Fundamental Security

Nuts & Bolts Building Basics FROM THE PROP TO THE CABLES the washer. Cut it to size that control the rudder, the Fundamental if necessary. A pair of components that make an duckbill pliers or safety aircraft complete and con- Security wire pliers are handy to trollable are connected by bend the prongs, and an array of fasteners. Be- Aircraft safetying you can use a light ham- cause builders put these mer to tap the prongs connectors into airplanes, RONALD STERKENBURG close to the bolt for the it means an aircraft's natu- final installation. ral vibration and component move- head is parallel to the slot in the ment can loosen these fasteners. To castellated nut and bend the top Safety Wire keep fasteners from vibrating loose prong over the bolt head. Safety wire (also called lockwire) and falling out, builders must comes in many types and sizes, and "safety" them. There are a number you must first select type and size of of "safetying" methods, with cotter To keep fasteners wire for the job. Common wire sizes pins and safety wire being the most are: 0.020, 0.032, 0.041, and 0.047 common. Which one you use de- from vibrating loose inch. In most applications, the size pends on the fastener. of the safety wire should be between and falling out, 1/3 and 3/4 of the hole diameter, ex- Cotter Pins cept when using the single wire Cotter pins secure bolts, screws, builders must method. For the single wire method, castellated nuts (which have slots on use the largest standard wire size one side), and pins (like the ones in "safety" them. that will fit the hole. a clevis or turnbuckle that connect Stainless steel is the most com- the cable to the rudder horn). The monly used safety wire material. To most commonly used cotter pins are Preferably, the bent-back prong make sure you're using the correct made of cadmium-plated carbon should extend to the center of the wire for the job at hand, you can steel, but some of them are made of bolt end. You can cut the prongs to verify its composition and its size by stainless steel. the right dimension using a diagonal decoding its part number. For exam- Cotter pins come in different cutter (cup the cotter pin and bolt ple, the safety wire part number of sizes, and they should fit into the in- with your hand while you cut it so MS 20955C32 designates (C) corro- tended hole in the nut, bolt, or pin that you can recover the end piece sion-resistant (stainless) steel wire with enough of the prongs showing and prevent eye injury). that is (32) 0.032-inch in diameter. on the other side. To safety a castel- Bend the bottom prong down, Note: There is a second type of lated nut, install a cotter pin so its but not to the point where it touches safety wire—called shear wire—and Loop one wire around the bolt and cross it Insert safety wire of the correct size and material. under the other wire. 94 FEBRUARY 2001 Safety Wire Rules •After installation, all safety wires must be tight, but not under so much tension that normal handling or vibration will break the wire. •The wire must be applied so that all pull exerted by the wire tends to tighten the nut or bolt. •The loop of double wire must pass around, not over, the head of the bolt or screw. •When safetying nuts and bolts, tighten them to the low side of the selected torque range and, if necessary, continue tightening until a slot aligns with the safety hole. •Twists should be tight and even, and the wire between nuts should be as taut as possible without over twisting. Twist Per Inch Pull the wires tight and make the Safety Wire Diameter 0.020" 0.032" 0.041" 0.047" first clockwise twist. The angle be- Twist Per Inch 9 to 10 7 to 10 7 to 10 5 to 8 tween the two wires will determine the number of twists per inch. ; < it safeguards emergency Hands & Pliers switches and seals first aid When installing safety wire, use kits. This wire must break your hands as much as possible. by hand pressure. Be care- Some aviation maintenance text- ful not to install safety books say that you're not supposed wire for shear wire appli- to use pliers, except to create the end cations. Generally, shear twist (or pigtail). In the real world, wire is made of copper. most airframe and powerplant (A&P) There are two ways to mechanics use some kind of pliers to install safety wire, the make the job easier. double-twist method and The disadvantage of pliers is that Twist the safety wire until it's just short of the the single-wire method. they can mark or score the wire, hole in the second bolt. Generally, you use the which potentially weakens the wire. double-twist method for To help prevent this, use smooth all applications. The ex- duckbill pliers or plastic-coated pli- ceptions are those that use ers. Many people like to use safety the single-wire method: wire pliers, which perform three when you must safety functions: they can twist the wire closely spaced small screws by a pulling action, they can be in a pattern, such as a used as a diagonal cutter, and their square or triangle, and pointy nose can easily bend safety when you must safety wire. Safety wire pliers can be handy parts in an electrical sys- in many situations, especially in tem where accessibility tight spaces. or frequent removal Basic safety wire pliers cost around Insert the uppermost wire through the hole that makes the double-twist $30 and only rotate clockwise. Pliers is in the 9 and 12 o'clock position. method impractical. that rotate both ways are substan- tially more expensive, around $90. Either way, it's a good investment. I use my basic safety wire pliers all the Pull the wire tight time, and not just for safety wire ap- through the bolt (you can plications. They are also very handy use pliers). Bring the free for the installation of cotter pins. end of the safety wire When using safety wire pliers, around the bolt head in a make the first twist in the safety wire counterclockwise direc- by hand. Then pull the two wires tion and under the end of until they are just past the hole of the wire protruding from the second bolt, grasp the two wires the bolt hole. with the pliers, and pull the bottom Sport Aviation 95 Bf Building Basics Twist the free ends of the safety wire counterclockwise, making at Bend the wire into a pigtail. This will Final product. Note that the wire will least six twists. Cut off the wire prevent future injury if you are per- prevent counterclockwise movement with diagonal cutters, but make sure forming maintenance in the area of both bolts. ? :.v that you have enough wire left to around the safety wire. make a neat pigtail end. First aid is an important safety check if your safety wire twist is just wire skill. Even the most experi- knob of the pliers. The pliers' rotat- short of the bolt hole. 11 the twist is enced mechanics cut themselves oc- ing action will twist the wires. Re too short, hand-twist the wires until casionally with safety wire. When careful that you don't make the they are just short of the bolt hole. this happens to you, wash your wires too long because they will hurt Insert one wire through the bolt and hands and treat the cut with a disin- you; sometimes it works if you wrap the other around it. If you're using fectant and antibiotic cream. Also the wires around the pliers. basic safety wire pliers, you'll have protect your eyes, especially when Pliers make it easy to over twist to hand-twist the pigtail end be- using long pieces of wire, by wearing the wires. Release the pliers and cause it must be counterclockwise. safety glasses. SPORT FLYING #16 SPORT FLYING #19 Country entertainer and children's author Rick 90 MINUTE EPISODE! Speedvision's sec- Van Shelton pilots his very own Bonanza and goes ond annual special devoted to EAA AirVen- for a P-51 ride . the time honored Piper Tri- ture Oshkosh the greatest aviation event in Pacer... Jack Roush's "Old Crow" P-51 Mustang, the world. 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