LOP operations

Discussion in 'Pilot Training' started by Dave Siciliano, Apr 5, 2005.

  1. azure

    azure Final Approach

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    Yes, I am talking about fuel injected engines only -- I thought the OP (well, necroposting OP) was too. He's flying a Mooney with a brand new engine that he's like to keep around for awhile, IIRC.

    Okay, that makes sense, and should be safely ROP at least in my limited experience (never taken off at high enough DA to need the technique) -- but it's not what I've heard some folks say. Full throttle on the runway, lean to maximum power, and go. I should check my POH to see what they say, but I believe what you say is correct, lean to peak RPM at runup RPM. I'm not sure if they say to enrichen from there.

    What do you mean by "it won't matter for detonation"? The red box is still there, albeit pretty small, at 75% power which is very possible in my IO-360 at 6000. I would really hesitate to set it to max power in a full power runup before takeoff unless the DA was at least 8000, maybe even 9000. 23 squared at 8000 is 65% power per the POH.

    I don't doubt it. Luckily around here, by the time I'm at 6000 MSL, it's cool enough that I've never seen CHTs above the low 300s no matter how hot it is near the surface. But I'm still wary of the red box even up there.
     
  2. Ted DuPuis

    Ted DuPuis Touchdown! Greaser!

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    Liz, I forget whether your plane has a 180 HP IO-360 or a 200 HP IO-360. If it's the 180 HP, you have no red box running 100LL. If it's the 200 HP, you'd need to make quite the effort to make it detonate.

    High CHTs are possible without detonation, as a function of mixture setting, power setting, OAT, and airspeed.
     
  3. Henning

    Henning Ejection Handle Pulled

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    One more time, it has nothing to do with listening for detonation, it's listening to the note and resonance of the exhaust and it is easily differentiated from the sound of the prop, they are different instruments playing from separate sheets of music if you will.

    BTW, 421 is easier since the prop noise is disassociated by speed as well.

    One last thing lol, you hear the load in the prop resonance as well, that is where it starts.
     
    Last edited: May 5, 2012
  4. Henning

    Henning Ejection Handle Pulled

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    I have never seen a plane I couldn't safely operate LOP using the ancient tried and true 'big grab' method: Reduce power demands to detonation safe levels, grab the mixtures back till power falls off, enrichen until the surge of power and stabilize there and watch the result become cool and favorable. If there is defect in balance that can be detected most easily of course with a monitor, but most engines will have all cylinders within a safe area; some more safe than others, but all well cool and clean. Once you are set you can advance power again safely on the lean side by advancing the throttles. If you like you can occasionally richen up to see how LOP you are but I don't find it a necessary exercise in reality. I do it when I hit level off.

    I admit I have not tried in an Aztec but it's exactly how I was shown to do it in a 421 and I know it works in a Chieftain and 325CR.

    With the 310 as long as I'm turning 2625, there's not much chance I'll see detonation on a full power lean pull at sea level. It's one of the things I like about my power package, I can fly it safely and efficiently LOP where I like to fly without having to get too fussy.
     
  5. Tom-D

    Tom-D Touchdown! Greaser!

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    It's a physical impossibility to cause detonation by removing fuel.
     
  6. Henning

    Henning Ejection Handle Pulled

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    Right, but that requires losing power. You can do it adding/maintaining power by adding air and shifting ICP timing by adding RPM.
     
  7. Ted DuPuis

    Ted DuPuis Touchdown! Greaser!

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    No, happens all the time.

    It is possible to get out of detonation by continuing to remove fuel.
     
  8. Ted DuPuis

    Ted DuPuis Touchdown! Greaser!

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    I've understood what you said the first couple of times, and I still think you're fooling yourself. But hey, have fun, just so long as it's not with my plane. :rolleyes:
     
  9. Ted DuPuis

    Ted DuPuis Touchdown! Greaser!

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    The problem on the Aztec is not detonation - it's CHTs. If you can hear a CHT, well... I guess you'll claim that next, too.
     
  10. alfadog

    alfadog En-Route

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    Nah, you can't hear CHT.


    You smell it. :D
     
  11. Henning

    Henning Ejection Handle Pulled

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    If I am making my power LOP my CHT will, be lower than if I'm making my power ROP.:confused:
     
  12. azure

    azure Final Approach

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    It's the 200 HP (I'm pretty sure all the Cardinal RGs have the 200 HP engine, unless they have something STC'd for higher). So, what are my chances of detonation running at 24/2400 with two cylinders about 40 LOP and the others 0-25 ROP? Unless you're sure they're essentially zero I think I'll pass on trying it, thank you. Of course I can get all the cylinders safely LOP, but then I'll have noticeable roughness. My richest cylinder (#2) doesn't really start coming down from peak on the lean side until my leanest (#3) is about 100F LOP.

    I'm more concerned about the opposite scenario, since I've never had a CHT issue I couldn't manage with mixture and airspeed, and 8-9 months out of the year my CHTs read in the low 300s at just about any combination of power, mixture setting, and airspeed.
     
  13. Henning

    Henning Ejection Handle Pulled

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    No reason you should have that spread on a Lycoming IO-360. You have an issue to square away, but the answer to your question at 24/2400 you're pretty safe but you could increase your margin for little to cost by either leaning even further or going 23"/2500. Your cold cylinders ought to go 75 before rough if the ignition is set up properly. First thing I would look at is your plug condition/function/gap as well as mag set up.
     
  14. azure

    azure Final Approach

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    My mech checked my ignition system thoroughly last fall, after I complained about large RPM drops on single mag operation when full rich. He'll be checking it again at annual (which should be NOW... he's gone incommunicado again, still trying to raise him), but I really doubt it's an ignition issue, more likely the injectors themselves. As I said, GAMIs are in my future, but so is a fuel totalizer and I'm not springing for either until I know what this year's annual is going to cost me.

    Not sure what you mean by "go 75 before rough"?? 75F LOP or something else? My leanest is at 100 LOP at onset of roughness... :confused:
     
    Last edited: May 5, 2012
  15. DouglasBader

    DouglasBader Line Up and Wait

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    Detonation isn't really an issue on turbine engines. A compressor stall, perhaps, but that's not an issue of mixture, but airflow.

    Absolute claptrap. You hear impending detonation in the propeller? That's such an utterly ridiculous statement as to destroy all credibility. If you're suggesting that you hear the exhaust because it's a different sound than that of the propeller, obviously so, but you're still not able to discern detonation by the resonance of the exhaust. You're a very valuable commodity if you can do what you claim, and quite possibly one of a kind.

    Not even in large radials where we set the mixture based on the color of the exhaust flame did we try to avoid detonation by the methods you suggest, and all of us were very experienced mechanics in general, and specifically on the equipment we operated. Almost nobody flew as a crew member on that equipment without being a fully qualified mechanic, and usually, inspector. You've got a very special, mythical talent there.

    The propeller is "disassociated by speed" in the 421? Because it's geared? Because it's constant speed? You spin quite a yarn, but it just gets better and better.

    Ah, so you're accomplishing this magic by listening to the propeller after all, then? Good stuff. Right up there with tales of the Easter Bunny. Pure talent.
     
  16. Ted DuPuis

    Ted DuPuis Touchdown! Greaser!

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    That depends on where LOP vs. where ROP you are running.

    They're essentially zero, especially at your low CHTs.

    Certainly, I respect everyone's decision to run their engine as they see fit. So, you should run your engine in the way that you see comfortable. The ROP operation you described earlier is perfectly safe, too.
     
  17. azure

    azure Final Approach

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    Why is that? Lower temperature leading to lower pressure inside the cylinder?

    But my CHTs are low when the OAT is standard or below... come the summer it's a different ballgame. They're never alarming at the rich mixture settings I've been running at but... at what CHT does the risk of detonation become significant, at those power settings, in a cylinder just barely ROP?

    (Even phrasing the question that way starts to sound like Mike Busch's approach of just making sure your CHTs are below some target limit. Or is there really something to what he's saying there?)

    If I was convinced I could safely do it, I would. I burn a LOT of fuel 100 ROP in cruise, typically 11gph at 24 squared, though I can get that down to 10 at "economy cruise", 23/2300, at the expense of about 5-10 kts. But leaning to "smooth by ear" at 65% power, 8500 MSL puts me right around 8 gph at 120 KTAS, a savings of $15-20/hour at current fuel prices. If I'm lucky I can pick up a few knots by adjusting my flaps and scraping the dead bugs off. :rolleyes:
     
    Last edited: May 5, 2012
  18. Ted DuPuis

    Ted DuPuis Touchdown! Greaser!

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    Detonation is a function of a number of factors, but ultimately temperature is what allows the self-ignition of detonation to occur. Lower CHTs mean that it's harder for this to occur.

    On your engine? Pretty much not at all. But I would be trying to keep them at or below 380F in all conditions. So long as you're doing that, you're pretty well golden.

    Keep in mind that CHTs will decrease significantly faster on the lean side than the rich side.

    Well, I do offer the service of flying with you to help you establish good and safe power settings, and explain why...
     
  19. azure

    azure Final Approach

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    So basically then, on my engine, Mike Busch's approach is pretty much valid?

    Yep I know... the problem with my engine/injectors is the spread is such that I get roughness before I can bring #2 very far past peak EGT. Hopefully the CHT will be cool enough even so.

    If I can get over there sometime I may take you up on that -- it would be nice to get some hands-on guidance from someone who really knows these engines. My CFI's advice is basically to not lean at all below 5000 feet, and then only enough to smoothe it out. He's also an A&P, but doesn't claim to be an engine specialist.
     
  20. Ted DuPuis

    Ted DuPuis Touchdown! Greaser!

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    Yes, provided you can keep your CHTs reasonable.

    Right, that's what to watch.

    Your CFI's approach isn't what I'd do at all. For more info, fly on out to IPT. :)
     
  21. azure

    azure Final Approach

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    Are you available tomorrow... err, today? (it's after midnight)

    I'm not 100% sure, but if the weather holds and the forecast doesn't move the rain into this area too early, I might be able to fly over there early-mid afternoon. My mech's jacks are still sitting under the wings. He literally hasn't touched my plane yet.
     
  22. Ted DuPuis

    Ted DuPuis Touchdown! Greaser!

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    Yes, I am. PM sent. :)
     
  23. Henning

    Henning Ejection Handle Pulled

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    Yes, 75LOP, if you can get to 100LOP on your leanest before onset of roughness then you can easily get your hottest EGT to 15*LOP with a smooth engine; you don't have an issue so far as running a cylinder at risk. The issue is not making enough power on that little fuel. You don't necessarily need GAMIs, you can experiment with swapping nozzles on hot and cold cylinders first. You only have 16 combinations to try and often you can greatly improve the situation.
     
  24. azure

    azure Final Approach

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    Well, that's just it, by the time #2 is 15 LOP #s 3 and 4 are so lean that it's getting rough. There might be power settings where it's a little better, but that's what I found doing the lean test. Bottom line is it ISN'T easy to get them all "safely" LOP without roughness. From what Ted says it might all be moot, as long as my #2 CHT is cool enough at peak EGT. With #3 @ 40 LOP I'm still making decent power with no roughness. But I've never tried it at higher than 65% by the book.

    Trying different combinations at random, sure I can do that but it could end up costing as much as just buying GAMIs and still not narrow the spread much. I was going to ask my mech to try swapping the front and back cylinder injectors at annual and see if that makes a difference. If not, I think that's as far as I want to follow that idea.
     
  25. Henning

    Henning Ejection Handle Pulled

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    It takes around an hour to swap though all the possible combinations of nozzle arrangement, it's about 10 minutes to swap hot for cold. If you can rearrange them and maintain the same results, you have a cam issue.
     
  26. gismo

    gismo Touchdown! Greaser!

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    While this varies among engine (or more specifically intake system) designs, unbalanced mixtures in IO aircraft engines exists with perfectly good cams. It is true that given the somewhat loose tolerance on OEM injector flow rates, swapping can improve the overall balance but unless you happen to have a pair that inversely match the effects of the intake system on mixture you may see little improvement with swapping. That said, as you pointed out, swapping is relatively easy and costs nothing by time if you do it yourself (assuming you don't damage anything in the process).
     
  27. Henning

    Henning Ejection Handle Pulled

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    Not that big of an imbalance, not without other problems. If swapping around the nozzles has no effect then there is a cam or other induction failure issue.
     
  28. gismo

    gismo Touchdown! Greaser!

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    Mike's approach is "pretty much" valid but there are some caveats that would give me some concern if you focus exclusively on CHT. For one thing, CHTs vary considerably with the amount, density, and temperature of air flowing over the cylinders so I suspect (but honestly don't know) that you could experience damaging ICP with a CHT at or below 380F with some combinations of high power, adverse mixture, cold dense air, and relatively high airspeed.

    Secondly, one goal of LOP operation is to learn "typical" combinations of power settings and fuel flow that yield safe and efficient engine operation so you don't have to go through a complicatetd leaning process every time you fly or change altitude. And I fear that relying entirely on CHT for that is likely to result in setting that work well under certain conditions but fail to give the same results in terms of efficiency and safe ICP under others (e.g. summer vs winter).

    One issue that makes this unlikely without reasonably balanced mixtures is the fact that power falls off dramatically with fuel flow when LOP. As a result, even if the leanest cylinder is still firing consistently, there will be a large imbalance in the power produced between the richest and leanest cylinder and this will increase vibration as well as reduced efficiency.

    One final note: It's pretty much accepted by all the "experts" that when the engine is producing less than 60 (some say 65%) power you cannot develop excessive ICP regardless of the mixture setting as long as there are no glowing deposits or small metal objects capable of igniting the fuel air mixture (pre-ignition) in the cylinders. And since most (non rental) pilots flying with normally aspirated engines typically operate at or below 65% in cruise flight this makes mixture management more of an efficiency issue than one of engine longevity. Also keep in mind that the %power is lower than the ROP based tables in your POH would suggest when you are on the lean side of peak EGT.
     
  29. Henning

    Henning Ejection Handle Pulled

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    I take some exception to that. While it is true that the detonation, heat, and immediate damage issues of longevity with LOP fall by the way side, the sticking/burned valves and engine deposit reduction advantages to engine longevity of running LOP are still very much in play even at reduced power settings.
     
  30. gismo

    gismo Touchdown! Greaser!

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    Yes, I agree. I was referring to the more immediate longevity issues involved with detonation, pre-ignition, cylinder head separation, and other failures instigated by excessive ICP. Also FWIW, very little mention has ever been made WRT the potential for harm caused by LOP induced/enhanced vibration when there is a mixture and power imbalance between cylinders and/or as a result of inter cycle variation.
     
  31. Henning

    Henning Ejection Handle Pulled

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    There really is no question as to the viability of running LOP, the question is one of running LOP under manual control at high power settings. With EFI & digital ignition it is the norm in any racing scenario involving multiple fuelings. You only give the fuel you need for the requirements and you don't go ROP until the very top.

    To do that right now you have to cough up the money for the FADEC 94UL engines available. Teledyne Continental is ready to meet your FADEC needs. So we have to do it by hand, it still works. Thing is, consider how the digital system approaches the problem, from the lean side, not the rich. Once it's stable running at temp the only time the engine will go ROP is when required to make terminal power. It avoids detonation by limiting heat saturation as well, another ingredient required in the detonation cycle. This is the real reason you want to keep your CHTs low as the value is much lower than the thermal destructive value.
     
  32. alfadog

    alfadog En-Route

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    So correct me is I am wrong but my take-away from this thread and Mike Busch's webinar is that I can do little if any harm by simply leaning to roughness and then enrichen until the roughness goes away. And I can do this at any time other than intial takeoff.

    I am talking about my Arrow II with 200 HP IO-360-C1C.

    I understand from this thread that I will not damage my engine by leaning to any degree at 65% power and below, roughness or not.

    And from the webinar that I should lean all the time except TO.

    So this morning I practiced that a bit. Used to be I would only lean at or above 3000' DA and use my single-cylinder EGT/CHT to lean ROP at cruise. Today I leaned starting at 500' as part of pulling the power for cruise climb and at every altitude just by feeling for the roughness. The EGT said I was just a little LOP but I was prolly a bit conservative when I enriched to remove roughness. I did my run-up leaned also.

    How did I do?
     
  33. Henning

    Henning Ejection Handle Pulled

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    Very well, that is the WWII technique I was taught early in my training which consequently was also the system taught per 152 instructions for leaning however you are cutting a finer deal with advanced information and starting leaning earlier.
     
  34. Ted DuPuis

    Ted DuPuis Touchdown! Greaser!

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    I'd agree that this does present some possibilities for problems, and why strictly running on CHT isn't in all cases the best idea.

    That said, Liz's engine is also quite stout, and the ICPs aren't that high on it, even at 75% power when leaned out. I wouldn't want to run it at 25-50 ROP, but I wouldn't want to run any engine there.

    To be clear, that isn't what I was suggesting. What I was suggesting was that, so long as her CHTs are reasonable, the way she was talking about running it either LOP or ROP was fine.

    I'd agree with this as well.

    These sorts of questions are why I offer the service of providing individual engine instruction, as well as flying in the plane with pilots to teach them settings that work for them. The APS course I think is very good, but the lack of time in the plane I think is an important part for many pilots, especially ones who don't have a tremendous amount of engineering background. I suspect that you (Lance) knew a good bit about how engines worked prior to starting to fly, as did I.

    It's pretty difficult to try to teach this stuff online.
     
    Last edited: May 6, 2012
  35. azure

    azure Final Approach

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    For the record, I was never seriously considering leaning by CHT alone, that simply doesn't make sense. Mike Busch doesn't say that anyway -- what he does say is that you don't need to worry about the effects of excessive ICP (including, he seems to imply, detonation) as long as your CHTs are reasonable. I gather that although there are engines for which this might not be true, the 200 HP IO-360 isn't one of them, though it's possible to make it detonate if you try hard enough. My question was whether it's safe for me to operate with my leanest cylinder solidly LOP (40* or so) and my richest at peak or even slightly ROP, and I understand Ted to be saying, yes, as long as your CHTs are reasonable. That's the best I can do without incurring roughness. Of course it's safe to operate that way below 65% power, the red box disappears below 65%, but we weren't talking about that, we were talking at power settings that would normally yield 70-75% according to the POH. I haven't tried doing that at higher power settings yet so I'm not certain what my CHTs would be like, but I'd be very surprised if they were much above 350, except maybe during summer heat, OAT >30C or so.

    Yes Lance, I know that the values in the book percent power table are for specific mixture settings -- I think they're at economy cruise in the Cardinal POH but I'll have to check to be sure (my spare copy is in my car). Since I don't know exactly how much power I lose LOP vs economy cruise, I use the book values to give me a safety buffer, knowing that my actual power output will be somewhat (though maybe not a lot?) less. As long as I'm below 65% book power, I consider running at any mixture setting to be safe, and my own experience shows that at 65% and around or even a little above standard temperature, there is no mixture setting where I'll see CHTs above 310F in cruise.
     
  36. gismo

    gismo Touchdown! Greaser!

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    I don't like the idea of leaning just short of roughness at high power (e.g. climbout below about 8000 DA) as this has a pretty good chance of putting you squarely in the "red box" if the cylinder to cylinder mixture isn't well balanced. I'm also not a fan of reducing power for cruise climb beyond a slight RPM reduction for noise abatement. That said, I do believe that you should lean during climb, but unless you're very comfortable with LOP ops and have a decent engine monitor I wouldn't try climbing LOP with a NA engine. The proper technique for initial climb (works for high DA takeoff as well) is to lean to the same EGT indication that you normally see shortly after takeoff with a full rich mixture at or near sea level DA.
     
  37. gismo

    gismo Touchdown! Greaser!

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    FWIW, there are two somewhat related issues with high CHT. One is that abnormally high CHT is often an indication of detonation and if the CHT is rising rapidly it's quite likely that you are experiencing thermal runaway and pre-ignition, something that can happen with any high performance engine under the right conditions. The other is that the potential for many scenarios of combustion event induced damage (e.g. detonation, pre-ignition, etc) are "enhanced" by high CHT so keeping the CHTs in check will reduce the chances for such at the very least. Of course there are other issues associated with high CHT such as inadequate valve cooling, cylinder head structural weakening, but those are relatively independent of the bad combustion events.


    [/quote]Yes Lance, I know that the values in the book percent power table are for specific mixture settings -- I think they're at economy cruise in the Cardinal POH but I'll have to check to be sure (my spare copy is in my car). Since I don't know exactly how much power I lose LOP vs economy cruise, I use the book values to give me a safety buffer, knowing that my actual power output will be somewhat (though maybe not a lot?) less. As long as I'm below 65% book power, I consider running at any mixture setting to be safe, and my own experience shows that at 65% and around or even a little above standard temperature, there is no mixture setting where I'll see CHTs above 310F in cruise.[/QUOTE]
    Sounds good. Typically going from 50-100 ROP to the mixture for true best economy (which is usually leaner than the POH might suggest) will result in about a 10% reduction in power output so if you start with 70% and go safely LOP you'll be at or below 65%.

    And I tend to believe Ted when he says your 200 HP IO-360 is fairly robust even though from a purely logical perspective it would seem to need more ICP than an IO-550 producing 300 HP since a six cylinder equivalent of your engine would be a 300HP IO540.
     
  38. Ted DuPuis

    Ted DuPuis Touchdown! Greaser!

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    All correct.

    Correct, which is part of what helps you with LOP operations.

    I do agree that the ICPs should be higher. Of course, damaging ICPs for one engine may be fine for another engine. Diesels are a great example of this, and why the gasoline engines converted to diesel haven't worked well. I don't know what the numbers are in 520s/550s and what they are in 540s, nor do I know the comparative strengths.

    That said, given the fact that Lycoming cylinders are typically known for better reliability than Continentals, it would stand to reason for me that they are built stronger, and thus would be more tolerant of higher ICPs. This is based strictly on what I've observed as an aircraft owner/operator.
     
  39. Ted DuPuis

    Ted DuPuis Touchdown! Greaser!

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    I need to finish this book of mine...
     
  40. azure

    azure Final Approach

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    I didn't want to say anything here until I'd had a chance to check my POH to see what mixture setting Cessna bases their power table values on. It turns out it's not "economy cruise" at all but something called "recommended lean". I guess from the description that it's how they recommend you run your engine in cruise.

    Guess what: it's not 50-100 ROP, it's 25 ROP. Right where Ted said he'd never want to run an engine.

    But I'm really not sure whether I could still expect 10% less power as compared with "recommended lean", with the mixture set where I'm talking about, which isn't quite "safely LOP" but with the two back cylinders LOP and the front two at peak or slightly, maybe 10-15 ROP. That's the best I can do without roughness. It seems there would be a lot of variables going into a calculation like that and it would depend to some degree on the design of the cylinders.