Engineers and entrepreneurs alike have searched for ways to achieve more horsepower since the introduction of the internal combustion engine. The traditional two-magneto system that provides the spark for combustion in an aircraft piston engine, however, has remained essentially unchanged for decades. In pairs, magnetos have proven reliable when properly maintained. Their disadvantage though is many moving parts subject to failure and an inability to adjust for altitude or wide variety of temperatures.
Because magneto settings don’t vary in flight, they can’t cope with the changing atmosphere, leading to a longer combustion burn, missing the optimal spot for achieving peak power. The efficiency issue is exacerbated by a magneto’s relatively mild 12,000- to 13,000-volt spark.
Electronic ignition systems were created with far fewer moving parts for improved reliability. They can improve the operating efficiency of almost any engine because of their adaptability to the ever-changing atmosphere outside the aircraft.
The simplest electronic ignition system consists of a coil pack, an ignition controller, a wiring harness, a manifold absolute pressure sensor to gauge the strength of the vacuum inside the intake manifold and a mag timing housing, which replaces a traditional magneto, to couple the ignition to the engine.
The coil in an electronic ignition system creates a more powerful spark in the 70,000- to 80,000-volt range. This allows for a larger spark-plug gap, translating into more efficient combustion.
Electronic ignition typically replaces just a single aircraft magneto. Replacing only one provides a significant enough improvement in efficiency that a second one is usually unnecessary.
How it Works
Whether you have an experimental or certified aircraft, the system is basically the same. One magneto is replaced with a timing head which provides crankshaft position and RPM information. The controller, the brains of the system, is installed on the cool side of the firewall and receives crankshaft and RPM information. The controller in turn uses this information to instruct the inductive coil to fire the appropriate spark plug. The controller gives this order twice per cycle, initially on the compression stroke and then again on the exhaust or waste stroke. This is known as a waste spark system and serves to burn any residual fuel thus completely cleaning out the cylinder and reducing deposits. Once the aircraft is at altitude, and operating below 24" of manifold pressure, a Manifold Absolute Pressure sensor lets the controller know it's time to start advancing the timing. This allows the engine to perform more efficiently, with less fuel, while also producing more power.
Electronic Ignition Benefits
Smoother engine operation
Longer spark plug life typical
Ignition timing automatically adjusts with altitude
Reduced maintenance costs
10-15% gain in fuel efficiency
Reduces spark plug fouling
Improved high altitude performance
More horsepower
The major advantage of electronic ignition is that it incorporates modulating the spark, thus compensating for changes in flame-front speed due to altitude, temperature and fuel mixture. This pays off when cruising at altitude, where more timing advance is required due to less dense mixtures. The result is better fuel economy when cruising at altitude where electronic ignitions excel. The rising cost of avgas further enhances this benefit if you spend most of your time at cruising altitudes.
Greater spark energy from electronic ignitions is also an important advantage because it supports a wider spark-plug gap, allowing them to light low-density mixtures at high altitude, as well as withstand high cylinder pressures from high-compression or supercharged engines.
A reduction is maintenance costs is another huge factor. Reduced spark plug fouling means lower maintenance costs and eliminating magneto overhauls every 500 hours saves those maintenance labor hours as well as downtime.
Replacing one magneto will typically improve fuel economy on average by 10-15% (fuel savings of 1.5-2.0 gph or greater). Additionally, there will be an improvement in horsepower, smoother engine operation, easier hot starts and improved high altitude performance.
Electronic ignition kits are available for a variety of experimental as well as certified aircraft, and most are available for either 12V or 24V systems.
Should You Move to Electronic?
Well, it depends on what and how you fly.
A fuel savings of 1 gallon per hour is a rule of thumb for engines operating electronic ignitions at around 10,000 feet. If you regularly cruise at these altitudes, it may be worth your while to determine how long it would take to recoup the investment. Don't forget to calculate for reduced maintenance too.
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