Aircraft Ignition and Electrical Power Systems Part 1

gadihija's version from 2016-04-13 13:59

Jeppesen Ebook Q & A

Question Answer
What happens in a conductor when it cuts across lines of magnetic flux?A voltage is generated which causes current to flow in the conductor
What determines the amount of current that will be generated in a wire moving in a magnetic field?The rate at which the lines of magnetic flux are cut.
Does induced current aid or oppose the current that caused it?It opposes it.
Does the spark from a battery ignition system become stronger or weaker as the engine speed increases?It becomes weaker.
What provision is made in a magneto or battery ignition system to minimize the arcing across the breaker points?A capacitor is installed in parallel with the points.
Does the spark from a magneto become stronger or weaker as the engine speed increases?It becomes stronger
Is the primary current in a magneto pulsating direct current or alternating current?Alternating current
At which position of a rotating magnet is the change type the greatest?In the neutral position
Why does the maximum primary current not occur at the neutral position where the maximum rate of static flux occurs?The magnetic field caused by current flowing in the primary coil delays the buildup of primary current until the magnet has rotated beyond its neutral position.
Is the primary capacitor in series or in parallel with the breaker points?Parallel
Of what material is the core of a magneto coil made?Laminated soft iron
When a magneto switch is open, is the magneto "on" or "off?"On
How does a dual magneto differ from a single magneto?A dual magneto has a single rotating magnet, cam, and housing; but there are two of each of the other components of the ignition system
How can a low-tension magneto produce a spark in an engine cylinder?Low voltage is generated in the magneto and carried through the distributor, but it is changed into high voltage in transformers located near each spark plug.
Why is there little danger of flash-over in the distributor of a low-tension magneto?The brush-type distributor used in a low-tension magneto carries no high voltage.
Where does a booster magneto direct its output?To a trailing finger on the distributor of one of the magnetos
What is the purpose of an impulse coupling?The impulse coupling holds the magneto and winds a clock-like spring as the engine rotates beyond its firing position. When the coupling releases, the spring spins the magneto and produces a late and hot spark for starting.
What is the purpose of the extra set of breaker points in a magneto equipped for the Shower of Sparks starting system?The retard points are in the magneto circuit only when the ignition switch is in the "start" position. They provide a late spark for starting.
Name four things that happen when the ignition switch for an engine equipped with the Shower of Sparks system is put in the "Start" position.1. The right magneto is grounded. 2. The retard points are placed in the primary circuit of the left magneto. 3. The induction vibrator is energized, sending pulsating DC into the primary circuit of the left magneto. 4. The starter solenoid is energized.
What is the condition of the primary current at the moment the breaker points open on a properly timed magneto?The maximum amount of primary current is flowing
Which is more important in checking the timing of a magneto, the time the points open, or the amount they open?The time in relation to the position of the rotating magnet and the piston of the engine.
Where is the piston in the cylinder when normal ignition occurs?Somewhere around thirty degrees of crankshaft rotation before top center on the compression stroke.
Who do high-performance radial engines use compensated cams in their magnetos?To assure that the spark will occur when the piston is at the proper linear distance from the top of its stroke. On a radial engine this is not consistent with angular distance.
What should be done to an impulse coupling on a magneto when timing the magneto to the engine?The propeller should be turned until the impulse coupling snaps and then backed up enough to close the points on the magneto.
How is a Slick magneto held in its E-gap position when the magneto is installed on the engine?A timing pin is inserted through a hole in the bottom of the magneto housing into a matching hole in the rotor.
What provision is made in the nonserviceable-type Slick magnetos to maintain the proper internal timing for the entire engine overhaul period?The magneto is engineered so that the wear of the breaker cam should exactly balance the wear of the breaker points.
What are the two functions of the capacitor in a Bendix D-2000 dual magneto?It serves as a radio interference filter, as well as an arc suppressor for the points.
Are the retard points opened by the same cam as the regular points on a Bendix D-2000 dual magneto?No, a second cam, stacked on top of the regular cam, operates the retard points.
What two types of conductors are used for aircraft ignition leads?Stranded wire and coiled or spiraled wire
What type of material is currently used for the terminal insulator fora shielded spark plug lead?Silicone rubber
What are the two sizes of terminal end nuts for modern shielded ignition leads?5/8-24 and 3/4-20.
How are the ends of the shielding usually terminated in an ignition harness?The shielding is usually clamped between a tapered inner and outer ferrule
What are two advantages of a fine-wire spark plug over a massive-electrode plug?Fine-wire spark plugs are less susceptible to lead fouling, and they can produce their spark with a lower voltage than massive-electrode plugs.
What size thread is used on the firing end of most aircraft spark plugs?Eighteen millimeters
What is the purpose of shielding on a spark plug and ignition lead?It prevents radiation from the high voltage in the ignition system from causing radio interference.
What is an "all weather" spark plug?A shielded spark plug with a 3/4-20 shielding. A resilient plug fits into a recess in the shielding and forms a watertight seal, keeping moisture out of the spark plug.
Of what material is the center electrode constructed on a massive-electrode spark plug?The center electrode on a massive-electrode spark plug is a copper-filled nickel alloy sheath.
On what type engine would a "hot" spark plug be used?A low-compression engine that does not produce enough heat to keep all of the lead deposits burned off of the spark plug nose insulator.
What is the purpose of a resistor in a resistor spark plug?The resistor limits peak current that flows during discharge of the spark and minimizes spark plug electrode erosion.
Of what material are the electrodes made for fine-wire spark plugs?Platinum or iridium.
What is a good indication of excessive wear on a massive-electrode spark plug?When the center electrode wears away about 0.030 inches of its outer diameter, it is worn beyond its usable limit.
What inspection should be made e 'a spark plug shows signs of having been severely overheated?The cylinder should be checked for other indications of damage from detonation.
What is the best way to remove the lead deposits from the firing end cavity of a spark plug?By using a vibrator-type cleaner
What could likely be indicated by a black, oily deposit in the firing end cavity of a spark plug?There is possibility of a broken piston ring or excessively worn valve guides.
What are the two natural attritional forces which determine the operational life of a spark plug?Gap growth and fouling
Why is it recommended that spark plugs be rotated from top to bottom, and to the next cylinder in firing order when they are replaced after being serviced?Rotation of the spark plugs each time they are serviced evens out the electrode wear
How much abrasive blasting should a spark plug be given after all of the lead deposits have been loosened?The absolute least amount that will remove the loosened deposits.
What can properly be used to clean the terminal end of a shielded spark plug?Bon Ami on a swab, or a special cleaning tool
What should be done with a massive-electrode spark plug that has had the electrode gap closed too much?It should be discarded. It is not recommended that the gaps be opened.
What special precautions should be used when gapping a fine-wire spark plug?The ground electrode is very brittle and should not be bent more than is required to properly close the gap.
What would be indicated by a spark plug that occasionally "blacks out" when it is being tested in a combination cleaner-tester?The spark plug is likely to fail in service and should be replaced
What is the danger of installing a spark plug with too much torque?The shell could be stretched or the threads overstressed letting gas escape
What is the danger of installing a spark plug with too little torque?An imperfect seal could result, causing gases to escape and damage the spark plug or the cylinder head.
If the fingers of the left hand encircle a conductor in the direction of the lines of magnetic flux, in what direction is the electron flow?In the direction pointed by the thumb.
If the ends of an armature coil are attached to slip rings, which will be produced, AC or DC?AC
What three things determine the amount of current produced in an electromagnetic generator?1. The number of lines of magnetic flux. 2. The number of conductors cutting the flux. 3. The speed at which the conductors move through the flux.
What determines the distance the neutral plane of a generator moves away from the brushes?The amount of current in the armature windings; the load current
Name three methods of minimizing brush arcing from armature reaction.1. Movable brush rigging. 2. Interpoles. 3. Compensating windings
How is the voltage output of a generator controlled?By controlling the excitation current in the generator field windings.
What makes a series-wound generator impractical for use in an aircraft power system?Voltage control of a series-wound generator is difficult
Which field has the greater effect in a compound generator if the output voltage increases with an increase in load current?The series field
What type of current limiter is used in large, high-output generators?A special heavy-duty fuse.
Why do alternators not require a reverse-current cut-out relay, as generators do?The diodes in the output circuit prevent reverse current flow into the stator windings.
Why must generators which concurrently feed the bus of a multi-engine aircraft be paralleled?If the generators are not paralleled, one will carry all of the load.
What is the purpose of the accelerator winding on some vibrator-type voltage regulators?When the points open, the field of the accelerator winding collapses instantly and allows the points to close more rapidly than they would if the accelerator winding were not used.
What is done to the generator field circuit when the points of a vibrator-type voltage regulator open?A resistor is inserted into the field circuit, decreasing the field current
What causes the points of a reverse-current cut-out relay to close?They close when the generator output voltage rises to the pre-set value.
What causes the points of a reverse-current cut-out relay to open?When generator output voltage drops below battery voltage, reverse current flows through the series winding and cancels the field of the voltage coil, allowing the spring to open the points.
How does a vibrator-type current limiter decrease the generator current output?Inserting a resistor into the generator field reduces the output voltage and therefore the current.
What is the difference between the Delco-Remy "A" circuit and "B" circuit generators?In the "A" circuit, the field attaches to the insulated brush inside the generator, and in the "B" circuit it attaches to the grounded brush.
What is the purpose of the upper set of points on some double-contact vibrator-type voltage regulators?When voltage output is high and the regulator points are vibrating off of the upper contact, the field either has a resistor in it, or both ends are grounded, decreasing the field flux to zero.
In a three-unit generator control system, which two units have heavy windings?The current limiter and the reverse-current cut-out relay.
What two forces act in a carbon pile voltage regulator to vary the force on the carbon pile?The force of the spring decreases carbon pile resistance, and the pull of the electromagnet increases it.
What happens to the resistance of the carbon pile as generator output voltage increases?It increases.
In a twin-engine aircraft using carbon-pile voltage regulators, what is used to hold the output of the two generators equal?The equalizing coils on the two voltage regulators will hold the voltage constant by increasing the voltage of the low generator and decreasing that of the high generator
What causes a differential-voltage reverse-current relay to take the generator off of the line?reverse flow of current through the reverse-current coil.
What type of rectifier is used with a DC alternator?Six silicon diodes arranged as a three-phase, full-wave rectifier.
Why does a DC alternator not require heavy brushes for the load current?All of the load current from a DC alternator comes from the stator, the fixed winding.
Why does a DC alternator normally put out its rated current at lower engine RPM than a DC generator?DC alternators normally have a greater number of poles in their field than DC generators
How many diodes are used to form the rectifier in a DC alternator?six
Why does a brushless alternator not require brushes for its operation?The excitation voltage is induced into the rotor, rather than being taken in through slip rings.