Avionics News July 2012 - 59

indeed requires, quality and reliability. Homebuilders and manufacturers build spars strong, often to take both negative and positive gravitational forces. Both use aircraft grade aluminum. Both may use composite materials, which are stronger than steel. Often, the aircraft will be painted to prevent corrosion or reduce damage by light in the ultraviolet spectrum. Aircraft use reliable engines. Builders should pay attention to their electrical and avionics systems, but too often they don’t. Instead, they allow their pocketbook, or perhaps lack of knowledge, to drive them to bad choices. Manufacturers will pay an equal amount of attention to avionics and electrical systems; however, retrofitters may not. An aircraft with a retrofitted avionics stack deserves special attention. Getting your head under the panel and looking at the wire itself is a good place to start. Generally, a wire of smaller diameter is less expensive than larger American wire guage sizes. Smaller wire also is lighter. As a result, builders want to build wiring harnesses with the smallest wire possible, and in general, this is good. Installers must take care not to go too small and make a bad choice. Typically, wires will be at least 24 AWG, with power carrying wires larger. Avionics wires connected to the bus will be either 16 or 18 AWG. If you look under the panel and see many tiny wires, then you should begin to suspect the reliability of the avionics installation. Wire too small for the current being drawn will dissipate too much energy in the form of heat. This can cause two problems. The obvious problem is the wire will cook itself and other wires around it. Not quite so obvious is with energy being used to make heat, less energy is available for the equipment. Heat-related problems are bigger than they might seem. Bundling wires together will exaggerate the heat problems, and altitude makes it all worse. When you look under the panel, count the splices. Ideally, there would be none. Each splice is a potential problem. Each automotive-style crimp splice is a bigger problem, since the typical automotive splice does not include wire strain relief. Recently, a team of my students replaced a wire that had four splices over a 2-foot

length. The system is now four times more reliable, at least. Circuit protection in the form of circuit breakers or fuses is a choice builders must make. Some older-production aircraft used fuses, but most aircraft manufactured during the last 30 years use circuit breakers. The only advantage offered by a fuse is installation cost. In the case of a malfunction in flight, which causes an excess load on the electrical system, both fuses and circuit breakers will open the circuit, protecting the wiring from overheating or causing a fire. An open circuit breaker can be identified by scanning the panel. An open fuse cannot. Imagine a system going dead in flight and not knowing why. A fuse would have to be removed and visually inspected. Removal and inspection may not be an option in certain flight conditions. If the aircraft you are considering for purchase is full of fuses, then you should consider those fuses to be a negotiating tool, since a trip to the avionics shop should be in your future.

Invisible problems make one of the best arguments for circuit breaker uses. For example, perhaps a wire breaks on the landing-gear motor in an aircraft equipped with fuses. The bare end of the wire touches the airframe, causing a short. The fuse does its job and opens the circuit. The pilot will have no idea of any problem until it’s time to lower the gear. The same problem in a circuit breaker-equipped aircraft will cause the circuit breaker to “pop.” A vigilant pilot will detect the problem during a normal instrument panel scan and long before the final approach. If I am about to purchase an aircraft full of fuses on the bus, then I will plan to have enough money left to install proper aviation circuit breakers. One of the most important factors for purchasers to consider is relief of wire strain. I have worked on certified aircraft with an individual wire so taught, you could play it like a fiddle. A taught wire or wire harness
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Avionics News July 2012

Table of Contents for the Digital Edition of Avionics News July 2012

Point of Communication
AEA Now
The View From Washington
International News and Regulatory Updates
Going Glass
Member Profile
Extra Avionics
Member Profile
Glass Panel Upgrades
Aviation Aces
Business Basics
Member Profile
A Conversation With...
Making A Difference
Theory & Practice
Legal Ease
Meet the AEA Staff
What's New
Marketplace Classifies
Avionics News July 2012 - Cover1
Avionics News July 2012 - Cover2
Avionics News July 2012 - 1
Avionics News July 2012 - 2
Avionics News July 2012 - 3
Avionics News July 2012 - Point of Communication
Avionics News July 2012 - 5
Avionics News July 2012 - AEA Now
Avionics News July 2012 - 7
Avionics News July 2012 - 8
Avionics News July 2012 - 9
Avionics News July 2012 - 10
Avionics News July 2012 - 11
Avionics News July 2012 - 12
Avionics News July 2012 - 13
Avionics News July 2012 - The View From Washington
Avionics News July 2012 - 15
Avionics News July 2012 - International News and Regulatory Updates
Avionics News July 2012 - 17
Avionics News July 2012 - 18
Avionics News July 2012 - 19
Avionics News July 2012 - Going Glass
Avionics News July 2012 - 21
Avionics News July 2012 - 22
Avionics News July 2012 - 23
Avionics News July 2012 - Member Profile
Avionics News July 2012 - 25
Avionics News July 2012 - 26
Avionics News July 2012 - 27
Avionics News July 2012 - Extra Avionics
Avionics News July 2012 - 29
Avionics News July 2012 - 30
Avionics News July 2012 - 31
Avionics News July 2012 - 32
Avionics News July 2012 - 33
Avionics News July 2012 - Member Profile
Avionics News July 2012 - 35
Avionics News July 2012 - 36
Avionics News July 2012 - 37
Avionics News July 2012 - Glass Panel Upgrades
Avionics News July 2012 - 39
Avionics News July 2012 - 40
Avionics News July 2012 - 41
Avionics News July 2012 - 42
Avionics News July 2012 - 43
Avionics News July 2012 - Aviation Aces
Avionics News July 2012 - 45
Avionics News July 2012 - 46
Avionics News July 2012 - 47
Avionics News July 2012 - Business Basics
Avionics News July 2012 - 49
Avionics News July 2012 - Member Profile
Avionics News July 2012 - 51
Avionics News July 2012 - 52
Avionics News July 2012 - 53
Avionics News July 2012 - A Conversation With...
Avionics News July 2012 - 55
Avionics News July 2012 - Making A Difference
Avionics News July 2012 - 57
Avionics News July 2012 - Theory & Practice
Avionics News July 2012 - 59
Avionics News July 2012 - Legal Ease
Avionics News July 2012 - 61
Avionics News July 2012 - Meet the AEA Staff
Avionics News July 2012 - 63
Avionics News July 2012 - 64
Avionics News July 2012 - 65
Avionics News July 2012 - What's New
Avionics News July 2012 - 67
Avionics News July 2012 - 68
Avionics News July 2012 - 69
Avionics News July 2012 - Marketplace Classifies
Avionics News July 2012 - 71
Avionics News July 2012 - 72
Avionics News July 2012 - Cover3
Avionics News July 2012 - Cover4
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