Take off MP reduction

Discussion in 'Flight Following' started by Martin__, Dec 5, 2021.

  1. Martin__

    Martin__ Filing Flight Plan

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    Came from 700 hrs in a fixed pitched Tiger to a Glasair III recently. Following transition training instructions, reduce MP and then RPM after takeoff. Okay.

    Now after a while I’m wondering why reduce the MP/throttle at all? I understand the RPM noise issue, but what is the rationale for reducing MP for “cruise climb” or whatever?
     
  2. David Lloyd

    David Lloyd Filing Flight Plan

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    Whoever taught that, regard everything else they said with suspicion.
     
  3. jnbcfi

    jnbcfi Pre-Flight

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    Some aircraft limit takeoff (full) power to a time during and just after takeoff. Whether that is the case with the Glasair III I don't know.
     
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  4. Magman

    Magman Line Up and Wait

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    MAP will come down about 1 inch per thousand feet as you climb.

    Reducing MAP may also lean your mixture.

    Carbs usually have an Economizer that richens mixture at Full Throttle for cooling.

    FI often similar.

    Left over from radial days. Just like me.
     
  5. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    Good wondering. Manually reducing MP along with RPM after the initial takeoff climb was standard fare for decades and even appears is some aircraft POH. There can be reasons to reduce RPM but, in modern engine management, rarely a reason to manually reduce MP until cruise (max continuous power limits are one) But those kinds of changes take time to filter through the aviation community. It's pretty much in the same category as running 50 ROP.

    ("Manually" as opposed to the natural reduction with altitude)
     
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  6. FORANE

    FORANE En-Route

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    I'm in a Lancair. I don't reduce throttle in climb. I do reduce RPM's after airborne around pattern altitude per guidance from the engine manufacturer Titan (likely due to it being a stroker motor). Of course my cylinders are off now due to a broken ring so you may not want to do as I do.
     
  7. BladeSlap

    BladeSlap Pre-takeoff checklist

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    Might it depend on which engine?

    Being experimental isn’t there a large variety of possibilities?
     
  8. midwestpa24

    midwestpa24 En-Route

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    Only aircraft I have ever reduced MP after takeoff were turbocharged. Is the OP's aircraft turbocharged?
     
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  9. Tarheelpilot

    Tarheelpilot Final Approach PoA Supporter

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    The only ones I’ve reduced power after takeoff were the ones that required it per procedures from the manufacturer or company SOP.

    Your instructor may be correct or not.
     
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  10. kaiser

    kaiser Pre-takeoff checklist

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    I don’t fly a Glassair but I don’t cruise climb at 100% unless the POH asks me to (like in the Cirrus SR22 TN).
     
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  11. Clip4

    Clip4 Final Approach

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    I guess if you are the guy paying for the maintenance you can do what you want, but I reduce climb power to 90% on several models of higher performance airplanes with normally aspirated engines and I believe it is a good operational practice.

    As an example, you might notice Cessna provides maximum and normal climb data on the 182S, 172RG, 182RG and 210N models. My interpretation is normal is what you should use unless you need maximum performance, but it is not an operation limitation.
     
    Last edited: Dec 5, 2021
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  12. Martin__

    Martin__ Filing Flight Plan

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    Thanks for the responses. As far as the engine, It’s a NA IO-540, Lycon had it at 350hp on the dyno. 10:1.
     
    Last edited: Dec 5, 2021
  13. dmspilot

    dmspilot En-Route

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    I agree with what Clip said. Consider that in your 700 hours of fixed pitch flying, you were probably climbing out at 85-90% power, because that's all that it was capable of. And that happens to be what the typical recommended climb power setting in a CS-equipped aircraft will give you. That said, I haven't seen convincing empirical evidence that one way is better than the other, but as a CFI I almost always teach following the book.
     
  14. Clip4

    Clip4 Final Approach

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    Yes, you want to reduce climb power on that engine unless you enjoy replacing cylinders really often.
     
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  15. Martin Pauly

    Martin Pauly Line Up and Wait PoA Supporter

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    Your POH may specify limitations for MP and RPM during take-off and/or climb - maybe because of the original design, or maybe because of an aftermarket modification. If yours does, follow it.

    For the majority of us where the POH does not have such limitations: leave the levers forward. What you think is good for the engine and what actually IS good for the engine can be different things. Case in point: Most of our engines are set up such that a reduction in MP brings with it also a reduction in fuel flow. That is to avoid the famous "red box" on take-off when maximum horsepower is needed, so full throttle results in a little extra fuel being made available. Retard the throttle a little bit, and you will likely increase CHTs and internal cylinder pressures while still making a ton of power - not a good place for your engine.

    John Deakin describes this much better than I could. Here is one of his best articles summarizing engine operations. Start with the takeoff and climb sections:
    https://www.avweb.com/features/avwe...-perch-63where-should-i-run-my-engine-part-1/

    I am fully aware that most CFIs teach it differently. I am also fully aware that most CFIs know preciously little about engines and how to operate them. Do yourselves a favor and learn about them - your aircraft, your engine and your wallet will thank you for it.

    - Martin
     
  16. Stewartb

    Stewartb Final Approach

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    Reduction of RPM and full throttle is less than 100% power. Full throttle assures adequate fuel flow to cool cylinders in the climb. Advice that it’s bad for cylinders is incorrect. It’s how to take the best care of your cylinders.
     
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  17. flyingron

    flyingron Touchdown! Greaser! PoA Supporter

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    What does your POH (and engine manufacturer) say? In my plane, it calls for a reduction of RPM once you don't need the full power but the throttle stays in during the climb.
     
  18. steingar

    steingar Taxi to Parking

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    My aircraft is quite old, and back then they really didn't have a good understanding of air flow and cylinder cooling. As a result my model is notorious for cylinder heating issues. To when i take off I reduce throttle and RPM and lower the nose to keep the engine cool. I have heard anecdotally that this results in less oil burn.
     
  19. kyleb

    kyleb Final Approach PoA Supporter

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    IF there is a POH in a GIII, it is/was written by the "last guy". If I was curious enough to ask, I'd go to primary sources - Lycoming, Lycon, or whoever built the engine.
     
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  20. texasclouds

    texasclouds Pattern Altitude

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    Trust whatever your manual says.
     
  21. kyleb

    kyleb Final Approach PoA Supporter

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    Odds are, there isn't one. If there is one, it was probably written by the builder, who may or may not have had a great understanding of how to manage his engine/prop.
     
  22. AKBill

    AKBill En-Route

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    I always hear the float planes reduce throttle after TO. Beavers, Otters and Cessna's. I always figured it was a max manifold pressure/max continuous throttle time set.
     
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  23. 455 Bravo Uniform

    455 Bravo Uniform En-Route

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    Some engine & cowl combos might call for MP reduction after initial take-off climb for cylinder head temperature control. Some engines might not be rated for continuous full power for more than a few minutes. Don’t ask me for written references, all I have are anecdotes from watching videos from the designer of my plane’s STC (not a Glasair).
     
  24. Clip4

    Clip4 Final Approach

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    Your link states, “Any other suggestion in the POH to reduce power for the climb should be viewed with extreme suspicion. I am tempted to say it should be universally ignored as bad advice, but that may be too strong.”


    Lycoming says,

    “These tips are directed specifically at TI0-540-J series engines, but they may be applied to other Lycoming engines as well.”

    “The following suggestions deal with the engine areas that lead to the necessity of overhaul by attempting to minimize wear rates and potential cylinder problems, and to maximize turbo system and wastegate life through changes in operational procedures.”

    “Climb should be accomplished with engine cooling in mind. Cowl flaps should always be open for climb. A higher than normal climb speed of 140 MPH is recommended to aid cooling. The maximum normal operating power of 2400 RPM, 40” Hg manifold pressure with partial leaning, in accordance with the POH, is permissible where terrain or conditions permit. A conservative climb power setting of 2400 RPM, 35” Hg manifold pressure is also recommended while maintaining cylinder head temperature as cool as 400˚ F by manual leaning. For maximum engine service life, an exhaust gas temperature of 1,400˚ F should not be exceeded.”


    So I guess the question is do you trust Lycoming or writers on Avweb.
     
    Last edited: Dec 5, 2021
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  25. Captain Larry

    Captain Larry Filing Flight Plan

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    That is a significant pontification. If you have any others, maybe a book might be in order. You could debunk other traditions. And yes, I have reduced power in each aircraft I have checked out in. But my instructors were old idiots who did not know that this was wrong. Of course, I will still do it as my engine is rated at full power for two minutes.
     
  26. Stewartb

    Stewartb Final Approach

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    You can’t hear MP. You hear RPM reductions. With a constant speed prop throttle doesn’t impact RPM, at least not in the context of this discussion. And, FWIW, a Beaver is supercharged, so reduction in MP is different than with normally aspirated engines.
     
  27. Martin Pauly

    Martin Pauly Line Up and Wait PoA Supporter

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    They are both valid. Let me quote another sentence from John Deakin's article:

    In this column, I’d like to suggest an SOP (Standard Operating Procedure) for a normally aspirated engine like the IO-550. This advice will apply to all the normally aspirated (in other words, non-turbo) engines of four and six cylinders with fuel injection.

    What you quoted was from the manual of a turbocharged engine. That's a different world, with somewhat different rules for operation.

    Regards,
    Martin
     
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  28. Clip4

    Clip4 Final Approach

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    I don’t operate a 230 HP IO-540-AB1A5 in a 182 and a 305 HP IO550-N in a SR22 the same.
     
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  29. Martin Pauly

    Martin Pauly Line Up and Wait PoA Supporter

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    Would you elaborate on how specifically you are operating these two engines differently, and what makes one way better for one engine vs. the other?

    There may very well be good reasons for those differences (in particular, POH limitations).
     
  30. IK04

    IK04 En-Route PoA Supporter

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    I usually hesitate to change anything with the engine controls until established in a gear-up climb configuration and high enough to make an emergency landing without an immediate descent or return to the airport.

    Remember in that video of the C-210 that blew the connecting rod? It blew up right after he reduced RPM and power. Watching hat right there gave me the willies!

    I was always taught that a turbine engine will most likely fail during a power change and it has been proven to me twice...

    Always follow the recommended or described procedures for each airframe. They may know something you don't!
     
  31. Narwhal

    Narwhal Pre-takeoff checklist

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    The POH says to reduce MP and RPM, that’s why I do it. C182B with an O-470L. From experience, CHT gets way hotter if you keep it at 28”/2600 for more than a few minutes vs the usual 500 foot reduction to 23/2450. Easy to spike it well over 400 F quickly in summer. I haven’t experimented with full throttle and 2450 RPM though. Incidentally, all 3 jet types I’ve flown change power at 1500 AGL or when the flaps are partially retracted. I say change, because on some VERY derated takeoffs climb thrust results in a higher N1 RPM than takeoff N1 RPM. I only see that on the GenX motors though.
    1D2C4401-6DD1-41E6-B82C-6B2F86FD4E20.png
     
    Last edited: Dec 5, 2021
  32. Doug Reid

    Doug Reid Line Up and Wait

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    Depends on the engine. Some older engines are rated full power only for a couple minutes during take off.
     
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  33. LesGawlik

    LesGawlik Pre-takeoff checklist

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    I was taught for my 182E to reduce MP to 24.5 and RPM to 2450 at 400' AGL. I just started flying this airplane, and this is what the previous owner did. I just borescoped the cylinders, and I had 6 burnt pizzas, so I'm not going to change a thing.
     
  34. Rgbeard

    Rgbeard En-Route

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    Such is the case with my bird. Takeoff power and maximum allowed continuous are two different things.
     
  35. Checkout_my_Six

    Checkout_my_Six Touchdown! Greaser!

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    follow the limitations in the POH....or full forward until we level off. Pulling back reduces enrichment....and could raise CHTs.
     
  36. sarangan

    sarangan Cleared for Takeoff PoA Supporter

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    Unless specifically prohibited by the SOP, or noise abatement procedures, leave things where they are until you are at a safe altitude. In most normally aspirated engines, this is cruise altitude. As for max continuous power limitations, by the time you get to 4000ft you will be below 80% power anyway. So that's 3-4 minutes. That's not long enough to count as "continuous".
     
  37. BladeSlap

    BladeSlap Pre-takeoff checklist

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    Every aircraft I have flown had had a max continuous and a timelimited higher threshold

    6FD4416F-CDF6-4C34-BB40-69F758D0622C.jpeg
     
  38. Clip4

    Clip4 Final Approach

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    I’d baby the 305 hp 550 and run the hell out of the 230 hp 540.
     
    Last edited: Dec 5, 2021
  39. RudyP

    RudyP Cleared for Takeoff

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    You're not wrong but I'm still amazed that we have to baby engines that make 33 hp/L (like that IO550 that I used to run) - that's barely a third of what your typical auto engine puts out...

    Anyway, jet engines also commonly have max take off power limitations. The Citations I fly limit T/O thrust to 5 min with both running or 10 min if OEI for durability reasons. It's a serious factor for engine programs so operators definitely abide by these limitations.
     
  40. Clip4

    Clip4 Final Approach

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    Yes, your auto can produce that much, but you aren’t running anywhere close to 190 hp cruising down the highway. Even at 80 mph, you are at <50 hp.