N8RV

N8RV

Well Known Member
I was going to tag along on another thread, but I'm hoping that there are others out there with similar questions who might benefit from starting with a clean thread. I'll be the goat who asks the stupid question -- how high is TOO high for EGTs?

Here are the particulars: AeroSport IO-360M1 with LSE Plasma II+ on R, mag on L. Dynon EFIS & EMS. All EGT probes are mounted 3" from exhaust flanges.

My typical cruise readout at 2350rpm/22" MP at 56*F OAT show CHTs from 333* - 349* and EGTs from 1282* - 1398*, burning 8.4 gph. The CHTs have always been within about 15* of each other.

I understand that EGTs can be all over the board, depending on where the probes are mounted and other factors, but I've always kept the cruise EGT on #1 cylinder (always the hottest) at or below 1400*, except on takeoff and climbout. In fact, I have never leaned to peak.

In my old Yankee, with almost no engine instrumentation, I would pull back the mixture until the engine ran rough, then push it back in a tad and be done with it. If I did that with this plane, I'm sure that the #1 EGT would climb past 1500*.

My questions then would be:

1) If EGTs are arbitrary due to probe placement, how significant are they?

2) As long as CHTs are below 400*, is the engine OK despite high EGT readings?

3) Should I ignore my EGT readings just once and lean the engine until it stumbles, then richen it again to smooth and see just how high my #1 EGT will actually go?

4) If I do that and peak EGT is 1500 or even higher, is there anything wrong with that as long as CHTs are all good?

Obviously, all the talk about running LOP or ROP are meaningless when I can't even bring myself to lean the engine to peak because of high EGT readings. I would love to bring down my fuel flows but don't want to hurt the engine in the process.

Input is appreciated. :)
 
Don

Answers are,
Significant but not the absolute value.
No!!!!
No.
No! Don't do that either.

The answer lies in education.

I am using my iPad to type this so I will follow up later with details, but first thing to do is sign up for at least an online course from APS.

Your world will change. Better still do that and book into the live course in a few weeks.

Expect a pm too,

Regards

David
 
Don,
No such thing as "too high". Per Lycoming you can set max EGT at cruise power, thus any EGT less than peak is obviously fine, ROP or LOP, depending on your desire for power or economy.
 
Follow up question for Dan

Dan, following on the discussion and this may be a dumb question but if CHTs never exceed limits is it possible to burn a valve ? Reason I am asking is that I was wondering if you had a carbed engine but were trying to run LOP and the CHTs were 50 to 100 degrees apart but not exceeding 400 or so,..... is there any chance of doing damage. Maybe one cyl on the lean side and one on the peak but CHTs still good. No problem watching that with the engine monitor.

In short, if you never exceed CHT limits on any cyl, can you damage the engine ?

Hope you can make Petit Jean!

Thanks Bill
7a with a new suit :)
 
The answer is you can do damage at below 400F, however most damage is caused by poor valve / seat fit. Other than that if you ran high power settings and only a bit LOP, I doubt you could create problems.

There is a good reason to have all cylinder monitors and a good knowledge to understand what it is telling you.
 
I have always run our planes at LOP by leaning at altitude until engine stumble and then turning mixture in 1 full turn. This GENERALLY produces a temp of about 1450 on the hottest EGT. I run 2350 to 2420 RPM's and have had no problems. All three of my RV's have been run the same way and the engines have gone beyond TBO with no problem. Lycomings like to be pushed a bit.
 
Woodie

That probably works just fine.

Even though you may not know why, you have been fine, even if for the wrong reasons.

On most IO320 or 360, and for that matter O-320/360 and with a fixed pitch prop, if you are at altitude, and say 2450-2500 and lean until the RPM drops, you are probably at peak on the richest and the rest LOP, so that works fine. :)

If at altitude, say 5500+ and you can get to your 65% rating by fuel flow. You Are FINE

HP x 0.65 = 65% power

Then divide that HP by 14.9 = GPH

If you can get to this number..... you are fine! ;)

But I must say.....there is more to engine management than just setting a fuel flow.

You really need to invest in your education. ;)
 
Can EGT's ever be too high?

My understanding of EGT is this. The temp of combustion in your engine is based on the ratio of fuel/air upon ignition. The more you lean from rich the less fuel you mix with the same air volume. At the point where this ratio is at its optimum, best power is produced, as well as the combustion temp being the hottest. Thereafter as you lean more the combustion temp declines as the mixture becomes too lean, as well as power output reducing.

The engine starts to run rough when the volume of fuel to air becomes leaned to the point that the combustion becomes marginal and lacking in intensity. An associated lowering of combustion temperature occurs in this, the LOP environment.

The reason why these values are different in our engines is because the measuring system (probes, their relative position in the exhaust header and the differing performance of the probe itself) and the relative differences in fuel quantity each cylinder is receiving, are very rarely the same.

Please give me some guidance if this is a wrong viewpoint, or too simple in its content
 
Arrrrgggh!

RV10inOz said:
...Even though you may not know why, you have been fine, even if for the wrong reasons ....

...But I must say.....there is more to engine management than just setting a fuel flow.

You really need to invest in your education. ;)
Click to expand...

After reviewing some more threads on the subject, David, I see that there are some rather strong opinions on the matter. :D

What is your relationship with APS? Are you a lecturer, consultant, owner, investor or simply a fan? I ask because anytime I see a financial commitment in a recommendation I like to make sure I know if the recommendation is based on any financial considerations.

And, pertaining to my original questions, perhaps I should refine or amend them. As ignorant as this will sound, one of my frustrations with previous threads on LOP operation has been with the depth of the discussions by engineering types. I really have little interest in obtaining a graduate degree in engine technology. Yes, a basic understanding of HOW and WHY things work is important, but correctly operating a 4-cylinder, horizontally-opposed, air-cooled, reciprocating engine really can't be that difficult, can it?

My questions boil down to EGT readings. My #1 EGT is hotter than the others by 100-200 degrees, which is apparently not that unusual. And, given the variability of installations, the readings are somewhat arbitrary compared with CHTs.

*sigh* The more I think through the issue, the more frustrated I am becoming. I don't even know how to accurately phrase the question without starting some kind of war between the LOP and the ROP adherents.

IF I decide to experiment with LOP or ROP operations, at what EGT reading of my hottest cylinder (#1) should I be concerned? When I was breaking in the engine (which is apparently another argumentative issue), I relied on my Dynon EMS %power readout to keep things at 75% or above, and wasn't concerned about EGTs.

However, now that the engine has over 200 hours on it, I thought that I should learn to properly lean the engine and run it more efficiently -- but that #1 EGT worries me when it climbs above 1400*.

Perhaps I should unplug the EMS and just fly the stupid plane ... sometimes too much information is ... well, too much. :mad:
 
N8RV said:
Perhaps I should unplug the EMS and just fly the stupid plane ... sometimes too much information is ... well, too much. :mad:
Click to expand...

When I was first breaking in my engine and getting it dialed in, A very sharp A&P told me.

"well it seems the only problems I can find with your engine operation is You" "quit looking at all that info" "get up to cruise, set your prop, pull the mixture until rough and nudge it back in"

I started doing just that then I started looking at the info again...guess what I running 60-70%power. Usually running right near Peak, but it isn't a problem at that power level.
 
What Hydroguy2 said

...is what I've taken away from reading all these various threads about CHT And EGT. I've stopped worrying about it. I've got a carb and a FP prop and huge variations in both readings....oh well...I am gealous of your fuel flows though, I plan on 10.5 gph for cruze.
I do look at my valves at annual, and they all look good. Seems that is all that matters.
 
BillSchlatterer said:
Dan, following on the discussion and this may be a dumb question but if CHTs never exceed limits is it possible to burn a valve ?
Click to expand...

Possible? Yes, although it would not necessarily be your fault. For example, poor valve seat contact when delivered new is a future burned valve. It's machining error; seat non-concentric, off-angle, too narrow, etc. It happens.

Reason I am asking is that I was wondering if you had a carbed engine but were trying to run LOP and the CHTs were 50 to 100 degrees apart but not exceeding 400 or so,..... is there any chance of doing damage. Maybe one cyl on the lean side and one on the peak but CHTs still good.
Click to expand...

CHT is not a direct indicator of exhaust valve temperature. Valve temp mimics EGT (at a lower value). Peak CHT is typically found at a mixture setting well rich of peak EGT.

Overall a cooler head does mean a cooler valve, but in the context of valve temperatures it's not a big deal. Published data suggests that lowering CHT by 50 degrees (a big drop in CHT terms) might lower exhaust valve temperature by 30 degrees, maybe 2% (25/1300).

Hope you can make Petit Jean!
Click to expand...

It's on the list. Patti had a good time.
 
Don, I will address each point as best I can below in RED for clarity

After reviewing some more threads on the subject, David, I see that there are some rather strong opinions on the matter. Yes there are, however strong the opinion is, the one that is data backed fact based is the opinion I prefer.

What is your relationship with APS? Are you a lecturer, consultant, owner, investor or simply a fan? I ask because anytime I see a financial commitment in a recommendation I like to make sure I know if the recommendation is based on any financial considerations. How do you buy anything???
What did you do every time someone with an RV Grin gave you a recommendation to buy an RV? Besides my almost offence at your suggestion, why would it matter? I really do feel all your questions here are irrelevant but you asked....be prepared for the answers!
My relationship with APS, not that it matters is I am a satisfied customer. That there should be enough but since you asked, I am not a share holder, or in any way financially involved with APS. The same could almost be said for George John and Walter. They do not run these courses as a source of income. In fact I would think that any small residual change left over from running their courses would mean they have an hourly rate in terms of cents per hour. I know George would be better off not doing them. Walter and John could probably entertain themselves better elsewhere too. The thousands of hours they collectively spend each year helping us all for no return is in my opinion stupid. I spend around 10-15 hours a week helping folk in Australia, and I wonder why I bother when I find the continual defending a position like I am now to be an unproductive waste of my time.

Even if I did have a financial stake in APS, it would not change a thing. There is only one source globally of this kind of education, and you folk in the USA do not know how lucky you are it is on your doorstep and almost free of charge. $1000 for 3 days and the online course before hand to get you onto the page to begin with.... They are not charging anywhere near enough.

And, pertaining to my original questions, perhaps I should refine or amend them. As ignorant as this will sound, one of my frustrations with previous threads on LOP operation has been with the depth of the discussions by engineering types. I really have little interest in obtaining a graduate degree in engine technology. Yes, a basic understanding of HOW and WHY things work is important, but correctly operating a 4-cylinder, horizontally-opposed, air-cooled, reciprocating engine really can't be that difficult, can it? No I don't think so, however after years of engine company manuals and flying instructors spreading OWT's this has become a little difficult, and you will spend thousands learning to fly, an instrument rating perhaps, but nobody spends any time understanding the power plant that keeps the thing flying. :roll eyes: The problems with many of these threads is there is too much OWT stuff hanging around, too many posts of I was told this by my CFI etc.... most of them know stuff, but they know the wrong stuff and spread it wilfully!


My questions boil down to EGT readings. My #1 EGT is hotter than the others by 100-200 degrees, which is apparently not that unusual. Yep, My #1 is 100 lower! And, given the variability of installations, the readings are somewhat arbitrary compared with CHTs. You betcha!

*sigh* The more I think through the issue, the more frustrated I am becoming. I don't even know how to accurately phrase the question without starting some kind of war between the LOP and the ROP adherents. I did offer to spend an hour or two on Skype did I not for this exact reason, the whole process of asking a question and then participating in a volley of Q&A's is how you will learn. These threads can only ever address one or two questions at a time, and compared to the APS online and then live course (30 hrs worth of high intensity tuition), a thread on here is never able to compete. It is no wonder you get confused.

IF I decide to experiment with LOP or ROP operations, at what EGT reading of my hottest cylinder (#1) should I be concerned? NO!! I do not understand your infatuation with your #1 EGT....let it go! The absolute number is often not relevant to anything. The EGT numbers are most useful when referenced to PEAK EGT under the circumstances of the day. If your high EGT was due to a partially clogged injector, yes you might, but if you have determined that it is just a difference in readings, don't stress. When I was breaking in the engine (which is apparently another argumentative issue), I relied on my Dynon EMS %power readout to keep things at 75% or above, and wasn't concerned about EGTs. Well I assume you did like most people and did this at full rich, so no big deal. Nothing wrong with ROP, just LOP has several benefits.

However, now that the engine has over 200 hours on it, I thought that I should learn to properly lean the engine and run it more efficiently -- but that #1 EGT worries me when it climbs above 1400*. Again, if you had a good education here you could easily determine if the C1 is a problem, chances are it is not and 1400 is not a limit anyway. TIT limts of 1600/1650 etc are actual limits but that is for a different reason. Have a look at this video and watch the EGT's.....should I be scared? By your reasoning yes, but the truth is no not at all.
http://www.youtube.com/watch?v=s155lSZxsKQ&list=UU-KheOmXOz79f5wrOVPOADg&index=10&feature=plcp

Perhaps I should unplug the EMS and just fly the stupid plane ... sometimes too much information is ... well, too much.
Click to expand...
No, that is silly, and I am sure you do not really mean it. But learn about what you are getting from your EMS. There would have been many hundreds of fatal accidents and thousands of people alive today had the pilots involved had decent instrumentation and been trained in what it was telling them. Whyalla Airlines is one close to home for some of us. Double engine failure in a certified piston twin. Failures brought on by poor engine management..AS PER THE MANUALS and the company SOP, and even with poor SOPS the impending failure may have been partially avoided. Engine Monitors and training such that APS provide, this and many others would never have happened.
 
PART TWO FROM ABOVE.... due to character limit of 8600

To finish off on this point, it is not just about "knowing" a power setting or some particular "rule of thumb". The benefit is far beyond that, knowing what is the best most efficient and healthy way to operate your engine in a variety of scenario's is often a changing and dynamic operation. More important things are maintenance diagnosis which can save you thousands of dollars and hours of frustration. Most important of all is knowing when an EMS is telling you something urgent......like a problem about to kill you.

Here is a little mind flight that I have proposed before, it is a classic from APS, and I use it in my lectures as well, yes I do some lectures at various events from time to time down under!

You are flying along at night, 14,000' over the Rockies, the LSALT is 12000' your wife is enjoying the view of the moon over the clouds, the kids in the back are sleeping, and your EGT on one cylinder alters ever so lightly, and the CHT on that cylinder starts climbing at a rate of sat 1-2 degrees per second. It was nicely stable at 350F before. What do you do? And Why? You have 60 seconds to make the right decision or you will surely die in a fiery crash into the Rockies. You can't descend due LSALT, no diversions anywhere within 20 + minutes.

If you don't care about your EMS and what it really is telling you..... you might want to reconsider flying, especially if it is at night or in IMC or over anything but farm lands and golf courses.

I had a fellow in one lecture who had this happen to him, he had no idea about why what he did saved his life, but by sheer luck the old single point EGT and CHT was on that very cylinder that almost killed him. He would have been shark food for sure!

I hope this answers your questions above. And has been helpful, as well as encouraging to you and anyone else wondering why I bang on about this all the time. One day when George Walter and john are long gone (and they aint young) this sole source will be gnu also.....don't put if off forever!
 
Dan
CHT is not a direct indicator of exhaust valve temperature. Valve temp mimics EGT (at a lower value). Peak CHT is typically found at a mixture setting well rich of peak EGT.

Overall a cooler head does mean a cooler valve, but in the context of valve temperatures it's not a big deal. Published data suggests that lowering CHT by 50 degrees (a big drop in CHT terms) might lower exhaust valve temperature by 30 degrees, maybe 2% (25/1300).
Click to expand...

That is simply not true. Please I know you are a smart guy, and do a lot of good contributing on here, and when it comes to your aerodynamic and cooling advice, I would defer to your superior experience, but the above is not reflective of your talents.

Peak CHT does not occur well ROP at all, it is around 30-40ROP and CHT is a much more direct indicator of valve temp than anything else. If you can find a copy of the old NACA report, I do not have it, you will see what they discovered. And Lycoming repeated it in the 60's, and not surprising, with identical results.

As for your 2% you might want to rethink that in light of the above. The exhaust valve is not at 1300F at all, the gasses going past your probe might be, but that is it. The drop in temps of 30+ would actually be a 10% drop.

Your logic could suggest that because the combustion temp is at 3000-4000 therefore the exhaust valve is 3000F..... after all the big valve face is stuck right in there. The truth is it is not.
 
What is your relationship with APS? Are you a lecturer, consultant, owner, investor or simply a fan? I ask because anytime I see a financial commitment in a recommendation I like to make sure I know if the recommendation is based on any financial considerations. How do you buy anything???
What did you do every time someone with an RV Grin gave you a recommendation to buy an RV? Besides my almost offence at your suggestion, why would it matter? I really do feel all your questions here are irrelevant but you asked....be prepared for the answers!
My relationship with APS, not that it matters is I am a satisfied customer. That there should be enough but since you asked, I am not a share holder, or in any way financially involved with APS. The same could almost be said for George John and Walter. They do not run these courses as a source of income. In fact I would think that any small residual change left over from running their courses would mean they have an hourly rate in terms of cents per hour. I know George would be better off not doing them. Walter and John could probably entertain themselves better elsewhere too. The thousands of hours they collectively spend each year helping us all for no return is in my opinion stupid. I spend around 10-15 hours a week helping folk in Australia, and I wonder why I bother when I find the continual defending a position like I am now to be an unproductive waste of my time.

Even if I did have a financial stake in APS, it would not change a thing. There is only one source globally of this kind of education, and you folk in the USA do not know how lucky you are it is on your doorstep and almost free of charge. $1000 for 3 days and the online course before hand to get you onto the page to begin with.... They are not charging anywhere near enough.


David, I appreciate your passion and efforts to impart your knowledge to others on this very important topic. However, if you don't understand my intent in questioning your association with APS, then you won't understand my reasoning. It's basic business sense.

In my profession, it is expected that someone endorsing a product or profession disclose any affiliations -- especially financial -- so that any concerns about conflicts of interest can be determined. In essence, if you're plugging a product or service because you will gain financially from the purchase, it's nice to know that beforehand. Will it make a difference? Perhaps. Like I said, it's basic business, and if my questioning whether you have a financial interest in APS causes you offense, that's your problem, not mine. You seem to appreciate bluntness and accuracy, so that's as blunt and accurate as I can be.

That said, does your status with APS change my interest in hearing what you have to say? No, but at least I know where you're coming from. I'm sure that you and APS have lots of great information to offer, and I may consider looking into their course. However, having already confessed my ignorance and disinterest in fully understanding all of the nuances of how my engine works, I'm not sure that I could fully appreciate or comprehend most of what would be presented.

I will let you and Dan duke it out on your own. You may consider his knowledge base regarding engine management to be lacking, but he has forgotten more about engines than I will ever learn. Tread lightly.

Thanks again for your offer of help, David. I truly appreciate it.
 
RV10inOz said:
Peak CHT does not occur well ROP at all, it is around 30-40ROP....
Click to expand...

Excuse me. Next time I'll quantify "well".

....and CHT is a much more direct indicator of valve temp than anything else. If you can find a copy of the old NACA report, I do not have it....
Click to expand...

Obviously not, but I do.

The reports you want are:

NACA 754 (air cooled, WWII)
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091833_1993091833.pdf

NACA 813 (air cooled, WWII)
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091891_1993091891.pdf

NACA 1209 (water cooled, postwar)
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930081891_1993081891.pdf

As for your 2% you might want to rethink that in light of the above. The exhaust valve is not at 1300F at all, the gasses going past your probe might be, but that is it. The drop in temps of 30+ would actually be a 10% drop.
Click to expand...

Specific to CHT as an indicator of valve temperature, consider Fig 10 in NACA 754. We operate our flat Lycomings in the 5" to 10" H2O cooling pressure drop range. This data was taken at a constant mixture ratio (0.08). Doubling cooling air reduces CHT about 50 degrees, just what we might expect. Valve temperature reduction in this figure is 25~30 degrees. Valve temp average is roughly 1075 at this mixture, so the valve temperature reduction is still less than 3% in return for a major increase in cooling drag.

ot28zs.jpg


You figure 30 degrees is 10%, so exhaust valve temperature temperature would be 300 degrees? Go back and look at your APS material again. No way George and Walter are teaching that. Heck, click the links for all three papers above and look at the measured exhaust valve temperatures in Fig 8....in all of them.

BTW, while you're in 754 note the spark plug bushing curve at the bottom of Fig 8. It is just what you've been taught...peak CHT at best power mixture, declining as you move toward peak EGT.
 
Last edited:
N8RV said:
... However, having already confessed my ignorance and disinterest in fully understanding all of the nuances of how my engine works...
Click to expand...

Here's a couple of hard data points from Lycoming that should make it easier for you:

1. There's no EGT limit for Lycomings unless it's a turbo - and that limit is all the way up to 1650.

2. You can run at peak EGT for economy cruise as long as you are less than 70% power (IIRC). So don't be afraid of exploring a temperature if the engine manufacture endorses it as an "approved" continuous setting.

Consider that this newfound attention to exact values, splits, etc, is only because we now have to tools to see them. The engines have been flying just fine for half a century with essentially zero visability. In the old days, "the pull to rough" action was going LOP... Yet nobody cared because we were completely blind. Don't worry about it so much.

Finally, the EGT split is not so much about absolute values, but where each cylinder peaks in relation to each other. That's the best measure of fuel delivery efficiency. I see my EGT's peak within 10 degrees of each other, but the actual temperature value is often 100 degrees apart.

I think it's best to think that we have 4 distinct 90 cubic inch engines under the cowl and let them just "do their thing" sometimes.
 
Thanks Dan for digging them up.

Now in terms of engine mixture settings, well ROP would to the vast majority of folk reading this suggest something more like 125F-200F ROP. 30-40 ROP is barely a squeeze of the lever, so to go from peak to even 50ROP takes very little, but to get to 200....well that takes a lot. You can be pedantic at times over splitting hairs, yet when you make a grossly vague statement, which many readers will take as gospel because you regularly provide good tech info, I do believe that is worth pulling you up for. You would do the same to me in a heartbeat.

Now that graph in particular is a great example of where you go from being wildly vague to pedantic and back again. In your earlier post you stated the Valve Temperature was 1300F, and in that graph which is about the effect of cooling airflow at a fixed power setting it demonstrates that all these parameters are related, as you would expect. Increase the cooling airflow, and all other things remain equal, temperatures roll off.

At no point is the exhaust valve crown at 1300, in fact it starts at <1150, and drops along with everything else. As you would expect.

Dan, the Exhaust valve is not just the crown, it comprises the seat, the stem and the valve guide as a working unit, so I guess to be fair, even I am being a bit vague on specific when I refer to "the valve". As I am sure you know, you pointed it out in another post, valve life and failure is often more about the guide and the seat. And lets look at those...... nowhere near the 1300 F temperature.

So what is the point of all this?

The graph we are looking at is based on changing airflow, nothing else. In our airplanes the airflow in cruise is somewhat steady, and what we change is mixture.

Now as this graph above points out, if the points in contact being valve parts and head are very much aligned, and I lean to peak and beyond, the EGT is much higher yet the CHT(and related valve parts) is lower.

So.... my point being, in our installations, where we can alter EGT up and down , and CHT does not exactly follow...... I will stand by this statement in the absence of anything better, and available in our cockpits "CHT is a much more direct indicator of valve temp than anything else"

Just because we have a higher EGT number does not mean we have a higher CHT (and valve gear). Don was concerned about his 1400F being a hard limit or something.

None of us were talking about cooling drag or airflows..... But if you want to go on about the effects of airflow etc, I am all ears, and especially the way airflow does strange things like parked into wind Vs downwind, and why the latter may well give better cooling. Here is something I know happens but do not understand why at all.:confused:

PS I can't open those links, I have seen these doc's before, but damned if I know if or where I kept them. I had a HDD failure a year or so back, and they could well be in the list of victims of the bit bucket! Lesson learned....make sure all folders are backed up! :(
 
Last edited:
Just some minor clarifications especially for others reading this.

Cheers Y'all

Here's a couple of hard data points from Lycoming that should make it easier for you:

1. There's no EGT limit for Lycomings unless it's a turbo - and that limit is all the way up to 1650. YEP!

2. You can run at peak EGT for economy cruise as long as you are less than 70% power (IIRC). So don't be afraid of exploring a temperature if the engine manufacture endorses it as an "approved" continuous setting. Yep and you can run slightly ROP at best power or anywhere in-between, and usually when in the FL's that is a better place to be.

Consider that this newfound attention to exact values, splits, etc, is only because we now have to tools to see them. The engines have been flying just fine for half a century with essentially zero visability. In the old days, "the pull to rough" action was going LOP... Yet nobody cared because we were completely blind. Don't worry about it so much.Not always true, some engines brand new from Lycoming will not even run at peak smoothly, if you have injectors that are at opposite ends of the flow tolerance and they are in the worst cases for airflow, ask me how I know, had to do a rough injector tune or two before we could do a proper one. I have found one IO540, identical straight out of the box with a result that would be more like an IO550 with GAMI's. I was stunned. So the old pull her till she runs rough is not a very precise method at all.

Finally, the EGT split is not so much about absolute values, but where each cylinder peaks in relation to each other. I think what you mean to say at what Fuel Flow each peaks t relative to the other. The actual EGT value matters not.That's the best measure of fuel delivery efficiency. I see my EGT's peak within 10 degrees of each other, but the actual temperature value is often 100 degrees apart.

I think it's best to think that we have 4 distinct 90 cubic inch engines under the cowl and let them just "do their thing" sometimes.
Click to expand...
 
RV10inOz said:
Thanks Dan for digging them up.
Click to expand...

Come back after you read them.

At no point is the exhaust valve crown at 1300, in fact it starts at <1150, and drops along with everything else.
Click to expand...

All the data in Fig 10 is taken at a fixed fuel-air ratio of 0.08. As noted, exhaust valve temperature vs mixture is found in Fig 8.

NACA 754 is titled Operating Temperatures of a Sodium-Cooled Exhaust Valve as Measured by a Thermocouple, so even the abstract includes the peak measured value....1337F
 
RV10inOz said:
...I think what you mean to say at what Fuel Flow each peaks t relative to the other. The actual EGT value matters not...
Click to expand...

Nope - I meant just what I said.

Example - when using the "Peak" function on an EMS, the first cylinder to peak will display a -xx value. In other words, it's peaked, but we dont care what the absolute value is... We only want to know how far down hill it is. Now, if we can get the other three (or 5) cylinders to peak and start downhill before the first cylinder has cooled 10 degrees, that's a pretty tight spread and a desirable outcome. OTOH, if our first cylinder is at -50 before the second peaks, then the nozzles need work.

My engine will maintain a spread of 10 degrees for all 4 cylinders at fuel flows greater than 8 GPH, but once into the 7's the nozzles simply loose their ability to meter accurately and I get a 40-50 degree split.
 
Gents,



2. You can run at peak EGT for economy cruise as long as you are less than 70% power (IIRC). So don't be afraid of exploring a temperature if the engine manufacture endorses it as an "approved" continuous setting.

Does this apply to a carbed engine as well???

Thank you,
 
YES

dealfair said:
Gents,



2. You can run at peak EGT for economy cruise as long as you are less than 70% power (IIRC). So don't be afraid of exploring a temperature if the engine manufacture endorses it as an "approved" continuous setting.

Does this apply to a carbed engine as well???

Thank you,
Click to expand...

In an atmospheric engine (non-turbo) the actual EGT reading is irrellevant. Lean to peak and enrich the mixture by 75 deg F. is the way I was taught, but have since learned that even that is wrong. Lycoming has no EGT limit...carb'd or FI'd.
 
Dan, thanks for not addressing the question again!

I did rediscover the NACA files, but not via your links, for some reason my access was forbidden!

None the less right now I am about to head to the USA, and don't have time to re-read them all, and there are some pearlers there on other topics.........another day!

The bottom line here is, and as you have pointed out before valve life or failure is dependent on other factors not heat alone, its machining errors mostly or some other debris or defect. That being said, it is critical that valve face to seat alignment and thus concentricity of guide to seat are maintained. Surely you agree.

So with that in mind, CHT is a far more significant driver for concern, and the bulk of the valve heat goes through the seat (more so on TCM and less on Lyc), and as EGT is not the best determination of all the factors combined, (Valve guide, seat the rest of the head staying in shape). Valve crown is not really what we are so worried about.

Some of the Lycoming data is more recent and perhaps more relevant, but I am over the argument, I have too many other things to do.

But just out of left field......look what I stumbled over. A blast from the past. I think this taught me something totally unrelated to engines :)
http://www.vansairforce.com/community/showthread.php?t=16293&highlight=erich&page=4

Now for something of use to the others like Don who was questioning the use of Engine monitors and knowledge as combined diagnostic tools.
http://i849.photobucket.com/albums/ab58/jaba430/Detonation1.png

This tells you that the Vans mixture cables are too short, the FCU mixture arm too long and you are not maintaining full rich due to the engine pulling forward Vs the cable mounts flexing.

Now if you had no EMS like in the god old days......how would you have known? Maybe when the repair shop blamed it on LOP operation!!!!

:)

HooRoo!
 
Last edited:
RV10inOz said:
Here is a little mind flight that I have proposed before, it is a classic from APS, and I use it in my lectures as well, yes I do some lectures at various events from time to time down under!

You are flying along at night, 14,000' over the Rockies, the LSALT is 12000' your wife is enjoying the view of the moon over the clouds, the kids in the back are sleeping, and your EGT on one cylinder alters ever so lightly, and the CHT on that cylinder starts climbing at a rate of sat 1-2 degrees per second. It was nicely stable at 350F before. What do you do? And Why? You have 60 seconds to make the right decision or you will surely die in a fiery crash into the Rockies. You can't descend due LSALT, no diversions anywhere within 20 + minutes.

If you don't care about your EMS and what it really is telling you..... you might want to reconsider flying, especially if it is at night or in IMC or over anything but farm lands and golf courses.

I had a fellow in one lecture who had this happen to him, he had no idea about why what he did saved his life, but by sheer luck the old single point EGT and CHT was on that very cylinder that almost killed him. He would have been shark food for sure!

I hope this answers your questions above. And has been helpful, as well as encouraging to you and anyone else wondering why I bang on about this all the time. One day when George Walter and john are long gone (and they aint young) this sole source will be gnu also.....don't put if off forever!
Click to expand...

David,

Not intending to cross swords with you...well, OK, maybe a little gentlemanly fencing...but I've seen you pose this scenario before, yet I've never seen the punchline...or more importanly, the instructional goal of the scenario being met (the teaching part). If the goal here is to share, educate and entertain, I'd really like to hear (as Paul Harvey would have said)...the rest of the story. That would be far better than leaving readers scratching their head about a fiery demise in the Rockies; and far, far better than to tell someone trying to figure out what his EMS is telling him (or wondering if its all TMI) to take up bowling (or flying only over farms). So, even though I've flown over those rocks at all hours of the night in multi-engine turbine air ambulance mo-chines, and would not likely do it at night in my RV or any single, I'll nibble...

I would add a couple questions about the scenario as well.
-What type of mixture was the subject pilot running?
--"Well" ROP? (To clarify, richer than best power, though I understood what Dan was saying earlier)
--"Slightly" ROP? (perhaps stoichiometric or best power +/-)
--Peak?
--LOP?

-Which way did the EGT "alter ever so lightly"

One's action under this scenario may depend on the answers to those questions...unless I'm missing the point altogether.

Possible punchlines:
What did the EGT shift indicate?
What actions are correct, and conversely, which lead to the fiery crash? And Why?

So there's a few direct questions. If the scenario is proprietary to APS, then lets change the names to protect the innocent, and reach the educational objectives...let's teach and make safer pilots.

I'm not an APS grad, I've read Deacon, fly my 10:1 IO-540 both ROP down low (at race power), and LOP up high (or at low power down low). I fly WOT almost all the time (except formation), and I only reduce RPM a bit for noise, and then in cruise, if I'm looking for range. I've done extensive data recording of my FF, EGTs and CHTs and speed as I lean, and my engine does well LOP. My peaks are not quite GAMI close, but I'm fortunate to have them all within 0.5 gph (first to last, less for the majority) out of the box. I'm still studying the relationship between the delta temps (from peak, when LOP), and would like to get them closer together. I'm not comfortable with the big pull and power recovery down low, but am willing to learn more. One of my goals is to determine how much I can lean at a sea level race and be sure I'm not in detonation (but that's the topic of the other thread going on). However, I tread lightly on the big pull and the race scenario (in the other thread, there are smart guys saying detonation in a atmo engine using 100LL is unlikely...but I have the 10:1 concern, and need more research to lean more aggressively at high power down low). If there are nuggets of gold in your scenario above, I'd really like to hear and explore them...so how 'bout it! ;)

At the same time, I'm not sure how much we've helped our buddy Don (the OP). For Don, its been mentioned already a bit, but if you want to explore LOP ops, as a knowledgable buddy told me a few years ago...just do it...so I did (after more study, and it works well). Here's an experiment for you...just one technique. Start high...say a nice 9,500' X-C to Florida (I know you do those!). WOT and 2300-2500 RPM or so...no detonation likely there at any mixture (per Deakin and conventional wisdom). Lean to "well" ROP, say 11 gph as a starting point (guessing a bit on a 360, may be high, but seems in the ballpark). Record FF, EGT and CHT temp readings on all cylinders, and IAS/TAS. Lean to drop FF 0.2 gph. Let stabilize, take readings. Repeat, repeat, repeat, till the engine stumbles...will take you a long time to get all the data...perhaps an hour. Note the trend in airspeed. Compare peaks, and see how far LOP the engine will run smoothly. Do it again at 8,500 or 10,500 on the way back. It will help you learn your engine, in a way that won't hurt it. I'm no guru, so if anyone has any issues with this test method, please say so...but I think its how Gami has you check your injectors for matching.

Thoughts?

Punchlines David?

Cheers,
Bob
 
Hi Bob, no swords needed :)

Ok doing the GAMI lean test as they call it is pretty much as you say. small incremental changes and until all have crossed over the fence.....like chickens jumping over a fence! The difference in fuel flow as the first and last to peak is the spread.

At 0.5 that is quite workable indeed.

So as I have no financial gain ;) I can thoroughly recommend a seminar for you.

So the punch line..... well it matters not whether you were rich or lean of peak. It matters not what the get is doing exactly, it has just changed or wanders 10-0 degrees maybe. You have most likely a cracked ceramic and a bit has fallen out, and the result is a nice dose of pre-ignition.

Now in a twin you have a choice, but a single you have a destroyed cylinder in your very near future and even if the engine runs semi OK on 5 the oil will be pumped out soon enough anyway.

The only thing you can do is go full rich or almost shutting the engine down with too much fuel, until the low compression (early in the stroke) mixture is too hard to get away, and then the plug stops being a pre-igniter, and it fires with normal timing once again. You divert and land, pull the plugs and find a mess inside, but not such that it killed you.

Have an engine monitor, know what it tells you.

In some of the lectures I have done down here about EMS's the wives squirm when I tell the story, and when they hear the answer, their husbands are being asked...why don't we have one! I just point out where the nearest avionics shop is!

The one lecture I had, an old bloke had it happen, he did not know why, but he did go full rich, and he landed instead of being shark fodder, his cylinder was toast, but it got him there.

I attribute that story to APS. Not the bloke who was almost shark food, the Rockies scenario. ;)

Off to the Great land of the USA in the morning, nite all.


PS: I am a bit disappointed that nobody chirped up with the right answer. Surprising in fact as I have asked a couple of times. There is a message there. The mind flight killed most of our VAF buddies and their families off :eek:

Thanks for writing Bob, well done!
 
Last edited:
rvmills said:
...For Don, its been mentioned already a bit, but if you want to explore LOP ops, as a knowledgable buddy told me a few years ago...just do it...so I did (after more study, and it works well). Here's an experiment for you...
Click to expand...

Thanks for the thoughtful response, Bob. I really didn't want to incite any violence here on VAF. Glad nobody broke out the swords. :D

I took the son-in-law up for his first RV flight this morning while it was only 90 degrees. With temps over 100 today, I think I'll wait for things to cool down a bit before spending the time to explore the topic of leaning. I have similar instructions from the guys at Airflow Performance for compiling data to evalulate the flow matching of the injectors, so I just need to do it. I just wanted to make sure that having EGTs over 1400 are OK, or if they signaled something wrong. From what I've read, I've heard everthing from "NO!" to, "you can't get EGTs too high in a Lycoming." Clear as mud to me now. :D

When the heat wave breaks later this week, I'll see what happens when I start recording temps and fuel flows at various lean settings and report back. Well, as long as I don't go down in flames over the mountains and get eaten by sharks ... or something like that. :eek:
 
Toobuilder said:
Nope - I meant just what I said.

Example - when using the "Peak" function on an EMS, the first cylinder to peak will display a -xx value. In other words, it's peaked, but we dont care what the absolute value is... We only want to know how far down hill it is. Now, if we can get the other three (or 5) cylinders to peak and start downhill before the first cylinder has cooled 10 degrees, that's a pretty tight spread and a desirable outcome. OTOH, if our first cylinder is at -50 before the second peaks, then the nozzles need work.

My engine will maintain a spread of 10 degrees for all 4 cylinders at fuel flows greater than 8 GPH, but once into the 7's the nozzles simply loose their ability to meter accurately and I get a 40-50 degree split.
Click to expand...
Michael,
I have read all of the posts on this thread as well as the others going on about similar discussions of running LOP. To me, you have helped considerably in detailing what I am trying to understand when operating LOP by this one post. I have run LOP down low (as low as 2500' MSL) and up high (12,500' MSL) and everywhere in between. The EGT spread that you discuss is a vital piece of information I find myself monitoring. You mentioned fuel flows below 8 GPH causing greater spreads for EGT temps. I find my #4 cylinder to be the one that most often stays the hottest and more often than not is the last one to go lean. Even so, the differences between the first and last to peak and the other two tagging along tend to stabilize on longer flights to within a 15-30 degree range at a fuel flow of anywhere from 6.5-7.5 GPH. With the experiences I have had with my engine I think this is about as good as it gets. I will say it is a rare incident, if I really can recall ever really seeing it, when the EGT temp differences are within 10 degrees of each other. However, what I do observe is the CHT temperature differences are very often within that 10 degree spread.

Here is a pic from my latest flight this past weekend. At the point of this picture we had been flying for about 1.5 hours at this altitude with very little variation on the EGT's and absolutely no variation of the CHT's. In fact, one of the thoughts I had at the time I took this pic was how long the CHT's had been stable at these temperatures. They did not move one tic for well over an hour prior to this pic. As you can see, the EGT spread was -47 to -28 (a 19 degree spread). The CHT temps were 316 on both front cylinders to 322 for #4 and 321 for #3 (a 6 degree spread). Notice the fuel flow of 6.7 GPH. This also, was an extremely stable reading for the duration of the flight. Another note of interest to me is the oil temperature (175 degrees). I have made this comment before about my engine in previous posts: "This is one COOL engine!" One last comment concerning the RPM and MP. This was NOT at WOT. Notice the 58% Power reading in the bottom left. I think I could have still pushed the throttle in and reached the 65% HP mark but I typically try to cruise in the 150-160 MPH TAS area so once I reach that speed I tend to set the throttle there. Perhaps I could have pushed the engine to WOT and gained a little speed. I am sure the temps and fuel flow would have shown differently had I done so but I think they would have still been realitively similar to this just different actual numbers. I guess that means I now have justification for flying another mission. It is important to always be pursuing new reasons to go fly! :)

IMG_1302.JPG
 
David,

Thanks for closing the loop on that scenario. As you examine the different pieces of the puzzle, eliminate the distractors and peel the onion a bit, it does show that individual cylinder monitoring is of much value. Its a good exercise to show that the motor is telling you something. The fact that only one cylinder's CHT is rising, and EGT really isn't doing anything significant tells you something is amiss, granted. That its a cracked plug causing preignition may not be something that comes to mind immediately, as I imagine it could also be debris on that cylinder (unkown bird strike, FOD moving into the wrong position, etc). Other timing issues (partial coil failure on an EI, for one) would likely show as EGT and CHT changes on one cylinder, and of course anything that affected the entire motor would be more obvious (rough running). So its a good thought provoker...which becomes an even more effective training tool when you strip off the firery crash emotional thing, and talk about changing EGTs, changing CHTs, mixture settings and how they affect EGT and CHT...and what failures can cause what changing indications. I'm sure the firery crash thing sells some EMS boxes (you sure you got no skin in that game? :p;))...but the value really comes in the details of what's going on.

In terms of absolute EGT and CHT...some of the racers have perhaps been heard to say, "well, Lyc says 500 is the real CHT limit"...but then again, in Reno, their TBO only needs to be 6 laps when the chips are down. I race my daily ride, and don't have deep pockets, so no way I'm going there! In racing, and in X-C leaning, I rarely see 400, though it'll creep up just over on hot days with multiple flights. #2 is always hottest, since that dern governor is sitting in the breeze in front of it (no dams currently installed). In some of my higher power leaning exercises however, I have seen EGTs in the mid 1400's, and one particular test showed over 1500 on one cylinder (5, also normally the first to peak). I couldn't help feeling some angst about that, as its not usually near that...but it was a hot/high day. CHTs were under 400, so I continued the test to LOP. So I share Don's original concerns, but temper it with other measures, as he does. I also have read about the combined CHT/EGT limits, which I think was called an OWT earlier...but thought I read it in Pelican's Perch. I don't want to mis-quote, and my current digging is coming up empty on a ref for that rule of thumb. So the question remains...is there an ultimate no-detonation-occuring indicator? I think Don can explore LOP safely free of detonation by a wide margin, and from my study, and reading some of David's, Ross's and Dan's writings (among others), I believe most of my flight ops fall into the same category (and where they may not, I don't push it, temp-wise). But where does one draw the line?...I think that gets back to Don's original intent. I know where my comfort lines are currently, so this is meant to stimulate conversation about where the deto-monster may live.

I also think Michael and Steve have a good point about temps, and the spread of "Leaness of Peak" temps achievable. The FF at which each cylinder peaks is one measure of injector matching, but narrowing the delta or spread of deviation from peak across the cylinders would seem to be an important metric, especially if you want to go LOP at high power...and still avoid Deakins' red zone. I'm very 20th century with my VM-1000...I can read all the cylinders, but have to toggle through them and manually calculate how far LOP I am, if I want to record that. I've flown a Rocket with Skyview, and RVs with D-180s, and they are great for quick recognition. The AFS and GRT and Garmin boxes have awesome displays too. Even with them, I still would like to see where folks feel the deto-line should be drawn at high power...this being just one source of data for a decision and best practice formulation.

Cheers,
Bob
 
Last edited:
RVbySDI said:
...You mentioned fuel flows below 8 GPH causing greater spreads for EGT temps. I find my #4 cylinder to be the one that most often stays the hottest and more often than not is the last one to go lean. Even so, the differences between the first and last to peak and the other two tagging along tend to stabilize on longer flights to within a 15-30 degree range at a fuel flow of anywhere from 6.5-7.5 GPH. With the experiences I have had with my engine I think this is about as good as it gets. I will say it is a rare incident, if I really can recall ever really seeing it, when the EGT temp differences are within 10 degrees of each other...
Click to expand...


Sorry I missed this back when you posted, but I have a comment on your situation. I'm no expert by any means, but I have gleaned info from various sources (including Don - a big help), and have also added some of my own experience to reconcile what's going on. Here's how I make it work in my feeble brain:

One factor in regulating/fuel scheduling with the Bendix type system is as simple as the nozzle orifice size. This orifice in the nozzle provides a certain amount of backpressure in the lines, flow divider and servo which is used as the scheduling logic for the system. With high fuel flows, the fixed nozzles are providing a more significant percentage of restriction than at lower fuel flows, so because of hydraulic principles, the lines upstream of all nozzles should have equal pressure on them. Now at fuel flows below about 8 GPH (or 2 GPH per nozzle x # of cylinders), the nozzles are providing very little restriction to the system - the fuel is just dribbling out. Since the servo is really scheduling a big slug of fuel to all the nozzles at once, it then falls on the individual nozzle performance to determine equal distribution. At low fuel flows, the differences in individual nozzles (and lines, routing, and flow divider orifice) really becomes a significant factor in delivery and you will get the divergence we see. At high flow, these differences are simply overshadowed by the volume and pressure of fuel, so we get a more balanced delivery. A really farfetched analogy might be pigs at the feeding trough - when there is plenty of supply, all the pigs (nozzles) are happy . However, when the supply gets lean (low fuel pressure), the weaker pigs lose out.

So we might conclude that reducing nozzle size will bring the pressure back up to a more useful value at the lower power settings - and it would. But then we'd hit the limit of delivery volume at the other end. Without significantly increasing the pressure of the whole system, we just couldn't move enough fuel through these small nozzles to satisfy takeoff power. This form of injection is very crude and really was not designed to satisfy a wide operating envelope (at least compared to modern EFI in cars). The primary goal is proper fuel delivery at relatively high power settings. The fact that we now routinely run LOP and have the ability to monitor individual cylinders to a resolution down to 1 degree is not something the designers considered or cared about. This also doesn't mean there is a problem with the system, but there is some tuning involved if you expect high resolution.

So anyway, I suspect that if you try flying LOP at a low enough altitude that pushes you into the 8 GPH range (remember, GPH is a result, not a target), your EGT split will get much tighter. I'd also suggest WOT too (better VE), but that's another debate. When I'm up high, the EGT split is pretty wide, and gets worse with altitude. But as soon as I get above 8 GPH, the thing just tightens up. Coming back from OSH last year we were at 3500 feet, WOT, and 50 LOP - My EGT spread was less than 5 degrees TOTAL! (CHT was tight too).

Finally, if anyone has a correction to my view of the world as it relates to mechanical fuel injection, I'd sure like to hear it. I certainly don't want to lead anyone astray with bad info.
 
Last edited:
You must log in or register to reply here.