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Buckaroo

EGT question for the experts?

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My ride is a 2007 CTSW. Just to ease my mind while flying today as other days my left EGT was measuring 1470 or so and my right was about 1380. These numbers concern me as the left side is approaching the yellow scale. The temps were OST of 28 degrees. 

Please educate me as to the concerns with regard to EGT and what indications should worry me. My Dynon maybe giving me too much unnecessary information! 30 years ago I would of wondered what EGT was! I never had that on my Cessna airplanes of the time!

 Thanks 

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One higher than the other is perfectly normal. It just means one EGT probe may be off a little, the carb with the lower temp is slightly richer than the other or you could have a tiny air leak on the higher temp carb. Depending on throttle position these temps change. A carb synce may change this some. Typically you may even see higher temps in the 4K rpm range because the carb run a bit leaner there. (don't run in the 4K range for cruise, I was just mentioning it)

Your temps are fine.

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It does run hotter but that isn't the reason. Many engines are designed to run within a specific rpm range and to do so otherwise puts unwanted stress on them over time. The Rotax was designed to run over 5K rpm. This doesn't include reduced throttle for landings because that's not where you spend most of the engine's life. It can be run at 5500 rpm its entire life and Rotax basis many of its stats on the fact it can get to 5800 rpm and 5500 rpm. Most owners cruise around 5100-5400. 

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EGT readout's primary use is to determine where peak is so the pilot can choose a setting relative to peak like ROP or LOP.  The actual temp isn't terribly important.

The Bings Otto lean or at least try to so the EGT gauge ends up being mostly decoration for us.

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1 hour ago, Roger Lee said:

It does run hotter but that isn't the reason. Many engines are designed to run within a specific rpm range and to do so otherwise puts unwanted stress on them over time. The Rotax was designed to run over 5K rpm. This doesn't include reduced throttle for landings because that's not where you spend most of the engine's life. It can be run at 5500 rpm its entire life and Rotax basis many of its stats on the fact it can get to 5800 rpm and 5500 rpm. Most owners cruise around 5100-5400

Thanks for the clarification.

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i have a 2006 CTSW -  i am considering  installing a EGT.   Just to match my current gauge sizes i opted for UMA 1 1/4 gauge.   Would it be best if i install 2 probes and could i just have a switch to flip flop between the 2 probes or is 1 probe sufficient.?    (is a special switch needed for this - or can i just install any toggle switch? )  Thanks!

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Someone will correct me if I'm wrong I'm sure, but...

In my mind EGT is primarily a function of mixture.  In a CT with no mixture control, there is no practical way for you to adjust the mixture to change EGT in flight unless you install something like a HACMan, so it's kind of a useless metric.  Let the Bing carbs do their job.  Flight Design and/or Rotax would probably require all CTs to have EGT installed if it were critical to safe operation of the engine.

There are of course circumstances where it might be helpful, like if you're doing a lot of high altitude flying and deciding whether to change the needle position.

Just IMO.  

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I have seen airplanes with a selector for multiple EGT probes displayed on one gauge. All I have seen were rotary type switches.

Andy, The dual EGT can be helpful in providing information on a carb imbalance issue.

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The EGT can also be used to troubleshoot a defective spark plug (or associated wire) -- if the engine is running rougher than usual and the EGT is higher than usual in the specific EGT cylinder then one of the two spark plugs may not be firing correctly.  This results from partially combusted burning gases flowing past the EGT probe.

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Hi Cdarza,

Make it two gauges or like Tom said make it a simple duel gauge. One gauge and two needles. This is fairly common. Put the EGT probes on cylinders #3 & #4. Mount the probes 100 mm (3.9") back from the exhaust flange as specified in the Rotax installation manual. Easy to install. Just need to drill a hole in the exhaust pipe and clamp the EGT in place. Wiring is very straight forward and easy.

I to like EGT read outs. Helps me correlate and confirm with other numbers what's going on in my engine.

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Clear this up for me.  Lean running produces higher or lower EGT?  Same for fouled plug.  Would cylinder with fouled plug run higher or lower EGT temp

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4 minutes ago, Runtoeat said:

Clear this up for me.  Lean running produces higher or lower EGT?  Same for fouled plug.  Would cylinder with fouled plug run higher or lower EGT temp

With leaning the temp will go up until the point where it starts to go back down. That is called lean of Peak. As you lean beyond peak the engine will start to run rough.

A cylinder with one sparkplug fouled may or may not indicate a different exhaust gas temperature. When you do an ignition check, the engine will run rough and the cylinder with the fouled plug will be significantly colder.

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The 1400F+ EGT range tells me I'm getting a better more complete burn and a squeak more power vs something down in in the 1200's & 1300's. The max is 1616F. So if you have too cold EGT's that just means burning rich which means poor fuel burn, more carbon build up and less power and less efficiency.  

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Is it written somewhere that a Rotax is designed to run 5000 or more, not any lower RPM for

extended amount of time?

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Another use for EGT is to indicate when the pilot has done something incredibly stupid.

Starting off on a trip to New York last week I had less than 150 rpm drop on either side during the "Mag" check. However, incredibly, I left the ignition switch in the "Left" position instead of returning it to "Both" after the run-up.

It is difficult even for me to believe that I did this. Normally I count the switch clicks back and forth and never take my hand off the key until its back on "Both". Lame as it sounds, the only excuse I have is the distraction of a P-51 in the runup area. I was rushing to take a couple pictures and still get out in front of it so as to avoid getting blown over when he turned toward the active.

Anyway, the first indication was rough idle performance. I had to nudge the throttle forward to keep the engine running at the runway hold line. Any reasonably prudent pilot would consider this reason enough to abort but I had just successfully completed the run-up, demonstrating takeoff power, and so was on my way.

18 minutes later the "Caution" light started blinking along with one of the four EGT readings on my FlyDat (an old-style engine instrumentation system). I pulled the power back and returned to my home field.

It wasn't until I shut the engine off that a realized the problem.  

The highest EGT temperature I saw was 1660F right before I pulled the power. Though this is above the 1616F limit the engine was still operating normally and sounded fine so I started it back up, repeated the run-up and headed on my way again with no further anomalies for the duration of the trip.

Mike Koerner

 

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Mike,

Thanks for sharing that. It's a good lesson for all of us. I have fell victim to similiar events over my two flying careers.

This is a little off the subject of "EGT" but . . . . . Distractions are the #1 reason why pilots make mistakes.

When unexpected things happen, it draws attention away from present tasks (like adding oil during a routine oil change, setting the proper QNH altimeter setting, completing a checklist for a phase of flight or yes . . . even completing a mag check.

If flying solo, the only thing that I know of which guards against distractions is . . . good training and self discipline.

 

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Totally agree Bill.  My most recent flirtation with distraction last summer caused me to takeoff with the pilot door wide open.  Not just unlatched, but OPEN.  It seems impossible, but my friend behind me in another airplane was impatient and making fun of me for being slow as I went through my takeoff checklist.  He annoyed me, I got distracted, and I was a hundred feet up before I realized my door was wide open.  I was able to reach out and close it easy enough, but I kicked myself for days about making such an obvious, boneheaded mistake.  Never would have happened if I was on my game and not distracted.

A guy in a DA-40 took off two years ago for my home field with the rear door unlatched, and it departed the airplane.  Only the specifics of my airplane’s design prevented a similarly bad (or worse) outcome.

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