- Joined
- Oct 14, 2017
- Messages
- 2,790
- Reaction score
- 2,976
Probably the best part about sites such as this is the exchange of information and experiences. Now sometimes the conclusions drawn from these events leave me scratching my head, but they all are useful and interesting none the less and this brings me to the point of this post. A lot has been hashed back and forth over the various methods to achieve a long trouble free life out of our engines, some claim the path to salvation is by leaning the heck out of it, typically citing the reductions in CHT’s as the proof of the viability of the concert or perhaps the experience of operators of large radial engine airliners of yesteryear, and even Charles Lindbergh. Others say hogwash, run ROP or you will “burn up” your engine.
If nothing else it make for interesting reading, and of course each side will cite examples that reinforce their particular point of view. Nothing new there, but look a bit further and a couple things do stand out that unfortunately rarely are mentioned. One of the first is how the term “data” is used to describe opinion from what is often a minuscule sample pool or, one that is so far out of context the relevance is laughable; the old airliner ops come to mind. Another is the one fact everyone does seem to agree on, that the more you run your engine the more trouble free hours you can expect. Now this last one is interesting because if it really was about mixture management that than the frequency of operation shouldn’t matter, but clearly id does, so why? Now don’t get me started on the “most of the wear is at start-up” thing, if that was actually a valid consideration flight school airplane that rarely run for more than an hour at a time would have horrible service records when in fact they have some of the best, or how about the new cars that shut the engine off as soon as you stop for more than a couple seconds? If it really was the dreaded start that accounts for most the wear, these cars would have service lives measured in weeks rather than years. But I digress, back to the TBO issue. So what commonality is left that can explain the fact that no matter how you operate your engine, the more you fly it the more hours you can expect it to run? Corrosion, plain and simple; the more time it spends flying the less time it spends rusting.
Think about this from a minute, almost never is the service life of an aircraft engine cut short due to bearing wear, it is almost always issues with the top end, parts of the engine that are prone to corrosion as soon as you shut down. Now not just nasty rust pits you can see without your glasses, but rather the ultra-thin flash corrosion that forms quickly on an unprotected surface, especially one that contains iron like your cylinder walls, and valves. In turn this abrasive mixture of oil and rust particles does a number on your rings and valve guides/seats upon your next flight.
So how does the whole LPO/ROP thing figure into this? Well for one thing we may want to re-think the notion that cleaner is automatically better, if the deposits within the combustion chamber and on the valves are helping protect from the corrosive effects of moisture and oxygen then perhaps that squeaky clean bore-scope shot really isn’t all that desirable after all. Diesel engines by comparison are nasty inside, and they last a magnitude longer than aircraft engines even though they have a lot of design and operation similarities to our aircraft engines. In my early years I operated a number of air-cooled Deutz diesels, typical TBO? 10-20,000 hrs. Again these engines ran for weeks at a time without being shut down. Perhaps the great TBO’s cited for the old airliners that is often the “data” quoted as proof for the benefits of LOP ops has nothing to do with the mixture, rather it is a reflection of the engines spending more time in the air than on the ground? If nothing else it bears consideration.
Another thing I see discussed a lot is the lowering of internal cylinder pressures as being a good thing and is often cited as a significant benefit to LOP ops. Now if broken crankshafts, cracked cylinder barrels and tuliped valves were common problems on our little flat GA engines I would most certainly agree with this, but the vast majority on engine problems I see discussed doesn’t appear to have any correlation to cylinder pressure, one way or the other.
We all have seen both sides describe how their methodology is better because they ran a couple engines well past TBO on some plane. Now think about that for a minute, a couple engines well past TBO?? That’s a lot of time spent in the air, more than a handful of “avenge” recreational pilots will accumulate in a lifetime.
Jeff
If nothing else it make for interesting reading, and of course each side will cite examples that reinforce their particular point of view. Nothing new there, but look a bit further and a couple things do stand out that unfortunately rarely are mentioned. One of the first is how the term “data” is used to describe opinion from what is often a minuscule sample pool or, one that is so far out of context the relevance is laughable; the old airliner ops come to mind. Another is the one fact everyone does seem to agree on, that the more you run your engine the more trouble free hours you can expect. Now this last one is interesting because if it really was about mixture management that than the frequency of operation shouldn’t matter, but clearly id does, so why? Now don’t get me started on the “most of the wear is at start-up” thing, if that was actually a valid consideration flight school airplane that rarely run for more than an hour at a time would have horrible service records when in fact they have some of the best, or how about the new cars that shut the engine off as soon as you stop for more than a couple seconds? If it really was the dreaded start that accounts for most the wear, these cars would have service lives measured in weeks rather than years. But I digress, back to the TBO issue. So what commonality is left that can explain the fact that no matter how you operate your engine, the more you fly it the more hours you can expect it to run? Corrosion, plain and simple; the more time it spends flying the less time it spends rusting.
Think about this from a minute, almost never is the service life of an aircraft engine cut short due to bearing wear, it is almost always issues with the top end, parts of the engine that are prone to corrosion as soon as you shut down. Now not just nasty rust pits you can see without your glasses, but rather the ultra-thin flash corrosion that forms quickly on an unprotected surface, especially one that contains iron like your cylinder walls, and valves. In turn this abrasive mixture of oil and rust particles does a number on your rings and valve guides/seats upon your next flight.
So how does the whole LPO/ROP thing figure into this? Well for one thing we may want to re-think the notion that cleaner is automatically better, if the deposits within the combustion chamber and on the valves are helping protect from the corrosive effects of moisture and oxygen then perhaps that squeaky clean bore-scope shot really isn’t all that desirable after all. Diesel engines by comparison are nasty inside, and they last a magnitude longer than aircraft engines even though they have a lot of design and operation similarities to our aircraft engines. In my early years I operated a number of air-cooled Deutz diesels, typical TBO? 10-20,000 hrs. Again these engines ran for weeks at a time without being shut down. Perhaps the great TBO’s cited for the old airliners that is often the “data” quoted as proof for the benefits of LOP ops has nothing to do with the mixture, rather it is a reflection of the engines spending more time in the air than on the ground? If nothing else it bears consideration.
Another thing I see discussed a lot is the lowering of internal cylinder pressures as being a good thing and is often cited as a significant benefit to LOP ops. Now if broken crankshafts, cracked cylinder barrels and tuliped valves were common problems on our little flat GA engines I would most certainly agree with this, but the vast majority on engine problems I see discussed doesn’t appear to have any correlation to cylinder pressure, one way or the other.
We all have seen both sides describe how their methodology is better because they ran a couple engines well past TBO on some plane. Now think about that for a minute, a couple engines well past TBO?? That’s a lot of time spent in the air, more than a handful of “avenge” recreational pilots will accumulate in a lifetime.
Jeff
