02_2 Ignition Systems

Why do aircraft engine ignition systems incorporate a means of spark augmentation?

• Because, at high engine speeds, a fat spark is needed to extract maximum power from the air-fuel mixture.

• Because the speed of rotation of the engine, during starting, is too low for the magneto to produce enough energy to ignite the air-fuel mixture.

• In order to overcome the problem of spark-retard during starting.

• All of the above.

Magnetos are:

• Generators, driven by the cam-shaft, used to supply electrical equipment.

• Used to generate low voltage sparks for the spark-plugs.

• Fitted within the distributor, and fire in the same sequence as the spark-plugs.

• Self contained, engine driven, electrical generators which produce high voltage sparks.

Which of the following are true regarding an Impulse Coupling?

• It supplies a stream of high voltage impulses to a trailing brush on the distributor rotor.

• It supplies the primary coil of the magneto with a low voltage during engine start.

• It is a mechanical device which uses a spring to temporarily increase the speed of rotation of the magneto.

• All of the above.

The function of the contact breaker in the primary circuit of a magneto is:

• It allows the magneto to be switched on and off.

• It assists in the collapse of the magnetic field created by the permanent magnet generator.

• It times the sparks to the spark-plugs.

• It prevents the build up of excess static charge.

Which of the following are functions of the capacitor in the primary circuit of a magneto? (i) Assists in collapsing the magnetic field. (ii) Smoothes the output of the magnetic field. (iii) Helps prevent erosion of the contact breaker points. (iv) Prevents sparking at the contact breaker points.

• (i) and (ii) only.

• (iii) and (iv) only.

• (i) and (iv) only

• (i), (iii) and (iv).

The distributor arm rotates at:

• One quarter engine speed.

• A half engine speed.

• Engine speed.

• Twice engine speed.