Running at Peak Performance

Before writing the article for this week, I first donned full body armor. Why? Because we’re taking on a topic so hot that it’ll max out any EGT indicator.

But first, let’s talk about the parts we all agree on. Managing the fuel-air mixture in a piston aircraft impacts engine performance. Lean of Peak (LOP) and Rich of Peak (ROP) operations offer distinct advantages and drawbacks.

From there, opinions amongst pilots vary widely on which method is superior, making it a highly charged topic. Let’s look at the reasons pilots employ these methods, the pros and cons of each, how to mitigate the cons, and *gulp* draw conclusions on which technique might be best based on different flying scenarios.

Lean of Peak

LOP involves adjusting the fuel mixture so the engine operates with a fuel-air ratio leaner than the stoichiometric mixture, where the peak Exhaust Gas Temperature (EGT) is achieved. You might use LOP to:

• Improve fuel efficiency: Generally, running LOP results in lower fuel consumption, which extends aircraft range and reduces operating costs. Fuel savings can be significant, sometimes up to 20%.
• Reduce engine temperatures: Properly managed LOP can help maintain cooler engine temperatures, which is beneficial for engine longevity, provided that rapid temperature changes in either direction are avoided.

Lower carbon deposits are an additional benefit of LOP. Leaner mixtures result in fewer carbon deposits on engine components.

However, there are a few potential cons to LOP.

• Complexity: Achieving proper LOP operation requires precise engine monitoring and adjustments, which can be challenging, especially if you don’t have multi-probe CHT temp sensors. Although EGT is used to determine LOP/ROP, different cylinders can and often do run at different temperatures, which can result in…
• Valve and seat wear: The potential for uneven cylinder temperatures can lead to differential wear.
• Potential for engine roughness: Incorrect or quickly-applied leaning can cause the engine to run rough.  

You can take a few steps to mitigate the possible downsides of LOP operation. First, ensure you have sufficient and calibrated engine instrumentation and training on proper LOP techniques. Bear in mind that in the absence of overwhelming expert advice to the contrary, your POH should have the final say.

Second, get regular engine inspections and proper balancing of injectors if applicable.

Rich of Peak

Running ROP means running the engine with a richer fuel-air mixture than the stoichiometric ratio. Reasons for using ROP include:

• Maximized power output: ROP is preferred when maximum engine power is needed, such as during takeoff, climb, and other high-demand phases of flight.
• Enhanced engine cooling: The additional fuel in the mixture helps cool the engine, reducing the risk of overheating during high power settings.

Additionally, ROP is easier to manage than LOP, making it more straightforward to maintain engine performance without extensive adjustments.

Like LOP, there are a few potential cons to ROP.

Increased fuel consumption: Higher fuel burn rates lead to reduced range and increased operational costs.
Carbon: Incomplete combustion due to a rich fuel setting allows carbon buildup. 
To mitigate the downsides of ROP, use it selectively, primarily when high power is required. Additionally, ensure you stay on top of your engine maintenance.  

The choice between LOP and ROP operation depends heavily on the type of flying a pilot does regularly and personal preference, which is often influenced by training and experience.

For pilots who often embark on long cross-country flights where fuel efficiency is paramount, running LOP can provide significant benefits. On the other hand, those who frequently engage in short flights with multiple takeoffs and climbs might choose to run rich. Pilots preferring power over economy, based on their own preference, might find ROP offers the more desirable performance and simplicity.

In practice, some pilots find a balance by using LOP for cruise operations to maximize efficiency and switching to ROP during high-demand phases of flight. This hybrid approach can take advantage of the strengths of both techniques, ideally optimizing engine performance when needed (and longevity).

Carbureted engines add another dimension to this topic since they often struggle to achieve a consistent and precise fuel-air mixture across all cylinders, which can make running LOP effectively a challenge. They also require more attention to mixture settings to avoid issues like carburetor icing.

Ultimately, the debate between LOP and ROP remains a hotly contested topic in the aviation community, with strong opinions on both sides.

So what should you do?

Read as much as you can about this topic. Experiment (within reason) and gather data for your airplane, then draw conclusions based on your specific flying needs and preferences.

By understanding and effectively managing these mixture control strategies, you can affect the health and performance of your engine second-by-second and year-by-year. 

Know Before You Go