Ignition starting system

100問 • 1年前

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A safety feature usually employed in direct cranking starters that is used to prevent the starter from reaching burst speed is the

stator nozzle design that chokes airflow and stabilizes turbine wheel speed.

In a four-stroke cycle aircraft engine, when does the ignition event take place?

Before the piston reaches TDC on compression stroke.

What likely effect would a cracked distributor rotor have on a magneto?

Ground the secondary circuit through the crack.

Sharp bends should be avoided in ignition leads primarily because

weak points may develop in the insulation through which high tension current can leak.

Using a cold spark plug in a high-compression aircraft engine would probably result in

normal operation.

The purpose of an undercurrent relay in a starter generator system is to

disconnect power from the starter-generator and ignition when sufficient engine speed is reached.

How does high-tension ignition shielding tend to reduce radio interference?

Receives and grounds high-frequency waves coming from the magneto and high-tension ignition leads.

Ignition check during engine run-up indicates a slow drop in RPM. This is usually caused by

incorrect ignition timing or valve adjustment.

The secondary coil of a magneto is grounded through the

primary coil.

When installing a magneto on an engine, the

piston in the No. 1 cylinder must be a prescribed number of degrees before top center on the compression stroke.

A certain nine-cylinder radial engine used a non- compensated single-unit, dual-type magneto with a four-pole rotating magnet and separately mounted distributors. Which of the following will have the lowest RPM at any given engine speed?

Distributors

A defective primary capacitor in a magneto is indicated by

burned and pitted breaker points.

When the ignition switch of a single (reciprocating) engine aircraft is turned to the OFF position.

the primary circuits of both magnetos are grounded.

The capacitor-type ignition system is used almost universally on turbine engines primarily because of its high voltage and

high-heat intensity.

What test instrument could be used to test an ignition harness for suspected leakage?

high tension lead tester.

The greatest density of flux lines in the magnetic circuit of a rotating magnet-type magneto occurs when the magnet is in what position?

Full alignment with the field shoe faces.

Failure of an engine to cease firing after turning the magneto switch off is an indication of

an open P-lead to ground.

In a turbine engine dc capacitor discharge ignition system, where are the high-voltage pulses formed?

At the triggering transformer.

Ignition check during engine run-up indicates excessive RPM drop during operation on the right magneto. The major portion of the RPM loss occurs rapidly after switching to the right magneto position (fast drop). The most likely cause is

faulty or fouled spark plugs.

When internally timing a magneto, the breaker points begin to open when the rotating magnet is

a few degrees past the neutral position.

When a magneto is disassembled, keepers are usually placed across the poles of the rotating magnet to reduce the loss of magnetism. These keepers are usually made of

soft iron.

What components make up the magnetic system of a magneto?

Rotating magnet, the pole shoes, the pole shoe extensions, and the coil core.

Magneto timing drift is caused by erosion of the breaker points and

wear of the cam followers.

What would be the result if a magneto breaker point mainspring did not have sufficient tension?

The points will float or bounce.

Magneto breaker point opening relative to the position of the rotating magnet and distributor rotor (internal timing) can be set most accurately

during assembly of the magneto before installation on the engine.

(1) The platinum and iridium ground electrodes used on fine wire spark plugs are extremely brittle and can be broken if they are improperly handled or adjusted. (2) When gapping massive-electrode spark plugs, a wire gauge should be inserted between the center and ground electrodes while moving the ground electrode in order to avoid setting the gap too close. Regarding the above statements.

only No. 1 is true.

Magneto pole shoes are generally made of

laminations of high-grade soft iron.

What will be the result of using too hot a spark plug?

Pre-ignition.

Hot spark plugs are generally used in aircraft powerplants

with comparatively low operating temperatures.

In an aircraft ignition system, one of the functions of the capacitor is to

facilitate a more rapid collapse of the magnetic field in the primary coil.

Inspection of pneumatic starters by maintenance technicians usually includes checking the

oil level and magnetic drain plug condition.

Which of the following statements regarding magneto switch circuits is NOT true?

In the BOTH position, the right and left magneto circuits are grounded.

.The spark occurs at the spark plug when the ignition’s

primary circuit is broken.

Spark plug fouling caused by lead deposits occurs most often

when cylinder head temperatures are relatively low.

Generally, when removing a turbine engine igniter plug, in order to eliminate the possibility of the technician receiving a lethal shock, the ignition switch is turned off and

the igniter lead is disconnected from the plug and the center electrode grounded to the engine after disconnecting the transformer-exciter input lead and waiting the prescribed time.

What is the electrical location of the primary capacitor in a high-tension magneto?

In parallel with the breaker points.

The numbers appearing on the ignition distributor block indicate the

sparking order of the distributor.

When performing a magneto ground check on an engine, correct operation is indicated by

a slight drop in RPM.

The type of ignition system used on most turbine aircraft engines is

capacitor discharge.

It is found that a shielded ignition system does not adequately reduce ignition noise, it may be necessary to install

a filter between the magneto and magneto switch.

In a typical starter-generator system, under which of the following starting circumstances may it be necessary to use the start stop button?

Hung start.

A spark plug is fouled when

its spark grounds without jumping electrodes

When internally timing a magneto, the breaker points begin to open when

the magnet poles are a few degrees beyond the neutral position.

What is the purpose of a safety gap in some magnetos?

To discharge the secondary coil’s voltage if an open occurs in the secondary circuit.

Magneto breaker points must be timed to open when the

greatest magnetic field stress exists in the magnetic circuit.

What are two parts of a distributor in an aircraft engine ignition system? 1. Coil. 2. Block. 3. Stator. 4. Rotor. 5. Transformer.

2and 4.

What are two parts of a distributor in an aircraft engine ignition system? 1. Coil. 2. Block. 3. Stator. 4. Rotor. 5. Transformer.

2and 4.

If an aircraft ignition switch is turned off and the engine continues to run normally, the trouble is probably caused by

an open ground lead in the magneto.

When removing a snieiciea spark plug. Which of the following is most likely to be damaged?

Core insulator.

The constrained-gap igniter plug used in some gas turbine engines operates at a cooler temperature because

the construction is such that the spark occurs beyond the face of the combustion chamber liner.

When does battery current flow through the primary circuit of a battery ignition coil?

When the breaker points are closed and the ignition switch is on.

How many secondary coils are required in a low tension ignition system on an 18-cylinder engine?

Which of the following breaker point characteristics is associated with a faulty capacitor?

Coarse grained.

How are most radial engine spark plug wires connected to the distributor block?

By use of cable-piercing screws.

How are most radial engine spark plug wires connected to the distributor block?

By use of cable-piercing screws.

What is the relationship between distributor and crankshaft speed of aircraft reciprocating engines?

The distributor turns at one-half crankshaft speed.

In a low-tension ignition system each spark plug requires an individual

secondary coil.

The purpose of staggered ignition is to compensate for

diluted fuel/air mixture around exhaust valve

Why are high-tension ignition cables frequently routed from the distributors to the spark plugs in flexible metallic conduits?

To reduce the effect of the high-frequency electromagnetic waves emanated during operation.

In a high-tension ignition system, a primary capacitor of too low a capacity will cause

the breaker contacts to burn.

As an aircraft engines speed is increased, the vo1tage induced in the primary coil of the magneto

increases

A spark plugs heat range is the result of

its ability to transfer heat from the firing end of the spark plug to the cylinder head.

When using an electric starter motor, current usage

is highest at the start of motor rotation.

Why are turbine engine igniters less susceptible to fouling than reciprocating engine spark plugs?

The high-intensity spark cleans the igniter.

Great caution should be exercised in handling damaged hermetically sealed turbine engine igniter transformer units because

some contain radioactive material.

Which of the following are included in a typical turbine engine ignition system? 1. Two igniter plugs. 2. Two transformers. 3. One exciter unit. 4. Two intermediate ignition leads. 5. Two low-tension igniter leads. 6. Two high-tension igniter leads.

1,3,6.

A magneto ignition switch is connected

parallel to the breaker points.

Spark plugs are considered worn out when the

electrodes have worn away to about one-half of their original dimensions.

When timing a magneto internally, the alignment of the timing marks indicates that the

breaker points are just closing.

Which of the following are distinct circuits of a high- tension magneto? 1. Magnetic. 2. Primary. 3. E-gap. 4. P-lead. 5. Secondary.

1,2,5

Which malfunctions will allow the igniters to operate when tested but be inoperative during a start attempt? 1. Conductor No. lo broken. 2. Conductor No. li broken. 3. Ignition relay inoperative. 4. Conductor No. 12 broken.

1 or 3.

What is a result of flashover’ in a distributor?

Conductive carbon trail.

Which statement is correct regarding the ignition system of a turbine engine?

The system is normally de-energized as soon as the engine start

When the switch is off in a battery ignition system. The primary circuit is

opened

If staggered ignition timing is used, the

spark plug nearest the exhaust valve will fire first.

When a •Shower of Sparks ignition system is activated at an engine start, a spark plug fires

only while both the retard and advance breaker points are open.

(Refer to Figure 5.) Which malfunctions will allow the igniters to operate normally during start but be inoperative when tested? 1. Conductor No. 14 broken. 2. Conductor No. lo broken. 3. Conductor No. 15 broken. 4. Conductor No. 12 broken.

1 or 3

When a magneto is operating, what is the probable cause for a shift in internal timing?

The cam follower wear and/or breaker points wear.

What will be the results of increasing the gap of the breaker points in a magneto?

Advance the spark and decrease its intensity.

What is the purpose of using an impulse coupling with a magneto?

To produce a momentary high rotational speed of the magneto.

How does the ignition system of a gas turbine engine differ from that of a reciprocating engine?

A high-energy spark is required for ignition.

The E-gap angle is usually defined as the number of degrees between the neutral position of the rotating magnet and the position

where the contact points open.

In reference to a •Shower of Sparks ignition system, (1) the retard breaker points are designed to keep the affected ignition system operating if the advance breaker points should fail during normal engine operation (after start). (2) the timed opening of the retard breaker points is designed to prevent engine kickback during start. Regarding the above statements.

only No.2 is true.

Spark plug heat range is determined by

its ability to transfer heat to the cylinder head.

The term reach, as applied to spark plug design and/or type, indicates the

linear distance from the shell gasket seat to the end of the threads on the shell skirt.

When using an electric starter motor, the current flow through it

is highest at the start of motor rotation.

At what RPM is a reciprocating engine ignition switch check made?

The slowest possible RPM.

In the aircraft magneto system, if the P-lead is disconnected, the magneto will be

on regardless of ignition switch position.

(Refer to Figure 5.) The type of system depicted is capable of operating with

either battery or external power.

Aircraft magneto housings are usually ventilated in order to

provide cooling and remove corrosive gases produced by normal arcing.

Air turbine starters are generally designed so that reduction gear distress or damage may be detected by

inspection of a magnetic chip detector.

The primary advantage of pneumatic (air turbine) starters over comparable electric starters for turbine engines is

high power-to-weight ratio.

(Refer to Figure 5.) With power applied to the bus bar, what wire supplies standby power to the starter relay contact?

In the event a pneumatic start valve will not operate and the manual override must be used, the starter T-handle must be closed at scheduled starter drop out because

the starter will overspeed at a given NA2.

Why do turbine engine ignition systems require high energy?

To ignite the fuel under conditions of high altitude and low temperatures.

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

A low-tension system uses a transformer coil near the spark plugs to boost voltage, while the high- tension system voltage is constant from the magneto to the spark plugs.

Capacitance after firing of a spark plug is caused by

the stored energy in the ignition shielded lead unloading after normal timed ignition.

Pneumatic starters are usually designed with what types of airflow impingement systems?

Radial inward flow turbine and axial-flow turbine.

Which of the following could cause damage to the nose ceramic or to the electrode of an aircraft spark plug?

Improper gapping procedure.

100

The purpose of a safety gap in a magneto is to

protect the high-voltage winding from damage.

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