Is It Better to Fly at 55% Power or 75% Power, in Terms of Engine Health?

Discussion in 'Pilot Training' started by Penguinforce, Aug 1, 2021.

  1. George Mohr

    George Mohr Line Up and Wait

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    Here's one clear bit of guidance... the big killer of piston engines is either heat or detonation (resulting in lots of heat, btw). Most engines will be immune to detonation at or below 65% power, regardless of mixture settings. So its safer to be at lower power settings vs higher power settings based on this standard.

    The second is heat. Most engines have a very high published CHT 'redline' that has been found to be far too ambitious. A good operational redline is something around 400F. Google Mike Busch for his work on this guidance.

    So, keep it below 400F, and keep it in the no-detonation zone, and you'll be doing everything you can to have long engine life.

    -G
     
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  2. George Mohr

    George Mohr Line Up and Wait

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  3. EdFred

    EdFred Taxi to Parking

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  4. George Mohr

    George Mohr Line Up and Wait

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    Agree, but the principle is the same. Below 65% you can lean to max economy, above that you need to lean only to max power in order to avoid detonation.

    -G
     
  5. David Megginson

    David Megginson Pattern Altitude

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    I'd tweak that slightly. At 75% power you need to lean a little or a lot, but not in-between: Lycoming's "Max economy" (around 50°F lean of peak) or Lycoming's "Max performance" (around 150°F rich of peak) should both be fine. The mistake is following the old-fashioned-guidance like "lean to roughness then enrich slightly", which may or may not land you dead in the middle of the red zone, depending on the mixture spread among your cylinders.
    leaning.png
     
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  6. Skyknight320

    Skyknight320 Pre-Flight

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  7. Daleandee

    Daleandee En-Route

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    Good deal! I think that fella might know a little about engines ... :D
     
  8. George Mohr

    George Mohr Line Up and Wait

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    The point I'm making is that at some point at or nearly below 65% power (depending on the engine), there is no red box (i.e. detonation is impossible). So to the OP's point, if you fly at lower power settings, you can't break the engine with the red knob. In our 182's O470U, the magic point is 65% power.

    https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2012-12_red-box-red-fin.pdf

    Regards,
    G
     
  9. Tantalum

    Tantalum Final Approach

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    I've always been taught to let engines breath.. IE, high power, good RPM. With the most critical items being CHT 360-380 and EGT 1300-1500. I've heard this from both mechanical engineers and instructors

    If only we had loads of data centralized that someone could use to plot this out and look for empirical optimums..... (sad how low tech aviation is an how much voodoo knowledge we rely on)
     
  10. chemgeek

    chemgeek En-Route

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    Just a wild guess, but I bet most GA engines fail to reach a long and happy lifetime due to inactivity, and not due to being operated at 65-75% power. The trainers I used during my primary instruction just ran and ran and ran, and they were typically run at WOT in cruise and without careful attention to the red knob by many students. But they operated every flyable day.
     
    Last edited: Aug 5, 2021
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  11. Sac Arrow

    Sac Arrow Touchdown! Greaser!

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    Bro do you even lift
    Any way you break it down, more power = more wear. The real question is where is that breakpoint as you increase power where the wear factor starts to become significant - is it within the range of normal GA piston engine operational limits. The limitations on takeoff power and climb power duration are probably more temperature related, but why a cruise limitation of 75% (or 65%, depending on your engine?) Heat? Wear?

    @Ted ?