The ignition system of the Kfir aircraft comprises two ignition units and an afterburner ignition system. The ignition units convert 28V DC power to high voltage pulses to spark the main igniter plugs. Ignition unit 1 additionally powers the afterburner igniter plug. When switches are closed, the units charge capacitors and generate sparks to ignite fuel mixtures. The system ensures ignition during normal operation and allows for re-ignition in an engine failure.

1. KFIR AIRCRAFTKFIR AIRCRAFT
IGNITION SYSTEMIGNITION SYSTEM

2. OBJECTIVE
At the end of this Lesson to make you all
aware,
a. Purpose and principle of
ignition system.
b. Construction and operation of
ignition system of kfir aircraft.
3

3. LESSON COVERAGELESSON COVERAGE
Introduction.
System components.
No 1 ignition unit
No 2 ignition unit
A/B ignition switch
A/B igniter plug
Speed and time delay relay
Operation
Conclusion.
Question. 33

4. INTRODUCTIONINTRODUCTION
The ignition system comprise three separate
circuits and 2 ignition units, one of which is a dual
purpose unit. All three circuits are independent in
operation except that the No 1 and No 2 main circuits
operate together with the actuation of a single switch.
The A/B circuit is mounted within the No 1 ignition unit
and is operated by a fuel pressure signal.
Cont…

5. The system incorporates two identical igniter
units and 2 igniters installed in combustion chamber.
The igniter units convert 28 V DC power from DC 1-
1 bus into high voltage pulses. Igniter unit No 1 also
supplies ignition pulses to the A/B ignition torch
through AC -2 bus
55
Cont…

6. IGNITION SYSTEM COMPONENTIGNITION SYSTEM COMPONENT
 No 1 ignition unit (Dual purpose)
 No 2 ignition unit
Main igniter plugs
Afterburner ignition switch
Afterburner igniter plug
Speed and time delay relay
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7. NO 1 IGNITION UNITNO 1 IGNITION UNIT
The ignition unit changes the 28 V DC power into
periodic high energy electrical pulses necessary for
main igniter plug operation. It also changes the 115 V
400 cycle AC A/C power into periodic high energy
electrical pulses for A/B igniter plug operation .
77

8. 88
28v DC
Power
Vibrator
&
Transfor
mer
Rectifier
Bridge
Tank
Capacito
r
No:01
Spark
plug

9. 99

10. MAIN IGNITIONMAIN IGNITION
• Input voltage : 28V DC
• Input current : 3.0 AMP
• Spark rate : 1 to 10 spark per second
• Output voltage : 2650 to 3500 DC
1010

11. • Input voltage : 115V AC 400 cycle
• Input current : 0.5 AMP
• Spark rate : 4 spark per second
• Output voltage : 2650 to 3500 DC
AFTERBURNER IGNITIONAFTERBURNER IGNITION
1111

12. NO: 2 IGNITION UNITNO: 2 IGNITION UNIT
The ignition unit increases the 28 V DC aircraft
power into periodic high energy electrical pulses
necessary for ,main igniter plug operation. This unit
operates in conjunction with the main circuit of the
No 1 ignition unit.
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13. 1313

14. AFTER BURNER IGNITION SWITCHAFTER BURNER IGNITION SWITCH
The afterburner ignition switch permits the flowThe afterburner ignition switch permits the flow
of current from an aircraft power source to theof current from an aircraft power source to the
afterburner ignition circuit of the ignition unit duringafterburner ignition circuit of the ignition unit during
afterburner operation.afterburner operation.
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15. AFTERBURNER IGNITER PLUGAFTERBURNER IGNITER PLUG
The afterburner igniter plug produces the sparkThe afterburner igniter plug produces the spark
that ignites the fuel air mixture inthat ignites the fuel air mixture in the torch igniterthe torch igniter
for afterburner operation.for afterburner operation.
1515

16. 1616

17. 1717
115V Ac
Power
Transfor
mer
Rectifier
Bridge
Tank
Capacito
r
AB
Spark
plug

18. 1818

19. 1919

20. 2020
SPEED AND TIME DELAY RELAYSPEED AND TIME DELAY RELAY
 At 40% RPM de-energizes the starting relay, ignition
stops and the engine accelerates on its own.
 60 seconds after depressing the STARTER push
button , de energizes the ignition relay and starting
relay if not de energized at 40%RPM.

21. 2121
At 40% RPM
After 60
seconds
de energizes
the ignition
relay and
ignition stops

22. OPERATIONOPERATION
2222

23. 2323

24. 2424

25. 2525

26. 2626
STARTING AND IGNITION SYSTEM
Once the fuel valve is open and LP pump are on
signal the ground crew to supply the air pressure for
start . when RPM is alive depress the STARTER push
button . at 10% RPM the pilot opens the throttle to idle ,
the ignition units starts to operate and fuel is supplied to
the engine . at 35% signal to the ground crew to stop air
pressure . the engine continues to accelerate and stabilizes
at 66%- 68% RPM.

27. OPERATION
NORMAL OPERATION
When the ignition switch is closed, 28 V DC current flows to both
main ignition units. here it is converted to AC, increased in
amplitude, and rectified to DC to charge the tank capacitor. The
tank capacitor discharges when voltage becomes high enough to
ionize the sealed gap. The discharge passes through the igniter
plug lead, a heavily insulated cable, to the igniter plug. A semi-
conducting material shunts the igniter plug electrodes. When the
voltage between the electrodes reaches approximately 1000 volt
current flows across the surface of semi-conductor and ionizes the
air gap between the electrodes, permitting the tank capacitor to
discharge completely. The periodic high-intensity sparks initiate
combustion .
2727

28. AFTERBERNER SYSTEMAFTERBERNER SYSTEM
When the afterburner ignition switch contacts close, currentWhen the afterburner ignition switch contacts close, current
passes from the aircraft 115v ac power source to the afterburnerpasses from the aircraft 115v ac power source to the afterburner
ignition circuit of the no:01 ignition unit. The ignition circuitignition circuit of the no:01 ignition unit. The ignition circuit
increases the applied voltage in amplitude and rectifies it.Theincreases the applied voltage in amplitude and rectifies it.The
direct current charges a tank capacitor within the ignitiondirect current charges a tank capacitor within the ignition
subsystem. Normally a potential of 1000-1500 volts between thesubsystem. Normally a potential of 1000-1500 volts between the
igniter plug electrodes is sufficient to ionize the air gap. Theigniter plug electrodes is sufficient to ionize the air gap. The
discharge produces the spark that ignites the fuel-air mixturedischarge produces the spark that ignites the fuel-air mixture
within the torch igniter. The flame from the torch igniter thenwithin the torch igniter. The flame from the torch igniter then
ignites the fuel-air mixture within the tailpipe. The afterburnerignites the fuel-air mixture within the tailpipe. The afterburner
ignition system functions continuously during afterburnerignition system functions continuously during afterburner
operation.operation.
2828

29. AIR RE-IGNITIONAIR RE-IGNITION
When the engine failure occurs during flight,When the engine failure occurs during flight,
pilot desires to re-ignite the engine.when re-light switchpilot desires to re-ignite the engine.when re-light switch
put to forward position,both main igniter plugs areput to forward position,both main igniter plugs are
directly powered through the DC 1-1 bus and igniterdirectly powered through the DC 1-1 bus and igniter
plugs continuously operate until re-light switch onplugs continuously operate until re-light switch on
forward position.forward position.
2929

30. 3030

31. CONCLUSIONCONCLUSION..
Introduction of ignition system.Introduction of ignition system.
Description of ignition system.Description of ignition system.
Ignition system component.Ignition system component.
Description of component.Description of component.
3131

32. REFERENCEREFERENCE
• Aircraft maintenance manualAircraft maintenance manual
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34. 3434