Yet another LOP question... WOT, Low altitude..

[Dr. O]

I had a mag dropout on the right engine last week. Only way I noticed at the time, because I was at cruise and leaned back was that the EGT was now higher than expected for the mixture setting (benefits of really knowing your machine)
'whut the hey?' I said, keen mind racing and steely pilot eyes scanning the panel as i waggled the red knob and noticed that the CHT was now higher than the left engine.
Long story short: When folding and clipping a chart (remember those?) the clip board had slid forward on my leg and the corner was resting on top of the right mag switch for the right engine and it finally snapped down as I was getting things arranged
(so Garmin is right, GPS is a safer way to navigate)
With the knee board hiding the switches from direct view it took me a few seconds to catch on after I noticed the rising EGT and CHT.

 

[Aaronk25]

I was using that excerpt only to show that light detonation does not necessarily present itself with extra high cylinder temps. The poster above me stated that if the cylinder temps are 380 or below, you are not detonating.



If I run the swift, which has excellent cooling, at 26" MP and 2600 RPM and then lean to 50F ROP it will be running smooth, the cylinder/oil temps will be reasonable, but the engine is likely detonating at those power/mixture settings.

Light detonation isn't harmful. I doubt it's possible in a naturally aspirated plane to even get into any detonation under 380.

Moderate or even light detonation will cause a increase in cht.

 

[dans2992]

....and your diagnosis of the metal???

FYI, turns out the metal was a spalling Cam/Lifters. Engine is apart and new cam on order.

The checkbook is standing by.....

 

[dans2992]

This actually surprised me because the engine was overhauled just about 3 years ago and has a few hundred hours on it since then. It sat for 8 weeks while we did the interior, but it's surprising that was enough to do it...

 

[Ted]

Somebody page Dr. DuPuis.

Oops, missed this one. I was a bit busy around OP, something about the twins being born.

Eggman was basically spot on. There's nothing wrong with what Dan did. For those who don't know otherwise, 25-50 ROP is the worst. LOP is good. Proper ROP is good. High CHTs are bad. It gets much more complicated beyond that and I've explained it many times in other places, including two stickies in the Maintenance Bay section. Read those, learn something, ask questions if I wasn't clear and I'll answer them.

Dan, I doubt if that downtime was sufficient to cause the cam spalling. Honestly it becomes something of a crapshoot. Many things can cause spalling. Keep in mind that the cam and lifts were probably reused at overhaul. Lycomings seem to especially have issues with this over Continentals, but it happens to both. Some people get lucky, some don't.

For what it's worth, I use Phillips 20W-50 and CamGuard, which I believe overall offers the best corrosion protection. Philips is junk for corrosion protection, but the CamGuard makes up for it.

 

[dans2992]

Yep, we use Camguard also. Guess it was just luck of the draw...

 

[Alexb2000]

Just for another data point I have been running my TIO-540 at ~32", 10-12K, 14.5GPH at ~50 LOP to yield 150 knots (big draggy airplane). CHT's are very good for a Lycoming at 350 or less. All this is thanks to Ted and his incredible background. I am saving about 2 GPH for the same speed, so over the life of the engine 2000 hours X 2 GPH or 4000 gallons or $20K@$5 per gallon. Controlling CHT's to 400 was always the challenge before, so this is nice and I have a much better margin of safety.

Ted is a great resource if those here take the time to read his stickies and consider what he has to say.

 

[Henning]

OK, so I have a Comanche 260B (Normally aspirated Lycoming IO-540). Most of the time, I cruise around 8-10k+, so I run it at peak EGT, or slightly ROP, because I need the power up there. CHTs stay below 400.

The other day I went on a roundtrip flight of about 0.5 hours each way. I was at around 4000 ft., and decided I was going to go LOP. I do not have GAMIs, but I do know that my GAMI-spread is about 0.9 gph. Reading some of the Deakin (and other) material, I know that when LOP there is a rule of thumb saying that "HP produced = 14.9 x FuelFlow".

.65 x 260 hp = 169 hp for 65%.
169 hp / 14.9 = 11.3 gph

Since when LOP, the limiting factor for power is fuel, I figured that if I was at 11.3 gph, I would be at 65% (hence OK to be LOP), so wide open throttle, and 2300-2400 rpm, and 11.3gph LOP should be ok at 4000 ft. (all cylinders were LOP) CHTs were 360 max (and often much lower.)

Was this a mistake? Is it bad to run the engine like this?

My concern was elevated today when a look at the oil filter yielded more ferrous (and some non-ferrous) metal than normal, along with more carbon than would be typical. The only other "out of the ordinary" thing occurring between the last oil changes was six weeks of sitting due to interior work.

Would these findings be at all related to about 1 hr. of these sorts of LOP ops? Any thoughts? The mechanic says check the filter in another 25 hours, and see where we're at.

Nope, that's fine, basically how I operated the 310, I was LOP on my first power reduction, and I do the grab to known fuel flow parameters. You do want to cross reference TAS in cruise as to % power, however as long as CHT stays 360° or below, mehhh, not that critical IMO. CHT will tell you you're getting in trouble area before you get there. A 420° CHT isn't really a big metallurgical problem, however you still don't really want to get there because it indicates you have conditions happening in the combustion chamber that are getting into the 'red box' destructive range. If you have a 360°CHT, you aren't close.

 

[Ted]

Thanks for the kind words, Alex. Glad my suggestions are working so well for your plane.

 

[ahkahn]

Here is an on topic question:

Let's say you're running a configuration that is "inside the red box"... say 25 ROP. CHT's are still very low (let's say around 310*). Are you still doing "damage" do your engine or is your engine just that darn healthy and can handle the configuration?

 

[Ted]

Here is an on topic question:

Let's say you're running a configuration that is "inside the red box"... say 25 ROP. CHT's are still very low (let's say around 310*). Are you still doing "damage" do your engine or is your engine just that darn healthy and can handle the configuration?

CHT is a function of heat produced and heat removed (cooling). It is possible to have low CHTs at bad operating points with good cooling.

There's also the power setting that matters. 85% power or 55%?

Wear is cumulative, so basically the answer is the ICPs are higher than they could be, which contributes to more wear added than if you were running at a better point.

The SR22 is a great example of low CHTs with high wear rates. 2 tops in a TBO, not uncommon.

 

[Alexb2000]

CHT is a function of heat produced and heat removed (cooling). It is possible to have low CHTs at bad operating points with good cooling.

There's also the power setting that matters. 85% power or 55%?

Wear is cumulative, so basically the answer is the ICPs are higher than they could be, which contributes to more wear added than if you were running at a better point.

The SR22 is a great example of low CHTs with high wear rates. 2 tops in a TBO, not uncommon.

Not because of the SR22 per say, but the pilots running them hard ie. 85%?

 

[Ted]

Not because of the SR22 per say, but the pilots running them hard ie. 85%?

Correct. The plane has excellent cooling, but CHTs aren't the whole story.

 

[Henning]

Here is an on topic question:

Let's say you're running a configuration that is "inside the red box"... say 25 ROP. CHT's are still very low (let's say around 310*). Are you still doing "damage" do your engine or is your engine just that darn healthy and can handle the configuration?

Nope, you're fine from a detonation perspective.

 

[Ted]

Nope, you're fine from a detonation perspective.

Detonation is not all that matters.

 

[Henning]

Detonation is not all that matters.

True, over cooling can get you clearance/interference problems, but that's more 'increased wear' zone than 'destruction'.

 

[James_Dean]

Here is an on topic question:

Let's say you're running a configuration that is "inside the red box"... say 25 ROP. CHT's are still very low (let's say around 310*). Are you still doing "damage" do your engine or is your engine just that darn healthy and can handle the configuration?

I think you very well could be doing cumulative harm faster than you would want to be. Whatever the CHT your high ICP's are working to push those raging hot exhaust gasses past the valve seat. One annual, sooner rather than later, you will have low compressions and some green valves. Having said that, I think that your experience of running a Lance at 75% power ROP and keeping CHT's below 300 would be an outlier in the typical owner experience and would question the instrumentation.

With the recent very cold OAT's I can run high power settings ROP and still have sub 360 CHT's. Those same power settings and fuel flows in the summer would easily be north of 400.

 

[Henning]

If you are 75% power ROP with CHT below 300°, you are washing out your rings, but it won't matter because your valves will burn or stick before the ring problem becomes fatal. Plus you're using a buttload of fuel.

340°-370° is pretty much a sweet spot. Too cold is as bad as too hot, you just replace parts for different reasons.

 

[Ted]

True, over cooling can get you clearance/interference problems, but that's more 'increased wear' zone than 'destruction'.

High ICPs without detonation will still wear the cylinders.

 

[Henning]

High ICPs without detonation will still wear the cylinders.

True, but I question how high the ICP can be if you are not seeing 300° CHT. Air/Oil Cooling only gets so efficient, and ICP = heat, and if I'm not mistaken, it's an exponential relationship. If you get so rich that you can get that kind of cooling, I'm not sure that the combustion speed will be sufficient to build that high of an ICP to do damage. I would think the damages done would be due to excess fuel and destructive by products of incomplete combustion rather than ICP.

 

[Ted]

You have heat production and cooling mass air flow as well as cooling air temperature. It is very possible to have enough cooling air to maintain low CHTs with bad ICPS. It's possible to even have low CHTs with detonation, although that usually takes some tricks you can only do in the lab or bad fuel/bad timing.

 

[Henning]

You have heat production and cooling mass air flow as well as cooling air temperature. It is very possible to have enough cooling air to maintain low CHTs with bad ICPS. It's possible to even have low CHTs with detonation, although that usually takes some tricks you can only do in the lab or bad fuel/bad timing.

Ok, but I still think it will show up as 'excessive wear' rather than 'destructive force', and I still think that carbon deposits and other related issues will take you out before ICP related issues. I also don't think you can get there LOP without a lot of boost going on.

 

[overdrive148]

Are you guys talking about that funny red knob in the panel that is like the gas pedal but not? :wink2:

Semi-seriously though, I see these threads a lot and I don't know where to stand. I was taught during training to pull the mixture out until RPM's dropped and then turn once or twice in above that. That was a Lycoming 0-320 in a '74 Cessna 172M in the desert in CA. Dunno what that means or if that's bad or not

 

[Ted]

Ok, but I still think it will show up as 'excessive wear' rather than 'destructive force', and I still think that carbon deposits and other related issues will take you out before ICP related issues. I also don't think you can get there LOP without a lot of boost going on.

Correct. My point is "destructive force" isn't the only bad thing.

 

[Alexb2000]

Are you guys talking about that funny red knob in the panel that is like the gas pedal but not? :wink2:

Semi-seriously though, I see these threads a lot and I don't know where to stand. I was taught during training to pull the mixture out until RPM's dropped and then turn once or twice in above that. That was a Lycoming 0-320 in a '74 Cessna 172M in the desert in CA. Dunno what that means or if that's bad or not

I'm sure most of us were taught that. Now I notice some places don't even lean their trainers, so people don't forget to go full rich for a climb. I believe the stakes and dollars involved when running one or more bigger engines is where the management becomes more important. Not that everyone can't benefit from good engine management.

 

[Ted]

The problem with "my instructor told me" is that most instructors know nothing about engine management. A&Ps often aren't much better from what I've seen, unfortunately. This is why FADECs have an advantage, and since we don't have those learning from those who actually do know engine management. Often, specifics vary from plane to plane.

 

[Henning]

Correct. My point is "destructive force" isn't the only bad thing.

Gotcha, I was trying to keep to one issue for simplicity of discussion. Most certainly other factors come into play besides 'Red Box' issues. That's why I only pay regards to the numbers to back up what I am hearing is accurate, and I don't have something anomalous going on. If it sounds and feels right, the chances are if the fuel flow is correct and CHT is in the proper range, the conditions I believe to exist inside the engine do in fact exist as such.

 

[Checkout_my_Six]

I see a new career for someone.....

T - teaching
E - engine
D - disciplines

Academy

Just think of all the speaking engagements and notoriety.....you'd be famous.

 

[Ted]

I see a new career for someone.....

T - teaching
E - engine
D - disciplines

Academy

Just think of all the speaking engagements and notoriety.....you'd be famous.

I like it! I need to steal that.

 

[Checkout_my_Six]

I like it! I need to steal that.

You could even use a real-live engine test cell.....for teaching examples. Not, just some garage mock-up.

 

[overdrive148]

I'm sure most of us were taught that. Now I notice some places don't even lean their trainers, so people don't forget to go full rich for a climb. I believe the stakes and dollars involved when running one or more bigger engines is where the management becomes more important. Not that everyone can't benefit from good engine management.

The problem with "my instructor told me" is that most instructors know nothing about engine management. A&Ps often aren't much better from what I've seen, unfortunately. This is why FADECs have an advantage, and since we don't have those learning from those who actually do know engine management. Often, specifics vary from plane to plane.

Fair enough. What is the method I was taught called (if it has a name) and what are the downsides to it?

Googling "lean of peak" yields a ton of people arguing about whether to do it or not to do it but not about an actual definition.

Peak RPM for a given throttle setting? Peak temperature? If so, which?

I have just under 100 hours and haven't flown in a while, but I'd still like to be able to walk away with something from at least one of these discussions

 

[James_Dean]

Fair enough. What is the method I was taught called (if it has a name) and what are the downsides to it?

Googling "lean of peak" yields a ton of people arguing about whether to do it or not to do it but not about an actual definition.

Peak RPM for a given throttle setting? Peak temperature? If so, which?

I have just under 100 hours and haven't flown in a while, but I'd still like to be able to walk away with something from at least one of these discussions

This.

 

[Henning]

This.

That's a nice graph.

As for adding RPM to the discussion, that adds another level of complexity to the equation because there are multiple factors involved, some of them relevant here, and some not. However for the sake of this discussion, RPM is not really relevant and is not the reference in use for 'peak', although with a fixed pitch prop could be representative. When 'Peak' is referred to in an LOP discussion it refers to peak EGT.

 

[overdrive148]

Okay. Google says:

EGT-Exhaust gas yemperature
CHT-Cylinder head temperature
ICP-Internal cylinder pressure
HP- Horsepower
BSFC-Brake specific fuel consumption

I know what horsepower is! And there was an EGT gauge in the cessna. Not that I used it much, I was told a temp range and to ease up if it got too hot basically.

Never used CHT, ICP, BSFC before. But I see how the graph works more or less. Now what?

 

[dell30rb]

I was taught during training to pull the mixture out until RPM's dropped and then turn once or twice in above that. That was a Lycoming 0-320 in a '74 Cessna 172M in the desert in CA. Dunno what that means or if that's bad or not

That's fine for a wet rental with the O-320. With higher performance stuff (or if you own it, or rent dry) you'll want to learn and practice more advanced engine management. You can save fuel and save on maintenance

Just make sure you are at 75% power or less. There should be an RPM v altitude chart in the poh

Sent from my iPhone using Tapatalk

 

[Henning]

Okay. Google says:

EGT-Exhaust gas yemperature
CHT-Cylinder head temperature
ICP-Internal cylinder pressure
HP- Horsepower
BSFC-Brake specific fuel consumption

I know what horsepower is! And there was an EGT gauge in the cessna. Not that I used it much, I was told a temp range and to ease up if it got too hot basically.

Never used CHT, ICP, BSFC before. But I see how the graph works more or less. Now what?

CHT is a measure of how much energy is being wasted as heat. There is no direct reading of ICP available without very uncommon instrumentation. However since the ability to shed heat is a known factor and remains relatively stable we can use CHT as an indicator of what level of ICP we are operating at. As was pointed out earlier, there can be some anomalous situations where you can be running high wear ICPs without getting into destructive operation, so it is only one factor to be aware of, there are other factors that may limit you first.

True Airspeed is the most reliable indication of how much horsepower you are producing. The one other factor that is important to know in critical engine operation is fuel flow. Since fuel has known values for combustion, the fuel flow calculated against your true airspeed will tell you how efficiently you are operating. Now the cool thing here is this is really all you need to know, because the more efficiently you are operating the less residual heat you have to get rid of, plus at these levels of efficiency you aren't producing particularly high ICPs either. Since speed falls off at the square root of power, that means that load and subsequent ICP and CHT falls off rapidly with small decreases in speed as you reduce fuel flow.

If you are flowing as much air through an engine as you can, and give it just enough fuel that it comes up to the top of the heel in the torque band, that engine will give you a long life of efficient and reliable operation.

 

[ahkahn]

I think you very well could be doing cumulative harm faster than you would want to be. Whatever the CHT your high ICP's are working to push those raging hot exhaust gasses past the valve seat. One annual, sooner rather than later, you will have low compressions and some green valves. Having said that, I think that your experience of running a Lance at 75% power ROP and keeping CHT's below 300 would be an outlier in the typical owner experience and would question the instrumentation.

With the recent very cold OAT's I can run high power settings ROP and still have sub 360 CHT's. Those same power settings and fuel flows in the summer would easily be north of 400.

Let me show you guys a little something... TAS was around 160kts, and I have every speed mod imaginable (howl cowl, etc). EGT's were 1410-1460 across the board, and in this pic, CHT's were running around 300* (except for cyl #5 which has a spark plug probe and registers about 50-60* hotter). This was running around 75 ROP at 7000'. This is why I am asking the question... doesn't seem right.

 

[Checkout_my_Six]

different probe type and at a different location. Could be fine.

 

[James_Dean]

Let me show you guys a little something... TAS was around 160kts, and I have every speed mod imaginable (howl cowl, etc). EGT's were 1410-1460 across the board, and in this pic, CHT's were running around 300* (except for cyl #5 which has a spark plug probe and registers about 50-60* hotter). This was running around 75 ROP at 7000'. This is why I am asking the question... doesn't seem right.

Doesn't your POH call out a significantly higher fuel flow at 75% power? I seem to recall mine calling out 18 GPH at 100* ROP. I would almost certainly be LOP in my former plane when 75% and 15.5 GPH.

Can you describe your leaning procedure?


FYI. I am certainly no expert here and others in this thread are far more experienced and knowledgeable than I. I am only commenting because of my experience with a few similar airframes to yours.

 

[ahkahn]

Yeah, no problem, Mr. Eggman. I believe the POH calls for 16gph at 75% power at peak (best economy). It's an IO-540-K1...

I use the LeanFind mode on the EDM.

I was told by the seller of the plane that he ran it 65-75 ROP at 24/2400 (unless it couldn't hold onto 24", then highest it could hold). Engine has 500 hours on it and checked in at 79/80 across the board. It has been flown 200-250 hours per year, so that may be helping. His last engine ran 2800 TBO before he overhauled it, and he says it didn't even need it then, but opted for it.

I really like the LOP concept, but you can see why I am hesitant to mess with a good thing!