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On a traditional dual magneto system, both magnetos are timed to fire at 25 degrees before Top Dead Center (TDC). When starting the engine, the ignition switch grounds the ‘P’ lead to the right magneto, stopping it from firing. Meanwhile, the left magneto with the impulse coupling can still fire. The impulse coupling causes the magneto to fire at TDC, and will continue to fire at TDC until the engine reaches about 200 RPM. At this time, the impulse coupling disengages and the magneto falls back to firing at 25 degrees before TDC. Once the ignition switch is released from the start position, the right magneto also begins to fire. From now on, no matter what the RPM, power setting, or altitude the engine spark timing will remain at 25 degrees before TDC.
At any altitudes, a cylinder on the intake stroke draws in fuel and air. At lower altitudes, on the compression stroke (as the piston moves up) at 25 degrees before the piston reaches the top of the cylinder (TDC), the spark plug fires lighting the air/fuel mixture. The objective is to reach the peak pressure point (as a result of igniting the air/fuel mixture) by the time the piston reaches 11 degrees past TDC.
As altitude increases, thinner air reduces the oxygen available for the proper fuel-air mixture creating more space between the air/fuel molecules. When the spark plug fires at 25 degrees before TDC, the thinner air/fuel mixture will burn slower. Therefore, the peak pressure point occurs much later than 11 degrees past TDC, and hence there is a loss in power. By advancing the timing based on RPM and atmospherics, the peak pressure point can be maintained much closer to 11 degrees after TDC. This can only be done with an electronic ignition system and is best done with an Electroair Ignition System (EIS)!
Before discussing the detailed mechanics of how the EIS works, we should overview the benefits and general operation of the EIS. The EIS differs from standard magneto systems in one very significant way: TIMING. In a magneto, timing is permanently set; the EIS adjusts timing (or spark advance) based on RPM and manifold pressure. This ability to adjust the spark advance allows the EIS to determine the optimum timing setting which produces the most power with the least fuel.
The mechanical advance is set during the installation of the EIS timing housing or crankshaft sensor. This setting is usually zero degrees of TDC.
As the engine is started, the unit is set to remain with a zero advance up to 250RPM. After reaching 250 RPM, the EIS will advance the timing to 7 degrees and stay there until the engine reaches 400RPM. After 400RPM, the EIS will advance the timing to the setting correct for your engine (found on the data plate).
The final component for the total amount of timing comes from the vacuum advance, or Manifold Pressure Sensor. The manifold pressure is sensed and calculated in to the total spark advance. These two measurements are used together to determine the most efficient timing setting for the engine. The MAP Sensor will add a maximum of 15” of advance to the total Spark Advance. Refer to the following Vacuum Advance Curve Chart, fig. 1:
If the MAP Sensor (manifold absolute pressure or vacuum) option is not installed, then the vacuum advance value in the above equation would be zero. Without the MAP sensor installed, the advance remains zero up to the 250 RPM. At 250 RPM, it advances to 7 degrees BTDC, and then at 400 RPM, the unit advances to the spark advance setting for your engine (this is set at the factory) and will remain at that setting for operation.
1.1 How Direct Fire Ignition Works
What sets the Electroair Ignition System (EIS) apart is the ability to charge multiple ignition coils at the same time. This increased dwell time means that full spark energy is available over the entire RPM range (up to 9600 RPM at 12 volts). Unlike capacitive discharge systems that only put out one very short spark, the EIS puts out a full energy, long burning spark at your highest and most critical engine speeds. Long burn times assure effective burning of even lean fuel mixtures.
The brain of the EIS includes dual digital microprocessors using patented spark algorithms, which takes the electrical signal from the crankshaft (or mag timing housing) sensor, identifies top-dead center and then keeps track of the remaining rotation. The EIS determines engine speed and computes the spark advance using the settings pre-set at the factory for your engine as a base-line. Settings from the factory are for stock engines; however they can be modified to ‘tweak’ more power for racing applications. Additionally, the EIS receives engine manifold pressure information and advances the ignition to compensate for altitude and throttle position.
Beyond the synchronization and firing the plugs at the correct advance angle, the EIS also computes the exact dwell time to produce 9 amps of coil current. Coil charging is dynamically measured, so changes in RPM, battery voltage, or temperature are accounted for on every spark. This corrects any errors that are caused by battery voltage or coil temperature changes and insures maximum spark energy.
High Resolution Single-Crankshaft-Sensor Decoding
In summary, your Electroair EIS delivers more power because:
Spark Plug Wire Selection
SOLID CORE WIRES SHOULD NEVER BE USED.
Do not be misled by spark plug wire manufacturers claiming to give you a “power increase” from their wire. The bottom line is that with our charging method, different spark plug wires simply do not make a difference in terms of spark energy. However, there is a huge difference in noise generated by different spark plug wire types (solid core wires generate a very high amount of noise with our system).
Paraphrased from Magnecor’s Website:
Electrical devices, including spark plugs, use only the electrical energy necessary to perform the function for which such devices are designed. Spark plug wires are nothing more than conductors, and whereas a bad ignition wire's inefficient conductor can reduce the flow of electricity to the spark plug, an ignition wire that reportedly generates an "increase" in spark energy will have no effect on the spark jumping across the spark plug gap, since the energy consumed at the spark plug gap won't be any more than what is needed to jump the gap. For a more obvious example of this, a 25watt light bulb won't use any more energy or produce any more light if it's screwed into a socket wired for a 1000 watt bulb.”
Due to the extremely high energy in the EIS coil charging circuit, spark plug wires may wear out faster than with a standard ignition. As such, it is recommended that the wires be checked periodically for carbon tracking caused by a breakdown of the internal conductor element. Looking at the plug wires in a dark area and wetting them with a spray bottle of water will reveal carbon tracking. Pay close attention to the exposed section of the spark plug (where the rubber boot ends) during the test. To maximize spark plug wire life, keep the lengths as short as possible (i.e. mount the coil pack as close to the engine as possible). Replacement of the wires on an annual basis is recommended for high-rpm/high-horsepower applications.
Electroair uses the Taylor Pro-Wire Silicon Resistor Spiral Wire. This wire is an extremely high-quality wire with excellent noise suppression. Each wire supplied is made up of two terminated ends for the coil posts, you just need to cut the wires to the appropriate length and terminate the end with the hardware supplied to create the spark plug end.
Spark Plug Selection
The load at which a spark plug fails is different for all spark plugs. With the EIS’s charging circuit, the more load you put on an engine, the more voltage will be applied to the plug. This is a beneficial situation: for a high compression engine, the voltage at the plug will be inherently higher (since there is more load). The detriment is that spark plugs and wires are only rated to a certain voltage (30-40,000 volts is typical), and can begin to “blow out” at around 40,000 volts. If that voltage is exceeded by a large amount for a long enough length of time, the spark plugs will either blow out, break down or arc to somewhere other than the electrode (often through the insulator directly to the engine block).
Your installation manual specifies the recommended gap for your engine application. This gap will be larger than a typical aircraft plug gap because of the higher energy output from the EIS. This is perfectly acceptable with our ignition charging method, since the high load of the cylinder pressure will allow the voltage to be quite high at the electrode; the gap will keep the plug from seeing an over-voltage situation.
The bottom line is this: the EIS system uses an inductive (long duration charge at battery voltage) charging method for the coils, which is completely different than the capacitive (short duration charge at higher-than-battery voltage) charging method used by other manufacturers. What may work well for these systems may not work well for ours. Our experience has drawn us to the following guidelines for spark plug application:
Low Voltage Operation with Permanent Magnet-Type Starters
Most electronic ignition systems, Electroair’s included, require a minimum amount of power available in order to operate correctly. In the case of the Electroair EIS, the minimum system voltage required is 8V. If the system voltage falls below that value for any length of time, the EIS will not function properly and can potentially cause the engine to ‘kick-back’. This event can happen during the start-up of an aircraft engine using a permanent magnet starter if, for instance, the battery is not a peak charge. It is strongly recommended that an operator of one of these starters with an EIS always keep a full charge on their battery. Other suggestions that have come from some starter manufacturers include adding a dual battery to support the starting requirements. Electroair also supports the idea of a dual battery system, in particular, for potential emergency situations. This solution, however, has to be balanced with what the original weight considerations of the aircraft were in the first place.
One other alternative which has the benefits of a lightweight starter and does not have the draw backs of permanent magnet type starter is to use a series wound starter. Such an example is the starter built by B & C Specialty Products of Newton, KS. The B & C starter uses a series wound motor as the drive unit and draws much less power than a permanent magnet starter and is less susceptible to problems inherent to permanent magnet starters – like hot starts. A hot engine reduces the effectiveness of a permanent magnet starter. The B & C Starter has been used very successfully with electronic ignition systems. Of course, good battery condition and good grounding are vitally important for trouble free operation.
Another remaining solution to the low voltage problem associated with permanent magnet starters is to remain with the old style, Prestolite or Delco starter. These are heavier, obviously, than their counterparts, but there have not been significant problems reported about their operation with an electronic ignition system.
Please contact Electroair technical support if you are experiencing any starting problems. There are several solutions available.
email us here: planemakers@planemakers.com
Ignition System Technical Discussion
EIS Spark Advance (Timing) = Mechanical Advance
+ RPM Advance + Vacuum Advance
A "Direct Fire" ignition fires the spark plugs directly from the coils and not through a distributor cap and rotor. This is accomplished by using multiple coils, each with two spark terminals. The coil terminals are connected to the spark plugs, allowing one cylinder to fire on compression while its companion cylinder fires simultaneously on exhaust. Open spark gaps in the rotor and cap are eliminated, making wear and moisture problems a thing of the past.
The EIS uses a single, high resolution, 60-minus-2 tooth crank trigger wheel. This affords resolution unheard of in any other electronic ignition available today, offering spark accuracy of ¼ degree of crankshaft rotation. This accuracy means the system is ideal for the most demanding engine applications – that’s why it has set altitude and speed records.
The EIS outputs an extremely high-energy charge from the ignition coils. Spiral core wires work best with this charging method, since they prevent the electrical noise generated by the coil firing events from being transmitted. We recommend an 8mm or larger spiral core wire with a resistance of 300 ohms or greater per foot.
“What is not generally understood (or is ignored) is that the potential 45,000 plus volts (with alternating current characteristics) from the ignition coil does not flow through the entire length of fine wire used for a spiral conductor like the 1 volt DC voltage from a test ohmmeter, but flows in a magnetic field surrounding the outermost surface of the spiral windings (skin effect). The same skin effect applies equally to the same pulsating flow of current passing through carbon and solid metal conductors. A spiral conductor with a low electrical resistance measured by a 1 volt DC ohmmeter indicates, in reality, nothing other than less of the expensive fine wire is used for the conductor windings!
As was previously stated, spark plugs are generally more important to spark quality than spark plug wires. Most spark plugs exhibit failure when exposed to a large load. Failure usually consists of either intermittent sparking or arc-over. Arc-over is when the spark occurs between the spark plug wire and the engine block, instead of at the plug tip. Arc over is exacerbated by the use of low-quality wires, or wires that have cuts in the insulation.As was previously stated, spark plugs are generally more important to spark quality than spark plug wires. Most spark plugs exhibit failure when exposed to a large load. Failure usually consists of either intermittent sparking or arc-over. Arc-over is when the spark occurs between the spark plug wire and the engine block, instead of at the plug tip. Arc over is exacerbated by the use of low-quality wires, or wires that have cuts in the insulation.
There has been much discussion regarding the newer style, lightweight starters that use permanent magnets as the basis of their technology. To understand some of the issues, we must first understand one basic design characteristic of a permanent magnet lightweight starter: it needs a lot of power to get started! Since most permanent magnetic starters are derivatives of small automobile engine starters, their motors are first found in automobile chassis where batteries are substantially larger than typical light aircraft batteries and hence, have more available power. When these designs were adapted to aircraft, they failed to take into account the smaller batteries typically associated with light aircraft (25 amp-hour batteries and smaller). Permanent magnet starters typically draw between 30%-40% more energy than their larger, older style counterparts that they typically replace. This has left the entire aircraft electrical system, including the electronic ignition system, competing with the starter at the beginning of the flight cycle for power.