The fixed timing compromise matches only one power setting across the infinite combinations available to the pilot. That perfect zone exists only at one combination of manifold pressure and RPM in an engine with fixed-timing ignition. Providing the optimum spark timing for every possible combination of power levels improves an engine’s efficiency by burning its fuel for maximum power. Incomplete combustion wastes expensive fuel and prevents the engine from producing the maximum possible power from each explosion in each cylinder. The earlier the plugs fire, the more you can lean the engine to reach peak the more you can lean, the less fuel you consume. With the Bush Kit, a LASAR-equipped engine can be started with a dead battery, a failed controller box, or both. To fix this shortcoming, Unison developed the LASAR Bush Kit, which adds an impulse coupling to the left mag. The LASAR system needs at least seven volts to work, meaning that a dead battery prevents you from starting the engine, even by hand-propping it. If LASAR has a weak link, it’s in its power source.
A manifold pressure line from the engine plugs straight into the controller box, as does a bayonet-style cylinder-head temperature probe. The controller box gets its speed and crank-angle readings from sensors in the magnetos. The map, which is stored in the electronic brain or controller box of a LASAR system, helps the brain decide whether to fire the plugs earlier or later depending on the combination of engine speed and manifold pressure selected. As a result, the engine gets the best spark timing for any given power level, regardless of whether you use the highest RPM and lowest manifold pressure or flip the combination to the highest manifold pressure and lowest RPM. LASAR does not use a flat percent-of-power line, but a binary “map” that retards or advances the ignition timing based on the different RPM and manifold pressure combinations for the same power level. But with LASAR’s electronic “brain” controlling both magnetos’ timing, the system retards the timing of both mags and fires them during an engine start.
Many piston engines start on only the left magneto, with timing retarded by either an impulse coupling or a so-called shower-of-sparks circuit working through the left mag. In turn, this hotter spark helps burn away carbon and lead deposits, and overcomes flooding and worn or mis-gapped plugs. That integral circuitry sends roughly double the voltage that mechanical mags generate to the spark plugs, resulting in a hotter, cleaner spark across the electrodes. LASAR also incorporates its own spark-boosting hardware comparable to the circuitry in Unison’s SlickStart spark-booster system. The complete Unison LASAR system components for a Lycoming O-180, sans sparkplugs. LASAR delivers a hotter spark, uses both mags during engine start and provides an engine with seamlessly-variable spark timing precisely matched to the power setting. What you get in place of inefficient, fixed-timing magnetos is a system that matches the modern Capacitive Discharge Ignition, or CDI, that began replacing breaker-point ignition (coils, distributors and points) in automotive engines a quarter century ago. From the panel, all the pilot sees is an annunciator light that informs of a successful self-test cycle or a controller-box failure.
Of Brains and Maps The Basics…Īs far was what the left-seat occupant sees, Unison’s LASAR system simply replaces the old mechanical magnetos with newer ones designed for the LASAR, plus some black boxes and a bit of wiring. But before going any further, let’s discuss what the LASAR system is and what it does. At that moment, the thought of hundreds of equally-easy starts in the future erased any doubts built up during the prior 48 hours. The engine felt immediately smoother, without struggling a few seconds to clear its throat before settling down to a smooth idle after starting. Now, Air Comanche starts quicker and easier than most small-bore Lycomings. Even before that first circuit around 71K, we noticed differences in how easily and smoothly the Lycoming O-360 started. The good news is that, after working through a number of foibles and clearing a couple of unavoidable obstacles, we achieved a very clean installation of a cutting-edge ignition system, one that matches what today’s pilots and aircraft owners demand at every turn: modern powerplant systems to match the modern avionics they’re installing in their older airplanes.