PL - Ignition Systems
Ignition lead care
**Always use two wrenches to install or remove Ensure harness is not twisted or chafing against anything Torque to finger tight plus 1/8 of a turn
Fine Wire plug vs. Mass Electrode
-Last 2 to 3 times longer -more expensive -Fouls less because burning gases are able to get around the electrode -Most people choose massive electrode anyway
Internal timeing (3 things)
1. E-gap position on rotor 2. Points opening (on Slick, set timing and check gap) 3. Distributor rotor positioned to #1
Rotating Magnet Magneto (Memorize)
1. Rotating magnet causes magnetic flux reversals in the soft iron core of the coil 2. These flux reversals cause current to flow in the primary windings. 3. Current flow in the primary coil creates a strong magnetic field around the primary and secondary windings. 4. At the right time, called "E-gap," the breaker points open, stopping current flow in the primary winding and causing a rapid collapse of the magnetic field around the secondary winding. 5. This rapid collapse induces a high voltage current in the secondary winding, which is carried through the distributor to the correct spark plug. 6. A capacitor is located across the breaker points to prevent arcing and to help speed the field collapse.
FAR that requires dual mags
14 CFR 33.37 Ignition sources Dual magneto satisfies the legal requirement for 2 ignition sources but lacks redundancy of two separate magnetos.
Magneto Timing
3 requirements: Internal timing - 1. Magnet (rotor) at correct e gap position 2. Points just open 3. Distributor rotor at the #1 firing position External timing (to the engine) 1. Magneto set to the #1 firing position 2. Engine set to the #1 firing position 3. Two mated together
D3000 E-gap and Points setting
4 different Neutral positions: K, A, B, C E-gap is about 8 degrees past marked with L or R depending on which way the mag turns.
Modern spark plug leads are what size mm
5mm 7mm is old
Ignition leads
7mm (old) and 5mm (newer) 3/4" or 7/8" nut and 3/16" nut for smaller one
points on a magneto last about (hours)
800 hours That's why we replace them every 500 hours
Magneto System
Advantages: simple, reliable, relatively light weight does not require battery power Disadvantage: Fixed timing
Why does a magneto tend to arc more at high altitudes?
Air density at high altitudes is much lower and the insulating effect of air is reduced causing more arcing in the magneto
Torquing spark plugs
Always always always use a torque wrench
When you're done timing the mag
Always ask yourself: Is the mag (ignition) switch set to off? Are the P-leads reconnected?
Common results of Mag test
Amount of drop Difference between mags (split) Rough=single cylinder Smooth=timing No drop? grounding issue or running on one mag the whole time.
EGT gauge
An information gauge No limits, just a reference for engine performance. Single cylinder temp rise: spark plug problem All cylinder temp rise: magneto problem
Magneto Drop Check
At 1700 RPM Turn mag switch from Both to Right, watch for RPM drop, then turn switch back to both. Then turn mag switch from Both to Left, observe RPM drop and turn switch back to both. Engine should run smoothly in all positions; rough running may indicate a dead cylinder or magneto problems. Max allowable drop on one mag = 150rpm Max allowable difference between single magnetos = 50rpm
Aligning Rotor and Distributing Gears
Based on Placard info on magneto case. With a timing pin you line up the left or right hole with the line on the small gear.
500 hr ignition inspection
Basically overhaul lite Pull off engine Required by manufacturer AD on Bendix impulse couplings Industry practice
Common types of recip engine ingnition systems
Battery Magneto Electronic (FADEC; Full Authority Digital Engine Control)
Inspections
Bearings Impulse coupling contacts housing etc.
Magnetos Made by:
Bendix TCM Slick/Unison/Champion
Spark plug cleaner tester
Blast with media and the blow with air to remove the grit. The spark plug is screwed into the tester and pressurized air
High Altitude misfire
Caused by low air density at high altitude. May cause separate distributor contacts to short between each other through the air. Bendix mags defeat this arcing by making their mags physically bigger. Slick mags use pressurization provided by the upper deck pressure to defeat high altitude arcing.
Carbon Tracking
Caused by magneto flashover Dirt causes a low resistance path that will continue to cause flashover Light carbon tracks are acceptable but any damage caused by flashover is cause for part replacement.
What is the purpose of the silicone coating on harness wires
Chafing Mechanical protection
Hot or Cold Spark plug in a high compression, high power engine
Cold spark plug
Timing the Slick mag to the engine
Course setting: Install the mag on the engine with both magneto and the engine in the #1 firing position. Then REMOVE THE TIMING PIN! Fine adjustment - turn magneto Timing light hook up - Red on left (doesn't really matter) Turn ignition switch to "both" Final Torqing - can be confusing, what value?
Bendix S1200
Designed with larger space in case to perform better at higher altitudes.
Booster coil or Booster Magneto
Distributer has a second finger that acts as a retarder to assist with engine starting
Problems with mags
Do not function at low speeds The have fixed timing which causes the engine to kick back at low speeds Both of these are bad for engine starting
E-gap
Efficiency gap A point of rotation of the magnet that is a few degrees of rotation after neutral where the points open because that is point of Maximum magnetic stress. This causes a rapid reversal of the field and a high voltage is induced in the secondary coil.
Carbon traces inside the mag are an indication of what?
Flashover or arcing inside the magneto
Battery ignition system:
Good low speed performance; no minimum speed, Variable timing is possible. Has two electrical circuits Primary circuit- low voltage (12 to 24 volts) Secondary circuit- high voltage (20,000 volts) secondary coil, contained in the ignition coil Distributor: distributes current to the correct cylinder Capacitor is installed into circuit to keep the open points from arcing. However, the capacitor is in primary circuit and it does not have any part in causing the spark plug to fire
Spark plug parts
Ground electrode and center electrode.
Magneto primary circuit
Ground>Primary coil>Breaker points>Ignition switch>Ground
Two types of Magnetos
High Tension: high voltage Low Tension: Low Voltage
Spark plug heat ratings
Hot plug vs Cold Plug Cold plug is more capable of shedding heat Hot plug is less capable of shedding heat
Impulse coupling (on quiz)
Impulse is needed to help the engine start does two things: Provides hotter spark at slow engine speeds retards the spark to prevent kickback during start
Spark boosters
Induction vibrator Slick Start system
Timing
Internal timing: when magneto is put together correctly and it operates as intended Engine timing: The magneto fires at the correct timing with engine strokes to accomplish a smoothly running engine
K neutral position
K stands for keyway This is the position that you want to set your dual magneto in
100 hr/Annual ignition inspection
Mag Check Take distributer cap off and check timing and points
Preflight ignition inspection
Mag check
Full register
Magnet is in alignment with the pole shoes
Components of magnetic circuit
Magneto Coil Coil Core Rotating Magnet Laminated iron pole shoes
Most engine problems can be traced back to 3 possible problems
Mechanical Ignition Fuel/mixture
Magneto harness
Metal shielding on outside is woven and bonded to ground. Its purpose is to filter radio noise. The silicone on the outside is only for anti-chafing
Most common problems with Magnetos
Most common is Wear items: Worn bushings in the distributor block Worn carbon brush Impulse coupling-related issues -springs under the fly-weights wear out Second most common: Flashover in coil Other problems: Primary circuit issues
Which wears faster? Negative or Positive electrode on plug
Negative wears faster. This is why we rotate plugs top to bottom and next in firing order.
Inspecting Magneto Capacitor
No need to remove the capacitor to inspect. Loosen the nut and rotate the capacitor to inspect as to not damage the lead.
Slick Start system
No retard, just boost. Solid state version of induction vibrator Made for Slick and Bendix mags
Ignition system inspections intervals
Preflight 100 hour 500 hours
Magneto primary circuit components
Primary Coil - 200 turns of 18 gauge wire, part of the ignition coil Breaker Points (aka points) - Controls current flow through primary, and timing of the spark, operated by a cam. Condenser (capacitor) - protects points from arcing, and speeds the collapse of the magnetic field when the points open. Ignition Switch - Allows turning the system "off"
P-lead wire
Primary lead The connecting wire between the magneto and the ignition switch. Ignition switch connects to ground.
Spark plug ID numbers
R H B 37 E R-Resistor H-Barrel style B-thread size (b is 18mm) 37- heat rating (hot is high number or cold number lower) A plug must get hot to stay clean so on a powerful engine a cold plug is better but a smaller engine
Verifying internal timing in a dual magneto
Red tooth should be in one window and "K" should be in other window. The key is that both points must open at EXACTLY the same time. Start with left side: -Set Cam at highest point -Set left side points gap -Rotate cam to set left timing -Set right side points gap -Rotate cam to set right timing
Why is there a resistor in the spark plug
Reduces radio noise Capacitive after fire which causes erosion of the spark plug
Feed-through capacitor
Reduces radio noise by passing electromagnetic energy in the p-lead to ground. Test the capacitor by placing a probe on either lead and other probe on case.
D3000 mag to engine timing
Set engine to #1 cylinder firing position and mag to #1 cylinder firing position.
Dual mag timing and setting points
Set left mag first First set the gap of the points Then set the timing of the left. From this point the cam position cannot be changed Next, adjust the points on the right mag to correct the gap.
Batt Ignition review
System battery supplies current to primary coil, creating a magnetic field around primary and secondary windings
2 Spark plugs and better because
System redundancy More efficient: late spark for detonation protection, with 2 plugs to regain power loss
Magneto Check (running engine)
Test 1: When Idling, turn both mags off, then immediately back to BOTH. Engine should quit (off), then immediately turn mags back on (switch to both) Test 2: Run at specified engine speed (ie 1700rpm) Turn mag switch from Both to Right, observe change/drop in RPM. then back to both. Turn mag switch from Both to left, observe change/drop then switch back to both. Max drop 150rpm on one mag and 50rpm difference between mags.
Harness testing
Tester emits high voltage Uses the aircraft's battery for power (selectable 12/24volts) "Fail" indication is when the light does not illuminate, or does so sporadically.
In a magneto
The cam and the points are a matched pair. When you replace one, you must replace the other as well.
When Ignition switch is closed in magneto circuit...
The circuit is off because it is grounded
Induction vibrator
This is used in place of impulse coupling Gives a boost in spark; does not retard the spark Keeps the ignition off until after the first revolution Components: Vibrating Point Capacitor Relay
Spark plug sizes.
Thread size: Metric 14mm (rare) and 18mm Harness size: Metric 5mm (newer) and 7mm
Why is there a resistor in the Spark Plug?
To prevent capacitive afterfire This reduces the wear on the electrode Reduces radio noise from the ignition
Dual Magneto
Two magnetos in one One magnet shaft (4 pole magnet) with two 2 coils, qualifies as "2 ignition sources"
the FAA requires an airplane ignition system have:
Two plugs per cylinder Two separate electrical circuits Two Separate sources of electrical energy (part 33)
When is a spark plug considered worn out?
When 50% of the electrode material is gone.
When should spark plugs be replaced?
When it is worn 50% of either center or outer electrodes
Ground Safety Check
With engine at idle power, turn both mags to OFF position and immediately back to BOTH. Engine should quit briefly and immediately restart. This ensures the mag switch safes the mags in the OFF position.
Shower of Sparks system
Works in conjunction with the retard breaker to help start. Only left mag has retard breaker Left mag is used to start because it has retard breaker
Magnetos
Works similar to an alternator Two principle types: High tension: high voltage directly from magneto Low tension: Lower voltage from the magneto, with a coil to boost voltage at the spark plug
Cam and break point replacement
a mated pair; must be replaced together
What is the effect of a broken impulse coupling spring
difficult starting and retarded timing
Torque for magneto installation
if all else fails, use torques in the engine overhaul manual.
Capacitive afterfire
is a sustained high current flow through the plug caused by the capacitive effect of the spark plug leads. The capacitor in this case is the ignition lead. this high current erodes the plug electrodes Spark plugs have a resistor built into them to reduce the current (per ohms law)
a booster magneto is
it is a manual cranked booster for the magneto circuit the secondary coil in the booster magneto produces the starting spark retarded
With ignition in left position what will left p-lead be?
left p-lead will be open to ground and left mag will be hot
Spark plug reach
length of the thread reaching into the cylinder
Efficiency-gap is a
magnetic rotor position that gives best spark because of the best Found by: Slick - use timing pin dropped into hole in case Bendix - red tooth mark seen in window
Spark plug rotation is
next in order and swapped top to bottom
Resistor in spark plug
reduces wear on spark plug electrode by reducing current reduces radio noise
Radial Engine Harness
run through a conduit.
What is an advantage of a high-tension magneto
simplicity no transformer at the spark plugs
If e-gap is not correct how do we fix that
slick mag: Points should be specific gap; if it doesn't meet this, replace cam and points. Bendix: can adjust timing of points but if gap is wrong then you must replace the points. Cam shouldn't need to be replaced, it is made of steel.
How does an induction vibrator prevent kickback during start
starter and magnetos are on separate
Which plug fouls more readily
the bottom plug.
Establish #1 firing position on installation with
timing pin
Pressurized Magneto
used on high altitude turbo charged engines pressurized with upper deck pressure from the turbocharger Helps reduce high altitude misfires Pressurizing source causes corrosion problems inside the magneto.
Which electrode is worn out through use?
whichever electrode is the ground (negative)
How to remove lead fouling
with a dental pick or the vibrating removal tool.
