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08-10-2011, 09:36 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by RV10inOz
I talked about rapidly rising CHT's on takeoff and it was due to mixture not hitting full rich due to cables (too short in throw from Vans) and the mount flexing. This was detonation.
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Serious question David; why are you sure it was detonation?
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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08-10-2011, 09:49 PM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Quote:
Originally Posted by RV10inOz
...Those that have a higher margin might be hard to detonate on AVGAS, but I do not know this for sure. Do you? Not by your statement above so why encourage others to do so when you do not know...
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First off, if anyone reads a statement that begins with the disclaimer "this is just my (nearly) uneducated opinion..." as even the slightest form of encouragement, then they have a lot more to worry about in life than proper engine management!
Second, I'm no expert, and have NEVER promoted myself as such in this field. My complaint is that the "experts" have let all of us down because they can't seem to agree on much of anything. So in such a case, I'm forced to sift through all the BS published and try to find the few things that ARE held as universal truths among all the engine guru's, compare that to my own experience, and go from there. Though I have never seen detonation, I know how to read a CHT gauge... I expect that this will serve me as well as it has the hundreds of thousands of other pilots over the last 60 years or so. This may not be the perfect solution, but I like my odds.
Finally, the relatively newfound ability to monitor multichannel CHT and EGT to 1 degree resolution does NOT increase the chance of detonation - so even if the Lycoming DOES detonate under certain conditions, it's obviously been doing it for 60 years without any real problem - so when it's all said and done, we're no worse off than the previous generations of pilots, so who cares?
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
Last edited by Toobuilder : 08-10-2011 at 09:51 PM.
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08-10-2011, 10:41 PM
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Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,271
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Moura
Quote:
Since Don from AFP was mentioned, I did replace my restrictors and they were perfect. Only replaced 3 for 25 dollars (I think that is what I paid) each.
But you know what puzzles me, Don mentioned he would never run not even an inch above 24MAP when LoP!! Should I be confused?
Moura
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Yes I think you should be confused!!!  What on earth would make Don say that? He should know better. How do you think the big old radial airliners did it? This is exactly how Old Wives Tails begin.
As for down low , Toolbuilder has it pretty much nailed. WOT unless for some reason you need to pull way back. Pulling the throttle back is not unlike a clogged air filter, and you would not run around with a clogged up filter would you?
So set the RPM where you want, and slower is theoretically less power (Torque x RPM) but its a slower piston speed and closer to detonation  but anything like 2000+ is not that much of a deal, but if you choose more go, more RPM, a bit less, use less. Then set LOP according to this,
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Outside the Box
? At 65% power, use richer than 100 ROP, or leaner than peak EGT.
? At 70%, use richer than 125?F ROP, or leaner than 25?F LOP.
? At 75%, use richer than 180?F ROP, or leaner than 40?F LOP.
? At 80%, use richer than 200?F ROP, or leaner than 60?F LOP.
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How hard can that be?
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08-10-2011, 11:01 PM
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Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,271
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Dan,
A few tests, downloaded data sent to John Deakin, much discussion about all the likely things to do with pre-ignition first of all as that is really bad, such as a defect with a plug, helicoil, timing etc.
If it was not detonation of a mild kind what else could it be? and let?s be realistic here, it?s hard to determine without an engine test stand like GAMI have what is mild-med-high levels of detonation.
The way one or two or three CHT's all ran away at a very rapid rate compared to the normal 1 degree every few seconds during a take-off and climb were pretty obvious, and the data looked like what they get on their data.
We found the problem, and that explained it pretty darned well.
This was not just a few folk at the airfield shooting from the hip kind of investigation. I was lucky having had some acquaintance with John Deakin and good access to him to diagnose it. As usual he was onto it!
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08-10-2011, 11:20 PM
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Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,271
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I went and had a dig around, and this explains why the tell tail sign of rapidly rising CHT's is worth watching out for! One post I read recently this is what he saw and did the right thing immediately.
http://www.avweb.com/news/pelican/182132-1.html
It was too long an article to copy into this post, so please read this, several times even until it sinks in. Thats the only way I seem to learn.
And can I say again....attend the classes.
Last edited by RV10inOz : 08-10-2011 at 11:24 PM.
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08-11-2011, 05:05 AM
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Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,167
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I did some more testing yesterday. One question quickly came to mind. I post the chart on page 1 of this thread in the my aircraft. Had to go to 9500 feet for ATC and went to the chart to decide where to run the engine. I appears based on the chart on the first page of this thread that you can't fun LOP above 9000 feet and in fact they recommend 50 ROP at least. I am trying in my mind to understand the reason behind this since MAF is dropping as you climb and you are in the region where in past LOP writings you can't hurt the engine at any mixture setting. Any comments or ideas? Anyone running LOP at higher altitudes?
George
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08-11-2011, 07:02 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Quote:
Originally Posted by sailvi767
...Anyone running LOP at higher altitudes?..
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Yes. This is LOP:

__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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08-11-2011, 07:12 AM
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Join Date: Oct 2009
Location: Uberaba, MG, Brazil
Posts: 122
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Michael, 395 and 380 EGT aren't too high for LOP ops?
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08-11-2011, 07:12 AM
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Join Date: Feb 2005
Location: Chesterfield, Missouri
Posts: 4,514
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Quote:
Originally Posted by Toobuilder
First off, if anyone reads a statement that begins with the disclaimer "this is just my (nearly) uneducated opinion..." as even the slightest form of encouragement, then they have a lot more to worry about in life than proper engine management!
Second, I'm no expert, and have NEVER promoted myself as such in this field. My complaint is that the "experts" have let all of us down because they can't seem to agree on much of anything. So in such a case, I'm forced to sift through all the BS published and try to find the few things that ARE held as universal truths among all the engine guru's, compare that to my own experience, and go from there. Though I have never seen detonation, I know how to read a CHT gauge... I expect that this will serve me as well as it has the hundreds of thousands of other pilots over the last 60 years or so. This may not be the perfect solution, but I like my odds.
Finally, the relatively newfound ability to monitor multichannel CHT and EGT to 1 degree resolution does NOT increase the chance of detonation - so even if the Lycoming DOES detonate under certain conditions, it's obviously been doing it for 60 years without any real problem - so when it's all said and done, we're no worse off than the previous generations of pilots, so who cares?
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Michael,
I have not compared every statement and written word by Deakins and Busch, but they generally are in agreement. They advocate LOP is a better way to go but the gist of what is put forth is applicable mostly to 6 cylinder, high powered engines. Their theory is somewhat at odds with Lycoming but in fact Lycoming has come around somewhat to their way of thinking on leaning after a major flight school had to shut down operations with almost new airplanes a few years back due to fowled plugs.
To transfer the theory of LOP operations to the 4 cylinder low compression engines is not all that critical or complicated. If in doubt, follow Lycomings recommendations to the letter. But evidence seems to indicate LOP works. Mike Busch's Cessna twin is 200% beyond TBO.
The discussion here has drifted off into detonation. So how is detonation controlled in modern auto engines? By a computer that monitors knock and when it is detected timing is retarded until it detects no knock. If you minitor timing, as I did with an OBD scanner hooked up to the Subaru engine, it always ran more advanced than 25 degrees (magneto timing) even when flying around with WOT and 1700 rpm.
I don't think detonation is much of an issue with Lycoming unless an EI systm looses its brain. It does not monitor knock but it does respond to MP and RPM inputs. Unfortunately, the program could get out of wack with high MP (calling for 25 degrees advance) and low RPM (perhaps calling for 35 degrees advance). I don't know what advance the system would call for. I had a dwell meter hooked up with Electoraire when I used it and it sure responded well to normal MP and RPM with a fixed pitch prop. It was always advanced except for take off power.
With magnetos the timing is fixed and retarded considerably from where Ei and ECU computers normally set it. Mag timing is really out of the detonation range. If CHT goes up on take off due to a lean mixture, it is a matter of inadequate fuel and air flow cooling. I would be surprised if there is detonation. I suppose there could be, put how would one know?
These engines are low rpm, big displacement like an old farm tractor, it was very difficult to get them to detonate even under heavy load pulling a 3 bottom plow. They would get hot but did not detonate until RPM got really low and one did not shift to a lower gear quick enough. 
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08-11-2011, 07:35 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by RV10inOz
A few tests, downloaded data sent to John Deakin, much discussion about all the likely things to do with pre-ignition first of all as that is really bad, such as a defect with a plug, helicoil, timing etc.
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Ahh. Given the concern with preignition, you pulled the plugs and looked in the cylinder?
BTW, you are running the standard 8.5 compression and mags at 25, and burning 10LL? Was OAT 100F+, and CHT 400+?
Quote:
Originally Posted by sailvi767
It appears based on the chart on the first page of this thread that you can't fun LOP above 9000 feet and in fact they recommend 50 ROP at least. I am trying in my mind to understand the reason behind this.......
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Good question. George refers to this graphic; yellow circle added for emphasis.

__________________
Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 11-24-2014 at 12:12 PM.
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