Advanced Ignition for the 21st Century
Overview of the LASAR® electronic ignition system and its operation – Part I
By Harry Fenton
The years since the mid-1990’s have been exciting and revolutionary times for the piston-powered general aviation (GA) market. Many manufacturers have entered this "technology renaissance," offering new products for these aircraft. This article will provide an overview of one of these new products — Unison’s electronic ignition system called LASAR®.
What is it?
LASAR, which stands for Limited Authority Spark Advance Regulator, is the first and only stand alone microprocessor-based engine control system approved by the FAA for GA piston aircraft. It consists of a controller, two magnetos, a low voltage harness, a special status cockpit light, and a CHT probe. The controller is a sealed box, which mounts to the firewall and contains the electronics and software for controlling ignition. The magnetos are similar to conventional magnetos but also include electronic circuitry. The low voltage harness electrically connects the controller to aircraft power, the magnetos, the cockpit light, the ignition switch, and the CHT probe. The cockpit light provides an indication of system status (ON or OFF). The CHT probe is used as a control input in the LASAR system.
This system optimizes the timing of the engine by electronically advancing the timing in response to the absolute manifold pressure and the engine RPM, resulting in better fuel efficiency and improved horsepower. It can provide ignition timing advance angles from zero to 50 degrees before top dead center (BTDC). The net effect is that the engine can develop more power output for a given amount of fuel input. An additional benefit is a smoother running engine.
During engine start, LASAR provides a high energy spark discharge. The higher available energy can contribute to better engine starting if the spark plugs are wet or carbon-fouled, and in cold temperature conditions when the fuel is less likely to properly atomize.
In order to provide optimum engine performance while at the same time providing ignition system redundancy as required by FAR 33.37, Unison elected to incorporate the best features of magnetos with the advantages of electronics into the architecture of the overall system. The overriding concept is simple: electronics are used to advance and enhance ignition, but if the electronics fail or lose electrical power, then the fail-safe backup is the tried and true magneto.
LASAR magnetos are similar in concept to conventional magnetos because in the back-up mode, they must function just like conventional magnetos. However, they are also a very integral part of the system’s operation when in the LASAR electronic mode. The engine rpm and crankshaft position inputs, the generation and distribution of the spark, and the fail-safe switching from LASAR magneto to conventional magneto all take place in the LASAR magnetos.
In operation, a relay in the magneto circuitry serves as the switching mechanism between LASAR mode and backup magneto mode. When the LASAR controller is providing power to the LASAR magneto relay, the relay contacts, which connect the controller to the magneto coil, are closed. If power fails or the controller commands backup operation, then the relay contacts open, connecting the magneto coil to the backup magneto circuit.