Plane & Pilot
Tuesday, May 10, 2011

Caring For Your Aircraft

Part III: All About Your Aircraft’s Ignition System

Aircraft ignition systems are one of those things that few pilots give much thought to. We turn the key, the prop turns, the engine catches, and we're off for another day of flying. We know that the engine keeps running based on electrical current, but many of us are confused as to the actual role of batteries, magnetos, spark plugs and all the rest. It probably wouldn't make pilots feel much better to know that the system that keeps them safely in the sky is strikingly similar to the one that runs their lawn mower.

Even if you're not mechanically inclined, knowing how ignition systems work is critical to safety in the air. You'll need to know when it's time to head for the shop, and what to look for during preflight and routine inspections. Before you decide all this might be technical and unnecessary, know that in his autobiography, Chuck Yeager attributed much of his success as a pilot to his understanding of aircraft systems. To assist us in our explanation, we talked to Josh Christopher, Senior Piston Products Engineer for Champion Aerospace.

The Pieces
"Even though we've made them more reliable and efficient, the basic design of these ignition systems hasn't changed much since the '60s," says Christopher, "and much of the technology is from over 100 years ago." But before you start calling it "outdated," you have to realize that the ignition systems used today are the way they are because they're proven, incredibly reliable and safe. Like fabric covering, wood spars and rubber tires, ignition systems haven't changed much because they're great at what they do.

Starting inside the cockpit, your ignition system consists of a starter switch (can also be called a "mag switch"), two magnetos, a wiring harness with leads (wires) going out to each cylinder, and finally, spark plugs. The starter and battery are—believe it or not—unnecessary parts of your ignition system, and there are plenty of Cubs, Luscombes, Taylorcrafts and many other airplanes out there to prove it, but we'll include these parts in our explanation since modern aircraft are equipped with them.

Turning the master switch "ON" sends electrical current flowing from the battery to the starter. It also "un-grounds" the magnetos—think of them as electrical generators—opening a path for electrical current to flow within them. Turning the key to "START" engages the starter, causing it to turn.


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