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

[PT20J]

1 hour ago, Hank said:

 t 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.  

Exactly When I had gauges with only green bands, I took a grease pencil and marked the position of the needles on a day when everything seemed normal. After that it was very easy to note variations. And, it's easier than remembering numbers!

EGT is part of the exhaust system, not the engine, and the absolute value is somewhat installation sensitive. Engine manufacturers don't care about EGT because if the engine is operated properly, it won't get high enough to hurt anything.

But as I said earlier, if it changes significantly for a given operating condition on a given airplane, it means something has changed and bears investigation.

Skip

 

[carusoam]

The biggest things we are typically looking for with EGTs…

• A partially blocked fuel injector… causing an early peak, on one cylinder.
• EGT rise when doing a run-up… all should rise evenly, on either mag…
• Finding peak when going ROP or LOP…
• Timing changed, visible when doing the run-up…. different peaks in the L and R parts of the JPI graph.
• Dead spark plug in flight… higher EGT than normal… on that cylinder…
• Setting mixture… everyday, every flight, everywhere along the way…

PP thoughts that came to mind…

Best regards,

-a-

[Hank]

Another big EGT issue is a dead magneto. I had to richen up twice in less than a half hour to recapture my cruise setting (1450°), then suddenly it was over redline, way above 1600. Turned ignition from Both to Right, not much change; back to Both then to Left and the noise got really quiet and the plane pitched strongly nose down. Back to both and it started up again. Went to Right and releaned . . . .

[Yetti]

On 7/7/2021 at 3:08 PM, A64Pilot said:

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.

 

I think the 172 had a movable thing to mark the peak.   But wet rates said you never worry about leaning.

 

This is all a bad use of computers.   What computers are supposed to do is turn data.  (the raw CHT numbers) into information.   So what the computer should be doing is telling you that "Hey dummy your plugs are fouled on cyl 4"  

[MikeOH]

7 hours ago, Yetti said:

I think the 172 had a movable thing to mark the peak.   But wet rates said you never worry about leaning.

The term is, "Full rental power!"

[A64Pilot]

20 hours ago, Yetti said:

This is all a bad use of computers.   What computers are supposed to do is turn data.  (the raw CHT numbers) into information.   So what the computer should be doing is telling you that "Hey dummy your plugs are fouled on cyl 4"  

Might be tough to do, many failures sometimes cause nearly identical symptoms, a stuck valve may show similar symptoms EGT wise to a fouled plug, but when a device fault isolates something and says it’s X, people have a tendency to believe the thing and are hesitant to trouble shoot or think of other possibilities.

‘One Military aircraft I worked on had what your speaking of, it was called FDLS or Fault Detection and Location System, primarily electronic of course but FDLS would flag a box as bad and sometimes people would install multiple boxes fo fix the issue, and sit back and scratch their head after the third box didn’t fix the problem, when the problem was a pushed back pin in the cannon plug. Used to be the trouble shooting started at “buzzing” wires and checking cannon plugs, but when FDLS fault isolated to a box, it’s understandable why people start there.

Mostly younger people have become more enamored with electronics in general than older mechanics, with the rapid growth and capability of modern electronics it easy to understand why, modern electronics have added capabilities that even a couple of decades ago woud have been considered Science fiction.

‘But sometimes it really is as simple as a loose plug wire or magneto cap.

[Yetti]

8 minutes ago, A64Pilot said:

Might be tough to do, many failures sometimes cause nearly identical symptoms, a stuck valve may show similar symptoms EGT wise to a fouled plug, but when a device fault isolates something and says it’s X, people have a tendency to believe the thing and are hesitant to trouble shoot or think of other possibilities.

‘One Military aircraft I worked on had what your speaking of, it was called FDLS or Fault Detection and Location System, primarily electronic of course but FDLS would flag a box as bad and sometimes people would install multiple boxes fo fix the issue, and sit back and scratch their head after the third box didn’t fix the problem, when the problem was a pushed back pin in the cannon plug. Used to be the trouble shooting started at “buzzing” wires and checking cannon plugs, but when FDLS fault isolated to a box, it’s understandable why people start there.

Mostly younger people have become more enamored with electronics in general than older mechanics, with the rapid growth and capability of modern electronics it easy to understand why, modern electronics have added capabilities that even a couple of decades ago woud have been considered Science fiction.

‘But sometimes it really is as simple as a loose plug wire or magneto cap.

There are people who can trouble shoot and people that can try everything that worked for them in the past.    I stopped by the fancy jet end of the field and found the guys working on a Citation.  They were stuck at a fuel sensor that computer said was bad.  (Just for clarity I have never flown on a Citation)   The fuel sensor was ohming out good.   So I said show me the rest of the circuit.   There were two things upstream that could also be throwing the flag.  So I said look there.   Back to modern GA engine monitors, they still are lacking in that they only show data and require the pilot to create the information.    I do believe some have the auto lean function like the G1000 and the Skyview.    But with all that sensing of data it needs to go further.   Since pilots are getting less informed.    Like the poor guy on FB that had a glass fuel bowl on his Mooney that was leaking.   Pretty sure I have fixed several of those on tractors.