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.
Advanced Ignition for the 21st Century Overview of the LASAR® electronic ignition system and its operation – Part I By Harry Fenton May/June 2001 The years since the...
Advanced Ignition for the 21st Century — Installing the LASAR Electronic Ignition System — Part II By Harry Fenton July 2001 An overview of the LASAR® electronic ignition system...
The techniques and opinions on how to start aircraft engines are as varied as the airplanes, engines, and operators that encompass this topic.