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  #21  
Old 07-30-2018, 05:17 PM
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f14av8r f14av8r is offline
 
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Originally Posted by Bicyclops View Post
You're right about that. Using EGTs and logging fuel flow when each cylinder peaks is necessary for nozzle tuning but not for every day flying. The big pull to an expected fuel flow takes you right through the peak and the dreaded red box and gets you to the LOP condition too quickly for any detonation problems to have developed. Once on the LOP side of things, you can fine tune for whatever cruise power/fuel flow you want with CHTs being primary. Don't care what EGTs read anymore. If the cylinders are not over 380-400 and rising, a dangerous level of detonation is not occurring. Maximum available LOP cruise power will be at your personal maximum continuous CHT on the hottest cylinder. If you want to go faster, set it to max CHT on the rich side of peak. My personal max continuous CHT is 380F.

Ed Holyoke
Ed has perfectly summarized the Mike Busch approach to LOP operations and my personal technique. Big Pull to far below peak EGT/CHT then richen to desired fuel flow limited by maximum desired CHT. No need to ever reach or establish peak EGT.

One big caveat though, If you've read Bill Ross's book on Engine Management, he'll tell you that if you are operating below Maximum Recommended Cruise Power (MRC), it just plain doesn't matter what you do with the red knob. You can't hurt your engine below MRC. Bill defines MRC as , “the power setting at or below, which full leaning authority is safe, allowable and engines are tested for durability.” This maximum setting can be found in your POH or engine operations manual. He takes care to note that MRC is not Maximum Continuous Power (MCP), which is the power setting the engine can run 24/7 in a full rich condition.

So, if you are operating at or below MRC, feel free to feel for that EGT peak using your engine monitor. You can't harm your engine. If you are operating above that performance level though, Bill Ross and Mike Busch would agree that you should avoid the Red Box, Red Fin, Zone of Maximum Cylinder Internal Pressure, etc. Knowing where MRC is in your experimental engine / experimental installation, is the trick. For me, since I don't know precisely where MRC is in my airplane, I'll just use Mike Busch's technique and avoid the danger zone altogether.
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  #22  
Old 07-30-2018, 05:32 PM
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Originally Posted by f14av8r View Post
Ed has perfectly summarized the Mike Busch approach to LOP operations and my personal technique. Big Pull to far below peak EGT/CHT then richen to desired fuel flow limited by maximum desired CHT. No need to ever reach or establish peak EGT.

One big caveat though, If you've read Bill Ross's book on Engine Management, he'll tell you that if you are operating below Maximum Recommended Cruise Power (MRC), it just plain doesn't matter what you do with the red knob. You can't hurt your engine below MRC. Bill defines MRC as , “the power setting at or below, which full leaning authority is safe, allowable and engines are tested for durability.” This maximum setting can be found in your POH or engine operations manual. He takes care to note that MRC is not Maximum Continuous Power (MCP), which is the power setting the engine can run 24/7 in a full rich condition.

So, if you are operating at or below MRC, feel free to feel for that EGT peak using your engine monitor. You can't harm your engine. If you are operating above that performance level though, Bill Ross and Mike Busch would agree that you should avoid the Red Box, Red Fin, Zone of Maximum Cylinder Internal Pressure, etc. Knowing where MRC is in your experimental engine / experimental installation, is the trick. For me, since I don't know precisely where MRC is in my airplane, I'll just use Mike Busch's technique and avoid the danger zone altogether.
This might apply with stock compression ratios, fixed mag timing and 100LL. Certainly a blanket statement like this is not accurate if you're running higher CRs, mogas and EI with more advance than a mag. All that original validation goes out the window with these common changes in the Experimental world.
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  #23  
Old 07-30-2018, 05:37 PM
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Originally Posted by rv6ejguy View Post
This might apply with stock compression ratios, fixed mag timing and 100LL. Certainly a blanket statement like this is not accurate if you're running higher CRs, mogas and EI with more advance than a mag. All that original validation goes out the window with these common changes in the Experimental world.
Well, what would be your advice for those of us running higher compression ratios and electronic mags Ross? I'm all ears, seriously!
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  #24  
Old 07-30-2018, 06:02 PM
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Well, what would be your advice for those of us running higher compression ratios and electronic mags Ross? I'm all ears, seriously!
Too many variables to give one answer here but blanket statements like this are irresponsible in my view. I'd prefer to give advice on an individual basis.

If these folks are commenting about certified configurations running on 100LL, possibly valid.

It's unlikely that 35-40 degrees of timing (common on some EIs) combined with 9.5 or 10 to 1 pistons and 87 or 91 octane mogas is safe with hot heads and high IATs even at medium cruise rpms and say 25 inches MAP which is less than 75% power.
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  #25  
Old 07-30-2018, 06:33 PM
Bicyclops Bicyclops is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
This might apply with stock compression ratios, fixed mag timing and 100LL. Certainly a blanket statement like this is not accurate if you're running higher CRs, mogas and EI with more advance than a mag. All that original validation goes out the window with these common changes in the Experimental world.
I'm running 10:1, dual electronic ignitions, and 100LL. Haven't tried mogas - probably won't. What I said before works for my engine. No runaway CHTs - no worries. My red box is probably a bit bigger than with a stock engine and that means that with high manifold pressure, I have to stay rich of peak to keep it cool. With a bit more nozzle tweaking I think I'll be able to get LOP far enough to run it that way down low even with high MAP. Right now, it runs rough when I try. Remember, LOP means less power which means lower CHTs. All that said, I can run about 27", 2300 RPM and about 10.5 GPH at 3K' and make about 175kt true with 90* OAT. Contrary to what they teach, my engine runs cooler oversquare. Lower RPM = lower power = lower heat production and lower prop drag. If I find it running hotter than I like, I reduce MAP and/or go further rich (or further lean if it will run smooth). If I'm willing to accept ~160kt TAS, I can do that at 3K' at about 8.5 GPH LOP at lower MAP.

Ed Holyoke
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  #26  
Old 07-30-2018, 11:24 PM
lr172 lr172 is offline
 
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Originally Posted by Bicyclops View Post
No runaway CHTs - no worries.

Ed Holyoke
You should do some research before being comforted by that statement. detonation has many levels of severity and many don't create "runaway CHT's" but can do a lot of damage over an extended time.

Larry
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  #27  
Old 07-31-2018, 07:04 AM
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Originally Posted by f14av8r View Post
I don't understand your statement at all. An EGT probe obviously doesn't display the instantaneous EGT but it should display a very accurate average which is derived over a fairly short period of time. A "few minutes" certainly isn't my experience with the reaction time of my EGT probes. They respond within a few seconds of my changing engine parameters.
I did edit my reply to correct "minutes" to "seconds" but you may have been writing your reply before I did so.

My point is that while the thermocouple might give a useful piece of data, it is not an "accurate" measure of anything other than its own average temperature. It bears a very loose relationship to anything going on in the cylinder itself.

However, that data can be very useful for adjusting engine operation and for diagnosing problems. Watching a trend of the values can expose problems such as developing valve damage, as Busch shows in his new book.

It wouldn't make much sense to compare EGTs between cylinders, however, because of the major differences in what each thermocouple will see from jug to jug.
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  #28  
Old 07-31-2018, 07:32 AM
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Originally Posted by Bicyclops View Post
All that said, I can run about 27", 2300 RPM and about 10.5 GPH at 3K' and make about 175kt true with 90* OAT. Contrary to what they teach, my engine runs cooler oversquare. Lower RPM = lower power = lower heat production and lower prop drag. If I find it running hotter than I like, I reduce MAP and/or go further rich (or further lean if it will run smooth). If I'm willing to accept ~160kt TAS, I can do that at 3K' at about 8.5 GPH LOP at lower MAP.
Ed, I too would suggest caution about running 27" and 2300. Not sayin' you can't, but it's the bleeding edge of what Lycoming allows for stock compression.

Less RPM = less CHT is not contrary to teaching, not if you go back to the old NACA papers. They expressed it as mass flow, but that's the same as RPM.

8.5 GPH for 160 KTAS is not very good. Climb to a more efficient altitude, set WOT and maybe 2400 RPM, then record speeds at three mixture settings, 100 ROP, peak EGT, and perhaps 25 LOP.

25~30 LOP, IO-390, 2014, loaded with camping gear and a few cases of Cow:



Peak EGT will net about 181 KTAS, which illustrates how fast power falls off on the lean side. 100 ROP will 185, but fuel burn will be near 11 GPH, which illustrates how fast fuel burn rises running ROP, for not a lot more speed.

Most recent cruise experiment, again an OSH return. Popped up high to get the tailwind. MPG was 25.7 nautical:



Note higher temperatures, which I attribute to reduced air density. See the Lycoming cooling air charts. So much for leaning to CHT.

Also note higher AOA compared to photo at 11.5K. The stubby wing seems to be a bit out of its sweet spot. All around, probably not the best altitude for this RV-8.
Where's that RV-9 wing when I need it?
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Last edited by DanH : 07-31-2018 at 07:44 AM.
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  #29  
Old 07-31-2018, 07:49 AM
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I attended the "Leaning the right Way" this year but I have also watched the webinar on youtube, https://www.youtube.com/watch?v=X-tKyiUZ3ts before. I also experimented a lot on the way home from Oshkosh. I have RV7, IO 360, Bendix Mags, burning 100LL. Experimenting at 8500' cruise, I lean with a fast pull until my engine looses considerable power to get on the LOP side, then moving slowly rich to find peak EGT's on my Dynon engine monitor. All my cylinders peak fairly close. When cruising at 8500', I have always ran full throttle and about 50 degrees LOP because I had read this gives the best fuel economy. This configuration gives me about 157 Kts per hr TAS at about 8.2 GPM. But, I have discovered, if I lean to about 15-20 degrees LOP, then pull the throttle back to establish a fuel flow of 7.9 GPH, I get 160 Kts per hr and my CHTs are the same running about 320-350. It seems, at any altitude, my engine is happy and getting best economy when I reduce my throttle to 65% power, then lean to 15-20 LOP....I wonder if this is normal? By the way,my engine does not run noticeably rough at 50 LOP.
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  #30  
Old 07-31-2018, 11:03 AM
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Originally Posted by MikeyDale View Post
my engine is happy and getting best economy when I reduce my throttle to 65% power, then lean to 15-20 LOP....I wonder if this is normal? By the way,my engine does not run noticeably rough at 50 LOP.
That matches my expectations and cruise SOP. My research tells me that max MPG will occur 10-20* LOP and seems to be validated in the testing on my 6A. While WOT can reduce pumping loss, it does not offset the efficiency of running at 10-20 LOP in my experience. The CS guys can tweak MAP to allow WOT at most any point LOP. Us FP guys need to throttle back to get into the efficient range.

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Last edited by lr172 : 07-31-2018 at 11:26 AM.
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