what are the two methods to producing a spark to ignite fuel
spark plug
high voltage electrical production from magneto
how safe is the system
fail safe
– will continue to work without any external electrical power e.g. battery
– ignition system is duplicated (two magneto, two spark plugs in every cylinder)
what are spark plugs
device that causes a high voltage to produce a spark
how is the spark formed in spark plugs
voltage jumps across air gap as a spark
– air gap has a specified distance to control strength of spark
what is spark plug fouling
at low rpm or rich mixture setting, lead or carbon deposits that form are not burnt off because of low spark plug temperature = short circuit = no or weak spark
with what kind of fuel does spark plug fouling happen
100LL (which is avgas)
what are the causes of spark plug fouling
long period of low engine rpm
dusty environments
failure to lean mixture at idle in accordance with POH
how to clear spark plug fouling
- set high rpm (2000)
- lean mixture until rpm drop of 300-400rpm
- maintain for 10s
- mixture rich and reset throttle to required rpm
- redo engine run up checks
what to do if spark plug clearing doesnt work?
repeat process with maximum power
how do magnetos work
using magnets and coils of wire to produce a high voltage spark
(the primary coil induces a higher voltage than secondary)
how do magnetos help to produce a spark
while engine turns -> magneto produces a spark that keeps engine turning
primary coil moving within magnetic field induces current to flow
when primary coil circuit is broken, the primary coil’s electric field collapsing induces a higher voltage onto second coil = fed to spark plugs
what is the P-wire
a safety feature that prevents sparks
why do we need a P wire
since magneto is always going to produce a spark whenever the engine is turned, we need a method of preventing this for safety
how does the P wire work
- by connecting a wire to low voltage side of magneto (the primary coil), and then it connecting to the ground
- this short circuits the magneto primary coil, so no current flows in it and no spark is produced
how does the P wire ensure safety when the magneto switches are off
the wire is connected to the earth (grounded)
why do we check magnetos?
to check that all spark plugs are firing
what is an impulse magneto
a magneto that produces a very strong and long lasting spark
how does the impulse magneto work
- during very low rpm, impulse magneto uses a spring mechanism that winds up
- mechanism then releases at correct time to spin the magneto quickly, producing a long lasting spark
why must spark timing be retarded
to ensure the engine fires during power stroke and not before
how to delay spark timing
using impulse magneto - delays distribution of spark when engine revs are low
which magneto normally has the impulse mechanism
the left
which magneto’s spark is used during engine start
the one from the impulse magneto (otherwise the non-impulse magneto would fire its spark too early)
what are the magneto run up checks
each magneto is grounded in turn to ensure the engine still runs acceptably
what causes rpm drop (think magnetos)
fuel not igniting as efficiently
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the airframe38
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undercarriage33
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retractable undercarriage6
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hydraulics10
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propeller & variable pitch propeller14
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super/turbo chargers14
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oil system29
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fuel system16
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induction system46
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ignition system26
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electrical system40
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cooling system9
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instrumentation18
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flight instruments62
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altering systems4
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communication systems7
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GNSS17
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safety5
