is fabricated. The rotary swager is another special tool for finishing cable ends. Swaged terminal fittings create the neatest looking installation, and they're often stronger than the cable itself. Their only drawback is that the process doesn't allow a handtool installation, and the power The most reliable, rugged, metal-working equipment euer built. When it comes to intricate metal work and detailed shaping, the finest craftsmen know the finest brand. MetalAce Imperial 44F - The largest, sturdiest, toughest machine you'll find. Designed especially for those big jobs. MetalAce Imperial 2SF - Perfect for medium-sized jobs—from motorcycle fenders to small autobody panels. MetalAce 44F - Excellent portability and versatility. A favorite of racing teams and aircraft restorers. 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But, a number of companies, like Aircraft Spruce & Specialty, FAA-approved repair stations, and some FBOs, will swag cables to order. The installation itself is simple. Builders slip a cable terminal, which has a hollow barrel on one end, over the end of a cable cut to length. The power swager, using high pressure and a set of dies, then squeezes the barrel of the terminal into the cable's crevices. It's a precise process, and builders check their work with a go/no-go gauge to ensure that the terminal is at least as strong as the cable itself. One finishing challenge is cutting the cable, but handheld cable shears cut the cable cleanly so the end will slip easily into the barrel of a swaged terminal. Many builders wrap the cut end with a short piece of tape to help keep the fine wires from fraying and piercing a finger. Some builders cut cable using a time-honored method that requires a deft touch with a hammer. After tightly wrapping plastic electrical tape around the cable where they will cut it, they put the cable on a hard surface, bisect the taped area with a sharp cold chisel, and give the chisel a good whack with a heavy hammer. With practice, the result can be a surprisingly clean cut. But a $25 to $50 handheld cable cutter provides more consistent results. Next month we'll address the rest of the cable story. •