• What is a magneto in an aircraft and how does it work?

We already explained, in one of our posts, what the Otto Cycle is and how four-stroke engines work, right?

Well, today, we’re going to go a bit deeper into what is a magneto, which is responsible for generating and distributing the energy needed for the spark plugs to spark and the engine to start working. Let’s get started!

What is a magneto?

A magneto is an electromechanical device that provides the electrical energy needed to ignite the fuel-air mixture in aircraft internal combustion engines. They are critical parts in the ignition system, and are mainly used in piston aircraft engines.

Magnetos are composed of several essential elements, such as the rotor, the stator, the wire windings, the breaker or contacts and the distributor. Together, these components generate and distribute the electrical current to the spark plugs at the right time.

How does a magneto work?

The basic principle behind the operation of a magneto is electromagnetic induction.

When the engine is running, the magneto is driven by the engine through gears. The magnet’s rotor, which contains permanent magnets, rotates inside the stator, which has coils of wire. This movement generates electric current in the wire windings of the stator.

The breaker interrupts the current at specific times, which causes an increase in voltage. This increased voltage is sent to the distributor, which delivers it to the spark plugs at the right time.

The spark plugs then generate the electrical spark needed to ignite the fuel-air mixture in the engine cylinders.

Interesting advantages of magnetos

The interesting thing about magnetos is that they are a stand-alone system, i.e. they are not dependent on the aircraft’s electrical system. This means that if the electrical system should happen to malfunction or fail completely in flight, the engine can continue to operate normally.

Compared to a car’s battery and coil, the aircraft’s magnetos generate a higher spark intensity, which exponentially increases the efficiency of the engine.

In addition, the system starts working with the first crankshaft revolutions and will continue to do so for as long as it keeps turning.

Double magneto, double security

Yes, we repeat ourselves a lot, but it’s the truth: aviation is the safest means of transport in existence, where every procedure has a plan B, and even a plan C. And further proof of this is the double magneto.

Aviation engines are equipped with two completely independent ignition systems, in order to avoid any possible engine failure. Each system consists of a magneto, distributor, wires and spark plugs.

Each cylinder is equipped with two spark plugs, which are fed by different systems, which greatly increases the safety of the system:

  • If one of the magnetos fails, the other can still supply power to spark the engine and keep it running.
  • Two spark plugs in each cylinder mean that if one fails, the other continues to function normally, and in normal operation they also increase the efficiency of the engine.

The magneto switch on the control panel

If you have seen the cockpit of one of our aircraft, you will have noticed that the key switch is very similar to that of a car, but how do they differ?

There are five different switch positions:

  • OFF: Off.
  • R: Only the right magneto supplies electricity to the spark plugs.
  • L: Only the left magneto supplies power to the spark plugs.
  • BOTH: Both magnetos supply power to the spark plugs.
  • START: Operates the starter which is used to start the engine.

Once the propeller is turning, it is important to turn the key quickly to the BOTH position, as keeping the starter engaged can cause serious damage to the engine.

Always test the engine before flying

Despite the redundancy of the system itself, before every flight, an engine test is performed: a procedure in which everything is checked to ensure that all is working as it was intended.

Although the engine test procedure is included in the checklist for each aircraft, it can be roughly described as follows:

  1. Raise the revolutions to a certain value.
  2. Move from the BOTH position to LEFT and see how much the revs drop.
  3. If the engine behaves strangely, return to the BOTH position and repeat the process but with RIGHT.

The RPM must not drop more than a certain number and the difference between the revolutions of one magneto and the other must not exceed a certain value. These differences are listed in the checklist.

The problem of greased spark plugs

Spark plugs are constantly in contact with the engine mixture, so they can sometimes become “greasy” and cause a sharp drop in revs or induce vibration.

This is why it is so important to adjust the mixture once we are in flight, as flying at high altitude and with the richest setting can cause a failure.

In our post about fuel mixture, we explained why it should be adjusted and how to do it correctly. Don’t miss it!

A good maintenance is essential

Undoubtedly, what is essential for the magnetos and the whole aircraft in general to work properly, is to have good maintenance.

And, at One Air, we can be very proud of this, as our own maintenance team ensures that our aircraft work perfectly.

In-house maintenance has many advantages, among which we can highlight: a reduction in work times and a great specialisation of the team.

Would you like to see the team at work? Here you have them on video!

We hope that, with this post, you have learned a little more about how general aviation aircraft engines work. If you want to continue learning and discovering new interesting facts, we recommend you to keep browsing our aviation blog.

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