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You could successfully argue that fuel is the most important "juice" in the airplane.

But when it's night, and you're in the clouds, maybe over rough terrain, the other kind of juice—the electric kind—shoots up to meet avgas at the top of the scale.

Your aircraft's battery is a storage device for this juice. When it's healthy, and your alternator or generator is healthy, and everything in the electrical system is working as it should, that battery charges effectively each time you fly. And it should hold onto enough charge to power the devices you need to navigate back to a runway in the event of a loss of the electrical system's primary source of power.

It's a simple system, but there are potential problems. The battery contactor relay (in the case of the 1977 Cessna Cardinal we've refurbished for this year's sweepstakes, it's on the aircraft's battery box) can be a major stumbling point.

Any time that the master switch is on, the battery contactor relay closes (completing the circuit), so juice from the battery can flow anywhere. Most of the time this is not an issue, but if there is a short on a bus or within a device connected to the system, current can flow from the battery, silently draining it.

What can you do?
When the master switch is off, that contactor opens, sealing in whatever charge the battery holds. It's trapped. That's why, when you suspect a problem with the electrical system—evidenced by a popped breaker, high discharge rate on the ammeter, or (worse case) the smell of burning wires—your most effective move to stop the problem is to stop the all discharge from the battery by shutting off the master switch. Now, this is not always practical, from an instrument navigation or panel lighting standpoint, so it would be nice to have another option.

If the problem exists on the avionics, electronic, or radio bus installed in many light aircraft, you may be able to isolate the problem by first turning off the avionics master, if that switch is installed as well. However, if the problem exists on the main electrical bus, your only recourse may be to start with the master. And this can make your cockpit mighty dark and awful quiet, depending on the circumstances.

Light general aviation aircraft manufactured in roughly the last 10 years, by and large, have another solution installed, in the form of an essential bus. We've put one in your Cardinal as well. An essential bus is a separate bus within the electrical system that ties together a handful of the most critical devices and powers them through a second source—or in the case of the essential bus installed in the Catch-A-Cardinal, a second set of wires supplied by a bus that bypasses the battery contactor relay.

So, in the event the battery contactor relay opens or a complete short to ground of the main bus results in high current flow, the future winner of the Cardinal has the option to kill the master switch and then activate the essential bus toggle switch on the left-side subpanel, energizing just the components on the essential bus straight from the battery.

We've ensured each component on the essential bus has a shut-off switch as well, allowing the pilot to further isolate each device in the event the short emanates from a device on the essential bus. That means we have a dedicated Bendix/King HSI (horizontal situation indicator) switch to complement the on/off switches on the number-two Garmin GNS 430W navigator and GTX 330 transponder.

Bringing it online
Because the Cardinal did not come with an essential bus tied into its electrical system, Dan Gryder, of the AvNet and I determined we would need either an FAA field approval or a designated engineering representative (DER) to obtain the blessing to add one to the airplane. This simple yet highly effective safety device is a no-brainer to most electrical engineering types, so in the interest of efficiency we opted to cover the system, paperwork-wise, via a DER.

David Chadwick, a DER with electrical engineering amongst his specialties, came to us through another friend of the project, Harold Kosola, of Kosola & Associates, which overhauled the Cardinal's engine mount and has helped significantly with past sweepstakes projects. Chadwick's company, DC Aerospace, holds several supplemental type certificates, and Kosola let me know that our essential bus would likely be "no sweat" for someone with Chadwick's credentials.

Indeed, Chadwick has visited the airplane on a couple of occasions now, and will be preparing his report shortly. Next week, we'll walk you through that process. The metal instrument panel has also undergone some final wish list improvements. After flying behind this panel for roughly 60 flight hours, we couldn't help but notice a few things ourselves. Close inspection showed some gaps we wanted to close up. A new panel at this late stage in the game is possible courtesy of the new technology in development at Jet Panels in Peachtree City, Georgia, because they can turn a panel around for us so quickly. This final panel has now gone to paint where the finish will be applied and the final silk-screening of all placards and text, courtesy of Precision Avionics, Advanced Aircraft Refinishers, and Air Capitol Dial.

E-mail the author at julie.boatman@aopa.org.

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