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 and controls, your first thought is that they are talking about their car or that they are discussing the latest in gas turbine control technology. Well, it's time to readjust your thinking because several companies are bringing these types of advanced technologies to today's general aviation market.

The revolution that is going on in the general aviation market today is similar to the revolution that occurred in the automotive industry over the last several decades. Automotive electronic controls for ignition, fuel injection, turbochargers, brakes, and more are now changing from "options" to becoming "standard features" on everything from economy to luxury class automobiles. These changes primarily came about in the auto industry in order to decrease pollution and increase automobile efficiency, performance, safety, reliability, and customer satisfaction.

Similar to the automotive engine revolution, aircraft piston engines are now experiencing major changes and will continue to do so over the next 10 years as new federal regulations for aircraft noise, cleaner burning fuels, and low emissions will be instituted. In addition, the demands of a very large customer base eager for modernization will also continue to drive the aircraft piston engine toward an ever increasing level of electronic controls content.

This contrasts with an industry often resistant to change due to deep rooted conservatism based on a dedication to safety with extremely high certification costs and ever present threats of product liability. As some technicians may ask, "Why put more cost and complexity into an aircraft that works fine just as it is?" The answer to this question is relatively easy. As evidenced in the automotive industry, the new electronic controls provide many benefits which far outweigh their initial costs and which make some current aviation technologies look antiquated.

With the new aircraft piston engine electronic technology comes requirements for aircraft technicians to acquire a whole new set of skills and knowledge in order to enhance their proficiencies and remain marketable. Unison Industries' LASAR® electronic ignition system is one example of a leap in electronic engine control technology which is sure to make a big impact on the general aviation market — making it worthy of a technician's further study.

System Description and Installation
Developed and certified in the early to mid 1990s, the LASAR® electronic ignition system is arguably the first step in a aircraft piston engine revolution. This system digitally processes engine speed (rpm), manifold pressure (MP), cylinder head temperature (CHT), and system health to increase engine performance without compromising safety or reliability.

There are five parts to the LASAR® system. The three main components are the computer controller and two dual mode magnetos. "Dual mode" refers to the mag's two operating modes: automatic and backup. The fourth piece of the system is a low voltage wiring harness used for communication and power distribution between the controller, magnetos, and the airframe. The fifth component is the high voltage wiring harnesses. Slick's high voltage harnesses are the only secondary harnesses currently certified with LASAR®. The controller is the brain of the system.


The controller makes decisions based on manifold pressure, rpm, cylinder head temperature, ignition switch position, and monitors its own health as well as that of the airframes' power source and the magnetos.

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

By Jim Melvin, Bryan Quillen, and Harry Fenton

February 1998

The low voltage harness electrically connects the controller to the magnetos and airframe. The harness consists of three connectors (one for the controller, two for the magnetos) and three sets of input wires. These input wires include: a set of power wires for battery and ground, a set of the cylinder head temperature wires, and two ignition switch wires.

Electronic Mixture Control from Precision Taps into the Power of LASAR®

By Roger Hall

Electronic fuel injection has been available in the automotive industry for many years, but has yet to appear on even the most expensive certified piston engine aircraft. One of the main reasons for this is a reliability and safety concern. In order to assure continuous operation of the engine, many changes to the automotive systems would be required.

Precision Airmotive Corporation and Unison Industries have joined forces in the development of an electronic fuel metering system, which offers many of the advantages of electronic fuel injection, while maintaining the proven reliability of mechanical fuel injection. The system, known as LASAR®+EMC, combines Unison's FAA approved LASAR® electronic ignition with an Electronic Mixture Control (EMC) mated to Precision's RSA fuel injection.

Like the LASAR® ignition system, the EMC is based on proven, reliable technology, and in the unlikely event of a failure of the electronic system, control reverts back to the proven RSA mechanical fuel injection system which is currently used on all Lycoming fuel injected engines.

The EMC works in conjunction with the RSA system to improve fuel efficiency and reduce pilot workload by leaning out the mixture in response to altitude changes and power levels. The primary function of the EMC is to automatically compensate for the air density changes experienced when operating an aircraft at altitude. Additionally, the system will reduce fuel flows at part throttle cruise settings, resulting in additional fuel savings. The initial system to be certified will be installed on a Lycoming IO-360 in a Mooney MSE, and will be a "basic" system with air density compensation and part throttle economizer functions. Follow-on development will focus on "closed-loop" control, allowing aggressive leaning during all phases of flight, while maintaining sufficient fuel flow for engine longevity.

The LASAR®+EMC system consists of a controller, LASAR® magnetos, and an Electronic Mixture Control unit mounted to an RSA fuel injection servo. The LASAR® controller provides the "brains" for both the EMC and the magnetos, although the fuel control and ignition functions are independent of each other. This initial system will use four simple inputs to control the fuel/air ratio. The EMC uses induction air pressure and temperature to compensate for changes in air density. This allows the system to maintain a fixed fuel/air ratio regardless of altitude or temperature — eliminating the need for the pilot to lean the mixture as the airplane climbs. The EMC uses RPM and manifold pressure to adjust the mixture based on engine power level. This allows the system to lean the mixture at part throttle cruise settings, resulting in lower fuel flows (as compared to full rich operation at cruise).

In order to provide the reader with a basic understanding of the EMC system, some knowledge of the RSA fuel injection system is required. The RSA system is a fuel/air ratio control system. It uses a venturi to "measure" the volume of air entering the engine. The pressure differential created by the venturi is proportional to the volumetric airflow. This venturi signal is routed to a diaphragm in the regulator where the fuel flow is metered to provide a predetermined fuel/air ratio.

The primary drawback of this type of system is that it measures the volume of air entering the engine, not the mass of air. Because of this, as the altitude of the aircraft increases, the air density decreases resulting in less mass airflow for a given volumetric airflow. The fuel/air ratio then increases and the engine runs rich. The EMC corrects this condition by bleeding off some of the venturi signal and "tricking" the regulator into thinking that there is less airflow then there actually is. In this manner, the EMC can control the fuel flow.

By using a system that can only lean the engine, it is a simple task to revert back to the purely mechanical system. In the EMC, a solenoid valve is used as the "metering" valve to bleed off the correct amount of venturi signal. A second solenoid valve is series with the metering valve, isolating the EMC system from the servo in the event of a fault. Whenever the EMC is turned off or has experienced a fault, the automatic leaning function is deactivated, and the pilot merely leans the engine using the manual mixture control as he would in an aircraft not equipped with the EMC.

The LASAR®+EMC can provide significant fuel savings. Initial flight tests have shown fuel savings of up to 15 percent for a medium distance flight, with savings in excess of 20 percent during climb and descent. In addition, the system can fly safer. Instead of pilots spending time with their heads in the cockpit adjusting the mixture, they can spend the time looking out the window, scanning for other aircraft. Look for LASAR®+EMC to be certified and available sometime this summer.

Roger Hall is the engineering manager at Precision Airmotive and has been with the company since 1990. He has been working on the EMC project since its inception. Questions regarding the EMC should be addressed to Precision's product support department at (425) 353-8181.

A 10 amp circuit breaker should be installed inline to a power source common to the master switch. This is a good idea for protecting the aircraft wiring, but also for use in the cockpit during flight evaluation. By pulling the breaker in flight, it forces the system into backup mode and makes differentiating between electronic and standard magneto ignition easier. The ground can be placed on any common ground. In composite aircraft or aircraft with ground busses, the most appropriate place is on the left magneto mounting stud. This placement eliminates any possibility for ground looping.

The cylinder head temperature wires are purple and white and install with the bayonet-style probe purchased with the system. If the aircraft already has a cylinder head probe, Unison has a dual probe that will provide a signal to both the aircraft's gauges and to the LASAR® controller.

The last set of wires required for installation are the ignition switch wires. The green and blue wires are attached to the ignition switch, but can also be spliced to the P-Leads already installed in the aircraft. Finally, leads to connect a cockpit indicator light and compatible electronic tachometers are provided in the low voltage harness.

An additional benefit to the LASAR® system is its troubleshooting features. Today, it's quite common for auto mechanics to use computer technology to assist in troubleshooting. The LASAR® system allows for this as well.

With any Windows-based laptop computer, an aircraft technician can monitor rpm, manifold pressure, CHT, battery voltage, and fault codes. The fault codes will pinpoint problems down to individual airframe and engine components. By using a communication cable via the controller's RS-232 port, a technician is capable of troubleshooting problems from the cockpit.

In order to utilize the LASAR® system's built-in troubleshooting feature or to conduct more manual troubleshooting procedures, Unison provides a detailed troubleshooting guide. A word of caution in troubleshooting: many nonignition factors influence the performance of aircraft ignition systems and the replacement or repair of ignition components may not remedy problems in all cases.

Keep it Legal
As is true of any aviation-related maintenance task, the job is not complete until the paperwork is done! In the case of the LASAR® system, it is FAA-PMA approved and does not require field approval.

After installation and all your logbook entries have been made, a 337 must be completed and filed with your local Flight Standards District Office (FSDO). A flight manual supplement is also required; this is part of the document package sent with the LASAR® controller. It is a small document which fits nicely into the pilot's operating handbook (POH). This document makes no changes to the POH, but is still required and of interest to pilots and aircraft owners.

Installation of the LASAR® system changes the aircraft's empty weight. For this reason, some technicians do a "weight and balance." Weighing about 1.5 pounds, the electronic controller is the only component which contributes to a net change in the aircraft's weight. The LASAR® magnetos and low voltage harness do not appreciably change the aircraft's weight. The net change due to the LASAR® system does not significantly impact the aircraft's C.G. Some FAA inspectors feel it is a requirement to do a "weight and balance" — others do not. The technician or IA should check with their local inspector.

System Checks
In general, the improved engine performance due to the LASAR® system will be immediately noticeable. The engine will typically start within a single prop rotation and will idle more smoothly. Before flying with the LASAR® system and in order to prepare yourself for demonstrating the newly installed system's proper operation and performance improvements, you might want to get comfortable with pulling the ignition breaker. Take the engine up to 2,000 rpm and pull the breaker. The only indication that you are running on backup ignition should be that fact the cockpit light (if installed) is illuminated. The transition is seamless. Once the breaker is back in its normal position, the cockpit light will not shut off for 30 seconds. Nothing to be alarmed about; this is a safety feature in case the aircraft has an intermittent loss of power in flight.

The first part of flight testing is done on preflight. When the pilot switches the ignition to the left or right position during a magneto check, the controller switches the system to backup. This check ensures the pilot that the backup ignition is functioning properly. Again, the POH has not changed so the pass/fail criteria for the magneto remains as the engine manufacturer originally intended. Once the magneto check is complete, the system will switch back to automatic mode. This takes approximately 20 seconds from the moment the switch is returned to the BOTH position.

The final stage of completely checking out a newly installed LASAR® system is conducting an in-flight check. It is during this stage that the best benefit of the LASAR® system can be demonstrated. With the system in the automatic mode, the pilot will be able to lean the engine to the maximum extent recommended by the engine manufacturer's operating instructions, thereby achieving greater savings than is normally possible without LASAR® installed. Unison Industries has put together a document called, "The LASAR® Experience, A Guide for Fixed Pitch Propeller Airplanes," which provides a good outline for conducting in-flight demonstrations of the LASAR® system. This guide also describes what the typical pilot can expect in-flight with a baseline LASAR® system. A copy of the document comes with each LASAR® Master Service Manual (Slick Manual L-1500). Topics discussed in the guide are easier starting, smoother engine operation, faster rate-of-climb, reduced fuel consumption, and increased horsepower. As with any guide, the document should only be used as a guide. Your actual experiences may vary depending upon the installation, test conditions, and state of the equipment.

In terms of cost, one of the design parameters for the LASAR® project was to bring this technology to market at a reasonable price. The list price for a complete LASAR® system is approximately $2,700 and approximately 3 hours of installation time is required. As with any new technologically advanced system, the first installation might take longer.

For the weekend pilot, the total equipment and installation costs may create some trepidation, but when offered as part of a total engine overhaul (when the mags usually receive maintenance anyway), the incremental cost becomes less of a budgetary factor. For flight schools, check haulers, and other high flight hour companies, the benefits far outweigh the cost.

Unison has put together several programs for companies that are retrofitting multiaircraft operations. In the past, these programs have included technical assistance during initial aircraft installation, free engine diagnostic software, and free training seminars for pilots and technicians. Call the manufacturer if your company or your company's clients have an interest in setting up a special program. Unison has high hopes for the LASAR® system, and initial customer reaction has been promising. There seems to be a pent-up demand for new equipment on the aircraft flying today and those just rolling off the newly revitalized general aviation assembly lines. Unison has provided one answer to satisfying the market's demand by providing the LASAR® system. Introduction of LASAR® has created a market opportunity for qualified technicians. As more and more of these new systems make their way into the field, you as the technician will be called upon to do the initial installations and provide field support. In addition, other new Unison LASAR® spin-off products for general aviation piston engine aircraft have either already been introduced or are in the works. Two of these new products include the SLICKSTART™ and the LASAR® with EMC. The dawn of a new age in general aviation technology is just emerging. The technicians with the knowledge and initial experiences with the new systems will be the ones to capitalize on the opportunities they present.