Post on 07-Apr-2018
8/3/2019 Aircraft Engine Electrical Systems
1/19
Engine Electrical Systems
Ben Fair
8/3/2019 Aircraft Engine Electrical Systems
2/19
Different types of electrical systemsfor different types of engines
Turbine Engines Typically use capacitor discharge type ignition
system Other electronics like temperature sensors are
also used to govern the operation of mostmodern turbine engines. (note these wont bediscussed in depth)
8/3/2019 Aircraft Engine Electrical Systems
3/19
Turbine Engines (cont.)
Components of a turbine engine ignitionsystem
Power- supplied to the ignition system byseveral possible sources
BatteryAPU generator Other operating engine Ground power
8/3/2019 Aircraft Engine Electrical Systems
4/19
Components (cont.)
Igniter plugs Two (typ.) of these receive high voltage which
they use to create a spark to ignite the fuel/air
mixture The spark is created when it jumps to ground at
the end of the igniter plug
Exciter unit
The exciter unit is typically a dual unit whichcreates the high voltage which is then distributedto either of two high tension leads.
8/3/2019 Aircraft Engine Electrical Systems
5/19
Components (cont.)
High tension igniter leads
Downstream from the exciter unit or box, thesereceive the high voltage and give it a path to theigniter plugs by means of conductive wires
The wires themselves are shrouded in aninsulating material which serves a dual purpose ofinsulating the wire from ground as well as
suppressing radio noise which is transmitted fromthe wires.
8/3/2019 Aircraft Engine Electrical Systems
6/19
Examples
8/3/2019 Aircraft Engine Electrical Systems
7/19
Examples (cont.)
8/3/2019 Aircraft Engine Electrical Systems
8/19
Reciprocating Engines
Components Power- may be supplied by these components
or similar devices BatteryAlternator Generator
8/3/2019 Aircraft Engine Electrical Systems
9/19
Components (cont.)
Spark plugs Create a spark to ignite the fuel/air mixture They are grounded to the engine and the voltage
delivered to them jumps from the center electrodeto the grounded electrode on the plug shell.
Simultaneous vs. staggered ignition Spark plugs may fire in staggered timing (racing
engines) for improved efficiency Spark plug near exhaust valve fires first since this
is the contaminated area of the cylinder
8/3/2019 Aircraft Engine Electrical Systems
10/19
Spark plugs (cont.)
Hot plugs have longer insulation exposed to thecombustion chamber Used for low temperature engines when cylinder
pressure is low => prevents plug fouling
Cold plugs are used in high temperature (highpressure) engines => prevents detonation Used for high temperature engines
Interchanging of hot/cold plugs is to be avoided
8/3/2019 Aircraft Engine Electrical Systems
11/19
Spark plugs (cont.)
Massive electrode vs. fine-wire spark plugs Fouling of plugs is caused by lead or carbon
buildup or by oil through the rings from thecrankcase.
Fine-wire plugs provide bigger area forbuildup of these fouling products before
fouling occurs.
8/3/2019 Aircraft Engine Electrical Systems
12/19
Components (cont.)
Ignition leads / wiring harness Shielded ignition leads
Prevents voltage leakageMost noticeable at high altitudes
Also prevent radio static interference
Terminals (cigarettes)
Connect ignition leads to spark plugs
Automobiles use simple clip connectors
8/3/2019 Aircraft Engine Electrical Systems
13/19
Components (cont.)
Magnetos Magneto components
Primary coil Rotation of magnet inside the magneto (attached toaccessory drive) induces the flow of current in theprimary coil
Points (breaker points)
Opened by internal cam rotation
Interrupts the flow of current in the primary circuit,resulting in collapse of the magnetic field andinduction of flow of current in the nearby secondarycoil
8/3/2019 Aircraft Engine Electrical Systems
14/19
Magneto components (cont.)
Condenser Promotes sudden collapse of the magnetic
field, leading to maximum induced current inthe secondary circuit
Condenser also prevents pitting of the pointsand serves as a radio noise suppressor
8/3/2019 Aircraft Engine Electrical Systems
15/19
Magneto components (cont.)
Secondary coil Distributor
Selects which cylinder gets the secondary current i.e., determines when the spark plugs fire
Spark plugs
Act as an open switch that can be closed whencurrent jumps the gap if the voltage produced inthe secondary circuit is large enough
8/3/2019 Aircraft Engine Electrical Systems
16/19
Magneto components (cont.)
Impulse couplings Produces high voltage needed for firing of spark plugs when
engine rotation speed is low during engine start
Internal spring winds until piston approaches TDC then thespring releases and the internal magnet is given a quick twist =sudden high voltage flows in secondary coil
Can hear this clicking sound as prop is rotated by hand
As engine RPM approaches idle during start, "dog ears" arethrown outward by centrifugal force and spring no longer winds
If spring breaks, engine may operate normally except forstarting
8/3/2019 Aircraft Engine Electrical Systems
17/19
Magneto Timing
Internal timing (E-gap) "Efficiency" gap
Assures that points open at desired time to maximizethe primary current
Timing magneto to engine (external timing) Use a "timing light"
Assures that points open at the time when the piston is at 30degrees BTDCAchieved by rotating the magneto at its attachment point to
the engine
8/3/2019 Aircraft Engine Electrical Systems
18/19
Examples
SlickMagneto
WiringHarness
Alternators
8/3/2019 Aircraft Engine Electrical Systems
19/19
Resources
Dale Crane. Powerplant 2003 Test Guide.Aviation Supplies & Academics, 2002.
pg. 74 91
My Brain