Chapter 8 Flashcards
How can the remaining service life of starter generator brushes be determined?
By visually inspecting the amount of wear groove remaining on the brushes.
What components of the starter generator require periodic inspection?
Both commutator and brushes should be inspected for wear beyond operational limits.
Between field and armature windings in starter generators, which ordinarily receive current for operation in the start mode?
Generally, both field and armature receive current for operation in the start mode.
What are possible sources of low pressure compressed air used for starting jet transport aircraft equipped with air turbine starters?
A ground power unit, (GPU), an on-board auxiliary power unit (APU), compressed bleed air form an already running engine.
When should ignition ideally occur?
A specific number of degrees (as determined by the manufacturer) before the piston reaches top dead center on the compression stroke.
Why are dual magnetos used in the engine ignition system?
To improve combustion efficiency, and provide redundancy for safety.
Why is magneto timing so important?
For an engine to run properly, the spark plug in a cylinder has to fire at a specific time. To produce the required energy for the spark at the required time, it magneto must be in the E-gap position, the breaker points must start to open, and the distributor must be electrically aligned with the particular cylinder. If any of these requirements are not correctly adjusted, the engine will run rough or may not run at all. When preparing a magneto for installation, first the internal timing must be correctly adjusted, then the magneto-to-engine timing is adjusted.
What function does a magneto perform?
It produces a high-voltage that forces a spark to arc across a spark plug gap.
Name the components of a high tension magneto system.
A permanent multipole rotating magnet, soft iron core, and pole shoes.
Name the three main circuits of a high tension magneto system.
Magnetic, primary and secondary.
What is an E-gap angle?
It is a point a few degrees beyond the neutral position of a rotating magnet where maximum magnetic field stress exists.
What reduces arcing in the points and also aids the collapsing of the magnetic field in the magneto?
A capacitor.
How does a magneto produce high voltage required to fire a spark plug?
In the rotation cycle, when the magnetic rotor is in the E-gap position, the primary points open, which interrupts the current flow in the primary circuit causing a high rate of flux change in the core, and inducing a pulse of high-voltage in the secondary coil.
What is the P-lead and how does it function?
The P-lead connects the ignition switch to the primary circuit of the magneto. When the ignition switch is turned off, the P-leads on both magneto are grounded. When the ignition switch is turned to the “LEFT” position, the right magneto is grounded, so that only the left magneto operates, and visa versa.
What is a magneto timing light used for, and what does it indicate?
It is used for both internal magneto timing and magneto-to-engine timing, and indicates the exact instant the magneto points open.
Why are turbine engine igniters generally not susceptible to carbon fouling?
Because the high energy sparks they produce clean off any deposits on the firing end.
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, and is then followed by a minimum specified cooling down period.
What are the three main components of a turbine engine ignition system?
Ignition exciters, high tension leads, igniters.
When the engine is operating, what does an ammeter / load meter indicate when connected to: 1. Battery positive lead? 2. Generator output lead?
When connected to the battery positive lead, the ammeter indicates whether the battery is charging or discharging. When connected to the generator output lead, it indicates the current produced by the generator, or electrical system load.
What is done to ensure that each generator shares the load in a multiple generator system?
The generators are paralleled.
Where would you find generator rating and performance data?
On the data plate attached to the generator.
How is the voltage of a DC generator controlled?
By varying the strength of the field current.
What is the most common type of alternator used in most aircraft AC systems?
The three-phase alternator.
How does a voltage regulator control the voltage of an alternator?
By regulating the voltage output of the DC exciter.
