Ignition system components piston engines Flashcards
(51 cards)
What are the two main classifications of ignition systems for reciprocating engines?
Magneto-ignition systems and Electronic Full Authority Digital Engine Control (FADEC).
What are the sub-classifications of Magneto Ignition systems?
Magneto Ignition systems can be subclassified as either single or dual magneto-ignition systems.
Describe the basic operating principle of a Magneto-Ignition System.
It operates as an engine-driven AC generator using a permanent magnet, which generates a magnetic field. This field induces a current in a coil, and when interrupted, produces high voltage necessary for a spark plug to ignite the air-fuel mixture.
What is the difference between high-tension and low-tension magneto systems?
The low-tension magneto system generates low voltage distributed to a transformer coil near each spark plug, while the high-tension system directly generates high voltage to fire the spark plug.
What three essential elements are required to generate electrical power in a magneto system?
A permanent magnet, a coil of wire, and relative movement of the magnetic field.
What happens when the magneto reaches the ‘full register position’?
The number of magnetic lines of force through the coil core is at a maximum, producing the highest amount of flux.
What is the significance of the timing in the magneto system?
The timing ensures that the spark occurs when the piston is on the correct stroke, typically a specific number of degrees before reaching the top-dead-center piston position.
What is the purpose of the secondary electrical circuit in a magneto?
The secondary circuit contains the secondary coil, distributor rotor, distributor cap, ignition lead, and spark plug, directing high voltage to the spark plug to ignite the air-fuel mixture.
What are the three circuits in a high-tension magneto system?
The magnetic circuit, the primary electrical circuit, and the secondary electrical circuit.
What occurs when the magneto is in the ‘neutral position’?
All flux lines are short-circuited, and no flux flows through the coil core, leading to zero voltage production.
What is the role of the magnetic circuit in a magneto?
It consists of a permanent magnet, soft iron core, and pole shoes. The magnet rotates, creating magnetic flux that produces voltage when it interacts with the coil core.
What components are part of the primary electrical circuit in a magneto?
The primary electrical circuit includes breaker contact points, a condenser, and an insulated coil.
Describe the role of the breaker contact points in a magneto system.
Breaker contact points open and close the primary circuit, controlling the timing of the magnetic field’s collapse and subsequent high voltage production in the secondary circuit.
Explain the significance of the ‘E-gap’ position in a magneto.
The E-gap position is where the magnetic rotor and primary coil are set to achieve maximum efficiency by holding the magnetic field at a high value until the breaker points open, causing a high rate of flux change and inducing high voltage in the secondary coil.
What is the function of the condenser in a magneto’s primary circuit?
The condenser prevents arcing at the breaker points and hastens the collapse of the magnetic field, which is essential for generating high voltage.
How does the ignition lead in a magneto system function?
The ignition lead directs high-voltage current from the magneto to the spark plug and also shields against electrical interference.
Why is shielding important in the ignition harness?
Shielding prevents electromagnetic interference from the high-frequency oscillations of the magneto, protecting sensitive electronic equipment.
How does lead capacitance affect the magneto system?
Increased lead capacitance requires more magneto current to fire the spark plug, as it stores electrical energy that discharges across the plug gap.
What happens when the ignition switch is in the ‘off’ position?
The primary circuit is completed through the switch to ground, preventing the magneto from generating high voltage and firing the spark plug.
What is the role of the ignition switch in an aircraft ignition system?
The ignition switch controls the system, turning it on and off by completing or breaking the primary circuit to ground.
What are the safety requirements for the maintenance of starting and ignition systems in reciprocating engines?
The safety requirements include ensuring that the ignition system is made safe before working on or around the magneto system or engine. This involves placing the ignition switch to OFF, turning the fuel switches OFF, and possibly isolating the primary lead on the distributor cap. A warning sign should also be placed over the ignition switch.
What is a magneto, and what is its significance in aircraft engines?
A magneto is a device that generates electrical current for the spark plugs in an aircraft engine. It is significant because it allows the engine to operate independently of the aircraft’s electrical system. Even if one magneto fails, the engine can still operate, but it is never acceptable to fly knowing that only one magneto is functioning.
What is a magneto drop test, and why is it important?
A magneto drop test involves running the engine at a designed speed (around 1700 rpm) and switching between magneto positions (left, right, and both) to ensure that the magneto disconnects when grounded. It is important because it checks if the magnetos are functioning properly, and if the rpm drop exceeds specified limits, the flight should not continue.
What is the risk associated with the high-tension (HT) part of the ignition system?
The HT part of the ignition system can be lethal as it typically generates voltages in excess of 10,000 volts, sometimes exceeding 25,000 volts. Proper precautions must be taken to avoid serious injury when working near it.
