Questions - Aircraft Powerplant Ignition and Starting Systems


1. 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
a. chrome magnet steel.
b. soft iron.
c. cobalt steel.

2. How is the strength of a magneto magnet checked?
a. Hold the points open and check the output of the primary coil with an ac ammeter while operating the magneto at a specified speed.
b. Check the ac voltage reading at the breaker points.
c. Check the output of the secondary coil with an ac ammeter while operating the magneto at a specified speed.

3. The E-gap angle is usually defined as the number of degrees between the neutral position of the rotating magnet and the position
a. where the contact points close.
b. where the contact points open.
c. of greatest magnetic flux density.

4. The greatest density of flux lines in the magnetic circuit of a rotating magnet-type magneto occurs when the magnet is in what position?
a. Full alignment with the field shoe faces.
b. A certain angular displacement beyond the neutral position, referred to as E-gap angle or position.
c. The position where the contact points open.

5. Magneto breaker point opening relative to the position of the rotating magnet and distributor rotor (internal timing) can be set most accurately
a. during the magneto-to-engine timing operation.
b. during assembly of the magneto before installation on the engine.
c. by setting the points roughly at the required clearance before installing the magneto and then making the fine breaker point adjustment after installation to compensate for wear in the magneto drive train.

6. Why are high-tension ignition cables frequently routed from the distributors to the spark plugs in flexible metallic conduits?
a. To eliminate high altitude flashover.
b. To reduce the formation of corona and nitric oxide on the cable insulation.
c. To reduce the effect of the high-frequency electromagnetic waves emanated during operation.


7. What will be the results of increasing the gap of the breaker points in a magneto?
a. Retard the spark and increase its intensity.
b. Advance the spark and decrease its intensity.
c. Retard the spark and decrease its intensity.

8. What is the purpose of a safety gap in some magnetos?
a. To discharge the secondary coil's voltage if an open occurs in the secondary circuit.
b. To ground the magneto when the ignition switch is off.
c. To prevent flashover in the distributor.

9. When timing a magneto internally, the alignment of the timing marks indicates that the
a. breaker points are just closing.
b. magnets are in the neutral position.
c. magnets are in the E-gap position.

10. When internally timing a magneto, the breaker points begin to open when the rotating magnet is
a. fully aligned with the pole shoes.
b. a few degrees past full alignment with the pole shoes.
c. a few degrees past the neutral position.

11. What is the electrical location of the primary capacitor in a high-tension magneto?
a. In parallel with the breaker points.
b. In series with the breaker points.
c. In a series with the primary and secondary winding.

12. In a high-tension ignition system, the current in the magneto secondary winding is
a. conducted from the primary winding via the discharge of the capacitor.
b. induced when the primary circuit is interrupted.
c. induced when the primary circuit discharges via the breaker points.

13. When a "Shower of Sparks" ignition system is activated at an engine start, a spark plug fires
a. as soon as the advance breaker points open.
b. only while both the retard and advance breaker points are closed.
c. only while both the retard and advance breaker points are open.

14. What is the radial location of the two north poles of a four-pole rotating magnet in a high-tension magneto?
a. 180" apart.
b. 270" apart.
c. 90" apart.

15. Magneto timing drift is caused by erosion of the breaker points and
a. excessive spark plug gap.
b. wear of the cam followers.
c. loss of magnetism in the rotor.

16. Capacitance afterfiring in most modern spark plugs is reduced by the use of
a. fine wire electrodes.
b. a built-in resistor in each plug.
c. aluminum oxide insulation.

17. What components make up the magnetic system of a magneto?
a. Pole shoes, the pole shoe extensions, and the primary coil.
b. Primary and secondary coils.
c. Rotating magnet, the pole shoes, the pole shoe extensions, and the coil core.

18. In an aircraft ignition system, one of the functions of the capacitor is to
a. regulate the flow of current between the primary and secondary coil.
b. facilitate a more rapid collapse of the magnetic field in the primary coil.
c. stop the flow of magnetic lines of force when the points open.

19. When will the voltage in the secondary winding of a magneto, installed on a normally operating engine, be at its highest value?
a. Just prior to spark plug firing.
b. Toward the latter part of the spark duration when the flame front reaches its maximum velocity.
c. Immediately after the breaker points close.

20. When the switch is off in a battery ignition system, the primary circuit is
a. grounded.
b. opened.
c. shorted.

21. As an aircraft engine's speed is increased, the voltage induced in the primary coil of the magneto
a. remains constant.
b. increases.
c. varies with the setting of the voltage regulator.

22. When internally timing a magneto, the breaker points begin to open when
a. the piston has just passed TDC at the end of the compression stroke.
b. the magnet poles are a few degrees beyond the neutral position.
c. the magnet poles are fully aligned with the pole shoes.

23. The purpose of a safety gap in a magneto is to
a. prevent burning out the primary winding.
b. protect the high-voltage winding from damage.
c. prevent burning of contact points.

24. A defective primary capacitor in a magneto is indicated by
a. a fine-grained frosted appearance of the breaker points.
b. burned and pitted breaker points.
c. a weak spark.

25. How many secondary coils are required in a low-tension ignition system on an 18-cylinder engine?
a. 36
b. 18
c. 9


26. A magneto ignition switch is connected
a. in series with the breaker points.
b. parallel to the breaker points.
c. in series with the primary capacitor and parallel to the breaker points.

27. The spark is produced in a magneto ignition system when the breaker points are
a. fully open.
b. beginning to open.
c. fully closed.

28. Shielding is used on spark plug and ignition wires to
a. protect the wires from short circuits as a result of chafing and rubbing.
b. prevent outside electromagnetic emissions from disrupting the operation of the ignition system.
c. prevent interference with radio reception.

29. What is the purpose of using an impulse coupling with a magneto?
a. To absorb impulse vibrations between the magneto and the engine.
b. To compensate for backlash in the magneto and the engine gears.
c. To produce a momentary high rotational speed of the magneto.

30. The purpose of staggered ignition is to compensate for
a. short ignition harness.
b. rich fuel/air mixture around exhaust valve.
c. diluted fuel/air mixture around exhaust valve.

31. Aircraft magneto housings are usually ventilated in order to
a. prevent the entrance of outside air which may contain moisture.
b. allow heated air from the accessory compartment to keep the internal parts of the magneto dry.
c. provide cooling and remove corrosive gases produced by normal arcing.

32. Failure of an engine to cease firing after turning the magneto switch off is an indication of
a. an open high tension lead.
b. an open P-lead to ground.
c. a grounded magneto switch.

33. Alignment of the marks provided for internal timing of a magneto indicates that the
a. breaker points are just beginning to close for No. 1 cylinder.
b. magneto is in E-gap position.
c. No. 1 cylinder is on TDC of compression stroke.

34. When using a timing light to time a magneto to an aircraft engine, the magneto switch should be placed in the
a. BOTH position.
b. OFF position.
c. LEFT or RIGHT position (either one).

35. What is the difference between a low-tension and a high-tension engine ignition system?
a. A low-tension system produces relatively low voltage at the spark plug as compared to a high-tension system.
b. A high-tension system is designed for high-altitude aircraft, while a low-tension system is for low- to medium-altitude aircraft.
c. 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.

36. What test instrument could be used to test an ignition harness for suspected leakage?
a. A high-tension lead tester.
b. A high voltage dc voltmeter.
c. A high amperage dc ammeter.

37. The amount of voltage generated in any magneto secondary coil is determined by the number of windings and by the
a. rate of buildup of the magnetic field around the primary coil.
b. rate of collapse of the magnetic field around the primary coil.
c. amount of charge released by the capacitor.

38. Magneto breaker points must be timed to open when the
a. rotating magnet is positioned a few degrees before neutral.
b. greatest magnetic field stress exists in the magnetic circuit.
c. rotating magnet is in the full register position.

39. 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,
a. only No. 1 is true.
b. only No. 2 is true.
c. both No. 1 and No. 2 are true.

40. The capacitor-type ignition system is used almost universally on turbine engines primarily because of its high voltage and
a. low amperage.
b. long life.
c. high-heat intensity.

41. In a low-tension ignition system, each spark plug requires an individual
a. capacitor.
b. breaker assembly.
c. secondary coil.


42. A certain nine-cylinder radial engine used a noncompensated 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?
a. Breaker cam.
b. Engine crankshaft.
c. Distributors.

43. What will be the effect if the spark plugs are gapped too wide?
a. Insulation failure.
b. Hard starting.
c. Lead damage.

44. When removing a shielded spark plug, which of the following is most likely to be damaged?
a. Center electrode.
b. Shell section.
c. Core insulator.

45. What likely effect would a cracked distributor rotor have on a magneto?
a. Ground the secondary circuit through the crack.
b. Fire two cylinders simultaneously.
c. Ground the primary circuit through the crack.

46. How does the ignition system of a gas turbine engine differ from that of a reciprocating engine?
a. One igniter plug is used in each combustion chamber.
b. Magneto-to-engine timing is not critical.
c. A high-energy spark is required for ignition.

47. In a turbine engine dc capacitor discharge ignition system, where are the high-voltage pulses formed?
a. At the breaker.
b. At the triggering transformer.
c. At the rectifier.

48. Which of the following breaker point characteristics is associated with a faulty capacitor?
a. Crowned.
b. Fine grained.
c. Coarse grained.

49. How are most radial engine spark plug wires connected to the distributor block?
a. By use of cable-piercing screws.
b. By use of self-locking cable ferrules.
c. By use of terminal sleeves and retaining nuts.

50. Thermocouples are usually inserted or installed on the
a. front cylinder of the engine.
b. rear cylinder of the engine.
c. hottest cylinder of the engine.

51. Capacitance afterfiring of a spark plug is caused by
a. the stored energy in the ignition shielded lead unloading after normal timed ignition.
b. excessive center electrode erosion.
c. constant polarity firing.

52. If it is found that a shielded ignition system does not adequately reduce ignition noise, it may be necessary to install
a. a second layer of shielding.
b. a filter between the magneto and magneto switch.
c. bonding wires from the shielding to ground.

53. When a magneto is operating, what is the probable cause for a shift in internal timing?
a. The rotating magnet looses its magnetism.
b. The distributor gear teeth are wearing on the rotor gear teeth.
c. The cam follower wears and/or the breaker points wear.

54. Why are turbine engine igniters less susceptible to fouling than reciprocating engine spark plugs?
a. The high-intensity spark cleans the igniter.
b. The frequency of the spark is less for igniters.
c. Turbine igniters operate at cooler temperatures.

55. The constrained-gap igniter plug used in some gas turbine engines operates at a cooler temperature because
a. it projects into the combustion chamber.
b. the applied voltage is less.
c. the construction is such that the spark occurs beyond the face of the combustion chamber liner.

56. What should be used to clean grease or carbon tracks from capacitors or coils that are used in magnetos?
a. Solvent.
b. Acetone.
c. Naphtha.

57. 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
a. disconnected from the power supply circuit.
b. 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.
c. the transformer-exciter input lead is disconnected and the center electrode grounded to the engine after disconnecting the igniter lead from the plug and waiting the prescribed time.

58. Great caution should be exercised in handling damaged hermetically sealed turbine engine igniter transformer units because
a. compounds in the unit may become a fire or explosion hazard when exposed to the air.
b. some contain radioactive material.
c. some contain toxic chemicals.

59. Igniter plugs used in turbine engines are subjected to high intensity spark discharges and yet they have a long service life because they
a. operate at much lower temperatures.
b. are not placed directly into the combustion chamber.
c. do not require continuous operation.

60. The electrical circuit from the spark plug back to the magneto i s completed by grounding through the
a. engine structure.
b. P-lead.
c.cockpit switch.

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