Raw EGT numbers. Why they do matter....sometimes.

[Shadrach]

Just to clear the air, this is not a ROP vs LOP thread.  Indeed, leaning is only incidentally related to the subject.  I don't post as much as I used to, but in 7,000 plus posts I have been called to the carpet many times when I ask for EGT numbers when attempting to understand an engine problem or peculiarity. It happened again just a few days ago in the thread on Reasonable M20J speeds. Rather than hijack that thread, I thought it better to respond in a separate post.

Pilots just learning to use and engine monitor frequently home in on EGTs and understandably express concern over the lack of consistency in raw numbers across the cylinders. It is true that two cylinders or three cylinders or more can and typically do peak at the same or similar fuel flows while displaying large differences in raw EGT numbers.  Those differences in raw EGT numbers are, as many will tell you, irrelevant. However, that does not mean that nothing can be discerned from raw EGT numbers. For that statement to be true, there could be no upper or lower range of reasonable EGTs.  Looking at just about any chart on the subject you will see that the scale for EGTs runs between 1000°F and 1600°F or even narrower for naturally aspirated engines.  Why? Because under most conditions a normally aspirated engine will not generate "measurable" EGTs outside of that range.  Indeed probe placement affects the raw number but it can only move the reading closer to the middle of the scale (cooler).  You can place a probe anywhere on the stack and it will not ever read much above 1550°F.  So how is that useful?  Well if my buddy with a C model who is complaining about high CHTs says that all EGTs are between 1400° and 1460° on take off, I can easily discern that his engine may not have adequate fuel flow. How?  I know the engine should be 250°(min) to 300°ROP for take off.  1460° + 300° is 1760°.  This is not with in the spectrum of normal EGT for a normally aspirated aeroengine. Whether the engine’s peak numbers are known or not, one can tell that the number would represent an abnormal combustion event.   So it can be surmised that this engine is likely much leaner. it could also be an ignition issue but in conjunction with high CHT, fuel (or lack there of) is probably the culprit.  What we know for sure is that the raw peak EGT number likely is not in excess of 1760° or should not be if the engine is in good working order.  In another scenario, my ATP rated partner called to tell me we had an injector problem and that he was unable to lean normally in cruise.  He told me cylinder 3 was peaking at something near 1700°.  but that the run up was fine. I told him to do a full power mag check. Sure enough the top plug was dropping out above 2200rpm.  Easy fix as we keep a spare in the onboard tool kit.  Why would an IO360 generate an EGT near 1700° (way outside the scale I just mentioned above)?  When running on a single ignition source, the combustion process takes longer. This means the flame front is still burning during the exhaust stroke and the probe is exposed to a still burning combustion event rather than expanding exhaust gasses. This leads to elevated EGT and is easily recognized. Again one can surmise this whether you know the engine's peak numbers or not.   So @Vance Harral @A64Pilot and others, if you are flying an unknown aircraft or looking at data from an unknown aircraft and see take-off EGTs in the mid 1400s you should not dismiss it as irrelevant, it's likely not. The plane may have been operated that way for a very long time, but that is testament to the ruggedness of the engine, not its state of tune.

I mentioned @dominikos 's EGT of 875°C (1607°F) because I knew that was an unlikely EGT reading for a properly set up engine.  It looks like he edited that number to 775°C (1470°F), which is in the normal range...and proves the point that if you understand how to interpret raw EGT numbers, you can recognize when something is amiss as I did. As it turn's out it, what was amiss was likely just a typo. 

This is not new information.  I'll leave you with John Deakin's words from his Where should I run my engine column back in 2003.  John is a very smart guy and even though he has, in other contexts, admonished pilots for focusing on irrelevant differences in raw EGT numbers, he knows when they are relevant as I am certain that Mike Busch, et al...do as well.

"In general, and speaking very roughly, if you see EGTs anywhere over about 1,300°F (lower will not hurt a thing and is probably better) during a sea-level takeoff, or CHTs above about 360° right after takeoff, YOUR FUEL FLOW IS TOO LOW"    -John Deakin

 

EDIT: As it turns out, John Deakin passed away just weeks after this thread was started. His contributions to the aviation community will continue to inspire and educate for decades to come.  I never met John but he took the time on several occasions to reply to my email queries about the subject matter in his columns. His writings had an incalculable influence on how I view engine operations. I am grateful for his knowledge and generosity.

[A64Pilot]

Among other things EGT’s will follow engine compression, it’s entirely normal to see a peak of above 1600 on a low compression Lycoming engine, so you shouldn’t make generic statements 

Mounting location will also effect the raw EGT number.

‘What’s important is not the actual EGT reading, but is it the same or close to where it always has been, or has it changed significantly?

I’ve not seen an engine manufacturer reference an EGT to set take off fuel flow, I guess they could but haven’t seen it myself.

‘I have seen fuel flow referenced to RPM and manifold pressure.

‘So far as referencing EGT on takeoff, sure look at everything if you can take your eyes off of the runway, but Manifold pressure and fuel flow are what’s important, RPM as well,but it’s likely you will detect low RPM by ear.

A few have killed themselves by taking off leaned out, if you reference the fuel flow you will detect that right off.

‘I taxi leaned out, but I lean the snot out of it, I have it so lean that about 2,000 it starts missing, that way I can’t take off leaned out.

Edited July 2, 2021 by A64Pilot

[PT20J]

Thank you for your comments, Ross. While the APS guys rail against OWTs, I think they (probably inadvertently) created a few of their own. One is that absolute EGT values are meaningless. I hear people repeat that all the time. But what I'm pretty sure the APS crew meant is that unlike the CHT probes, there is no standard placement for EGT probes and the absolute value is dependent on probe placement as exhaust gases cool rapidly as they leave the cylinder. But, on a given installation, if the absolute value of EGT changes for a given operating condition it means something's different. And if the absolute EGT spread changes, that means something, too

Skip

[Bartman]

I once used raw EGT numbers to diagnose a failed magneto in flight.  Everything was fine on run up and climb and at 6,500 when I leaned everything was as usual. Minutes later I noticed all 4 EGTs were well over 100 higher than I had ever seen. I don’t remember the exact number but they were all 4 EGTs in the 1650 range and all 4 CHTs were much cooler than normal. I could only think of one thing that would cause that.  Sure enough we had a failed magneto. 
 

So yes, absolute EGT values are meaningful in the right context. 

[A64Pilot]

Neither of those were raw numbers, but an increase or decrease from normal,You would have the same data and came to the same conclusion if your instrument had no numbers, just markings as all the old ones did.

Same as the factory oil temps and cyl head temps, just green arcs with maybe the min and max annotated, raw numbers are irrelevant, noticing a change from normal is relevant.

What are APS guys and OWT?

[Vance Harral]

Shadrach, I appreciate you taking the time to explain your thinking.  It made me think more about the subject, and that's always a good thing.

A salient point you make is that there is definitely an upper limit of measured EGT.  No matter how close the probe is to the exhaust port, what the compression ratio is, measured EGT will never exceed "X".  That's a fair point, no argument from me.

But it's my understanding that the actual "X" limit is higher than you've been saying here.  High enough to think it's sketchy when you say that if your EGTs are over (some number), you have a fuel flow or ignition problem.  Furthermore, given that some airplanes have much lower peak numbers than others due to probe placement, analyzing absolute EGT values creates a communication problem that concerns me.  I get that you're only saying numbers approaching this theoretical "X" limit are probably bad.  But it's very difficult to steer people away from the incorrect corollary conclusion that numbers significantly lower than "X" must be OK.  Again using my own airplane as an example, my peak EGTs are nowhere near the 1600F you argue is "normal" peak, due to the placement of the probes.  If I tell you I'm seeing 1350F on full-power climb-out, is that OK?  Is my fuel flow decent?  Ignition OK?  The answer is, you can't say one way or the other, because I haven't told you how far from peak that is in my airplane.

I guess what would settle this is a large-enough survey of pilots reporting their observed peak EGTs under normal operation conditions.  If an overwhelming percentage report absolute numbers in a very narrow range, your argument has merit.  If the range varies by, say, a couple hundred degrees, it doesn't.  I freely admit I don't have enough data to say one way or the other.  But in the absence of such data, I feel like "absolute EGTs don't matter" is the best way of thinking and talking about the subject.

[PT20J]

3 hours ago, A64Pilot said:

What are APS guys and OWT?

APS is short for Advanced Pilot Seminars https://www.advancedpilot.com/. APS is most well known for evangelizing lean of peak operation. It was formed by George Braly, an Ada, Oklahoma lawyer and aeronautical engineer and founder of General Aviation Modifications https://gami.com/ which is most well known for the GAMIjectors, Walter Atkinson, a dentist and pilot, and John Deakin, at the time a 747 captain for Japan Airlines and an active warbird pilot in the Commemorative Air Force. John wrote an AvWeb column "Pelican's Perch" back in the 1990s that has a lot of great information and is still available on AvWeb.

The team had a falling out a few years back. Walter has since passed away from prostate cancer and John suffered a stroke and no longer flies. George owns APS, but I believe all the seminars are now online as George is primarily consumed with getting his 100LL replacement certified.

OWT is short for Old Wives Tail -- something that is widely believed to be true but is of dubious veracity and origin. I believe it may have been first used in an aviation sense by Randy Sohn, a Northwest Airlines pilot and warbird DPE who was very active in the Commemorative Air Force. Randy was one of Deakin's mentors and I believe the term likely passed to APS via John. Randy wrote a series of articles he entitled Warbird Notes. Some are unfinished, most would be improved by editing, and all are a treat to read with many great tidbits of knowledge even if you never fly a warbird. Sadly, Randy passed away last year from COVID-19. https://www.swnewsmedia.com/coronavirus/remembering-randy-sohn-renowned-savage-pilot-is-countys-first-known-covid-19-death/article_edb73646-0903-5d00-8f14-36ce6a0c383e.html

Skip

WarbirdNotes.pdf

 

[Vance Harral]

2 hours ago, A64Pilot said:

What are APS guys and OWT?

APS = Advanced Pilot Seminars.  An educational endeavor from three guys who really pushed for advanced understanding of engine management in the GA pilot community, see https://www.advancedpilot.com/staff.html.  My understanding is they got a little cross-ways with each other about the business a few years back, and I believe one of the principles has flown west.  Not sure you can actually attend a seminar with them any longer, but their articles and online courses are still pervasive.

OWT = "Old Wives Tales".  The APS guys used this phrase to describe a lot of misinformation about engine management that was and remains prominent in the community.  Like most catch phrases, it wound up becoming a bit of a lightning rod.  Sometimes people say "that's an OWT" about any airplane management technique they don't like, justified or not.

[A64Pilot]

Thanks for the explanation of APS, I sort of thought OWT may be what it was.

‘Anyway Shardach and I aren’t really far off in what we are saying I don’t think. Yes I do believe that knowing what’s normal for your aircraft in all of its instrumentation, everything from amps to oil temp is good to know, and spotting any deviation from normal is a good thing, it may help you spot an impending problem before it becomes an emergency.

An example is steadily increasing oil temp and decreasing oil pressure, might want to find a place to land.

‘My point is that numbers don’t matter, trends do, you can’t say xxxx EGT is bad, because it may be normal on one engine and the next is about to detonate itself to death, for many reasons.

‘However ever since we have had all this digital instrumentation that gives pressures to 1 PSI and temps to 1 degree, many have desired to place values on the numbers, sometimes you can and sometimes you can’t, and just because a display is to a single digit does not mean it’s accurate to that, often times they are the same old analog senders that they have always been, just now they are hooked to a digital display, and usually that kind of accuracy is not necessary.  Ever heard of measure it with a micrometer, mark it with chalk, and cut it with an axe?

As an example the old Huey had a lot of gauges and especially when we started flying goggles it became difficult to scan them all, when the skids were in the trees at night

As they were individual round gauges and were mounted from the front and had a clamp with one screw that held them in, it became common practice to rotate all the gauges so that normal operation had them all being vertical, that way you didn’t have to do any thinking about what was normal, any needle that wasn’t pointing straight up, you looked closer, cause it’s not where it normally is.

‘So we are I believe sort of saying the same thing, but different, just I don’t like digital displays as they require you to think about what number your seeing and what number you normally see, where a needle you just glance at and know.

‘So fast forward from the old Hubert to the AH-64A model, the aircraft didn’t get simpler and the work load with managing weapons systems etc got harder, but what was done that made sense was ribbon instruments, with digital readouts on the bottom, these ribbons grew in length to indicate higher numbers and were green=good, yellow=cautionary and red=bad, interestingly you had the option of turning the digital display off, most of us didn’t, we just ignored it.

D model of course is two of the same displays used in the Space Shuttle, and brought in “management by exception” meaning the engine and other gauges would auto page if one was out of limits, but that’s beyond the scope of this, but the screens still had ribbon displays on them and changed color

So I’m a fan of instruments that you can quickly scan and determine if they are in normal range, not rows of numbers because numbers require you to mentally compare the displayed number with the limits, or what’s normal.

So I think whoever put numbers on EGT didn’t do us any favors, all we needed was a needle or ribbons for multiples.

Edited July 4, 2021 by A64Pilot

[Shadrach]

On 7/3/2021 at 12:07 PM, Vance Harral said:

Shadrach, I appreciate you taking the time to explain your thinking.  It made me think more about the subject, and that's always a good thing.

A salient point you make is that there is definitely an upper limit of measured EGT.  No matter how close the probe is to the exhaust port, what the compression ratio is, measured EGT will never exceed "X".  That's a fair point, no argument from me.

But it's my understanding that the actual "X" limit is higher than you've been saying here.  High enough to think it's sketchy when you say that if your EGTs are over (some number), you have a fuel flow or ignition problem.  Furthermore, given that some airplanes have much lower peak numbers than others due to probe placement, analyzing absolute EGT values creates a communication problem that concerns me.  I get that you're only saying numbers approaching this theoretical "X" limit are probably bad.  But it's very difficult to steer people away from the incorrect corollary conclusion that numbers significantly lower than "X" must be OK.  Again using my own airplane as an example, my peak EGTs are nowhere near the 1600F you argue is "normal" peak, due to the placement of the probes.  If I tell you I'm seeing 1350F on full-power climb-out, is that OK?  Is my fuel flow decent?  Ignition OK?  The answer is, you can't say one way or the other, because I haven't told you how far from peak that is in my airplane.

 

Thanks for your response Vance. I could’ve worded my post better. I was not suggesting that none of our normally aspirated Mooney engines will generate a measurable EGT of 1600°F. I was suggesting you won’t find a scale that goes above that and that many are narrower. The reason for this is because mid to low 1500s is about the top of spectrum for most of the engines we fly (8.5-8.7CR and timing from 20-25BTDC). Many peak in the 1400s (3 of my cylinders do). Lower compression engines are less thermally efficient so turbocharged engines (which I excluded in my original post), old radials and less common flat engines with low CRs will generate higher EGTs. The numbers you mention for your EGTS are perfectly normal but belabor the point that mid 1400s during a full rich take off should be a red flag whether it’s your airplane or someone else’s. I can also tell you that 1350 is less than optimal but likely acceptable enough. I know this because at 1350 you are almost guaranteed to be less than 250ROP.  It could be a lot better. If it were my plane, I would mention it to the fuel system specialist the next time the servo goes in for overhaul.  I did this last time my servo was out and the newly overhauled servo dropped full power, full rich EGTs into the high 1100s. I lean to 1250 in the climb (as temps permit) on the cylinder with the hottest CHT #3 (also happens to be the leanest). 350 is now at the high end of the CHT spectrum for me in the climb. 

 

 

[Jocbay]

I just want to thank all of y’all for sharing your knowledge. I am new to all of this (and it’s a lot) so I’m reading constantly. I don’t always understand everything, especially on the electronics, but the more I read the more I get. 
I just wanted y’all to know.  Thanks.

jb

[FloridaMan]

High EGTs — consistent or intermittent — are often a sign of a failing magneto. Plan on a potential AOG situation at your next stop. 

[Shadrach]

1 hour ago, FloridaMan said:

High EGTs — consistent or intermittent — are often a sign of a failing magneto. Plan on a potential AOG situation at your next stop. 

Can also be a sign that the bonehead behind the yoke didn’t get the ignition switch back to both after a run up. 

Edited July 4, 2021 by Shadrach

[Shadrach]

On 7/3/2021 at 8:25 PM, A64Pilot said:

Thanks for the explanation of APS, I sort of thought OWT may be what it was.

‘Anyway Shardach and I aren’t really far off in what we are saying I don’t think. Yes I do believe that knowing what’s normal for your aircraft in all of its instrumentation, everything from amps to oil temp is good to know, and spotting any deviation from normal is a good thing, it may help you spot an impending problem before it becomes an emergency.

An example is steadily increasing oil temp and decreasing oil pressure, might want to find a place to land.

‘My point is that numbers don’t matter, trends do, you can’t say xxxx EGT is bad, because it may be normal on one engine and the next is about to detonate itself to death, for many reasons.

‘However ever since we have had all this digital instrumentation that gives pressures to 1 PSI and temps to 1 degree, many have desired to place values on the numbers, sometimes you can and sometimes you can’t, and just because a display is to a single digit does not mean it’s accurate to that, often times they are the same old analog senders that they have always been, just now they are hooked to a digital display, and usually that kind of accuracy is not necessary.  Ever heard of measure it with a micrometer, mark it with chalk, and cut it with an axe?

As an example the old Huey had a lot of gauges and especially when we started flying goggles it became difficult to scan them all, when the skids were in the trees at night

As they were individual round gauges and were mounted from the front and had a clamp with one screw that held them in, it became common practice to rotate all the gauges so that normal operation had them all being vertical, that way you didn’t have to do any thinking about what was normal, any needle that wasn’t pointing straight up, you looked closer, cause it’s not where it normally is.

‘So we are I believe sort of saying the same thing, but different, just I don’t like digital displays as they require you to think about what number your seeing and what number you normally see, where a needle you just glance at and know.

‘So fast forward from the old Hubert to the AH-64A model, the aircraft didn’t get simpler and the work load with managing weapons systems etc got harder, but what was done that made sense was ribbon instruments, with digital readouts on the bottom, these ribbons grew in length to indicate higher numbers and were green=good, yellow=cautionary and red=bad, interestingly you had the option of turning the digital display off, most of us didn’t, we just ignored it.

D model of course is two of the same displays used in the Space Shuttle, and brought in “management by exception” meaning the engine and other gauges would auto page if one was out of limits, but that’s beyond the scope of this, but the screens still had ribbon displays on them and changed color

So I’m a fan of instruments that you can quickly scan and determine if they are in normal range, not rows of numbers because numbers require you to mentally compare the displayed number with the limits, or what’s normal.

So I think whoever put numbers on EGT didn’t do us any favors, all we needed was a needle or ribbons for multiples.

I’m saying that during certain flight regimes one can make deductions about ignition and mixture on individual cylinders without any other data or previous knowledge of an engine. So I think we’re still pretty far off. In addition to flying the plane, I am also the engine’s ECU. I will take all of the real time data that I can get.  I appreciate that you feel like having access to raw EGT numbers has done us all a disservice. I think you’re wrong, but we’re all free to our opinions. I’ve tried to support mine.

Our plane came stock with a numberless EGT gauge and a single cylinder CHT gauge. Indeed you’re correct that folks managed just fine on primitive set-ups. However, they did so less efficiently and did not have nearly the understanding or picture of what was going on underneath the cowl. 

Edited July 5, 2021 by Shadrach

[Yetti]

so just for reference my EGT single cylinder probe that I guess came from the factory did not have numbers on it.  Just tick marks.

[carusoam]

2 hours ago, Yetti said:

so just for reference my EGT single cylinder probe that I guess came from the factory did not have numbers on it.  Just tick marks.

Some got an asterisk next to one of the tick marks…

Sort of allowing a pseudo calibration for it. 

Best regards,

-a-

[A64Pilot]

On 7/5/2021 at 9:04 PM, Yetti said:

so just for reference my EGT single cylinder probe that I guess came from the factory did not have numbers on it.  Just tick marks.

There was a reason for that, best explained in this article. If you read it, he explains very succinctly why displaying actual temps is irrelevant.

So for those that disagree, go argue with him

https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2010-10_egt-myths-debunked.pdf

[A64Pilot]

On 7/5/2021 at 11:50 PM, carusoam said:

Some got an asterisk next to one of the tick marks…

Sort of allowing a pseudo calibration for it. 

Best regards,

-a-

It seems that  gauge could be adjusted so that peak EGT will occur at or near the asterisk, but as peak changes at different altitudes and OAT’s, power settings etc I’m not sure what that woud accomplish, I guess to ensure that peak wil occur in the gauges scale?

https://alcorinc.com/PDF/59185.pdf

 

Its been years, but something I flew had a movable mark that you could position over peak, so you didn’t have to remember which one of the tics  was peak.

 

Edited July 7, 2021 by A64Pilot

[PT20J]

I wonder why we think we need actual CHT numbers? You could easily have a gauge that displays degrees relative to redline. But pilots would probably complain. We have become accustomed to the idea that EGT values are relative and CHT numbers are absolute. But in reality we are always measuring relative to some limit (if there were no limits, why would we care?)

One use for actual EGT is if you use the target EGT method for leaning during climb.

Skip

[FlyboyKC]

While in cruise, I see a direct correlation between higher EGT temps and lower CHTs? (up to a point) or the inverse higher CHTs and lower EGTs. Obviously there comes a point where both seemed to be balanced. 

So I have been told:
1. Keep the CHTs below 400:
2. Keep the EGT's below 1250 so you don't burn up a valve.

I can do both if I want to run full rich and burn 13-15gph but that's not practical.
My normal cruise temps are around 300ish in the summer for CHT and 1370 for EGTs at 9gph. In the winter my CHT are down to about 270ish.

Occasionally I will see 1450s on the EGTs but my CHTs never seem to get above 320, so I am thinking that my normal cruise settings should be fine if EGTs really don't matter.

[A64Pilot]

1 hour ago, PT20J said:

I wonder why we think we need actual CHT numbers? You could easily have a gauge that displays degrees relative to redline. But pilots would probably complain. We have become accustomed to the idea that EGT values are relative and CHT numbers are absolute. But in reality we are always measuring relative to some limit (if there were no limits, why would we care?)

One use for actual EGT is if you use the target EGT method for leaning during climb.

Skip

You don’t really or if you did why didn’t Mooney have the gauges marked, well they did actually, max Cyl head temp is marked, but nothing else. but why not every 10 degrees?

‘In my aircraft, in my flight environment, I can keep the Cyl head temp gauge in the middle of the green by either climbing at a higher speed, going richer or cowl flaps, from memory I think the letter f is there. Is that 360, 370 380, I have no idea, but I know it’s in the middle of the green, and middle of the green is good.

‘I do wish the gauge had been calibrated though, because I am relaying on an OLD gauge who’s accuracy is suspect.

That's enough reason to get an engine monitor, and I will when I have the funds, but I need to pay for both knees being replaced first. Until then I’m comfortable keeping it in the middle of the green.

Another reason to have an actual temp display for cylinder heads I guess is because there is a max allowed temp, but there isn’t for EGT

You have digital temp displays for the reason quoted in the article, and that’s because greater accuracy is assumed, and it sells, but primarily the companies are in the business of selling their product. I know Rob Roberts and can tell you he wouldn’t do anything that wasn’t ethical and above board, but if putting a digital display on an instrument helps sell it, why not?

I just added two washers to my oil pressure relief valve, yes it was in the green, but closer to the bottom of the green, I feel better with it towards the top of the green.

Two washers should give me about 10 PSI I think, if it stops raining I’ll run it up and see.

‘Why would you need digital temps for the target EGT method, the tic marks give you relative temps, each one is often 25F.

Maybe I don’t understand the target method, I look at what my takeoff EGT is and just maintain that in climb, and as I burn 19 GPH on takeoff it’s way lower than max.

 

 

 

Edited July 7, 2021 by A64Pilot

[A64Pilot]

1 hour ago, FlyboyKC said:

While in cruise, I see a direct correlation between higher EGT temps and lower CHTs? (up to a point) or the inverse higher CHTs and lower EGTs. Obviously there comes a point where both seemed to be balanced. 

So I have been told:
1. Keep the CHTs below 400:
2. Keep the EGT's below 1250 so you don't burn up a valve.

I can do both if I want to run full rich and burn 13-15gph but that's not practical.
My normal cruise temps are around 300ish in the summer for CHT and 1370 for EGTs at 9gph. In the winter my CHT are down to about 270ish.

Occasionally I will see 1450s on the EGTs but my CHTs never seem to get above 320, so I am thinking that my normal cruise settings should be fine if EGTs really don't matter.

To a great extent CHT is relative to engine power output, and EGT’s are also to some extent correlated to power output, but not really LOP and not really at reduced throttle. In other words you can be running at peak EGT and 55% power and have high EGT’s  and low Cyl head temps.

Or the converse snd be at takeoff power down low and low EGT from being rich, but high cyl head temps from making so much power.

‘Altitude of course reduces manifold pressure, just like the throttle does (NA engines) 

 

Edited July 7, 2021 by A64Pilot

[PT20J]

1 hour ago, A64Pilot said:

Maybe I don’t understand the target method, I look at what my takeoff EGT is and just maintain that in climb, and as I burn 19 GPH on takeoff it’s way lower than max.

That works fine with an analog gauge - with a digital readout, it’s just easier to look at the number.

Which brings up a point. We make all sorts of assumptions about measurements  based on the type of display. Digital instruments are not necessarily more accurate than analog, though they may be more precise. And the reason that a lot of gauges just have a green band is that the aren’t very linear, though we assume the are. All the gauge guarantees is that it is accurate at whatever points are numerically marked. The manufacturer was OK with the rest just being green because they don’t really care — as long as it’s green, it meets the specification. 

Skip

[Hank]

2 hours ago, PT20J said:

. . . the reason that a lot of gauges just have a green band is that the aren’t very linear, though we assume the are. All the gauge guarantees is that it is accurate at whatever points are numerically marked. The manufacturer was OK with the rest just being green because they don’t really care — as long as it’s green, it meets the specification. 

My factory green bands stop 2-3 needlewidths below the redline. I'll grab a photo if necessary. So I make sure everything is inside the green, and am usually 2-4 needlewidths below.

EGT numbers are fine for your plane, but the problem is that people want to use their own EGT numbers on someone else's plane. Like the guy a couple of posts up who cruises at 1250°, which is where I generally am while taxiing from hangar to runway--and I generally peak 1500-1525° and cruise 1450-1475°, higher than his peak value. So there, absolute EGT numbers are hooey.  

[carusoam]

I like CHTs…

I feel better when the CHTs are 380°F or less….

But….

It all depends on…

• what instrument I’m looking at….
• what sensor is doing the reading…
• where that sensor is located…

Throw on some realism….

• The best sensors are TCs…
• The best location is in a TC well…
• But…. Isn’t that just one location on a giant jug?

 

Kinda close enough to know things are going as expected…

Or something needs further review…

 

So…  tying this to EGTs…

Thermodynamics plays a huge role in EGTs…

For a NA engine…. The exhaust gas temperature is cooling wildly as the gasses escape down the pipe…

The pressure is dropping incredibly fast from inside the cylinder, to the outside world… without much resistance in the way…

The pressure drops, the gasses expand, and the temp drops… all over a time frame of micro seconds…. Which equates to big changes in T for each mm down the tube…

Some EGT sensors installed after leaving the factory… have less precise positioning of the sensor locations… as if they had no intention to use the raw numbers… or thought sensor health would be better than raw number accuracy…

 

Meaning… the absolute numbers are extra challenging to make useful….

If everyone has the same equipment, mounted the same exact way…. It becomes less challenging to use the absolute numbers…

Mooneys built in the 90s with factory installed engine monitors and EGT gauges did a nice job adding the consistency to required to simplify the use of raw numbers….

 

When using the Target EGT method of setting the mixture for max climb…  helpful for when not at SL….  This can the use of Raw EGT numbers… when you know where 200°F ROP is…

In modern Mooneys the EGT gauge is marked with a blue box… in G1000 equipped birds the blue box is white…

Sure… you can use relative temps the same way… or raw numbers if your equipment is calibrated good enough…

PP thoughts only, not an instrument guru…

Best regards,

-a-