You've completed your preflight and it's time to "kick the tires, and light the fires." But how does your engine get your prop spinning?

The Components

To understand the finely tuned process of your aircraft's ignition system you'll need to know the basic parts.

• Battery
• Flywheel
• Magnetos
• Spark plugs

A battery provides power to the starter, a flywheel is attached to the propeller, with a set of magnetos mounted to the engine's accessory case, and two spark plugs are mounted inside each of your cylinders.

An Overview

The steps to get your engine started are:

• Prime the engine by putting fuel into intake manifold
• Start spinning the crankshaft (which spins the propeller), via the starter
• The magnetos start spinning, providing current to the spark plugs
• As you're rotating the crankshaft the pistons are being forced up and down. Then all of a sudden... *bang*... the spark plugs ingnite the fuel in the cylinders, starting the combustion process

With the engine started, you click the keys into the BOTH detent, and you're ready to get moving.

Some Engine Basics

Now that you have a broad understanding of the components and how they fit into the starting sequence let's dive a bit deeper.

How does your engine produce power? The majority of piston aircraft use four-stroke engines, meaning your engine's movement can be broken up into four phases: intake, compression, power, and exhaust.

How Magnetos work

Magnetos work on the principle of electromagnetic induction. Electromagnetic induction is the principle that if you spin a permanent magnet inside of a coil of wire you generate a current. This current travels to the spark plugs where they are used to ignite the fuel-air mixture in your cylinders.

You can control the operation of your magnetos with your ignition switch. Most aircraft have both a LEFT and RIGHT magneto, why?

The short answer is redundancy. If one of your mags stops firing, the other one will keep your engine going. Having two individual magnetos also helps you get a more even combustion, improving your power output. That's why when you do your run-up and you check the mags you'll, notice a small RPM drop between the BOTH and the LEFT/RIGHT detents.

So what is actually happening when you click the ignition switch to the LEFT and RIGHT detents? Effectively you're disabling one of your two mags by grounding it.

Another important design feature of the magneto ignition system is that they are independent of your aircraft's electrical system. As long as the engine is spinning and they aren't grounded, they will provide current. This is why if your electrical system fails your engine doesn't just quit.

The Starter

The starter runs off of battery power. Its' whole purpose is to spin the flywheel attached to the propeller to get your pistons moving. This is accomplished by a small gear that extends out from the starter unit that contacts the flywheel.

Keep in mind, if you attempt to start the engine more than once you might need to wait between start attempts, otherwise, your starter could overheat. Check your POH for suggested wait times in between start attempts. Some starters recommend waiting up to a minute between start attempts so your starter can cool down.

Common Problems

Let's face it, getting your engine started can be a challenge. Sometimes it's as simple as not priming or setting the mixture right, but other times there can be a deeper underlying problem at play.

One of the most common problems happens during the hottest months of the year. Vapor lock happens when the fuel in your fuel lines vaporizes, turning from a liquid to a gas. In other words, your fuel has boiled.

When your fuel lines are full of vaporized 100LL, your fuel pump can't get liquid fuel to the injector nozzles, which makes starting your aircraft frustrating, difficult, or impossible. Want to learn more about vapor lock? Click here.

Another common and potentially dangerous mistake you can make while starting your engine is overpriming and flooding. This often happens after an initial engine start attempt as you try to fix the problem by adding more primer. This results in fuel pooling in the cylinders. When you go to start the engine the next time the pooled fuel will splash around until...bang! it ignites, potentionally starting a fire and damaging your engine.

How do you know how much prime is too much? There is no 'one answer' for every aircraft. Talk to an experienced instructor who flies the same aircraft as you or a maintenance technician who specializes in your type of aircraft.

For more information on the reasons why starting your aircraft's engine might be so hard check out our article about common engine starting mistakes.

Your engine starts by getting the right components spinning while adding fuel and a spark. Knowing these basics doesn't just help you on your next flight review or checkride, they can be important for improving the lifespan and health of your engine.

Looking for how a jet engine starts? We also have a video for that.