Building Basics: Cable Corral

BUILDERS USE MANY FASTENers to connect the parts and pieces of their airplanes, and one of the handiest is the ubiquitous nylon tie wrap (or cable tie/strap) ...
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Nuts & Bolts

Building Basics

BUILDERS USE MANY FASTENers to connect the parts and pieces of their airplanes, and one of the handiest is the ubiquitous nylon tie wrap (or cable tie/strap). DAVE Originally designed to corral and secure bundles of wires, tie wraps come in two styles, defined by its “head” and its “buckle” or locking mechanism. With the traditional (high profile) head, the free end of the tie exits the buckle perpendicular to the bundle and leaves a “tooth” when trimmed. On the new lowprofile wrap (made by Cobra), the free end exits the buckle like a belt (parallel to the waist, or bundle), leaving a tooth-free smooth surface that conforms to the curve of the bundle. Whether low-profile or standard types, used externally or internally, tie wraps ultimately fail because they are made of standard 6/6 nylon, which is hydroscopic, meaning it eventually dries out and becomes brittle. The low-profile wraps, however, do have improved

or wing folds. They may not be used in high vibration areas, where failure of the strap would permit The ins and outs of tie wraps wiring to move against HATCH & TED STANLEY, A&P-IA parts, which could damage the insulation and foul mechanical linkages, or UV resistance because the locking other moving mechanical parts. pawl is under the strap and never They also may not be used where sees the direct rays of the sun. The they could be exposed to UV light, locking pawl in traditional cable ties unless the straps are resistant to faces directly off the center of the such exposure.” cable. Although cable ties primarily Because cable ties lose strength hold wires together in a bundle, with age, inspecting them should they are commonly used in many be part of every builder’s schedule other ways. Standard tie wraps are of routine maintenance. Visual commonly used in engine compartinspection is not enough. The tie ments without regard to their servwrap should be manipulated by ice temperature limit (typically hand. Ones that have become dry 185°F for standard nylon ties). and brittle will typically break with Special wire ties are available made little effort. of heat-stabilized nylon (250°F) or FAA Advisory Circular 43.13-1B, Tefzel (302°F). Improperly using tie “Acceptable Methods, Techniques, wraps can lead to larger problems. and Practices,” recommends that tie Here are some examples from the wraps (which it calls “straps”) “may FAA’s database of Service Difficulty not be used in areas of SWAMP [spe- Reports. ■ A hole worn in a propeller govcial wind and moisture problem] such as wheel wells, near wing flaps ernor oil line by a cable tie led to the

Cable Corral

Sport Aviation

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Building Basics loss of 10 quarts of oil. ■ Corrosion developing under wire ties due to trapped contaminants. ■ A short from wire insulation being cut by improperly installed wire ties. ■ Wires grounded due to insulation failure from being improperly attached to airframe structures such as engine mount tubes. ■ Wire ties used in an attempt to replace missing nylon locking rings on lap belt studs that retain shoulder harness belts. ■ A rough running engine from ignition wires damaged by over tightened wire ties. ■ A new antenna coax was deformed every 6 inches from the tail to the instrument panel by too tight tie wraps, leading to weak reception. ■ During an annual inspection, the technician tested the emergency locator transmitter (ELT) and found it inoperative. When activating the g-switch, the test light illuminated, but the unit didn’t transmit a signal. The ELT was installed using tie wraps instead of the rack provided by the manufacturer. Knowing the correct way to use cable ties is important, but so is knowing when not to use them. All too often cable ties are used in applications where cushion clamps or Koroseal lacing would be more appropriate. Wire ties should not be located in narrow radius bends of wire bundles. Wire ties can cause damage to wires or support structures subject to vibration. To install a tie wrap, regardless of style, use a “cinch and trim” tool designed for the job or diagonal cutting pliers. After looping the wrap around the bundle, ensuring that it’s not pinched or kinked, tighten the tie wrap by hand. Then grasp the tie gently at the base with the cutters and roll the cutters forward in the direction the strap exits from the head. The grooves in the rear of 80

SEPTEMBER 2003

Knowing when not to use wire ties can be as important as when to use them. Wire ties can cause damage to wires or support structures subject to vibration.

Special wire ties made of heat-stabilized nylon are available for use in engine compartments.

Don’t use tie wraps in areas that you won’t be able to access once your airplane is assembled. They will eventually dry out and become brittle leaving you with a bundle of loose wiring.

Fly straight the cable tie head act as a fulcrum to hold the lower blade while rotating the upper blade forward. When the required tension is achieved, push the lower blade back to the base of the strap exiting the head and cut. When using a tie-wrap tool, tighten the tie by hand and cinch and trim with the application gun. When using the high-profile style, before cinching and trimming the tie ensure that the locking mechanism doesn’t rub on anything. Because the low-profile ties have a smooth surface, they are better suited where wire bundles are closely packed into cable troughs

Although cable ties primarily hold wires together in a bundle,

to final assembly! Jump-Start Options

Jump Start Wings: • Leading edge and lower skins installed. • All flight control brackets and pulleys installed. • Anti-corrosion primer applied to all interior aluminum surfaces prior to assembly. • Upper skins fitted, drilled, dimpled and ready to rivet. • Strut beam assemblies installed.

Ailerons and Flaps: • Completed (Included in Wing Jump Start)

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Jump Start Fuselage: • Composite shells fitted, laminated together and fastened to cage. • External seams fitted, gel-coated and buffed to match. • Top deck installed. • All 5 bulkheads installed. • COM antenna installed. • Inside visible shell surfaces finished with Zolatone grey speckle interior paint.

they are commonly used in many other ways. and space is at a premium. They are also preferred when cables require an over braid or have shrink tubing applied. Most cable ties come in two colors—black and natural. To make them more visible, which makes inspection easier, use the color that provides the most contrast to the bundle. Finally, only use tie wraps in areas you can reach without having to take your airplane apart. Because they do dry out and become brittle with age, tie wraps do fail. And if you can’t replace them, because they are, for example, buried in the wing, the now loose bundle of navigation and strobe light wires will eventually fray and short. For more information, visit SPORT AVIATION on the Web at www.eaa.org

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Jump Start Tail: • Rudder: Complete, less trim tab and tip. • Stabilizer: Complete, less tips. • Elevator: Complete, less trim tab and tips.