Avionics News November 2012 - 21

and the new owner quickly saw the issue: adding loads of power-hungry 2012 technology into an airplane with a 1930s generator-driven electrical system. “Even if you had an alternator of a similar output, you’re still looking at a 45-year-old airplane designed to power the sparser panels of five decades ago and held together with 45-year-old wiring,” he said. The suggestion came clean and clear: Revise the update plans to include an electrical-system makeover – either as the first in a four-step project or an expansion of the first phase of the original three steps planned. One element must include an electrical system makeover for the old plane. “A 60- or 70-amp alternator conversion means all that other stuff you want to do will stay within the airplane’s electrical-system capabilities,” he said. The owner/pilot only recently became aware of the limitations of his airplane’s generator – specifically its lack of output below 1,200 revolutions per minute on the engine. Further, just like the mentor who advised against trying to squeeze 10 pounds of anything into a 5-pound package, pilots and aircraft owners must understand the problems with trying to install 55 amps of load in an airplane with a 35- or 50-amp generator or alternator. There’s no real hope that such a system will ever meet all the demands on it. Or, as the shop owner liked to say, “Fifty-amp service for a 40-amp load works; 50 amps of load on a 40-amp system doesn’t.” It’s smart to make modernizing an old airplane’s electrical system as much about modernizing the system than merely updating the generating source, whether the dynamo output of an AC alternator or the generated power of a DC generator. Let’s look at some of the options and opportunities for upgrading after we discuss the existing piston-aircraft systems, components and operating basics limits.

It’s smart to make modernizing an old airplane’s electrical system as much about modernizing the system than merely updating the generating source, whether the dynamo output of an AC alternator or the generated power of a DC generator.
components: a battery; a generating source, generally an alternator; circuit breakers to protect components and wiring; switches to control individual components; and a regulator to match the output of the generating source to demand of the active components. The battery stores power for engine starting, acts as a stand-by source should the generating source fail and buffers surges in system demand. Wiring allows power to move from the battery to the wiring through the circuit breakers; and switches route power to the individual boxes. And, in the wonderful realm of 12- and 24-volt directcurrent systems, we only need wiring to deliver power to the device; the airframe, or ground, provides the route back. Circuit breakers control banks of devices wired to the same circuit and adds a degree of over-voltage protection in the event of a regulator failure or wiring short. Switches control the flow of electrical power to individual components – navigation lights, rotating beacons, anti-collision lights, landing lights, landing-gear motors, pitot-tube heating and individual avionics gear – often
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avionics news

ELECTRICAL SYSTEMS: DETAIL THE ROLES OF THE PACKAGE COMPONENTS
The aircraft owner may not consider these basic components in an electrical system as integral to the health of the entire system and the performance of those individual

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Avionics News November 2012

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