Powerplant Chapter 08 Flashcards
Electrical, Starting, and Ignition Systems
What components of the starter–generator require periodic inspection?
Both commutator and brushes should be inspected for wear beyond operational limits.
How can the remaining service life of starter–generator brushes be determined?
By visually inspecting the amount of wear groove remaining on the brushes.
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.
