Primer for the LASAR electronic ignition system

Primer for the LASAR® Electronic Ignition System By Jim Melvin, Bryan Quillen, and Harry Fenton February 1998 When you hear pilots or technicians talk about electronic ignition, electronic engine controllers, or electronic fuel injection...

After sensing all these parameters and verifying that they are valid, the controller compares this data to an empirically derived look-up table, then triggers the magneto coils to fire at the optimum advance, duration, and energy. These decisions are made in approximately 10 milliseconds (that's faster than you can blink your eye).

The optimum advance, duration, and energy level are determined through dynamometer testing at the engine manufacturer. For each engine family, an engine is tested with a LASAR® system. The engine is set up for a particular power setting (MP and RPM) while the ignition is advanced. As the ignition advances, the horsepower increases until the optimal point is reached for that particular power setting. These peak power points make up the engine personality map (EPM) and are different for each engine family. This ensures optimal performance on each LASAR® application.

The control box can be installed essentially anywhere in the aircraft but is designed to be installed on the firewall. In cases where the firewall is too congested, it can be mounted in the engine nacelle with Adel clamps. Some technicians mount the controller in the cockpit and run the low voltage harness wires through the firewall. In this case, grommets and sealant are required for a professional looking installation.

Additional consideration must also be given to the manifold pressure input when installing the controller. A manifold pressure port is conveniently located on the face of the controller.

The installing technician can choose from two methods of tapping and plumbing a pressure line. The controller is shipped with a cylinder fitting that easily replaces an existing plug on the engine. For aircraft with a manifold pressure gauge, teeing off the existing hose is acceptable provided the pressure is dampened by using the fitting provided with the controller. Depending on where the controller is mounted, it will be necessary to route approximately 2 feet of standard rubber hose.

The magnetos are externally similar to the standard Slick magnetos used today, but internally are different. Internally, the new magnetos contain a printed circuit board (PCB) and an RPM sensor (left magneto only) along with the traditional magneto components. A relay is mounted on the PCB which is mechanically biased to the closed, back-up position. When the controller is commanding electronic ignition, the relay is electrically pulled open, which removes the backup contact points from the ignition circuit and gives the controller complete control of the ignition event.

During operation, the system interrogates itself every 10 milliseconds. The controller can command backup by interrupting power to the relay if an invalid input is detected. In the unlikely event of total electrical failure, the relays will fall back to the mechanically biased, backup position. The points in the magneto will then fire the magneto coils at a fixed timing angle in the same reliable way they have for years. Because the system's backup position relies on the traditional magnetos, the system is completely fail safe.

A special timing tool called SynchroLASAR® is required to install LASAR® magnetos. Due to the electronic circuit in the LASAR® magneto, the standard "buzz box" cannot be used. Some of the timing techniques are different for LASAR®, as well. The hall effect of the LASAR® magneto, which provides RPM and position reference to the LASAR® controller, must be synchronized to top dead center (TDC) so the LASAR® can calculate the proper advance angle based on RPM and manifold pressure.

The LASAR® sensor magneto is timed to TDC by turning the engine to TDC after loosely installing the magnetos at the engines fixed timing position. Once the engine is at TDC, the sensor magneto is turned slightly left or right until the red light on the SynchroLASAR® illuminates. Then the magneto is tightened to the appropriate torque specification. The engine is subsequently turned back to the fixed timing position; the green breaker point light will then illuminate indicating that the points have just opened. By slightly turning the right magneto left or right, synchronizing the right and left breaker light is the final step of the magneto installation.

Primer for the LASAR® Electronic Ignition System

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