No, the world is just as complicated as you want it to be.
I have been around engines all my life. Car engines, sports car engines, truck engines, airplane engines. I even overhauled a couple of Alfa Romeo sports car engines … when i was still a student.
The first engine of our Warrior broke down after 400 hours. The next one flew 1600 hours without any problems.
My father was an engine man his whole life, at one point when he was young he was the quality manager for Volkswagen for a part of Europe. He could take a VW engine apart blindfolded, and he did, and he knew everything about engines. He had two airplanes and he knew everything about the Lycoming engine too.
His opinion was always that we have less influence on engine life than we want to admit. Regular oil and filter change, yes … preheating very cold engines, yes … warm up engines, yes … but that’s about it.
Of course, if it’s fun for you – you can think about all that stuff day and night. But you can also just FLY and repair the damn engine when it breaks.
:-)
Presumably ring flutter refers to the ring oscillating between upper and lower walls of the ring groove due to inertia and cylinder wall drag. You could then suppose that the force to restrain the oscillation might at some points in the cycle be reduced by combustion pressure acting on the upper surface of the top ring, biasing the net force ‘downward’. Lower rpm and lighter, thinner rings would also reduce (both) inertial forces on the ring and wall drag.
Although (in common it seems with other posters 
) I haven’t done the slightest calculation to check that hypothesis for the apparently unknown definition and effects of ring flutter, it’s hard to imagine that cylinder gas pressure for any method of pilot operation could load the ring downward enough over all 4 strokes of the cycle so that it would remain in continuous contact with the bottom of the ring groove. What about during intake stroke? As Peter says, technical understanding is usually not simple. Maybe the ring moving from top to bottom in its groove is harmless in certain parts of the 4 stroke cycle, but harmful in others because the forces are higher then, but can be reduced by cylinder pressure. I would add that technical understanding in total detail is not always required and is mostly elusive in real world engineering. Lycoming may know enough based purely on experience and looking at worn parts to make a general recommendation.
PS Reading the “example” link in Peter’s original post (which I had not read prior to my prior post) you find the following statement…
“As the piston approaches bottom dead centre on the exhaust stroke, the combination of inertia forces acting on the piston ring and forces acting on the ring owing to the pressure differential across it act to push the piston ring up against the top side of the ring groove. This effectively causes a seal between the ring and the top of the groove”
This is poorly worded, amongst other things I’m guessing the author means top dead center, at the end of the upward exhaust stroke. That aside, it seems to imply that the sealing capability at the ring/cylinder interface is lost at the end of the exhaust stroke, with the piston ‘jerking’ downwards and the ring ending up sealed against the top of the groove so that cylinder pressure no longer acts on the inside diameter of the the ring to push it against the cylinder wall.
The question is then whether higher manifold pressure and cylinder pressure during the power stroke would result in higher residual pressure at the end of the exhaust stroke, acting against the inertia of the ring at that stage.
I think as pilots the only thing we can do to have perfectly seated piston rings is to follow the recommended break in procedure: higher cruise power setting at lower altitudes for the recommended time … but else?
I did not mean these things are “simple” but that it we have little influence on them.
As I wrote before, there is some indirect evidence that at low MPs you get increased contamination of the oil ring(s), and that this is a very gradual process.
It is also reversible (within some bounds) otherwise every engine that did a high altitude flight would need to be overhauled, and that is clearly nonsense since the fact would become widely known.
As regards piston groove damage (widening) due to this alleged “flutter” I have emailed some engine people in the USA where there is a lot more experience, asking if they have seen it.
When googling for this stuff, one finds a load of stuff which is a recycled version of other stuff which is a recycled version of yet other stuff. I have not found any primary data. That is a typical signature of an OWT. But, I don’t doubt that there is something in it. Whether it matters operationally is the question.
The break-in procedure requirement is not in doubt but is completely unrelated to this discussion.
The break-in procedure requirement is not in doubt but is completely unrelated to this discussion.
By which you probably mean that the quality of the seating of the rings has nothing to do with their tendency to flutter or not? I would have thought there’s a direct relation.
I prefer German engine engineering ;-), so here’s a link to a piston engine damage brochure by the MAHLE company, the main supplier of pistons etc for german car engines. A lot of this information is transferrable to aircraft engines.
http://epaper.mahle.com/mc/onlineCatalogue/2062863636375&lang=de
I prefer German engine engineering ;-), so here’s a link to a piston engine damage brochure by the MAHLE company, the main supplier of pistons etc for german car engines. A lot of this information is transferrable to aircraft engines.
I have gone through that doc and cannot find anything applicable to this topic. Is it in there somewhere?
By which you probably mean that the quality of the seating of the rings has nothing to do with their tendency to flutter or not?
It might be, but that’s a different debate i.e. whether the susceptibility of oil ring contamination is dependent on how well the engine was broken in. Probably there is a relationship because if you don’t do that phase right, you get glazed cylinder bores and high oil consumption because the oil rings are a lot less effective.
Is it a good time to mention German engine engineering? I don’t think ring flutter is a good description because it implies the ring move up and down in their groove. I don’t think that is the affect, the internal pressure expands the ring tightly onto the bore probably on the power stroke which is why you must run an engine heard to break it in. Low internal pressures don’t push the rings hard enough against the bore so over time they glaze the bore and/or start leaking. This is what has happened to Peters engine in my opinion.
The fluttering is movement on and off the bore not up and down in the groove. And, yes they flutter on every cycle but you don’t want that on the power stroke. High internal pressure stops that.
You can break in an engine perfectly then spend the next few hundred hours at 45% power and you will likely, eventually, suffer either glazing or ring bypassing or both. These engines are designed to be run hard and hot.
Is it a good time to mention German engine engineering?
Yes, it is, despite some criminal activities at VW (as pilots we should be aware about the way stuff like that is transported by the media …)
