Avionics News November 2012 - 23

panel-installed gear, where and how to arrange breakers and switches and how to run wiring to connect the entire system. You can do this with the old radios, while equipping the wiring system for the upgrades to follow.

ELECTRICAL SYSTEMS
An Aircraft’s Sole Unnecessary Must-Have
We wouldn’t need an electrical system if it wasn’t for things we want to do with our airplanes. But, when dissecting the peculiars and particulars of modern, even elderly, general aviation aircraft, two striking realities jump out: to fly, aircraft generally need neither of two of their most-ubiquitous systems – instruments packages and electrical systems. Acknowledging that aviation regulators decades ago made a basic instrument cluster integral to certification, airplanes don’t actually need them to fly. And, what’s required is a minimal list for operating day/VFR per Federal Aviation Regulation 91.205(b): compass; airspeed indicator; manifold pressure gauge; altimeter; lights (with a caveat); seatbelts; fuel gauge; oil-pressure gauge; old-temperature gauge; and tachometer for the engine. Nonetheless, thousands of airplanes emerged from factories without an electrical system, among them models still amazingly popular today. Piper’s 75-year-old Piper J-3 Cub and Taylorcraft, Aeroncas and Ercoupes, Luscombes and many others lack electrical systems and use air-driven systems to meet instrument regulatory requirements. So, again, why add the weight of an electrical system at all? First, electrical systems allow pilots to start our planes while saving countless fingers by moving us off hand-propping; besides, an electrical system should be considered mandatory for starting today’s high-compression, largedisplacement engines. Also, pilots have evolved to covet electrically powered navigation indicators driven by electrically powered navigation radios to show us which way to fly and where we are. Pilots also covet radios to communicate with controllers and airports, fixed base operators and other airplanes. And, let’s not forget autopilots, so the airplane doesn’t actually need constant human corrections to altitude, attitude and vector disruptions. True, absent the above luxuries, we have little real need for electrical systems. The old-style magneto-sparked reciprocating engine runs nicely without electrical power – and the plane can fly fine with no instruments. q

OPTIONS AND OPTIONS: ALTERNATORS, REGULATORS AND BREAKERS, OH MY
The customer must know the 70-amp system can handle the 55 amps of load planned, and going cheap on the 50-amp alternator is a bad idea. Regulators to control the alternator output should match the capacity of the system; encourage the owner/pilot to look for a solid-state, all-electronic model, one that ideally offers a warning light that flashes should over-voltage trip the alternator offline or the alternator output drop below a pre-set level. You can explain the so-called idiot light that serves as a graphic wake-up call for an electrical-system problem, as well as a reminder to flip off the master switch. Planning for the electrical-system upgrade also is an ideal time to encourage the owner to consider adding a stand-by alternator and/ or a stand-by electrical bus. Today, a common stand-by alternator bolts to the engine in place of the enginedriven suction pump driving air-powered gyros. A stand-by power source can provide a measure of life-saving auxiliary power in the event the main alternator system fails. If an STC’d system is unavailable, the FAA has a record of accepting well-planned, and appropriately documented Form 337 applications for field approvals. Finally, encourage the owner/pilot to consider building in capacity to grow. As the shop owner noted to the new owner/pilot, “Savvy owners never completely stop looking for upgrade paths. And, who knows what the next must-have cockpit device might be and how we’ll power it?” An airplane with an electrical-system update based on the largest alternator the engine can handle stands a much higher prospect of handling the new gear today, as well as tomorrow. q

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2012

Avionics News November 2012

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