H - Ignition and starting systems (Powerplant)

Name one general type of inertia starter

Hand, electric, combination hand and electric starters

What is a magneto

Self contained AC generator driven by engine for purpose of ignition in a reciprocating engine

Why are magneto ignition systems preferred over battery type ignition systems for reciprocating engines

Magnetos are an independent ignition source and do not rely on battery power to provide ignition

What can cause a reciprocating engine to continue to run when the ignition switch is in the off position

If there is a break in the p lead wire from the magneto to the switch, then the ignition switch cannot ground the magneto primary circuit

What is the purpose of the condenser in a high tension magneto electrical system

To prevent arcing at the points and to hasten the collapse of the magnetic field around the primary coil

What does a capacitor do in a magneto circuit

Prevents arcing at the points to hasten the collapse of the magnetic field about the primary coil

Where is the E gap position

When the poles of the rotating magnet are a few degrees past the neutral position. E gap is position at which the points begin to open

What are three major circuits of a high tension magneto system

Magnetic circuit, primary electrical circuit, and secondary electrical circuit

What are the components of a high tension magnetic circuit

Consists of permanent rotating magnet, soft iron core, and pole shoes

What happens when the primary breaker points open in a magneto

Opening breaker points stop the flow of current in the primary coil. Magnetic field emitted by the primary coil collapses. As it collapses flux lines that cut across the windings of secondary coils induce a pulse of high voltage current in the secondary coil needed to fire the spark plugs

What is the piston position when the spark occurs in a cylinder

Piston is a specified number of degrees before top dead center on the compression stroke

What is a dual magneto

Incorporates two magnetos in one housing. They share the rotating magnet and cam, however they have their own set of points, coils, and distributor blocks

What is the difference between a low tension and a high tension ignition system

In the high tension system, high voltage is generated in the magneto and flows through low tension leads. In a low tension systems, the low voltage is generated in the magneto and flows through low tension leads to the primary windings of a transformer coil located near each spark plug. There the voltage is increased to high voltage by transformer action and is conducted to the plugs by very short high tension leads.

When the ignition switch is in the off position, what is the condition of the primary circuit

It is completed through the ignition switch to ground

What three conditions are required to fire plugs in a cylinder when the piston is in the prescribed position

The magnetos magnet poles must be in the e gap position, the breaker points must open, and the distributor rotor must be aligned with a distributor electrode for that cylinder

What is the dual ignition system, and what part of the system is grounded when the ignition switch is placed in the RIGHT position

A dual ignition system uses two separate magnetos with the harness arranged so that each magneto fires one plug in each cylinder. If the switch is set to right, the left magneto will be grounded, preventing it from firing

What is the internal timing of a magneto

It is adjusting the breaker points to open when the poles of the rotating magnet are at the E gap position

What is the purpose of an impulse coupling used with a magneto

The impulse coupling is used to retard the timing of the spark to after too dead center for starting the engine. It provides a momentarily high rotational speed to produce a spark at low crankshaft rpm

What is staggered ignition timing

It is the firing of one spark plug before the other. Instead of firing them simultaneously

What is the proper spark plug reach

Is when the electrode end of the plug inside the cylinder is in the best position to achieve ignition

Why is it important to keep track of the cylinders that spark plugs are installed in

Because spark plugs can provide a lot of information about the health of a specific cylinder

What type ignition system is used in most turbine engines

A typical turbine engine is equipped with an electronic capacitor type ignition system

What is the function of the igniter plugs in a turbine engine

Provide a discharge gap for current, which is stored in the capacitor. The discharge results in a high intensity spark which ignites the fuel air mixture

When are turbine engine ignition systems normally in use

Ignition system is only required for starting or restarting an engine

What are two types of igniter plugs

Annular gap ( long reach plug extends into combustion chamber), constrained gap ( short reach plug that does not extend into the chamber bc spark plug isn’t close to plug)

What is the purpose of the dual magneto configuration

For redundancy and safety, in case one magneto fails

How can you tell if a starter commutator is dirty or worn

Excessively noisy starter

What does it mean when the starter relay clicks when the starter switch is placed in the start position

Indicates supply of voltage is too low to supply enough current to the relay coil to fully engage the contact points

What is an advantage of air turbine starters, when compared to electric starters, for large turbine engines.

They are light weight, and do not have the same cool down periods as electric starters

Why do turbine ignitors not get carbon fouled as often as reciprocating engine spark plugs

Due to extremely high rates of electrical discharge in the turbine ignitors

What are three parts of an ignition systems of a turbine

Exciter, ignition lead, igniter

What is the difference between a temporary magnet and a permanent magnet

A permanent magnet is one that retains its magnetic properties for a long period of time. Temporary magnets also called an electromagnet are those that simply act like permanent magnets when they are within a strong magnetic field or have current flowing near them

What does the ignition light indicate when timing a magneto

Indicates when the points are beginning to open

In terms of the engine crankshaft position, when does the ignition event occur

A specified number of crankshaft degrees before the top dead center on the compression stroke

What is the purpose of the capacitor in a magneto

Capacitor prevents arcing at the points and aids in the collapsing of the magnetic field

What is the main concern when prepairing a magneto for installation

Internal timing

What are the three events required to fire a spark plug in a cylinder when it’s piston is in the prescribed position

Magneto in E gap position, breaker points opening and the distributor electrically aligned with that cylinder

What is the function of a duty cycle in relation to a turbine engine ignition system

A duty cycle allows the operation of the ignition system for a given amount of time, to be followed by a minimum specified cooling down period

Name 3 sources of high volume, low pressure compressed air commonly used for starting jet transport aircraft equipped with air turbine starters

An onboard auxiliary power unit, a ground power unit and compressor bleed air from an already running engine.

Name two parts of a starter generator that commonly require periodic inspection to ensure that they do not wear at beyond operational limits

Commutator and brushes

Between the field and armature windings in starter generator, which ordinarily receive current from operation in the start mode

field and armature

What are the three components of a spark plug

Electrode, insulator and bore

Spark plug leads perform 2 functions

Carry voltage, shield power from radios