Optimize Engine Performance: Leaning Technique in Aircraft Operation

1. Love the One You’re With or Tom Bell Go Home with the One That Brought You

2. Why Are We Here? • How we fly the airplane can directly impact the life of the engine, the cost per flying hour, and the safety of our fellow pilots • In particular talk about leaning as a way to improve engine performance and engine life

3. Review of Engine Operation • Air through intake port to carburetor • Mixed with fuel; moves into the combustion chamber—burning optimized at 1/15 ratio • Four stroke engine—fuel/air ratio in first stroke determines: • Combustion temperature after the second stroke • Power generated by the third stroke • EGT of discharge gasses in the fourth stroke • Leaning the engine reduces the amount of fuel mixed with the air in the carburetor

4. Too Lean Too Rich • Too much fuel for the given amount of air • Engine roughness • Spark plug fouling from excessive carbon buildup on spark plugs • Due to lower temperature inside cylinder and incomplete burning of fuel • Higher engine temperature—not enough fuel for cylinder cooling • Detonation: explosive ignition of fuel/air mixture inside cylinder • Causes excessive cylinder temperatures and pressures • Can quickly lead to failure of piston, cylinder, or valves

5. From Lycoming Service Instruction 1094D

6. General Leaning RulesLycoming Service Instruction 1094D • Observe engine red line during takeoff, climb, and high power cruise • Lean or enrich the mixture slowly • Return to FULL RICH before adding power • Use care not to shock cool the engine (50º change in temperature per minute)

7. Phases of Flight • Ground Ops: • Normally FULL RICH • Consider leaning at high density altitude or to warm engine on cold day • Takeoff: • Goal is max power (highest RPM) • Aircraft Information Manual: “The mixture should be FULL RICH, except a minimum amount of leaning is permitted for smooth engine operation when taking off at high elevation.” • Lycoming 1094D: Use full power for takeoff and climb…except • When DA > 5000 feet, lean to max RPM at full power prior to takeoff

8. Phases of Flight • Cruise • Reduce throttle and set pitch (if applicable) • Lean at any altitude when in the 55% - 75% cruise power range • Lean at any power setting when above 6000’ DA

9. OK to Lean Don’t Lean From Warrior POH

10. Lean to Best Power • Set power approx 35 RPM below desired cruise RPM • Lean the mixture to peak RPM and airspeed • Adjust throttle, if necessary, for final RPM setting • With an EGT gauge (Archer), lean to peak EGT, then enrich mixture until EGT drops 100º

11. Lean to Best Economy • Set throttle and mixture full forward • Begin leaning the mixture • RPM will increase slightly, then decrease • Lean until desired RPM is reached • Below 5,000 ft use caution not to remain above 75% power with a leaned mixture for more than 15 seconds (due to detonation) • Above 6,000 feet engine cannot generate > 75% power • With an EGT gauge (Archer), lean to peak EGT

12. Comparison Best Power Mixture - Standard Day - 8000 MSL - No wheel fairings Best Economy Mixture • - 2-3 KTAS slower • - 1-2 gph savings • 13% greater range • Less engine wear From Warrior POH

13. Phases of Flight • Descent • Enrich the mixture slowly during the descent…the air is getting more dense and needs more fuel to maintain the proper fuel/air ratio • Pattern/Landing • Mixture to “FULL RICH” as part of Approach/Landing check

14. Summary • Leaning increases performance/decrease wear • Lean when appropriate • Takeoff / climb when > 6,000 ft DA • Cruise in 55% - 75% power range • Richen mixture before power increase • Richen mixture slowly on descent • Best power vs. best economy • Tradeoff of speed, fuel used, range, engine wear • Talk to your instructor for techniques