Understanding Magnetos
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The Magneto is its own powerhouse creating high voltage with help of a turning magnet completely independent of the on board electrical system (Alternator/Battery/…)
WHY DO WE NEED MAGNETOS?
So Magnetos produce a high voltage spark that is delivered to a spark plug in order to ignite the mixture inside a cylinder during the Power Stroke. Most reciprocating engines in aviation are based on a 4-stroke operating cycle:
- Induction / Intake: The mixture is drawn into the cylinder
- Compression: The mixture is compressed
- Power: The mixture is ignited by a spark plug, which forces the piston down creating the Power necessary to rotate the crankshaft, which turns the propeller to generate the necessary thrust to fly.
- Exhaust: Finally in the last stroke the burned gases are drawn out of the cylinder
So now you understand why we need magnetos? But how does it actually create the high voltage of electricity?
WHAT ARE MAGNETOS?
As mentioned before, the Magneto delivers high voltage to the spark plug in order to ignite the fuel-air mixture to create the Power Stroke within the cylinder. That turns the crankshaft and the crankshaft turns the propeller to generate thrust. The crankshaft not only turns the propeller but various other system to:
- Engine Driven Fuel Pump
- Camshaft → That controls the exhaust and intake valve open and closing
- Magnetos
- …
It is important to note that the MAGNETOS ARE ENGINE DRIVEN they are Connected to the Crankshaft through a gearbox.
HOW DOES A MAGNETO WORK?
As mentioned before, the Magneto is engine driven and so independent of the on board electrical system! Remember that if the electrical system were to fail the engine will continue to run! For safety reasons 2 Magnetos exist on most airplanes and also 2 spark plugs per cylinder also increasing engine efficiency! Both of the magnetos are independent of each other!
So now let's get to the more exciting part. I have drawn the magneto system, seen in this picture above, hopefully you're able to understand it ;)
- As the crankshaft turns it also turns a magnet also known as the rotor
Next to the Rotor is the COIL ASSEMBLY:
- In the middle is an iron core. This iron bar is winded with a Primary coil (200 turns of heavy coper wire), connected to the primary circuit.
- and on top is a Secondary Coil (20'000 turns of fine coper wire) connected to the secondary circuit
Once the Magnet is turning it induces a continuously changing flowing current in the primary current. Creating a strong magnetic field in the iron core expanding outwards.
As seen above the Primary current is made up of a condenser, contact breaker and a breaker cam,…
The breaker contact once open creates a collapse of the magnetic field inducing a huge voltage spike in the secondary winding. (20–30k Volt)
The Contact Breaker is controlled by the breaker cam
The condenser or also known as capacitor assists creating a rapid collapse and prevents burning or arcing along the contact breaker.
The high voltage in the secondary winding is directed by the distributor to the spark plugs in proper sequence. Note that the spark plugs aren't firing at the same time! Within the 4-stroke cycle there is only one power stroke at a time!
Aerodynamics for Naval Aviators: https://amzn.to/3bVQF5C
In my opinion EVERY pilot should read this book! This Book is about aerodynamics and much more, it was written for NAVY PILOTS and it became the foundation for every pilot textbook and it explains each concept of flying in an EASY way :)
Thanks For Reading and Happy Landings!
