The EGT Myth
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- čas přidán 8. 12. 2016
- Maintenance expert Mike Busch, A&P/IA, presents an informational webinar about the EGT Myth. Debunks myths about CHT and EGT, explains what they really mean and how they should be used in the operation and troubleshooting of piston aircraft engines. Savvy Aviation offers Professional Maintenance Services to owners of General Aviation aircraft, such as: Savvy Mx (Professional Maintenance Management), Savvy QA (Expert Consulting), Savvy Prebuy, SavvyAnalysis (Engine Data Analysis) and Savvy Breakdown Assistance. For more info see savvyaviation.com and www.sportys.com/pilotshop/spor.... This channel offers videos about those services, and webinars hosted by Mike Busch which were produced by the Experimental Aircraft Association (EAA) and sponsored by Aircraft Spruce and Specialty.
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Thanks to this webinar, I now understand why I had two failing cylinders I am overhauling (high CHT's) now because I was running only 50 degrees rich of peak on those short hamburger runs and less than full rich on takeoff on hot days.
I had a EGT on one cylinder go high on climb out. Was going to do the inflight mag check when I leveled off. Plug started firing again at the top of the climb and the EGT came back to normal. Cleaned the plugs for that cylinder after landing.
EGTs are important on liquid cooled engines. A liquid cooled engine with a good cooling system won’t show an increase in cylinder head or water temperature even when combustion temperature gets high enough to melt the pistons.
EGT is actually measuring the temperature of the gas entering the turbine of the turbo supercharger. This is important as to high a temperature will destroy the turbo.
Can someone just climb full rich, set MP and RPM, then pull the mixture til rough, then richen for more power as the CHTs allow?
IF (that's a big if) you use expensive materials, the TC at at near the junction of the two leads can have a "relatively" small thermal mass. Modern electronics can make "many"/"several" temperature measurements and determine the maximum temperature of the TC hot junction.
I just started renting a hangar in Santa Maria. I have a 1968 Cherokee 140 with the Lycon O-320 120HP STC. It's 1,500 hours SMOH, and the combustion chamber, oil consumption, and compressions are all great.
It has no EGT/CHT gauges. I'm going to install a multi-probe CHT gauge. Would you install EGT probes as well, or would you be comfortable operating a carbureted O-320 without EGT information?
EGT and CHT are related. EGT is a great indicator of AFR in a properly timed engine. It can also be a great indicator of timing slip. CHT is a more useful in keeping an engine safe from thermal destruction, but don’t discount EGT as a useful tool.
If EGT didn’t mean anything I would’ve melted down a lot more engines. Sustained vs current is a big difference.
EGT: Exhaust Gas Temperature. CHT: Cylinder Head Temperature.
@ 2400 rpm it takes .025 seconds to make one revolution. To make it easier to understand let’s just say every four revolutions take 1/10th of a second. Now you place a probe in that stream of hot gas that is cooling and heating. I don’t think it (the temperature probe) can tell that it’s heating and cooling. It’s happening so fast there’s no way the probe can measure the difference. Much less the gauge react to it even if it could. Now, can you make the gauge move up and down with the mixture control?
Sorry Mike. EGT is real, and it does have meaning.
A few things that I see
*Claim that the EGT probe has high thermal mass, but despite the thermal mass these engines are run at relatively static conditions so the average EGT is meaningful.
CHT has a much much hither thermal mass.
*EGT tells you when a cylinder has reached the stoichiometric ratio
*EGT tells you when a cylinder has started to reach lean missfire
*EGT can be used to identify best economy, or best power faster and more accurately than CHT can after finding peak EGT
*EGT can be used to verify combustion during a mag check, and to check timing to some extent
Is a GAMI spread of .1-.2 gph good? ;)
EGT is just a number. It has a lot to do with how far the probe is from the exhaust valve. That exhaust gas is cooling from the time it passes the exhaust valve. Agree, the numbers are meaningless.
They need valve temperature sensors.
Could have said this all in 30 seconds! But hey....gotta make an evening out of it! 🤷♂️
Funny, EGTs don't mean anything but he's constantly referring to them. I think most of what he is saying applies to fuel injected turbocharged engines because they can develop rated power all the way up to their critical altitude. Naturally aspirated engines loose power as altitude increases and above 5000 feet you can't develop more than 75% power so as long as as CHTs stay in line, lean to the engine until it starts to get rough and then richen until the roughness goes away. On carbureted engines, EGTs are an "Apple", learn what they are (for each cylinder) at different altitudes and power settings when your engine is healthy and if they change and stay changed you should check that things are ok. Very interesting subject but I think It would have been beneficial to the listeners to differentiate between NA, carbureted, fuel injected and turbocharged engine behaviors.
snaproll94e enrich after you peak? Are you one of those rich of peak drivers? There is a lot more to what a pilot should be doing to manage the engine than just lean to rough and then enrich the mixture.
EGT's are an Apple? what does this mean?
@@DiMoraDiamond , because of all the variables in the engine and probe installations, they just are a number. Learn the numbers for your airplane, what the peaks and normal values are at specific power settings for your plane/engine, and adjust the mixture based on the hottest one. If an egt strays from what you have found to be normal, then you or your A&P need to do some investigating.
@@doncarlson8391 aaah, you were making an “apples to oranges” type reference.
@@doncarlson8391 Your explanation on knowing what EGT and CHT temps are right and working for your engine is spot on , no two engines are alike and no to pilots and how they operate their engines are alike. Know your engine parameters best advice….
I have to disagree with this philosophy. I agree that EGT is not an absolute value but it does give a relative value of the temperature of the engine. As the CHT goes higher, the EGT will become higher. That's how the vapor and gases flow through the engine. From what he says, you can have EGT of 3000° and the cylinders may be running cool a sea breeze. NOT SO.
dvsmotions good thing you are not a well known aviation speaker. Keep your nonsense to yourself.
Does Mike remind anyone else of Captain Kangaroo ? Is he Captain Ks son ?
High EGT won't wreck an engine as the exhaust gas temp is a 'used' figure, as mentioned it's just a number, it's the CHT temp that is critical!
High EGT will certainly burn up a turbo. EGT is basically measuring the TIT of your turbosupercharger.
Funny, EGTs don't mean anything but he's constantly referring to them. I think most of what he is saying applies to fuel injected turbocharged engines because they can develop rated power all the way up to their critical altitude. Naturally aspirated engines loose power as altitude increases and above 5000 feet you can't develop more than 75% power so as long as as CHTs stay in line, lean to the engine starts to get rough and then richen until the roughness goes away. On carbureted engines, EGTs are an "Apple", learn what they are (for each cylinder) at different altitudes and power settings when your engine is healthy and if they change and stay changed you should check that things are ok.