Question on engine operation

Discussion in 'Pilot Training' started by Bill Weber, Jul 5, 2019.

  1. Bill Weber

    Bill Weber Pre-Flight

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    Good Morning,

    In the spirit of always learning, and like much of life there always appears to be a lot of conflicting information and so I figured I would ask peoples thoughts/opinions on a couple of items: -

    1.) Should you wait for oil temp to reach 90-100 before takeoff/run-up? I've heard many say that the engine needs to be warmed slowly to allow the metal parts to expand without undue stress. Others have told me that engines are meant to be air-cooled and the sooner you have air running over them, the better; that is assuming the engine is sufficiently warmed and so will not stutter upon advancing power to full.

    2.) ROP or LOP? Many out there seem to stick with the ROP theory (more fuel = more cooling), however, from all I read LOP is much better for the engine and results in lower CHTs and less engine wear.

    Any input is useful!

    Thanks.
     
  2. Challenged

    Challenged Pattern Altitude

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    For oil temps I just utilize the PoH and whatever it considers to be normal operating temperature plus maybe a little cushion to make myself feel better. I'm generally in the normal range by the time I get to the runway so I generally don't worry about this too much other than making sure it's normal.

    Martin Pauly, who posts here, has a really nice video on Lean of Peak operations:

     
    Last edited: Jul 5, 2019
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  3. Ryanb

    Ryanb Touchdown! Greaser! PoA Supporter

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    Might also help to know what engine you’re operating as far as being able to properly run it LOP vs ROP.

    For the small bore Lycoming’s, I’ll typically wait for the oil temp to bounce off the peg, which usually happens pretty quick in these hot temps. Much slower during the winter.
     
  4. chemgeek

    chemgeek Cleared for Takeoff

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    First stop should be the POH. There should be relevant info there.

    Oil temps
    While many pilots will wait for the oil temperature needle to come off the stop, the AA-5 POH says that you are good to go as soon as the engine will take full throttle without stumbling. The engine will warm up rapidly when you apply full power. Engines do not cool very well on the ground, with little airflow. Consult your POH or engine manufacturer recommendations.

    Leaning
    You should lean aggressively on the ground to discourage lead buildup if using leaded fuels. You can't hurt the engine doing this, as it is not developing much power.

    Unless you have appropriate engine instrumentation, you will find it difficult to determine what is LOP. If your aircraft is carbureted, and not fuel injected, it may be difficult to fly lean of peak at all as fuel-air mixture distribution between cylinders can be quite variable, making it difficult to get all cylinders to run at the same mixture.

    Without engine instrumentation, you can lean until the engine runs slightly rough, then enrich until it smooths out. This is approximately "best economy" according to Lycoming, and is the POH-recommended procedure for the AA-5. This should be a safe leaning procedure for almost any carbureted aircraft engine to give you reasonable economy and reproducible fuel consumption. The POH will also normally suggest limitations on leaning, e.g. Lycoming recommends leaning only at 75% power or less for the O-320. I've flown my engines that way for over 30 years.
     
    Last edited: Jul 5, 2019
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  5. flyingron

    flyingron Touchdown! Greaser!

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    I agree with Chemgeek. The AA-5 POH comment mirrors what both Lycoming and Continental say about their engines: the engine is warmed up when it can take full power without hesitation.
    There's nothing magic about the low end of the oil temperature gauge. In fact, many tightly cowled engines are done a disservice by leaving them running for long periods on the ground. They need the airflow of flight for proper cooling.

    If you don't have a multipoint EGT, you're going to have to be very conservative on your leaning. Chem's procedure works fine. Lycoming and Continental differ on leaning overall. Lycoming does tell you to avoid certain slightly rich of peak mixture settings to avoid detonation issues. Continental says as long as you are running at or below the max continuous power setting, you can run anywhere from full rich to so lean that the engine is misfiring without damaging the engine.
     
  6. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    Your engine or someone else owns it?
    If the latter, run it the way they want.
     
  7. LongRoadBob

    LongRoadBob Cleared for Takeoff

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    Thanks for that. That was a really well done explanation!
     
  8. Clip4

    Clip4 En-Route

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    First, if the oil temperature is less than 30F, don’t start the engine. Then oil temp should be off the peg on the oil temperature gauge before take off.

    You cannot run a carbureted engine lean of peak and you should not run an injected engine lean of peak without an engine analyzer.
     
  9. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    And balanced injectors.
     
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  10. Timbeck2

    Timbeck2 Final Approach

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    ???
     
  11. PaulS

    PaulS Final Approach

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    1.) Yes

    2.) It depends.
     
  12. sourdough44

    sourdough44 Pattern Altitude

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    Depends some with everything. On a hot summer day, usually by the time you taxi out and do a run up, things are sufficiently warmed. On a cold winter start, I’ll take preheat then a more serious warmup.

    Some can depend on the engine & type of monitor.

    I lean in most every phase of flight, then LOP for most cruise.

    Come to Oshkosh, go to a few operating briefs, see what the ‘experts’ have to say. No reason to follow in lockstep, but at least points to consider.
     
  13. flyingron

    flyingron Touchdown! Greaser!

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    The "experts" at Lycoming and Continental say do preheat if cold but warmup is only needed to the point that the engine can take power application without hesitation. There's nothing further gained by extended ground runs.