Aircraft Engine Electrical Systems

8/3/2019 Aircraft Engine Electrical Systems

1/19

Engine Electrical Systems

Ben Fair


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)


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


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.


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.


6/19

Examples


7/19

Examples (cont.)


8/19

Reciprocating Engines

Components Power- may be supplied by these components

or similar devices BatteryAlternator Generator


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


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


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.


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


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


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


15/19


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


16/19


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


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


18/19

Examples

SlickMagneto

WiringHarness

Alternators


19/19

Resources

Dale Crane. Powerplant 2003 Test Guide.Aviation Supplies & Academics, 2002.

pg. 74 91

My Brain

Aircraft Engine Electrical Systems

Documents

Transcript of Aircraft Engine Electrical Systems