Chapter 7 Aircraft Control Circuitry

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航空

Chapter 7
Aircraft Control Circuitry
POWER CIRCUITS
Figure 7-1.
Battery Circuit
A clipping diode is installed across the coil of the
solenoid to eliminate spikes of voltage that are
induced when the master switch is opened and the
magnetic field from the coil collapses. The resulting
spikes of voltage from a solenoid or relay coil may
cause damage to sensitive electronic components if
they are not controlled by a clipping diode. The diode
simply isolates, or blocks, the induced voltage from
flowing into the bus side of the electrical system,
thereby protecting the electronic components from the
high voltage.
Figure 7-1 Battery Circuit
Most aircraft have some components that
require power all the time, whether the master
switch is on or not. These low-current items,
such as clocks and flight-hour meters, are
connected to the main terminal of the battery
solenoid, and supply current to these
components anytime a charged battery is
installed in the aircraft. These circuits often
employ a fuse to protect the circuit.
GENERATOR CIRCUIT
Figure 7-2. Ammeter monitoring circuit
0
10 20
30
AMMETER
ALTERNATOR BATTERY
BUS
0
10 20
30
AMMETER
ALTERNATOR BATTERY
BUS
TO AIRCRAFT LOADS
TO AIRCRAFT LOADS
AMMETER INSTALLED IN
ALTERNATOR OUTPUT LEAD
(A)
AMMETER INSTALLED IN
THE BATTERY LEAD
(B)
Figure 7-4. A basic
generator circuit
B G F
F
A+
G
MAI
N
B
US
VOLTAGE
REGULATOR
MASTER SWITCH
GENERATOR
BATTERY
CONTACTOR
Figure 7-5. The internal circuit of a typical light-aircraft
DC alternator
Figure 7-6. A typical light-aircraft Dc alternator system
 The overvoltage warning light turns on when
the master switch is first closed, and it turns
off when the engine is started and the
alternator produces the correct amount of
voltage.
 If the voltage gets too high, the overvoltage
protector opens the alternator field circuit,
which turns on the overvoltage protector
opens the alternator field circuit, which turns
on the overvoltage warning light, showing
that the alternator has been shut off because
of an overvoltage condition.
 The capacitor installed between the battery
input of the voltage regulator and ground
acts as a shock absorber. During operation,
the electric motors in the aircraft can
produce a spike of voltage in the electrical
system high enough for the overvoltage
protector to sense, which prompts it to open
the alternator field circuit, shutting off the
alternator. To prevent this, the capacitor
absorbs the spike so it will not trip the
overvoltage protector.
A typical aircraft ground-power circuit
Starter circuits
LANDING GEAR CIRCUIT

 The squat switch in the circuit is mounted on
one of the structs so that it’s in one position
when the air plane weight is on the landing
gear, and in the other position when there in
no weight on the wheels. The purpose of the
squat switch in this circuit is to prevent the
gear from being retracted while the aircraft is
still on the ground. The hydraulic pressure
switch is used to turn off the pump motor in
the event hydraulic pressure exceeds its
limits.
net EMF
net EMF
 If any of the limit switches are in a NOT UP or
a NOT DOWN position, a red UNSAFE light will
illuminate. But when the landing gear selector
switch is in the LANDING GEAR DOWN
position and all three gears are down and
locked, the light will be out.
 Also, if the selector switch is in the LANDING
GEAR UP position and all three gears are in the
up position, the light will be out. If the airplane
is on the ground with the squat switch in the
GROUND position, and the landing gear
selector switch is moved to the LANDING
GEAR UP position, the warning horn will sound,
but the landing gear pump motor will not run.
END OF CHAPTER 7