How Becoming a Pilot and Aircraft Owner Can Change Your Life – Part Four
The Installation of Essential Equipment Should Be One of Your Top Priorities Early on Your Journey to Becoming a Pilot and Aircraft Owner.
Previously, we discussed the five rules for efficient and effective maintenance, the basic rules for working with your maintenance shop and aircraft mechanic, and the importance of establishing an engine condition monitoring system. To effectively monitor your engine, you need reliable data, which brings us to essential equipment. Every aircraft should be equipped with an engine monitor unit (EMU) with a GPS-coupled fuel totaliser, tuned fuel injectors (as required based on in-flight test procedures detailed below), and full-flow oil filters.
Engine Monitor Unit & GPS-Coupled Fuel Totaliser
Installing an engine monitor unit (EMU) with a GPS-coupled fuel totaliser is the best investment you can make for your aircraft. EMUs are incredibly useful for monitoring temperature limits and setting precise fuel flow targets for leaning purposes. These units provide invaluable data for engine condition monitoring. The cost of installing or upgrading an EMU pays for itself within several hundred flight hours. The GPS-coupled fuel totalizer, which most modern EMUs include, significantly enhances situational awareness.
Ideally, the EMU should display and record the exhaust gas temperature (EGT) and cylinder head temperature (CHT) for each cylinder, manifold absolute pressure (MAP), engine speed, fuel flow, and outside air temperature (OAT) for each engine.
Top Five Engine Monitor Units & GPS-Coupled Fuel TotaliSers
We have evaluated options from four different manufacturers to select the best engine monitor units with built-in GPS-coupled fuel totalisers for Continental and Lycoming engines. We chose five devices based on functionality, engine compatibility, certification, installation ease, and price. All the devices listed provide both EMU and GPS-coupled fuel totaliser functions:
- CGR-30P Premium Engine Monitor from Electronics International Inc.
- GI275 Engine Indication System (EIS) from Garmin
- EDM 350 from J.P. Instruments (JPI)
- EDM 930 from J.P. Instruments (JPI)
- G3X from Garmin
For more details on EMUs and GPS-coupled fuel totalisers, refer to our dedicated blog post: Link.
Tuned Fuel Injectors
Installing tuned fuel injectors becomes necessary when the GAMI spread is too high. The GAMI spread measures the evenness of fuel distribution across the cylinders in gallons per hour (GPH). We will explain how to determine the GAMI spread in the in-flight test procedures section below. Essentially, the GAMI spread is the difference in fuel flow between the first and last cylinder to reach peak EGT. A low GAMI spread indicates a uniform air-to-fuel ratio (AFR) across all cylinders, crucial for lean-of-peak engine operation, ensuring all cylinders lean simultaneously. A high GAMI spread indicates uneven fuel distribution, causing rough engine operation due to varying AFRs.
GAMIjector® and TurboGAMIjector®
We recommend installing tuned fuel injectors if the GAMI spread exceeds 1 GPH, but only after ruling out potential issues such as dirty or partially clogged fuel nozzles, improperly sized fuel nozzles, intake valve problems, or induction leaks. Our preferred choice is the fuel injector nozzles from General Aviation Modifications Inc. (GAMI). These are specifically designed to deliver precise fuel quantities to each cylinder, compensating for inherent imbalances in engine designs.
GAMI offers certified nozzles for normally aspirated (GAMIjector®) and turbocharged (TurboGAMIjector®) engines from Continental and Lycoming. Fine-tuning is possible if the GAMI spread exceeds 0.5 GPH for Lycoming engines or 0.7 GPH for Continental engines, assuming all other potential issues have been addressed.
Full-Flow Oil Filters
A full-flow oil filter is the final piece of essential equipment we recommend. In our opinion, it should be standard on any aircraft engine. This investment pays off quickly, depending on your annual flight hours. A full-flow oil filter keeps the oil cleaner, allowing you to extend oil change intervals from 25 to 50 hours. It also enables you to inspect and analyze particles caught by the filter. We recommend conducting an oil analysis and inspecting the oil filter element with every oil change. If uncertain, consider a dry particle analysis or a scanning electron microscope (SEM) analysis of detected particles.
Three brands offer full-flow oil filter conversion kits for both certified and experimental/amateur-built aircraft:
- Airwolf Filter Corp
- B&C Specialty Products Inc.
- Casper Labs, Inc.
Airwolf Filter Corp provides remote-mounted oil filter kits for conventional aircraft piston engines (Continental, Franklin, and Lycoming) and radial engines. These filters can be installed in more accessible locations, making oil and filter changes easier and cleaner. However, they are slightly heavier (less than 5 pounds) than direct replacement adapters and involve additional hoses and fittings, which could potentially leak.
B&C Specialty Products Inc. (and Casper Labs, Inc.) offer oil filter adapters that replace the original oil screen, designed exclusively for Lycoming engines. Casper Labs, Inc. products are available through several online retailers, but it appears the company may be inactive. Thus, we focus on B&C Specialty Products Inc. for oil filter adapters. B&C’s adapters are machined from solid aluminium billets and weigh just 2.25 pounds with a Champion 48108 filter. They provide the benefits of a spin-on oil filter without complex hoses and fittings, but they are limited to Lycoming engines.
In-Flight Test Procedures Are Like a Health Check for Your Aircraft Engine(s)
The need for tuned fuel injectors depends on the GAMI spread, as discussed earlier. Installing essential equipment and conducting in-flight test procedures go hand-in-hand. You want to install essential equipment as soon as possible to start gathering data and benefiting from its advantages. However, performing in-flight test procedures, like the mixture distribution test, will help you determine if you need tuned fuel injectors. We recommend installing the EMUs with GPS-coupled fuel totaliser functionality and full-flow oil filters immediately, then conducting in-flight test procedures to assess the need for tuned fuel injectors.
There are three essential in-flight test procedures to perform regularly:
- Mixture Distribution Test (GAMI Lean Test)
- Ignition Stress Test
- Induction Leak Test
Mixture Distribution Test
Conduct the mixture distribution test every twelve months or after every 100 flight hours, or whenever you suspect engine irregularities. The test examines mixture distribution and identifies issues such as dirty or clogged fuel nozzles, improperly sized nozzles, intake valve problems, induction leaks, and other engine anomalies that cause uneven mixtures among cylinders. It also determines the need for GAMIjector® fuel injectors.
Our partner, General Aviation Modifications Inc., has promoted the mixture distribution test for years, hence it’s often called the GAMI lean test. This test assesses the balance of the fuel/air ratio in the engine, known as the GAMI Spread, measured in GPH. The GAMI Spread is calculated by noting the engine fuel flow at which each cylinder reaches peak EGT, then subtracting the lowest flow rate from the highest.
GAMI Lean Test Methods
There are three effective methods for performing the GAMI lean test to determine the GAMI Spread. You need a way to measure the EGT of each cylinder and the total engine fuel flow, whether digital or analog. We recommend the download method if equipped with an EMU, or the shorthand method as an alternative.
- Download Method: This is the most convenient method to determine the GAMI Spread. It can be used only if the aircraft is equipped with an EMU that records all EGTs and total fuel flow.
- Shorthand Method: This method is quicker than the longhand method and does not require an EMU, though you will need to record data manually.
- Longhand Method: This is the most cumbersome but potentially the most accurate method. Like the shorthand method, it does not require an EMU, but you must manually record the data.
GAMI Lean Test Results
After completing the in-flight test procedures, you can calculate the GAMI Spread and Lean Range:
- GAMI Spread: Total Engine Fuel Flow (Last cylinder to reach peak EGT) – Total Engine Fuel Flow (First cylinder to reach peak EGT) in GPH
- Lean Range: Full-rich EGT – peak EGT in °F (for each cylinder)
Typically, the GAMI Spread must be under 1 GPH for the engine to run smoothly when lean-of-peak. A good fuel/air ratio balance is usually achieved if the GAMI Spread is less than 0.5 GPH.
The lean range for each cylinder should be around 250 to 300°F. If any cylinder has a substantially lower lean range than the others, this could indicate a clogged fuel nozzle or an induction leak, potentially leading to excessively lean operation during take-off and risking overheating or detonation.
Ignition Stress Test
Regularly perform the ignition stress test, ideally every second or third flight, and whenever you suspect engine anomalies. This test evaluates your ignition system under demanding conditions, in contrast to the pre-take-off magneto check on the ground. Since a lean mixture is harder to ignite than a rich one, an in-flight lean-of-peak magneto check effectively assesses your ignition system’s performance.
In-Flight Lean-Of-Peak Magneto Check
The in-flight lean-of-peak magneto check is a diagnostic tool to identify potential issues with magnetos, ignition harnesses, spark plugs, or ignition timing. A lean mixture can reveal a weak spark plug that a richer mixture might conceal. The goal is to choose a mixture that uncovers weak sparks without causing them to fail.
In-Flight Lean-Of-Peak Magneto Check Results
A healthy ignition system should cause all EGT bars to rise by 50 to 100°F when switching to single-magneto operation. The rise may not be uniform; it is normal for even-numbered cylinders to rise more than odd-numbered cylinders, and vice versa. What matters is that all EGT bars rise and remain stable at their elevated levels. During single-magneto operation, you may notice a slight power loss and increased roughness, but this roughness should not be concerning.
Induction Leak Test
This test consists of two parts: a high-MAP test and a low-MAP test.
- For the high-MAP test, start with high power settings—wide-open throttle for normally aspirated engines, or MAP equal to outside ambient pressure for turbocharged engines—and a full-rich mixture. Record the EGT for each cylinder.
- For the low-MAP test, reduce the MAP by about 10 inches and record the EGT for each cylinder again.
Ignore the absolute EGT values. Instead, calculate the EGT change (“delta”) for each cylinder between the high-MAP and low-MAP tests. Ideally, the EGT change should be similar for all cylinders. If one cylinder (or two adjacent cylinders) shows significantly less change, this could indicate an induction leak affecting that cylinder (or those cylinders).
Induction Leak Test Results
The principle behind this test is straightforward: During the high-MAP test, the induction manifold absolute pressure is close to outside ambient pressure, so an induction leak has minimal or no impact on engine operation. During the low-MAP test, the manifold absolute pressure is much lower than the outside ambient (by about 10 inches), so any induction leak will cause the affected cylinders to run leaner, resulting in a smaller drop in EGT than the other cylinders.
Engine Testing Insights
While the in-flight test procedures may seem complex initially, their importance becomes clear after you complete them. They are easier than they seem and provide invaluable insights into your aircraft engine’s health and efficiency. Regularly conducting tests like the mixture distribution, ignition stress, and induction leak tests helps you proactively identify and address potential issues, enabling close monitoring of your engine’s performance to ensure optimal efficiency.
For a more detailed discussion on in-flight test procedures, refer to our dedicated blog post: Link
Aircraft Engine Leaning and Over-Square Operation
In the next and final part of this series, we will discuss how to operate an aircraft engine correctly, including leaning techniques and over-square operations. Stay tuned for more!
Join the Waitlist
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About Quest Aeronautics
Quest Aeronautics is a state-certified engineering office for aviation, dedicated to shaping the future of general aviation by providing innovative and cost-effective solutions to enhance aircraft performance and operations. With a focus on CS/FAR-23 and experimental/amateur-built (E/A-B) aircraft, Quest Aeronautics provides a range of services including flight testing, aircraft operations and maintenance consulting, high-quality aviation products, and tailored support for E/A-B projects. Collaborating with industry-leading partners, Quest Aeronautics is committed to delivering unparalleled support and expertise to individuals and organisations in the general aviation market.
About Author
Sebastian, the founder of Quest Aeronautics, is a driven and enthusiastic individual with a passion for aviation. Before delving into aviation, he gained valuable experience as a chemical process engineer and laboratory technician. Sebastian holds a Master of Science in Engineering and a commercial pilot licence, with several fixed-wing aircraft ratings under his belt. He has also completed an introduction course for fixed-wing performance and flying qualities flight testing at the National Test Pilot School in Mojave, CA and is compliance verification engineer for flight.