When it comes to spark plugs, are two really better than one? Most car engines have just one spark plug per cylinder, and that seems to work just fine. But when it comes to airplanes, dual spark plugs are important for 3 major reasons.
1) Reliability. First off, reliability plays a major role as to why your aircraft’s engine has two spark plugs per cylinder. Picture this: you’re flying along in cruise, and your magneto fails. If you had a single ignition system with only one spark plug per cylinder, your engine would stop running. And your prop? Depending on your airspeed, it would either slowly windmill as you started descending toward Earth, or it would stop completely.
Remember the saying that a propeller is a big fan that keeps pilots cool, and when it stops, pilots start to sweat? There could be some major sweating from that kind of failure.
But that’s not the only problem. Let’s say you had a spark plug stop working in-flight. If you only had one spark plug per cylinder, you would lose more than 25% of your power, if you were flying a 4-cylinder engine. And if you’ve ever flown a small single-engine plane, you know that a power decrease like that could mean the difference between cruising and not being able to maintain altitude.
When it comes to spark plugs, are two really better than one?
Source: Why Do Aircraft Engines Have Two Spark Plugs Per Cylinder? | Boldmethod