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#21
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Thomas Borchert wrote:
Doug, At power settings above 65% you need to be concerned about running too lean, thus too hot. Uhm, no, not at all. He'd have to be concerned to run not lean enough, actually, since the temps decrease again when running leaner and leaner. The point is: You have to worry to run at the right point in relation to peak. I don't fully agree with that. The O-470 is normally aspirated rather than injected; without a tuned intake, the mixture arriving at each cylinder is going to be more varied; it is likely that you may have one or two cylinders lean, one or two cylinders rich and two cylinders in the worst part of the pressure curve. With monitoring all 6 cylinders it should be possible to run 50 to 100 rich of peak at these high power settings. 50 rich is about the worst point to run at. Yep, should be 100-150 rich. Most of us pilots lean to a specific EGT. Well, I sure don't. I don't know ANY other pilot (apart from you) who does. Those numbers are completely irrelevant. The relation to peak is key. The 182R I fly only has the single probe CHT that Cessna installed; lean it until it is rough, then enrichen it a couple of twists. I have an engine that is well over TBO and still going strong using this technique. I can't see any curvature of the earth from the ground, so it must be flat. Or, in other words: What proof do you have of a correlation? Lean on the ground for taxi as much as possible. Lean for takeoff at airports above 3000'. I lean to peak RPM with idle initially full rich at 900 RPM. |
#22
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"Thomas Borchert" wrote in message ... Doug, At power settings above 65% you need to be concerned about running too lean, thus too hot. Uhm, no, not at all. He'd have to be concerned to run not lean enough, actually, since the temps decrease again when running leaner and leaner. The point is: You have to worry to run at the right point in relation to peak. That's not what Continental says about their engine, and not what TBO Advisor recommends. Juan |
#23
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"john smith" wrote in message .. . Thomas Borchert wrote: Doug, At power settings above 65% you need to be concerned about running too lean, thus too hot. Uhm, no, not at all. He'd have to be concerned to run not lean enough, actually, since the temps decrease again when running leaner and leaner. The point is: You have to worry to run at the right point in relation to peak. I don't fully agree with that. The O-470 is normally aspirated rather than injected; Umm...it's normally aspirated vs turbocharged; it's carbureted vs injected. |
#24
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Yes, it is a carbureted engine. Leaning to peak at 50% power and then
using that temperature to lean to at higher power settings works. It gives about 50 degrees rich at 65% power and 100 degrees rich at 75% power and 150 degrees rich at 85% power etc. All without having to actually lean to peak at these high power settings, which even one time, can overheat and do damage. All this talk about running lean of peak usually doesn't work with carbureted engines because of uneven airflow. Running rich of peak aviods the peak settings that can overheat things and do damage. It is false economy to try and run lean AT HIGH POWER SETTINGS and possibly damage your engine. Below 65% or so, you can usually lean all you want and you will be fine. My method allows some "cushion" using the 50% setting for lean as possible instead of 65%. I would not want to advocate something that could cause damage, so I stayed conservative. If you want to experiment around, you are free to do so. Just look in your POH and see what 50%, 65% and 75% power settings are and jot those down so you have a reference when you start experimenting. And don't run things too hot. Heat weakens metal. That is what you want to avoid, even if it means burning a little more fuel. |
#25
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Doug,
Do you run high RPM/low MP or high MP/low RPM power settings at cruise? |
#26
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I run my rpm at 2450, mainly because that is where it runs the
smoothest. Most of my local flights are at 20". I fly at 6500' MSL locally (my airport is at 5300'). Cross country, I tend to run harder going into the wind and throttle back a bit if I have a tailwind. But if you want to save fuel, running at low rpm's and high manifold will get you the most power with the least fuel and save wear on the engine (fewer total revolutions). I've never heard an argument for different leaning procedures with high rpm/low mp vs high mp/low rpm though. My Husky's Lycoming carbureted 0-360A1P has 2200 tach time on it. No oil burn, good compressions, no metal in the filter. I use Aeroshell 15-50 and change it every 50 hours (along with the filter). I have put all but the first 250 hours on this since new engine. As I stated, I lean to 1350 degrees EGT on my one probe. Been all over North America in my bird. (Just got back from Quebec). Based in Colorado. I think the main thing is to lean enough to get proper burn, but don't lean so much as to burn things up. I have some friends with probes on all cylinders and carbureted engines who have tried to run lean of peak and they have mostly given up. Just doesn't work on carbureted engines. It doesn't on mine. Most of Deacons stuff is applicable to fuel injected, and ususually turbo charged engines being run at HIGH power settings (like 80% power). It is a technique that uses a lean mixture to keep things cool. Only works if you have fuel injection, gamis probes on all cylinders and a fuel flow meter. I don't run that type of equipment, so I can't really comment on it, though from what I hear, it does work, if done properly. The guy that asked the question has normally aspirated, carbureted engine. |
#27
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Doug wrote:
I think the main thing is to lean enough to get proper burn, but don't lean so much as to burn things up. I have some friends with probes on all cylinders and carbureted engines who have tried to run lean of peak and they have mostly given up. Just doesn't work on carbureted engines. If you said "most" carbed engines, I probably wouldn't quibble. However, it does work on some. It certainly works on my Continental E-225 with a Bendix PS-5C carb. Its harder to do, but can be done and does work. Here is what I had to do: 1) overhauled my carb and had it flow tested to make sure its doing its job. 2) Pull off the throttle back a bit less than one inch. This put the carb out of the enrichment mode that it is with full throttle. I think it may also put a bit of turbulence into the airflow that helps the fuel vaporization. 3) If I can't get smooth LOP operations with the above, I'll play a bit with carb heat (which is actually alternate air on my plane). Causing the induction air to be a few degrees warmer will often help get the vaporization (and hence good distribution) needed. I believe I've heard the GAMI folks say that getting good distribution is easiest on the large Continentals. Something to do with the way the stock induction is done. -- Frank Stutzman Bonanza N494B "Hula Girl" Hood River, OR |
#28
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I fly a C182P with O470S. Recently read the engine management and leaning
articles on AVWEB prior to a long (1200NM) cross country. I have a 6 cylinder analyzer with CHT and EGT for each cylinder. Cruising at 7500ft I would lean to about 75-100 ROP on the first cylinder to peak. I would have a large descrepancy between EGT temps between the cylinders due to uneven distribution of fuel air mixture in the O470S. I then tried a trick mentioned in those articles. I would back off the throttle until MP just noticably fell (about 1/4 inch MP). After a couple of minutes the EGT's were all within 25 degrees of each other. The idea put forward in the article was that by partially closing the throttle the turbulence created resulted in more even distribution of fuel. Don't know if there is any rational basis of this but seemed to work in my plane. Howard |
#29
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John,
Uhm, no, not at all. He'd have to be concerned to run not lean enough, actually, since the temps decrease again when running leaner and leaner. The point is: You have to worry to run at the right point in relation to peak. I don't fully agree with that. The O-470 is normally aspirated rather than injected; without a tuned intake, the mixture arriving at each cylinder is going to be more varied; it is likely that you may have one or two cylinders lean, one or two cylinders rich and two cylinders in the worst part of the pressure curve. Not sure at what point we disagree. -- Thomas Borchert (EDDH) |
#30
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Doug,
Running rich of peak aviods the peak settings that can overheat things and do damage. Not at all true. In fact, completely false. Sorry. It is false economy to try and run lean AT HIGH POWER SETTINGS and possibly damage your engine. lean? How lean? This statement is not true. -- Thomas Borchert (EDDH) |
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