Commercial Pilots who don't know about piston engines
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extralite:
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Perhaps the reluctance to run lean is from what we have all learned from early on about engine. Running lean can cause knocking..pre-detonation and damage to valves.
How are leaded aero engines immune to this?
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What we ACTUALLY learned (or should have learned) is that running "not rich enough" on the rich side was the cause of the above issues. Running not rich enough does result in high CHTs and high ICPs. It does NOT cause knocking, pre-ignition or damage to the vales, per se, but it does put the engine at a higher risk for those things.
Aero engines are not immune to any of the problems of gasoline, piston engines. It's just that while the observations may be accurate, the assignment of causality is flawed.
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Perhaps the reluctance to run lean is from what we have all learned from early on about engine. Running lean can cause knocking..pre-detonation and damage to valves.
How are leaded aero engines immune to this?
***
What we ACTUALLY learned (or should have learned) is that running "not rich enough" on the rich side was the cause of the above issues. Running not rich enough does result in high CHTs and high ICPs. It does NOT cause knocking, pre-ignition or damage to the vales, per se, but it does put the engine at a higher risk for those things.
Aero engines are not immune to any of the problems of gasoline, piston engines. It's just that while the observations may be accurate, the assignment of causality is flawed.
FFS. It's because no one's invented a perpetual motion machine yet. 
Ya can't save increasingly massive amounts of fuel and go increasingly faster. Get it?
Ya can't save increasingly massive amounts of fuel and go increasingly faster. Get it?
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It's easy to know your power output when LOP. If you have an 8.5:1 compression ratio, simply multiply 14.9 x FF in gph = HP output. Other CRs have different multipliers. For example, the TC engines with 13.75:1 CRs, have a multiplier of 13.75.
ROP power output is a little more complicated to calculate and the POH numbers are usually generalizations, not actual numbers.
I can promise you that the laws of physics will insist that 70% power ROP and 70% power LOP WILL produce the same TAS. BTDT thousands of times.
As for taking longer when slower, well, sure, but the 25% fuel savings offset the 3% loss in TAS quite nicely. If you need to get there 3% faster, you'd better not accept single vector from ATC.
ROP power output is a little more complicated to calculate and the POH numbers are usually generalizations, not actual numbers.
I can promise you that the laws of physics will insist that 70% power ROP and 70% power LOP WILL produce the same TAS. BTDT thousands of times.
As for taking longer when slower, well, sure, but the 25% fuel savings offset the 3% loss in TAS quite nicely. If you need to get there 3% faster, you'd better not accept single vector from ATC.
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CTRE
What aircraft do you fly and how do you fly it now? What speeds do you get? With this we can talk in real terms for your application.
Happy to do the mental maths to help you out. What I suspect is that if you lose way too much speed you are simply flying too far LOP. This is not uncommon. I can help you with this if you would like to detail what you have and how you are doing it.
This could make for an educational example for others watching.
What aircraft do you fly and how do you fly it now? What speeds do you get? With this we can talk in real terms for your application.
Happy to do the mental maths to help you out. What I suspect is that if you lose way too much speed you are simply flying too far LOP. This is not uncommon. I can help you with this if you would like to detail what you have and how you are doing it.
This could make for an educational example for others watching.
"160 LOP" cleared? 160?
As others have said, 70% power ROP is 70% power LOP. But here's the constraint if you're running a normally aspirated engine: You can't "add" manifold pressure if you're already at wide open throttle. (That's why the turbo-normalised engines are so popular.)
For my part, I'm happy to save about 15 litres an hour in return for about 6 knots TAS.
I fly lots of long legs. To make the maths simple, let's assume it takes me 15 minutes to climb to 8,500', after which I've 450 nms to go. Again to make the maths simple, let's assume it's nil wind and the GS will remain the same in the descent.
I'm going to use the same engine management technique to get to 8,500', irrespective of whether I'm going to choose subsequently to cruise LOP, ROP or at peak. So we can ignore the climb consumption and GS.
450 nms at 160 = 2.8 hours X 60 litres per hour = 168 litres
450 nms at 150 = 3.0 hours X 45 = 135 litres.
I'm happy to spend 12 minutes to save 33 litres. (In reality, flight after flight, the TAS sacrifice isn't as high as 10 knots and the fuel flow difference is greater than 15 litres per hour.)
Obviously there's not much of a difference if all you do is flog around in the circuit or go for 2 hour jollies for the hamburger on a Sunday.
But there's a key point that must be understood here, because it points up why some people get wider TAS differences and narrower fuel flow changes. When I run ROP, I run sufficiently ROP. That means I'm way cooler than 50 degrees F ROP if I'm running ROP.
If, instead, I were in the habit of setting my mixture to 50 degrees F ROP, I would save only about 10 litres per hour and lose about 15 knots' TAS running LOP (I'm rounding here). But I don't like flogging my engine to death at 50 degrees F ROP. So if you want to compare FF and TAS apples with apples, you have to compare sufficient ROP with sufficient LOP.
As others have said, 70% power ROP is 70% power LOP. But here's the constraint if you're running a normally aspirated engine: You can't "add" manifold pressure if you're already at wide open throttle. (That's why the turbo-normalised engines are so popular.)
For my part, I'm happy to save about 15 litres an hour in return for about 6 knots TAS.
I fly lots of long legs. To make the maths simple, let's assume it takes me 15 minutes to climb to 8,500', after which I've 450 nms to go. Again to make the maths simple, let's assume it's nil wind and the GS will remain the same in the descent.
I'm going to use the same engine management technique to get to 8,500', irrespective of whether I'm going to choose subsequently to cruise LOP, ROP or at peak. So we can ignore the climb consumption and GS.
450 nms at 160 = 2.8 hours X 60 litres per hour = 168 litres
450 nms at 150 = 3.0 hours X 45 = 135 litres.
I'm happy to spend 12 minutes to save 33 litres. (In reality, flight after flight, the TAS sacrifice isn't as high as 10 knots and the fuel flow difference is greater than 15 litres per hour.)
Obviously there's not much of a difference if all you do is flog around in the circuit or go for 2 hour jollies for the hamburger on a Sunday.
But there's a key point that must be understood here, because it points up why some people get wider TAS differences and narrower fuel flow changes. When I run ROP, I run sufficiently ROP. That means I'm way cooler than 50 degrees F ROP if I'm running ROP.
If, instead, I were in the habit of setting my mixture to 50 degrees F ROP, I would save only about 10 litres per hour and lose about 15 knots' TAS running LOP (I'm rounding here). But I don't like flogging my engine to death at 50 degrees F ROP. So if you want to compare FF and TAS apples with apples, you have to compare sufficient ROP with sufficient LOP.
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At normal cruise altitudes, the difference between the Best Power mixture (80dF ROP), and best economy (BSFC(min) which changes with power) is about 3gph for a 3 knot speed loss. We've tested this thousands of times. It's always very close to those numbers. If you are losing more than 3-4 knots TAS, the mixture is leaner than optimal. It's not hurting anything to do so, because all that is happening is a loss of performance.
So, as Lead Ballon has pointed out, that's about 25% fuel savings (with a much happier engine) for a 5% speed loss. What's not to like?
So, as Lead Ballon has pointed out, that's about 25% fuel savings (with a much happier engine) for a 5% speed loss. What's not to like?
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Burned valves are caused by machining errors at time of installation, the defects take time to appear, usually 600 hours +600/-200 and any mixture abuse is likely to speed up the process due heat and pressure, but the defect is there from the start and not pilot induced.
Or perhaps if you inspected every burned valve and found pre-existing machining errors in all.
I doubt that either has been done. This is the sort of blanket statement that turned me from a LOP believer 10 years ago when I first read John Deakin's columns to an APS sceptic now.
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i have heard this argument quite a few times, "running LOP burns valves!" yet how can a temperature, thats exactly the same if on the Rich side of peak, cause burnt valves, when the same temp on the rich side wont?
peak is peak, it can go no higher! (thats why its the peak)
so 50 deg lower on the RICH side is exactly the same as 50 deg lower on the lean side.. so it cant be temperatures on the lean side that cause burnt valves.
peak is peak, it can go no higher! (thats why its the peak)
so 50 deg lower on the RICH side is exactly the same as 50 deg lower on the lean side.. so it cant be temperatures on the lean side that cause burnt valves.
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Andrewr …….Is that all it took? 
If you ask a few of the leading engine builders around who actually know their stuff, and I am not one of them, the likes of Andrew Denyer, David Paynter, Bill Cunningham, the Barret's you will find the truth.
They find the exact same failures in ROP run cylinders, so how could it be LOP ops? They also comment on the deposits not helping and may in fact be accelerating guide wear.
I hope you can restore your faith in science and data now.
I am sure Walter can add to this if he reads this.
If you ask a few of the leading engine builders around who actually know their stuff, and I am not one of them, the likes of Andrew Denyer, David Paynter, Bill Cunningham, the Barret's you will find the truth.
They find the exact same failures in ROP run cylinders, so how could it be LOP ops? They also comment on the deposits not helping and may in fact be accelerating guide wear.
I hope you can restore your faith in science and data now.
I am sure Walter can add to this if he reads this.
Andrew, I can give you anecdotal evidence. I had a O300 rebuilt and balanced with all new cylinders fitted. This engine would not run rough when it was leaned out, it would simply loose power. When I had favourible conditions I would often see fuel flows around 26 litres per hour with the throttle wide open. Within 250 hours, all cylinders had been off due to leaking exhaust valves. Some were fixed under warrantee, some were fixed by a shop that specialised in vintage motorcycle repairs. (Taken there by my LAME)
I did not change the way this engine was operated and went on to do aother 600 odd trouble free hours in it. The new owner, who I keep in contact with, has had no issues either. Apart from the valve issues this has been an exceptional engine.
All evidence thus would tend to point at poor cylinder manufacturing.
I did not change the way this engine was operated and went on to do aother 600 odd trouble free hours in it. The new owner, who I keep in contact with, has had no issues either. Apart from the valve issues this has been an exceptional engine.
All evidence thus would tend to point at poor cylinder manufacturing.
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50 deg lower on the RICH side is exactly the same as 50 deg lower on the lean side
I would expect that if damage to valve sealing surfaces occurs, it would be most influenced by the gas temperature at the instant the valve begins to open and the temperature of the first perhaps <1% of gas to exit. The average gas temperature in the exhaust is not necessarily indicative.
Measurements I would be interested to see:
- Instantaneous EGT in the exhaust port through the combustion cycle vs measured EGT as the mixture changes
- Temperature of the valve head vs EGT as the mixture changes
Let me get this straight, Andrew
If someone makes the blanket statement that running LOP causes burnt valves, that's OK.
If someone makes the blanket statement that manufacturing defects cause burnt valves, that's not OK.
If you wish to ignore the science and data that prove that ROP is where you can give your engine the hardest beating you can give it, go forth and give it that beating. If your engine happens not to suffer burnt valves or other problems, you can tell yourself that it's because you don't run LOP.
Funny thing too is that the burnt valve problem is confined almost exclusively to CMI engines and not Lycomings. Clearly nothing to do with manufacture and everything to do with LOP?
Ignorance is indeed bliss.
The alternative is to register on a blog like BeechTalk, and do some research about what's happening in a first world GA country. The poor quality control of CMI cylinder manufacture is widely understood and discussed in detail, and the SOP of people considering cylinder replacement is to send the replacement to a competent engine maintenance organisation first, to get the valves installed properly. Those people are not doing that for fun or because their astrologer advised them to.
If someone makes the blanket statement that running LOP causes burnt valves, that's OK.
If someone makes the blanket statement that manufacturing defects cause burnt valves, that's not OK.
If you wish to ignore the science and data that prove that ROP is where you can give your engine the hardest beating you can give it, go forth and give it that beating. If your engine happens not to suffer burnt valves or other problems, you can tell yourself that it's because you don't run LOP.
Funny thing too is that the burnt valve problem is confined almost exclusively to CMI engines and not Lycomings. Clearly nothing to do with manufacture and everything to do with LOP?
Ignorance is indeed bliss.
The alternative is to register on a blog like BeechTalk, and do some research about what's happening in a first world GA country. The poor quality control of CMI cylinder manufacture is widely understood and discussed in detail, and the SOP of people considering cylinder replacement is to send the replacement to a competent engine maintenance organisation first, to get the valves installed properly. Those people are not doing that for fun or because their astrologer advised them to.
The alternative is to register on a blog like BeechTalk, and do some research about what's happening in a first world GA country. The poor quality control of CMI cylinder manufacture is widely understood and discussed in detail, and the SOP of people considering cylinder replacement is to send the replacement to a competent engine maintenance organisation first, to get the valves installed properly. Those people are not doing that for fun or because their astrologer advised them to.
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If someone makes the blanket statement that running LOP causes burnt valves, that's OK.
If someone makes the blanket statement that manufacturing defects cause burnt valves, that's not OK.
If someone makes the blanket statement that manufacturing defects cause burnt valves, that's not OK.
The statement that LOP does not cause burnt valves, and burnt valves are caused by manufacturing defects is more definite and I would be looking for evidence to support it.
Incidentally, I found a flight engineer's notes on operating the Pratt & Whitney R-4360 (one of APS's beloved radials):
R-4360Ops1
From those notes, when leaned at cruise power the ignition timing was advanced from 20 to 30 degrees which favored longer valve life.
Also, ignition timing advance maintained peak pressure at the most effective point as the mixture was leaned. Why then do APS say that it is a good thing to delay the peak pressure at cruise power (which is the same effect as retarded ignition timing)?
Everybody else I can find (including R-4360 operations) say that you want to advance the timing at cruise power compared to maximum power. APS want to effectively retard it...
Another thing arising from that document - APS tell us over and over that your Lycoming is effectively the same as a big radial. In this case it's obviously not - if you can't advance the ignition when LOP, that is a significant difference.
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450 nms at 160 = 2.8 hours X 60 litres per hour = 168 litres
450 nms at 150 = 3.0 hours X 45 = 135 litres.
450 nms at 150 = 3.0 hours X 45 = 135 litres.
How much fuel do you save? Are you sure that it is more than if you just reduced the throttle/rpm until you were at 150 knots while operating according to the engine manual?
My primary reason for running LOP is not to save the fuel, although that's a pleasant bonus. (The rounded fuel savings calcs are in my post, confirmed by many hundreds of hours of real world ops.)
My primary reason for running LOP is to save the engine.
I don't particularly care what the engine manual and POH say about settings. The engine and prop are rated to run at 2,700 and full power continuously, so I know that anything less than that isn't going to be prohibited. (There are no RPM range limitations.)
What I do know is the CHT for each cylinder, the EGT for each cylinder, the FF and TAS, +/- not much, at each point on the lean curve. I therefore know where on that curve I could give the engine the hardest beating I could give it, and when I'm not at that point.
There is no point in playing with MP of a normally aspirated injected engine like mine, unless I'm in the circuit or doing some low and slow sightseeing. I set wide open throttle at the start of the take off run and don't touch it again until joining the circuit at my destination. I'm a simple person and don't like unnecessary complications.
My primary reason for running LOP is to save the engine.
I don't particularly care what the engine manual and POH say about settings. The engine and prop are rated to run at 2,700 and full power continuously, so I know that anything less than that isn't going to be prohibited. (There are no RPM range limitations.)
What I do know is the CHT for each cylinder, the EGT for each cylinder, the FF and TAS, +/- not much, at each point on the lean curve. I therefore know where on that curve I could give the engine the hardest beating I could give it, and when I'm not at that point.
There is no point in playing with MP of a normally aspirated injected engine like mine, unless I'm in the circuit or doing some low and slow sightseeing. I set wide open throttle at the start of the take off run and don't touch it again until joining the circuit at my destination. I'm a simple person and don't like unnecessary complications.
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If anyone else has questions please fire away.
I want to know how you're getting 170 kt TAS at 10k LOP when 'book' figure should be closer to 160kt ROP.
..And why I only get about 154kt LOP on the -7!
Haydn
PS: Andrew, it's worth reviewing and marking the signifance of the brown curves in that set of curves that Jabba frequently posts.
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HC
That was well spotted. As you can see there was a fair amount of westerly wind, and some wave surfing going on. It would have been about TAS164 just prior to that. Don't get too upset by that. 
Yes Jabba,
I want to know how you're getting 170 kt TAS at 10k LOP when 'book' figure should be closer to 160kt ROP.
I want to know how you're getting 170 kt TAS at 10k LOP when 'book' figure should be closer to 160kt ROP.
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it's worth reviewing and marking the signifance of the brown curves in that set of curves that Jabba frequently posts.
All I know is that people keep posting their "fuel savings" from running LOP, and when you do the calculation it's no better than what you would expect from the speed reduction.
Here's the test we need to see:
Set your LOP 150 knot cruise and note the fuel flow.
Then set the recommended best economy setting and adjust the throttle for the same 150 knots (same rpm). How much does the fuel flow differ?
I know, this gives the highest temperatures and pressures etc...
BUT:
Temperature and pressure is what turns the prop around so it's not surprising that you get the best economy where temperatures and pressures are maximized for a particular fuel flow.
The important question is whether they are temperatures and pressures that the engine is designed to handle. If you are well below the temperature limits, and well below full power, temperatures and pressures should not be an issue.