Airframe and Powerplant: New ignition technology

Is there spark beyond the magneto?

February 1, 2010

It’s well into the twenty-first century and the prosaic magneto is still sparking new airplane engines to life. During the last decade general aviation avionics manufacturers have filled our airplanes with technology. Portable devices such as the Garmin 696 stun the uninitiated with capabilities that were only dreamed of a decade ago. Flat panels and highly integrated avionics systems do everything from warning of nearby traffic to showing terrain to helping pilots “see” near-real-time weather. Pilots can now use infrared-enhanced vision technology and gain almost Superman-like X-Ray vision to penetrate smoke, fog, dust, and darkness. Airframes are molded into sleek, low-drag pods thanks to composite technology, and lives are saved by airframe parachutes and seat-belt airbags.

Despite these paradigm shifts, every new piston-powered GA airplane delivered in the past decade, and every new airplane today—with the exception of the Teledyne Continental Motors FADEC-controlled IOF-240 installed in the Liberty XL-2—is delivered with a set of magnetos, the same technology that sparked Lindbergh’s Wright J-5C across the Atlantic in 1927. In spite of many drawbacks—the compromise of fixed ignition timing and mechanical impulse couplings being the most problematic—magnetos still provide ignition for the certified world. Experimental airplane builders have been able to install more powerful, modern “smart” ignition systems for nearly a decade. Only one “smart” system is currently FAA approved for certified aircraft and it is part of a larger and more expensive ignition and fuel control system. But there are signs a change is in the air.

The ideal ignition system

An ideal aircraft reciprocating-engine ignition system must be self-powered, or have a reliable back-up power system; must spark continuously and powerfully over a wide range of temperature and atmospheric conditions; must be adaptable to a wide range of engine configurations—four, six, or eight cylinders and normally aspirated or boosted induction systems; must be utterly reliable; and, most important, must be “smart” enough to increase engine efficiency.

Magnetos address almost all these issues but like the scarecrow, Dorothy Gale’s sidekick in the Wizard of Oz, magnetos don’t have a brain—so they are unable to adjust the spark timing to increase efficiency.

Here’s how E-Mag’s smart ignition system works. During engine start the spark is fired at piston top dead center (TDC) at the end of the compression stroke to insure a smooth start with no kickback. At idle rpm the spark occurs at 20 degrees before TDC. This slight retardation smooths low-speed operation. At takeoff and other high power settings, the spark occurs at the same time it would with a magneto (25 degrees BTDC for most Lycoming engines and 20 to 22 degrees BTDC for most TCM engines). This spark setting insures adequate protection against destructive detonation during worst-case high-rpm, high-manifold-pressure conditions. These spark settings are not much different from magneto settings; cruise power is where the modern, brainy systems shine.

Advancing the timing—firing the spark earlier in the combustion cycle—does two things. The earlier ignition causes the combustion gasses to start pushing on the piston earlier and for a longer duration during the power stroke. More energy from each gallon of fuel is delivered to the propeller. Cylinder head temperatures (CHT) go up slightly and exhaust gas temperature (EGT) goes down since less energy is passing out of the cylinder past the exhaust valve. The brain in the E-Mag system adjusts the spark timing automatically by sensing engine rpm and manifold pressure.

TCM’s FADEC and Lycoming’s Ei2

Both of the major engine manufacturers—Teledyne Continental Motors (TCM) and Lycoming—have incorporated “smart” electronic ignition systems in their full authority digital engine control (FADEC) systems. The goal of FADEC is to reduce pilot workload by automatically controlling ignition timing, fuel metering, and rpm from a single lever in the cockpit. TCM’s system is operational and certified for installation on IOF-240, IOF-550, and TSIO-550 engines but doesn’t yet have the rpm control (see “ Waypoints: The Future of Engine Controls,” December 2009 AOPA Pilot). Lycoming’s system is in development and testing as a 350-horsepower TEO-540 engine. However, these electronic ignition systems will not be offered as standalone products.

GAMI’s PRISM System

The most technologically advanced system in development is the Pressure Reactive Intelligent Spark Management (PRISM) system from General Aviation Modifications, Inc. (GAMI) in Ada, Oklahoma. PRISM continuously samples and analyzes combustion chamber pressure traces from each cylinder. If any trace shows signs of uncontrolled combustion—a harbinger of destructive detonation—the system adjusts the timing on the noisy cylinder(s) to provide an adequate detonation margin.

“In 12 months we’ll probably have a variant nearing certification,” said Tim Roehl, president of GAMI.

PRISM has been tested extensively at GAMI’s well-instrumented test stand and has proven to work so well that the six-cylinder, 350-horsepower Lycoming TIO-540-J2BD—a high-output engine that has a very low detonation margin when running 100LL fuel—has passed detonation tests while burning unleaded 94-octane fuel under worst-case conditions of 460 degree Fahrenheit CHTs and 300 degree F induction inlet temperatures. The PRISM system’s back-up power is provided by GAMI’s Supplenator, a small alternator that mounts on the engine accessory section.

E-Mag

“We would be happy to put our product on a certified airplane,” says Brad Dement, sales and marketing manager at E-Mag Air of Azle, Texas. Dement and company engineer Tom Carlson have spent the past five years developing a magneto replacement. They’ve sold more than 1,000 of their E-Mag units to experimental airplane operators.

“The cornerstones of our system will be a hotter, longer-duration spark and variable timing,” said Dement. The version being prepped for certification has one moving part. The back-up power dilemma is addressed by a built-in brushless three-phase generator that is sufficient to power the E-Mag if the aircraft electrical system fails. The first unit E-Mag will be submitting for certification would replace the dual (D-series) magneto built by Bendix.

E-Mag will expand its model line to a wide variety of engines and applications after the dual-mag model is approved by the FAA. “What other appliance that can be installed in less than one day that will have as much effect on economy, reliability, and dependability as one electronic ignition system?” Dement said.

Installations of E-Mags on Experimental aircraft have proven that more than 70 percent of the benefit of installing an E-Mag is gained by replacing one magneto. Many experimental airplanes fly with one magneto and one electronic ignition unit. Higher-powered airplanes and airplanes that fly at higher altitudes will have better results if both magnetos are replaced. E-Mag’s current price for a non-certified version of the internally powered, four-cylinder magneto replacement is $1,185.

Big players and ASTM acceptance

The flight of a 300-horsepower TCM IO-550-powered Beechcraft Bonanza from TCM’s facility near Mobile, Alabama, to Oshkosh, Wisconsin, for AirVenture 2009 was significant for two reasons. There was no 100LL avgas aboard—the entire trip was fueled by 94-octane unleaded fuel. And both companies are major players in GA. The march toward a suitable—and hopefully affordable—replacement for today’s tetraethyl lead-laced avgas is now on the big table.

This was followed by an announcement that the ASTM committee on unleaded avgas has accepted the establishment of a new specification for unleaded avgas for certification purposes. The new specification for the 94-octane unleaded fuel is exactly the same as D-910—the specification for today’s leaded avgas—sans lead. This acceptance of a standard gives magneto-replacement manufacturers a standard to test against and is an important cornerstone for alternative ignition system development.

These replacements promise to reduce the costly ongoing maintenance that magnetos require for dependability; they also deliver a hotter spark over a longer duration of crankcase rotation. The result is better starting, less engine vibration, measurably lower fuel consumption, and a reduction in maintenance costs. Sound too good to be true? Today it is—because although there are at least three smart ignition systems that have been flying for years in the Experimental world, as well as the PRISM and E-Mag systems, none has yet gained FAA approval. As soon as smart replacements for today’s magnetos hit the market, however, there will be magnetos galore for sale on eBay.

E-mail the author at Steve@EllsAviation.com.