Insight’s G3 (opposite) is a color engine monitor that fits in a standard instrument panel hole, and stores downloaded data on SD data cards. Dynon’s EMS-10 (above) is an engine monitor for use in experimental and sport category aircraft. Electronics International’s MVP-50P (right) is a large-screen engine monitor designed to replace conventional engine instruments.
Odds are, the only engine instruments available in your first primary trainer were a tachometer, fuel level, oil temperature and possibly a cylinder head gauge (CHT). You were probably told not to trust the fuel-level gauge as it’s notoriously inaccurate. You used the tach to set engine power, and were told to keep an eye on the other gauges to see that they were “in the green” throughout the flight.
As you moved up to larger airplanes with more powerful engines, additional instruments appeared, including manifold pressure (MAP) for airplanes with a constant-speed prop, and oil pressure and exhaust gas temperature (EGT) gauges. EGT was used for leaning, and was more accurate than just leaning until the engine ran rough and enriching to smooth it out, as was (and is) common in simple trainers.
But, how much information did those instruments provide about conditions in the engine? You had EGT and CHT for just one of the four or six cylinders in your engine. If you ran lean of peak, or rich of peak on just one cylinder, how do you know whether you’re rich or lean of peak on the others? If your CHT shows a hot 400 degrees in climb, can you be sure the others are running hotter, approaching the point that aluminum begins to soften?
Graphical engine monitors address this problem. Instead of a single EGT and CHT, multiple probes are attached to the cylinder heads and exhaust manifold for each cylinder in the engine. The display shows those temperatures graphically, so that you can instantly see if any one value is higher or lower than others. Many of these instruments offer additional features, such as accurate fuel-flow monitoring, and options for other engine parameters, such as battery voltage, oil temperature, vibration, etc.
Avidyne’s EX5000 is typical of glass panel MFDs that can display engine-monitor data.
If you’re flying an airplane with a factory glass panel, you probably have engine-monitoring features available on the multifunction display (MFD). On Garmin G1000-equipped aircraft, the Lean option on the Engine tab will give you bar graphs of EGT and CHT. Avidyne Entegra-equipped airplanes show it on the Engine page. If you don’t have glass, then adding an engine monitor can be a very helpful upgrade. Used properly, it will help you operate the engine both efficiently and safely, in many cases avoiding the need for early (and expensive) cylinder overhauls.
Using an engine monitor begins during preflight: If it’s equipped with a fuel-flow option, you’ll need to make sure the amount of fuel set matches what’s in the tanks. During run-up, watch the bar graph as you perform the magneto check. You should see a uniform rise of all EGTs (some monitors offer a normalize display mode that makes this obvious). If one cylinder doesn’t rise, you may have a fouled plug.
During climbout, monitor the CHTs. If temperatures on any cylinders rise beyond what’s listed as a safe value in the pilot-owner’s handbook (POH) for your aircraft, you’ll need to open cowl flaps, lower the nose, or reduce power to lower the temperature.
In cruise, the engine monitor allows much more accurate leaning than a single-probe EGT. The exact procedure varies (check your POH), but usually starts with the airplane leveled out, and appropriate cruise MAP and RPM set. A safe prelean mixture is set using fuel flow or a memorized EGT value on one cylinder, then a lean-assist mode is selected on the engine monitor. Slowly and steadily, lean the mixture until the monitor identifies the first cylinder to peak—which may not be the cylinder with the highest EGT. Once that’s done, you can enrich the mixture to achieve a specified temperature reduction (“50 degrees rich of peak”) for best power operation—or in some cases, you may have another option, operating on the lean side of peak.
|WE ASKED YOU!|
Lean-of-peak (LOP) operation is a controversial subject, and a full discussion is beyond the scope of this article. In brief, the major engine manufacturers discourage LOP because of the risk of fuel detonation, which can damage the engine. Proponents argue that if done properly, LOP actually results in lower CHTs, which should be easier on the engine than traditional best-power or best-economy operation, while reducing fuel burn by up to 40%. Some aircraft manufacturers, among them Cirrus, recommend LOP operation, typically at reduced power (65% or less). Check the POH to see what’s recommended for your aircraft.
|Engine Monitor Options|
|Some engine-monitor vendors specialize in experimental and sport-category airplanes. Others build monitors for certificated aircraft, which will require a supplemental-type certificate (STC). Some STCs are advisory-only, while others allow complete replacement of factory gauges. The latter can be a great option if you’re upgrading an old steam-gauge airplane to a glass panel.|
Entegra Flight Deck
Electronics International, Inc.
AuRACLE engine management systems
In descent, monitor CHTs to avoid shock cooling, in which cylinders cool too quickly. This is mainly an issue in high-powered engines. Some engine monitors offer alarm settings to alert you if cylinders cool too fast. The cure for shock cooling is to carry enough power to keep the engine warm, and use speed brakes, extended landing gear or flaps to keep your speed down.
After landing, many pilots do a magneto check before engine shutdown, and again this is a good time to look at the bar graph for a uniform rise in EGTs. If one cylinder isn’t behaving itself, have a mechanic check the plugs before flying the airplane again.
|J.P. Instruments’ EDM-930 (left) is STC’d and TSO’d to replace standard engine instruments. Flightline Systems offers AuRACLE engine management systems (center) for both single- and twin-engine aircraft. Garmin’s G1000 glass flight deck (right) offers a leaning function that displays per-cylinder CHT and EGT info.|
An engine monitor can be a lifesaver in flight. Plane & Pilot Publisher Mike McMann found that out in his Bonanza some years back: “I was taking off from Montrose, Calif., and the engine started running rough. Looking at the engine monitor, I saw a problem with the #5 cylinder. Returned to the airport, found a mechanic, told him there was a problem with #5, and he found a loose sparkplug wire.”
Beyond the basics of CHT and EGT for each cylinder, many engine monitors offer additional options. I personally am a big fan of fuel flow: For many years my wife (a pediatrician) and I have participated in medical mission trips to Mexico with Liga International (“The Flying Doctors of Mercy”). When an unexpected headwind develops, or word comes over the radio that the airport we planned our first stop at has run out of avgas, knowing exactly how much fuel remains becomes critical information. My personal rule is to divert if it looks like I’m at risk of landing with less than a one-hour reserve—and to do it early, because there aren’t a lot of airports available in the Sonoran desert!
Data logging can be a useful feature for monitoring trends, and in some cases dealing with problems—both Mike and I have identified cylinder problems in airplanes we bought after adding engine monitors to them. A pilot interviewed for this feature told us that he had loaned out a high-performance turbocharged single to a friend, and suspected when he got it back that the borrower had abused it. Downloading data from the engine monitor showed that excessive leaning had been used at high power.
Whether you add an engine monitor or have one already, spend a little time with the POH and any other documentation to make sure you know how to get the most from it. Knowing what goes on in your engine will help you fly efficiently and safely!