Yet another LOP question...

Discussion in 'Flight Following' started by Sluggo63, Nov 11, 2021.

  1. Sluggo63

    Sluggo63 Pattern Altitude

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    Okay, this will be probably be basic for most of you, but (although I wasn't a Marine [happy bleated birthday, btw, Devil Dogs!]) I need slow talking and lots of pictures apparently.

    What I'm looking for is a step-by-step for LOP ops. I think I have the basics, but I have a question about the last step, if there even is one.

    My plane (Seneca III w/TCM TSIO-360s) just came out of annual and I had an Insight G4 Twin engine monitor installed with hopes of trying some LOP flying. Before the G4 I had nothing but the factory gauges and additional EI gauges which were one cylinder measurements only.

    I've read the Mike Busch books and John Deakin's webpages. Here's what I have so far.

    1. Get to cruise altitude.
    2. Do a rough lean to a couple of gph greater than expected.
    3. Set MP/RPM to selected cruise. Let's call it 28"/2500RPM.
    4. Let the plane stabilize there for 5-10 minutes.
    5. Pull the mixture through peak EGT to LOP and pull until the EGT of the warmest cylinder is ~50° LOP.

    Here's my question. What do I now do with the MP? Obviously leaning the mixture had an effect on the MP. Do I just leave what I have now after leaning? Do I now reset my 28"? If I reset, am I now no longer 50° LOP?

    What do you smart gals and guys say? What am I missing?

    Thanks!

    Edited for clarity re: CHT and leaning.
     
    Last edited: Nov 11, 2021
  2. MonkeyClaw

    MonkeyClaw Pre-takeoff checklist

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    Timothy Miller
    Since you have a turbo, you can use TIT to get LOP.

    1. Get to cruise altitude
    2. Set MAP and RPM
    3. Lean to ~50-65f LOP TIT
    3a. When you lean through peak, you may want to approach again from the lean side to check peak again
    3b. If possible, verify that all EGT also go LOP by either observation or analysis after the flight

    Don't use CHT to determine if you are LOP. If they are high (>400) you can either lean more, lower MAP, or go ROP. CHTs react too slowly. Deakin has and article about this.
     
  3. Sluggo63

    Sluggo63 Pattern Altitude

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    Thanks for the confirmation. I get the concept of leaning to TIT. I’ll try to put in practice this weekend on my way to Vegas.

    My bigger question is what to do after leaning as far as MP. After leaning it’s no longer at the 65%, do I reset the MP from the performance chart, or just leave it where it settles after my leaning?
     
  4. MonkeyClaw

    MonkeyClaw Pre-takeoff checklist

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    That part is up to you. You will lose some speed when you go LOP. You can be happy with your savings and go a little slower, or bump up your MAP if you want to go faster - just make sure your CHTs stay low. The APS guys came up with GPH multipliers to find % power based on engine types and compressions ratios but it's different for every engine. Remember, when you're LOP, the amount of gas is the limiter, while when ROP the O2 is the limiter. This is why the multiplier vs. GPH works for determining % power when LOP. In general, you won't need to re-lean in a turbo to find peak. It's not exactly linear, but in a tuned engine you rarely need to check how far lean you are again. Again, watch CHT and either lean more, lower MAP, or go ROP (at least 150d) if CHTs get too high.
     
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  5. Lance F

    Lance F En-Route

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    Does the MP change when you go LOP? On my TCM TSIO520NBs MP doesn't change a bit as I go from climb ROP (28gph) to cruise LOP (15gph). I pull to cruise power settings and go to LOP as soon as plane's accelerated as much as it's going to. This is a minute or two at most. I can't think of any reason to continue in cruise ROP for 5 to 10 minutes. As said before you can add manifold pressure to get some lost airspeed back if you want to. There may be a TIT limit in your POH (There is no TIT limit, or TIT measurement for that matter, on my engines.1650dF is a typical TIT limit if you have one. KNOW THINE POH!
    And just to be absolutely clear, CHT does not in any way determine where you are LOP. Strictly EGT (or TIT). However as an effect CHTs will decrease as you go more LOP.
     
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  6. Sluggo63

    Sluggo63 Pattern Altitude

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    I'm almost sure mine will. It does when I pull it back to lean it ROP. The Seneca IIIs have a fixed wastegate, so I wonder if that has something to do with it. I really need to put the aftermarket Merlyn wastegates on this thing.
     
  7. flyingron

    flyingron Touchdown! Greaser! PoA Supporter

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    Warmest? I never look at the absolute values (EGT values are highly variable due to exactly where the probe is in the stack). I lean out until the LAST cylinder peaks and then keep leaning until that cylinder is 25 below peak. The others will be more lean.
     
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