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-   -   Shudder / vibe lasts about 1 second (https://vansairforce.net/community/showthread.php?t=107131)

selhardt 12-14-2013 06:22 PM

Gonna have to renew for 2014 to see how this comes out
 
Rv10inoz makes me weary.

Pay for the course - all secrets of the universe will be revealed....

RV10inOz 12-14-2013 07:05 PM

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. :cool: 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 12-14-2013 07:12 PM

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

aerhed 12-14-2013 07:20 PM

The pressure results from the ring land above the ring driving down on the side of the ring, whose profile (keystone on most of ours) creates torsion which increases pressure on the cylinder wall.....methinks.

AlexPeterson 12-14-2013 08:28 PM

Quote:

Originally Posted by RV10inOz (Post 834657)
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

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.

DanH 12-15-2013 09:07 AM

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.


Bavafa 12-15-2013 09:22 AM

Quote:

Originally Posted by DanH (Post 834768)
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.

DaAV8R 12-15-2013 12:07 PM

Ring Seating
 
Nice post Dan.

This is consistent with what I have always done. Fly the $#!% out of it and vary the power from time to time.

It's all a lot of data to simply say, "fly it like you stole it" :)

aerhed 12-15-2013 05:09 PM

Thanks Dan, I forgot all about the gas pressure behind the rings. Some things go glimmering if you don't, think about them for a few years.

RV10inOz 12-15-2013 06:29 PM

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. :eek:

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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