Van's Air Force
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RV10inOz
Well Known Member
Nice try?."why not say something nasty about my mother!" ??Smokey and the Bandit.
If you just realised. I have no vested interest in you going to a 2.5 day course. None whatsoever, so take the skeptical view and analyse it now.
I am skeptical about someone who wants everything for nothing. I think Doug Reeves might have a view on that.
Read the red block on the left of screen.
Facts are, that it is impossible to put all that education up in an internet post. Walter Atkinson did a BRILLIANT job of putting the online course together, these guys ploughed heaps of time and money into it. So you really can't judge until you have been. But there is still a price for that. It covers 75% of the live course but is 40% the cost.
Ask me to explain the beauty of Mt Rushmore or the Sydney Opera House?..unless you have been you have no clue.
?Nothing of value is free. Even the breath of life is purchased at birth only through gasping effort and pain.? ― Robert A. Heinlein
If you just realised. I have no vested interest in you going to a 2.5 day course. None whatsoever, so take the skeptical view and analyse it now.
I am skeptical about someone who wants everything for nothing. I think Doug Reeves might have a view on that.
Read the red block on the left of screen.Facts are, that it is impossible to put all that education up in an internet post. Walter Atkinson did a BRILLIANT job of putting the online course together, these guys ploughed heaps of time and money into it. So you really can't judge until you have been. But there is still a price for that. It covers 75% of the live course but is 40% the cost.
Ask me to explain the beauty of Mt Rushmore or the Sydney Opera House?..unless you have been you have no clue.
?Nothing of value is free. Even the breath of life is purchased at birth only through gasping effort and pain.? ― Robert A. Heinlein
RV10inOz
Well Known Member
Alex, great question.
The answers to the desired ring pressure over a wider range of time/distance were answered in the graph.
As for how the pressures work this video might be as good an explanation.
http://www.youtube.com/watch?v=tDk1TY-n0fM
The answers to the desired ring pressure over a wider range of time/distance were answered in the graph.
As for how the pressures work this video might be as good an explanation.
http://www.youtube.com/watch?v=tDk1TY-n0fM
AlexPeterson
Well Known Member
David, thanks, but the question I posed remains. It doesn't appear that the concept shown on the video is taking into account that the pressure also acts on the right hand, cylinder side, of the ring. Just because the ring is against the wall doesn't mean that the pressure isn't trying to push it away from the cylinder wall. This is a classic trap in understanding how pressures interact with objects. If the outer surface of the ring were conical, with only the top edge contacting the cylinder wall, we might be on to something of an explanation. It's been a while since I've looked closely at a ring, and I don't recall how they are fashioned.
Assuming the outer surface of the ring is indeed cylindrical, perhaps a more intuitive way to grasp this phenomenon (the classic trap mentioned above) is to imagine a ring set in a cylinder, with no piston. Now apply static pressure to the cylinder - is this static pressure pushing the ring harder against the cylinder wall in this case? It is not.
If larger areas under the curve of pressure vs time do indeed help engine rings break in, there might be some other mechanism at work.
The basic concept of combustion pressure applying radial ring pressure was settled 80 years ago. The bibliography in C.F. Taylor's The Internal Combustion Engine.. lists several research papers from the day. The best current pressure measurement information would probably require an SAE membership or similar, but you'll no doubt find reams on the net.
Practical example: Assuming a basic rectangular ring section, the standard has been about 0.0015" clearance between the top surface of the ring and its land in order to provide a path for combustion pressure. High RPM can float the ring within this clearance; some motorsports engines run a clearance of ~0.0005" and use drilled passages to port combustion pressure to the back of the ring land. Our Lycomings use wedge and half wedge sections, but the basic principles are the same.
Returning to focus...
The fundamental point in this conversation is that piston ring radial pressure is roughly proportional to gas pressure, and we require significant radial pressure for ring seating. That is why every break-in recommendation you've ever seen says "rich and high power", inter-spaced with short periods of light load to allow a degree of surface flushing and cooling. Failure to do so results in glazed cylinders and non-conforming rings.
Although LOP operation is a generally wonderful thing, it is not appropriate for all operations, and certainly not for ring seating. And yes, as stated, the reason is right there on the chart so kindly provided.
Practical example: Assuming a basic rectangular ring section, the standard has been about 0.0015" clearance between the top surface of the ring and its land in order to provide a path for combustion pressure. High RPM can float the ring within this clearance; some motorsports engines run a clearance of ~0.0005" and use drilled passages to port combustion pressure to the back of the ring land. Our Lycomings use wedge and half wedge sections, but the basic principles are the same.
Returning to focus...
The fundamental point in this conversation is that piston ring radial pressure is roughly proportional to gas pressure, and we require significant radial pressure for ring seating. That is why every break-in recommendation you've ever seen says "rich and high power", inter-spaced with short periods of light load to allow a degree of surface flushing and cooling. Failure to do so results in glazed cylinders and non-conforming rings.
Although LOP operation is a generally wonderful thing, it is not appropriate for all operations, and certainly not for ring seating. And yes, as stated, the reason is right there on the chart so kindly provided.
The basic concept of combustion pressure applying radial ring pressure was settled 80 years ago. The bibliography in C.F. Taylor's The Internal Combustion Engine.. lists several research papers from the day. The best current pressure measurement information would probably require an SAE membership or similar, but you'll no doubt find reams on the net.
Practical example: Assuming a basic rectangular ring section, the standard has been about 0.0015" clearance between the top surface of the ring and its land in order to provide a path for combustion pressure. High RPM can float the ring within this clearance; some motorsports engines run a clearance of ~0.0005" and use drilled passages to port combustion pressure to the back of the ring land. Our Lycomings use wedge and half wedge sections, but the basic principles are the same.
Returning to focus...
The fundamental point in this conversation is that piston ring radial pressure is roughly proportional to gas pressure, and we require significant radial pressure for ring seating. That is why every break-in recommendation you've ever seen says "rich and high power", inter-spaced with short periods of light load to allow a degree of surface flushing and cooling. Failure to do so results in glazed cylinders and non-conforming rings.
Although LOP operation is a generally wonderful thing, it is not appropriate for all operations, and certainly not for ring seating. And yes, as stated, the reason is right there on the chart so kindly provided.
Once again, thank you Dan. Explained in such a way that even I can understand it.
RV10inOz
Well Known Member
Dan, you have missed the point.
The area under the curve representing Mean effective pressure over a wider range, and further from the choke area.
At the nominal recommended 75% power or 80% power or whatever number you choose, the MAEN effective pressure is the determining factor is it not? As it is it is the mean pressure we want and not a peak.
The cylinder and rings have no idea what ROP or LOP is or means. They don't care even if they could care. All they care about is pressure, and they would not care how it is achieved.
By your logic why not run in the engine at 50dF ROP at 75% to 85% power? Draw your red lines on our graph and that now supports your argument even better.
For every bit of area under the curve on the left of the redline, to achieve the same HP, there is wastage on the right side. (Work in Vs Work out) Prior to your red lines starting at the peaks, there is a lot of high pressure over a very small distance travelled in the choke area. Compared to the green trace, which has less in that region, more work done during the region where you actually run the engine for the rest of its life.
So lets revisit a few things, what do we want to achieve?
Seat the rings?
Keep CHTs cooler?
Have high mean pressures with low peak pressures?
Peak pressures out of the choke area?
Keep the combustion chamber & oil cleaner?
So the choice is do it one way or the other. Its your engine, do what you like with it!
The area under the curve representing Mean effective pressure over a wider range, and further from the choke area.
At the nominal recommended 75% power or 80% power or whatever number you choose, the MAEN effective pressure is the determining factor is it not? As it is it is the mean pressure we want and not a peak.
The cylinder and rings have no idea what ROP or LOP is or means. They don't care even if they could care. All they care about is pressure, and they would not care how it is achieved.
By your logic why not run in the engine at 50dF ROP at 75% to 85% power? Draw your red lines on our graph and that now supports your argument even better.
For every bit of area under the curve on the left of the redline, to achieve the same HP, there is wastage on the right side. (Work in Vs Work out) Prior to your red lines starting at the peaks, there is a lot of high pressure over a very small distance travelled in the choke area. Compared to the green trace, which has less in that region, more work done during the region where you actually run the engine for the rest of its life.
So lets revisit a few things, what do we want to achieve?
Seat the rings?
Keep CHTs cooler?
Have high mean pressures with low peak pressures?
Peak pressures out of the choke area?
Keep the combustion chamber & oil cleaner?
So the choice is do it one way or the other. Its your engine, do what you like with it!
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BillL
Well Known Member
Dan, you have missed the point.
The area under the curve representing Mean effective pressure over a wider range, and further from the choke area.
At the nominal recommended 75% power or 80% power or whatever number you choose, the MAEN effective pressure is the determining factor is it not? As it is it is the mean pressure we want and not a peak.
The cylinder and rings have no idea what ROP or LOP is or means. They don't care even if they could care. All they care about is pressure, and they would not care how it is achieved.
By your logic why not run in the engine at 50dF ROP at 75% to 85% power? Draw your red lines on our graph and that now supports your argument even better.
For every bit of area under the curve on the left of the redline, to achieve the same HP, there is wastage on the right side. (Work in Vs Work out) Prior to your red lines starting at the peaks, there is a lot of high pressure over a very small distance travelled in the choke area. Compared to the green trace, which has less in that region, more work done during the region where you actually run the engine for the rest of its life.
So lets revisit a few things, what do we want to achieve?
Seat the rings?
Keep CHTs cooler?
Have high mean pressures with low peak pressures?
Peak pressures out of the choke area?
Keep the combustion chamber & oil cleaner?
So the choice is do it one way or the other. Its your engine, do what you like with it!
OK, so it is good that the peak pressure is lower and the pressure on the down stroke, (to the right of PCP) is higher, it helps the break-in as it = force against the cylinder wall. BUT, between TDC and PCP the pressure is lower - does that not adversely affect the break-in along this section of cylinder?
Are you just saying that this region of juste before and after PCP where the pressure is highest at 50dROP is better off with lower wear (break-in) relative to the other regions, so as to better balance the break-in process?
David, I think that when you say "higher MEP" is better that that peak lacks sufficient detail to understand why. Do you mean that break-in and resulting life of the engine would be improved if we hit the ideal of a fixed pressure all along the full stroke?
Thanks for your insights. I spent a decade ( at least) in engine performance and development, but mostly on diesel engines, some on natural gas. Not so much on the air-cooled spark ignited, only a couple.
RV10inOz
Well Known Member
Sorry if I am confusing you, and despite the snide comments of others this is one reason why I keep saying to gain a better understanding it takes 2.5 days in a class room, and that is why the course is still running 13 years later and with bigger numbers than ever. It is just hard to teach it all in an internet post without confusing someone.
Happy to have a chat via Skype one day. You could teach me a few things too!
"Mean effective pressure over a wider range"? Hmmm....
Consider the equation for BMEP:
BMEP = (brake HP x 792,000)/(displacement x RPM)
The 792K is a constant. Displacement and RPM are assumed to be fixed in the chart example, leaving brake HP as the only variable. We know the 50 LOP setting won't result in rated power, thus BMEP must be lower.
Range? The range extends from the pressure peak until exhaust valve opening. Exhaust valve opening is the same for either choice, thus the setting with the earlier peak has the wider range.
"Further from the choke area"? The choke in a Lycoming cylinder extends roughly 2 inches from the top. Given a 4.375" stroke and a 6.75" connecting rod, the piston's cylinder travel (from TDC) is 0.086" a 14 ATDC (the location of the rich peak in this example) and 0.248" at 24 ATDC (the location of the 80 LOP peak). The difference is little more than an 1/8", and either choice is well within the choke area. Not that it matters a heck of a lot. The whole point of having a choke when measured cold is to have a straight cylinder at operating temperature.
No. BMEP is an abstract yardstick useful in discussion of power (see the equation). It is nothing like actual ring pressure.
High CHT.
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RV10inOz
Well Known Member
Dan,
BMEP is as you say a useful yardstick for HP, I agree, however, despite what your mind is thinking I am saying, I am not referring to BMEP when I talk about the mean average cylinder pressure. I am assuming that whether a full Rich or 80dF LOP setting is used, that the comparison is at the same HP.
If as you say consider that "We know the 50 LOP setting won't result in rated power, thus BMEP must be lower." and this is a statement of fact, which is why I am trying to have an apples v apples comparison. That will mean perhaps a 2000' Vs 4500' with one LOP and one ROP.
So your point is irrelevant in terms of your post above.
What we are interested in is the average pressure over a sweep of the cylinder, and if you have a much higher peak in one region, to get the same average, from the same power setting, you will be getting less over the rest.
So just visually comparing the blue trace with the green over the range from 60degrees either side of TDC, one would appear to have a meaningful pressure over a wider sweep than the other, and one has a more severe peak than the other.
Ahhhh and what would cause that high CHT I wonder.
Just lucky we are not trying to break in a diesel engine, as they run LOP
So the choice is do it one way or the other. Either is valid. There are advantages in one. Its your engine, do what you like with it!
BMEP is as you say a useful yardstick for HP, I agree, however, despite what your mind is thinking I am saying, I am not referring to BMEP when I talk about the mean average cylinder pressure. I am assuming that whether a full Rich or 80dF LOP setting is used, that the comparison is at the same HP.
If as you say consider that "We know the 50 LOP setting won't result in rated power, thus BMEP must be lower." and this is a statement of fact, which is why I am trying to have an apples v apples comparison. That will mean perhaps a 2000' Vs 4500' with one LOP and one ROP.
So your point is irrelevant in terms of your post above.
What we are interested in is the average pressure over a sweep of the cylinder, and if you have a much higher peak in one region, to get the same average, from the same power setting, you will be getting less over the rest.
So just visually comparing the blue trace with the green over the range from 60degrees either side of TDC, one would appear to have a meaningful pressure over a wider sweep than the other, and one has a more severe peak than the other.
Ahhhh and what would cause that high CHT I wonder.
Just lucky we are not trying to break in a diesel engine, as they run LOP
So the choice is do it one way or the other. Either is valid. There are advantages in one. Its your engine, do what you like with it!
Total duration of pressure is identical: ignition to exhaust valve opening. Average pressure is higher for the rich mixture.
You like the retarded pressure between 23 and 60 ATDC. However, when appearances are quantified, the maximum difference is 6 degrees of crank rotation, 34 vs 40 degrees. The difference in stroke position is 0.1741 inches. Put another way, you're claiming it is somehow superior if the same ring pressure is applied less than 3/16" further down a 4.375" stroke.
You go ahead and lead the real men (and brave girls) into the land of useless knob twiddle. I'll stick with conventional break-in; limited twiddle for low level climb, and leaning for max power to seat rings. LOP for economy cruise comes later in the new airplane process.
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RV10inOz
Well Known Member
Go to Ada and do it on the Dyno.
I bet it costs you 10% per trip of what it costs me. I bet you don't bother.
Hang on?..so how is the average higher for the rich mixture over the same time interval??? When generating the same HP (BMEP)
In that graph over that 6 degrees we are 500 vs 400 PSI.
The PEAK is higher, sure ???? I see why Walter gave up on VAF.
So the choice is do it one way or the other. Either is valid. There are advantages in one. Its your engine, do what you like with it!
I bet it costs you 10% per trip of what it costs me. I bet you don't bother.
Hang on?..so how is the average higher for the rich mixture over the same time interval??? When generating the same HP (BMEP)
In that graph over that 6 degrees we are 500 vs 400 PSI.
The PEAK is higher, sure ???? I see why Walter gave up on VAF.
So the choice is do it one way or the other. Either is valid. There are advantages in one. Its your engine, do what you like with it!
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BillL
Well Known Member
Let me throw this report into the discussion.
http://deepblue.lib.umich.edu/bitstream/handle/2027.42/26638/0000180.pdf
Use it with extreme caution. Remember that these reports are written with the researched knowledge of the writer of the day and was not necessarily a vetted work. Having read thousands of GM, CAT, SAE and SwRI reports on engines, I would say little truths sneak through, but many so called conclusions can be outright wrong in the general sense.
Also, ring and cylinder wear are very highly related to the materials of ring, bore, surface finishes (either rough or fine), heat treatment and core metallurgy of the materials in detail.
A truth in this report is wear and oil films from TDC down to BDC of stroke. Pretty fundamental. Some combination of higher pressure and slower sliding velocity yields more wear. Sometimes one or the other will prevail.
TDC is no motion, slightly lower (in stroke) pressure picks up (PCP) and then velocity comes in there to begin developing some oil film effects. There is some transition. Clear definition of this transition point, and quantifiable effects on either "wear" or "break-in" seems to the at the core of this (off topic) discussion. [I would not call it an argument as this is just the type of discussion(s) engineering minded people love to have as it always promotes better understanding and communications when professionally carried to the end.]
In the details, it may have little measurable differences between ROP, and LOP break-in procedure. But in theory, lower pressures in the early part of the stroke, and higher pressures as the velocity picks up would improve the break-in wear down lower in the stroke. Again, quantifying one against the other and a clear measurement of the transition point might be the data we are seeking, cockpit time management notwithstanding.
My 2 cents, as Stein would say.
http://deepblue.lib.umich.edu/bitstream/handle/2027.42/26638/0000180.pdf
Use it with extreme caution. Remember that these reports are written with the researched knowledge of the writer of the day and was not necessarily a vetted work. Having read thousands of GM, CAT, SAE and SwRI reports on engines, I would say little truths sneak through, but many so called conclusions can be outright wrong in the general sense.
Also, ring and cylinder wear are very highly related to the materials of ring, bore, surface finishes (either rough or fine), heat treatment and core metallurgy of the materials in detail.
A truth in this report is wear and oil films from TDC down to BDC of stroke. Pretty fundamental. Some combination of higher pressure and slower sliding velocity yields more wear. Sometimes one or the other will prevail.
TDC is no motion, slightly lower (in stroke) pressure picks up (PCP) and then velocity comes in there to begin developing some oil film effects. There is some transition. Clear definition of this transition point, and quantifiable effects on either "wear" or "break-in" seems to the at the core of this (off topic) discussion. [I would not call it an argument as this is just the type of discussion(s) engineering minded people love to have as it always promotes better understanding and communications when professionally carried to the end.]
In the details, it may have little measurable differences between ROP, and LOP break-in procedure. But in theory, lower pressures in the early part of the stroke, and higher pressures as the velocity picks up would improve the break-in wear down lower in the stroke. Again, quantifying one against the other and a clear measurement of the transition point might be the data we are seeking, cockpit time management notwithstanding.
My 2 cents, as Stein would say.
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Firstly, this thread has been totally hijacked.
Secondly........yaaaaawn........
I'm not flying yet and I have very little piston time in my 17,000 hours. However, I've done a lot of research on breaking in the engine and how to treat it once it's run in. You guys are discussing minutae which makes, as far as I can see, no practical difference. I can almost smell the testosterone as you all try and prove your points.
Treat the engine right, run it in IAW Lycoming instructions and I am pretty sure the life will be +/- 5% of any of this clever stuff you can do.
Flame suit on..........
Secondly........yaaaaawn........
I'm not flying yet and I have very little piston time in my 17,000 hours. However, I've done a lot of research on breaking in the engine and how to treat it once it's run in. You guys are discussing minutae which makes, as far as I can see, no practical difference. I can almost smell the testosterone as you all try and prove your points.
Treat the engine right, run it in IAW Lycoming instructions and I am pretty sure the life will be +/- 5% of any of this clever stuff you can do.
Flame suit on..........
RV10inOz
Well Known Member
Paul, thread drifted not hijacked. Glass half full!
No testosterone involved, but it seems that whenever something is alternate to the establishment such as different from IAW Lycoming instruction manual XYZ and is offered as a better solution, if that option is available to you, it is hounded down.
The rings can't tell LOP from ROP, Diesels can't tell either. It just so happens that many things we thought were true, myself included, but more importantly George and co, have discovered that they were not as first thought.
The irony is that all the good advice (I assume it is, it sounds plausible) that DanH gives on cooling airflow and drag etc, is as best I can tell in many instances contrary to conventional wisdom. The same things that George and Walter discovered while doing several STC jobs relating to engine cooling airflow work etc for Turbo Beech and Cirrus.
There are a couple of approaches here, if you can do one, it gets the job gone cleaner and cooler. As GB has said himself he keeps looking and is yet to see a downside. (And he looks more than most ever have.)
So no need for the flame suit
How was the cricket?
No testosterone involved, but it seems that whenever something is alternate to the establishment such as different from IAW Lycoming instruction manual XYZ and is offered as a better solution, if that option is available to you, it is hounded down.
The rings can't tell LOP from ROP, Diesels can't tell either. It just so happens that many things we thought were true, myself included, but more importantly George and co, have discovered that they were not as first thought.
The irony is that all the good advice (I assume it is, it sounds plausible) that DanH gives on cooling airflow and drag etc, is as best I can tell in many instances contrary to conventional wisdom. The same things that George and Walter discovered while doing several STC jobs relating to engine cooling airflow work etc for Turbo Beech and Cirrus.
There are a couple of approaches here, if you can do one, it gets the job gone cleaner and cooler. As GB has said himself he keeps looking and is yet to see a downside. (And he looks more than most ever have.)
So no need for the flame suit
How was the cricket?
How was the cricket?
Ouch!!!!!!!
