Wednesday, April 22, 2020

Engines / Powerplants

  • Aspirated ROT:
    • Engine will lose about 3% of its power for every 1,000’ of altitude
  • CHT (cylinder head temperature)
    • If too high > Enrich mixture / decrease pitch attitude / reduce power / open cowl flaps
    • Shock cooling > avoid it by allowing CHT to drop slowly
  • EGT (exhaust gas temperature)
    • Lean to 100°F on rich side of peak EGT for best operation (technique)
  • Leaning
    • Whenever mixture is adjusted, rich or lean, it should be done slowly.
    • Use full rich mixture during take-off or climb below 5K density altitude (Lycoming).
    • Anytime power setting is 75% or less at any altitude
    • At high altitude airports (> 5K), lean for taxi, take-off, traffic pattern entry and landing. 
    • Landing at airports < 5K density altitude, adjust mixture for descent, but only as required.  You can't go wrong if you keep the engine running smoothly!
    • Before entering pattern, go full rich
    • Methods:
      • Fixed props: gradually lean mixture until either tachometer or airspeed peaks.
        • From a 1969 172 POH, “…the mixture should be leaded as follows:  pull mixture control out until engine RPM peaks and begins to fall off, then enrichen slightly back to peak RPM.
      • Controllable pitch props: lean until a slight increase of airspeed is noted.
        • Slowly lean mixture until engine becomes rough or until power rapidly diminishes as noted by undesirable decrease in airspeed.  When either occurs, enrich mixture to obtain an evenly firing engine or to regain most of the lost airspeed or engine RPM.
        • When leaned, roughness is caused by misfiring due to a mixture which can’t support combustion.  It’s eliminated by slightly enriching mixture.
    • With EGT: lean to 100°F on rich side of peak EGT for best operation.
    • At all times, caution must be taken not to shock cool the cylinders.  Maximum recommended temperature change should not exceed 50°F per minute.
    • FAA on leaning 
    • Lycoming on leaning 
  • Oil
    • Too warm > Enrich mixture / decrease pitch attitude / reduce power / open cowl flaps
  • Percent power RPM:  see separate post
- FIG -

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