Lean%20of%20Peak%20Operation

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Old wives tales of leaning

• EGT rises indefinitely with leaning
• Highest EGT shows leanest cylinder
• Hottest CHT is leanest cylinder
• Running LOP causes high CHT
• Running LOP will damage valves
• Running LOP will increase cylinder wear
• Gas is cheaper than engine overhaul

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• Cessna 414
• Engines at same power !
• Ball is centered.
• What is going on?

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75 ROP
50 LOP
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What might lead to detonation?

• Operation of any cylinder in The Red Box
• Inadequate baffling, Bird nests
• High power at low airspeed (poor cooling)
• Fouled fuel injector
• Incorrect magneto timing
• Bad fuel
• Bad spark plug acting as a glow plug
• Intake manifold leaks?
• No enrichment at full throttle?

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The Red Box
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THE RED BOX defined

• At and below about 60 power, there is no red
  box. Put the mixture wherever feels right.
• At 65 power, avoid 100ºF ROP to Peak.
• At 70, avoid 125ºF ROP to 25ºF LOP.
• At 75, avoid 180ºF ROP to 40ºF LOP.
• At 80, avoid 200ºF ROP to 60ºF LOP.

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A Catch to LOP Ops

• The spread between EGT peaks will be excessive
  without tuned injectors (or with a carbureted
  engine), and the engine will run rough LOP.
• Avoidance of roughness comes from tuning the
  injectors so they all peak within 0.5 gph
• What can you do with a carbureted engine?

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HP difference with
25 LOP
113 LOP
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Some Details

• As you lean, the first cylinder to peak is the
  leanest, the last to peak is the richest.
• If cruising ROP, you lean by the leanest
  cylinder, but
• If cruising LOP, you lean by the richest
  cylinder- because you are on the other side of
  the Red Box.
• And you need an engine analyzer to show you
  where all this is happening!

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SOME BASICS

• Absolute EGT numbers are inexact and of little
  value but degrees relative to the peak EGT are
  extremely important in defining landmarks in
  combustion for each cylinder.
• CHTs are important of themselves
• Running ROP or LOP are valid choices, but most
  pilots running ROP are not running far enough
  ROP, and are in the Red Box.

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When ROP When LOP

• Lean by leanest cylinder Lean by richest
  cylinder
• Air flow determines power Fuel flow determines
  power
• Extra fuel retards combustion Extra air retards
  combust
• Carbon monoxide plentiful Minimal CO
• Not most fuel efficient Fuel efficient at 20-30
  LOP
• Engine dirty Oil and engine stay cleaner
• Engine runs hot Engine runs cooler

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When LOP

• Fuel flow determines power
• Engines with 7.51 compression put out 12.7 hp
  per GPH
• Engines with 8.51 compression put out 13.9 hp
  per GPH

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What does an engine analyzer do?

• Shows EGT and CHT of each cylinder in real time
• Records that data every 6 seconds for later
  download and review
• Presents EGT and CHT with rising bars as well as
  numbers
• Lean find function shows richest and leanest
  cylinder as mixture is brought back
• Alarms can be set, like
• Any CHT above 380F.
• Excessive cooling rate
• Any EGT above 1600F

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Its WOTLOPSOP!