Lean of Peak!
Should I or Shouldn’t I?
Running and engine “lean of peak” is a hot topic among owners and pilots of piston engine aircraft operating in the industry today. Rising fuel costs make it look like an attractive option for reducing operating costs, and in some cases extending the fuel range of an aircraft to eliminate the need for a fuel stop on route to your destination.
The facts prove that under the correct conditions, engines can be run lean of peak successfully with good results. The real question is whether or not the correct conditions exist to successfully run lean of peak.
We feel that the most important requirements for running an engine lean of peak are:
- Pilot Knowledge!
- Adequate Instrumentation!
- Balanced Fuel and Airflows to Each Cylinder!
- Well-Maintained Engine!
Pilot knowledge is the single most important aspect of successfully operating lean of peak. A knowledgeable pilot is better equipped to make an informed decision based on conditions at hand and engine instrumentation. A knowledgeable pilot is also able to react appropriately to information gleaned from engine instrumentation.
Adequate engine monitoring instrumentation is also crucial to provide the pilot with enough information to make correct fuel mixture adjustments. An engine monitoring system is required which provides EGT readings for all cylinders, CHT readings for all cylinders and actual (as opposed to calculated from pressure) fuel flow readings.
Not every engine is created equal and not all engines are capable of running lean of peak. Uneven fuel and airflows to individual cylinders can result in one or more cylinders running excessively hot while others are in the correct temperature range. Leaning an engine such as this until all cylinder temperatures are comfortable lean of peak may result in an engine that stumbles, or runs rough. Balanced fuel and airflows are essential to provide EGT and CHT readings, which are close together throughout the operating temperature range for the engine. This will allow the fuel mixture to be leaned to the desired EGT lean of peak without damaging individual cylinders, and providing smooth engine operation.
Finally, it is very important for an engine to be well maintained and in good condition for it to be expected to operate safely lean of peak. Obstructed fuel injection nozzles, intake leaks, or ignition problems could have disastrous results when attempting to run lean of peak.
