ELECTRICAL SYSTEMS

1
ELECTRICAL SYSTEMS
2
Then this much water would exert more pressure or
voltage. 28volts.
The pressure behind a dam is similar to the
voltage stored in a battery.
If this much water behind the dam has an
equivalent pressure of 20 volts.
This much flow would be equivalent to 100 Amps of
current. However the pressure is still 28 volts.
The amount of water flowing is similar to
electrical current, this much flow is equivalent
to 50 Amps.
3
In an electrical system this is accomplished by
generating electricity to supply the system and
recharge the battery.
As the water continues to flow the pressure
behind the dam (battery) decreases.
If system pressure (voltage) is to be maintained
then more water must be added.
4
ELECTRICAL SYSTEM COMPONENTS

• Batteries converts chemical energy to electrical
  energy, becomes a source for the system.
• Lead-acid most commonly used in light aircraft,
  voltage drops off quickly when in use,
  insufficient for high start demand of turbine
  engines.
• Nickel-cadmium (Nicad) expensive but voltage
  doesnt drop off as quickly. Susceptible to
  developing memory ( it will become limited to a
  less than full charge over time, and must be deep
  cycled).

5
THERMAL RUNAWAY

• Nicad batteries are subject to a condition known
  as thermal runaway.
• If the battery receives a high rate of charge for
  an extended period of time (connecting a weak
  battery to external power) it can start a self
  sustaining chemical reaction.
• The battery will continue to charge internally,
  even once the power source is disconnected.
• A battery in this state will continue to charge
  and overheat. (fire hazard)

6
CAPACITY

• The capacity of a battery is expressed in
  ampere-hours.
• The amount of current for a specified time.
• A 24 volt, 34 amp/hour battery is capable of a 34
  amp current draw for one hour.
• If the draw on the battery is reduced ex. Turning
  off electrical equipment, the battery will last
  longer.
• A batteries rating applies to a new battery and
  will degrade with age.

7
AC/DC

• Alternating current The flow of electrons peaks
  and subsides, and periodically reverses
  direction.
• Much easier to generate in large quantities.
• Easy to change its voltage and current.
• It is able to travel long distances with a small
  voltage drop.
• Used in large aircraft where electricity must
  travel long distances.
• Usually used for high draw systems, such as
  weather radar.

8
AC/DC

• Direct current the flow of electrons is steady
  and maintains a single direction of flow.
• Used in small aircraft where distance for
  electricity to travel is shorter.
• Most electrical systems are low draw.

9
ALTERNATORS

• Aircraft electrical systems need a source of
  electrical production.
• Alternators produce electricity by rotating a
  magnet inside coil windings of conductive
  material.
• The material used as a magnet (electro magnet)
  must be energized to create the magnetic field
  (field current).
• Alternators produce AC electricity which is
  converted to DC by an internal rectifier.
• This makes the output of an alternator DC.

10
GENERATORS

• Generators utilize a permanent magnet and rotate
  a conductor within the magnet.
• The generator initially creates AC electricity
  which is rectified to DC internally.
• Generators are rpm dependant, so loads must be
  limited at low engine rpm.

11
STARTER/GENERATORS

• Some turbine engines use starter/generators as a
  source of electrical output and engine starting.
• The unit acts as a starter motor as electricity
  is applied to it during engine start, and a
  generator once engines are running to produce
  electricity.
• This design saves weight by utilizing the same
  piece of equipment for two duties.
• It is not capable of operating as a starter and a
  generator simultaneously.

12
VOLTAGE REGULATORS

• Voltage regulators control the field current to
  the alternator to stimulate and regulate
  electrical production.
• Maintain a constant voltage during variations in
  electrical load requirements.
• Protect against system over voltage by
  incorporating an over voltage relay.
• If an over voltage is sensed the over voltage
  relay will open blocking field current from
  reaching the alternator, taking it off line.

13
GENERATOR CONTROL UNITS

• Generator control units provide a variety of
  functions
• Voltage regulation.
• Generator paralleling.
• Reverse current sensing/control.
• Overvoltage protection.
• The generator control unit will take its
  generator offline if it senses a problem with the
  unit.

14
GROUND

• An electrical system must have a ground in order
  to create a continuous circuit for electrical
  flow.
• The system is usually grounded to the aircraft
  structure.
• It is possible for ground faults to occur. A
  failure or short of an electrical item which
  creates a ground. This would cause electricity to
  flow into the ground fault creating a fire hazard
  or possible electrical system malfunction.

15
CONTROL DEVICES

• Switches pilot actuated, control the flow of
  electrons to specific parts of the system.
• Relay/solenoid remote devices which close or
  open to complete or interrupt the circuit. When
  power is applied to the relay it will move to the
  applicable position.
• Fuse If the current increases through a fuse
  above limits the fuse will blow disrupting
  electrical flow.
• Circuit breaker protects against excessive
  current like a fuse but may be reset. ( CB rule
  of thumb only reset popped CBs if the item is
  essential for continued operation. Never reset a
  CB more than once. If it blows again leave it
  alone).

16
CONTROL DEVICES

• Switch/CB combo some aircraft incorporate
  switches which act as circuit breakers. The
  amperage rating will be stamped on the switch.
  (Is there one in the C-172?)
• Resistors provide resistance to the flow of
  electricity. Used to control the current reaching
  parts of the electrical system.
• Inverter changes DC electricity to AC
  electricity.
• Rectifier changes AC electricity to DC.

17
CONTROL DEVICES

• Transformer step up and step down AC voltage.
• Busbar a physically convenient place to
  terminate wires and distribute electricity. Acts
  like a manifold to direct electricity to
  different components. The arrangement of busbars
  allow for ground fault protection within the
  system.

18
MONITORING THE SYSTEM

• Voltmeter gives the pilot an indication of
  system voltage. On large aircraft there can be
  more than one gauge, or one gauge with the
  capability of displaying more than one busbars
  voltage. Valuable in determining the status of
  battery and other system components.

19
MONITORING THE SYSTEM

• Ammeter measures current flow and indicates to
  the pilot a state of charge or discharge within
  the system.

20
MONITORING THE SYSTEM

• Loadmeter measures current flow and indicates to
  the pilot the output load being placed on the
  generator. In the event of a generator failure in
  a multi engine aircraft the pilot must ensure the
  load remains within limits. Usually graduated in
  percentage. Ex. 100 is the generators maximum
  rated output.

21
STARTER

• The starter is usually the highest draw system in
  any aircraft. It creates a large draw on the
  battery which slowly decreases as engine speed
  increases.
• A large diameter cable is needed to handle this
  large current.
• A short cable minimizes the voltage drop so it is
  advantageous to keep the battery as close to the
  starter as possible.

22
IGNITION

• The magneto is the preferred type of ignition for
  light aircraft as it produces its own
  electricity. (not battery dependant)
• Magnetos are small generators which operate
  completely independent of the aircraft electrical
  system.
• The ignition system consists of mags, spark
  plugs, and wiring harness.
• Dual magnetos are used to provide redundancy and
  improve combustion. Each mag has its own set of
  plugs and wiring.

23
IGNITION

• In order to stop the mag from producing a spark
  (shutdown) the magneto must be grounded. A wire
  called a P-lead creates a ground for the magneto
  when the pilot positions the mag switch to OFF.
  If the P-lead is broken the mag will be live
  regardless of mag switch position.

24
IGNITION

• Engine start requires a hotter than normal spark
  from the plugs as well as a timing change to aid
  with starting.
• An impulse coupling engages during start which
  creates a hotter spark and retards timing.
• This allows the piston to be beyond TDC when the
  expanding gases exert their force.

25
IGNITION

• Another method of providing this hot and late
  spark is a vibrator system or shower of sparks.
• The vibrator produces pulsating DC which is
  directed to the magneto to produce a high
  voltage. This system puts out a stream of sparks
  instead of a single spark.
• The late spark is created by incorporating a
  separate set of contact points within one of the
  mags (usually the left).
• These retard points are utilized during start to
  create the late spark.
• The opposite mag must be grounded to prevent it
  from producing a spark.

26
LASAR MAGS

• The Selair C-172 fleet has a combination of
  conventional mags with the impulse couplings
  removed and an electronic Lasar ignition system.
• The Lasar system electronically varies timing
  according to engine power setting and ambient
  conditions to optimize performance and efficiency.

27
LASAR MAGS

• Provides a shower of sparks for start.
• If the Lasar system malfunctions the conventional
  mags take over.

28
RUNUP

• An rpm drop larger than normal indicates a
  problem with the ignition system. It could be a
  wire, plug (fouled) or mag.
• An rpm drop less than normal could indicate
  timing drift associated with mag wear. Timing
  tends to advance over time. If it advances too
  much it can damage an engine operating at high
  power.
• No rpm drop is indicative of a broken P-lead.

29
RUNUP

• The proper technique for a mag check is
• Set recommended rpm.
• Select L or R mag until rpm stabilizes.
• Note rpm drop.
• Select BOTH mags until rpm stabilizes.
• Select remaining mag (L or R) until rpm
  stabilizes.
• What is the recommended rpm drop for your
  airplane?

30
RUNUP

• Performing a mag check with the Lasar mag system
  differs slightly.
• When the L or R mag is selected the Lasar system
  disengages and the light illuminates.
• BOTH mags should be selected and recommended rpm
  reset. This gives an accurate baseline rpm for
  testing the conventional mags. (there is a 20
  second delay from the time BOTH is selected until
  the Lasar system engages)

31
RUNUP

• During your mag check in the C-172 you get a
  larger than normal drop, and suspect a fouled
  plug. What action would you take?
• Increase power to approx. 2100rpm, lean for peak
  EGT, for approx. 1 min.
• If the problem isnt cleared repeat process at
  full power.
• If the problem persists have the plane looked at
  by maintenance.

32
(No Transcript)
33
C-172

• What do the following abnormal indications mean?
  What action should you take?
• Low voltage warning light during taxi.
• Low voltage warning light during flight.
• Ammeter showing full scale deflection to the
  right.
• Ammeter showing more than three needle widths to
  the right for over 30 min.

34
(No Transcript)
35
(No Transcript)
36
(No Transcript)
37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
(No Transcript)
41
(No Transcript)