Leaning operation

[Tommy]

Hi everyone!

 

I have got an EGT / OAT gauge with degree celcius (see attached)

 

How do I lean with this gauge? 

 

50 degree F is equivalent of 10 degree C.

 

Does it mean, if I want to operate at 50F LOP, I lean it to peak then lean until the EGT comes down by half of the small devision?

 

Another stupid question: will LOP combined with high cruise power (24" and 2500 rpm) gives you high CHT?

 

Thanks guys!

 

 

[Jeff_S]

That gauge is either measuring just a single cylinder, or it measuring the composite exhaust gas stream further down the line. Either way, it's not going to give you the information you need to see how each cylinder is doing during the leaning process, so it would not be generally recommended to try going LOP with that instrumentation. Also, it's not clear what plane you're flying or whether you have a carburetor or fuel injection.  The former is also not generally recommended for LOP operations.

 

The answer to your second question is "No".  I routinely run my engine at WOT and 2500 RPM no matter what the altitude, LOP.  Instead of looking at the number of degrees LOP I'm running, I tune it so that my CHTs are in the 330-340 range as this is what really matters. But you need a real engine monitor like the JPI and decently balanced injectors to do this.

[Tommy]

Thanks for the reply!

 

It's a 1981 M20J. That's a EGT gauge. The CHT is next to Oil Temp above the instruments.

[Marauder]

The factory installed EGT and CHT instruments are installed on what they believe to be the "hottest" cylinder. Most of the time they are on the number 3 cylinder. To lean with it, you would pull back the mixture steadily until the EGT reaches the highest temperature before it starts to come back down. Note this temp on the gauge and then begin pushing the mixture back in until you reach a temperature below the peak specified up in your POH. Usually something like 50 to 100 degrees "rich" of peak. When I bought my Mooney, I installed a GEM engine analyzer and found that my hottest cylinder would change sometimes and it was not always the number 3 cylinder. To do lean of peak, you need to monitor all CHT and EGT temperatures. The JPI 830 I own has the ability built in to do a LOP or ROP lean. It doesn't sound like you have an engine analyzer. If true, this would be my next addition. Nothing more critical than knowing what your engine is doing. Sent from my iPad using Tapatalk

[N201MKTurbo]

Your gage shows each small increment as 25C which is 45F. We use 50F because it is two tick marks on the gage, nothing else magical about it.

So if you want to be 50F ROP or LOP just go a needles width more then one tick mark on the gage.

[scottfromiowa]

Just do the "Big Pull" and forget the EGT single probe. Steady/quick pull to engine rough. Then enrichen to smooth operation. You are lean of peak and burning 9.5-10GPH. If down low pull a little throttle to get MP at 25. You are out of red box.

[Tommy]

Pardon my ignorance, but what is the "red box?"

 

I tried LOP last 2 flights at 5500+ feet and the engine seems to be running quite smooth and reasonably cool even with two ticks (ie. 100F) lean. 

 

But I guess without individual CHT probe, it's best to run ROP then?

[Hank]

Tommy--

 

Each tick mark is a change of 25ºC, which is also a change of 25 x 1.8 = 45ºF. [On your gauge, 700ºC = 1292ºF; 800ºC = 1472ºF; D100ºC = D180ºF]

 

Proper leaning is generally done this way:

• Climb to desired altitude, level off and allow the airspeed to climb and stabilize.
• Set desired manifold pressure and RPM. Many people fly at full throttle and 2500. Scott recommends no more than 25" of manifold pressure to prevent high pressures inside your cylinders, which cannot be monitored or easily calculated.
• Lean the mixture in one steady pull, watching the EGT increase. At some point, it will reach a peak value then begin to decrease.
• If your engine continues to run smoothly, you are now Lean of Peak. Generally one or two tick marks is good.
• If your engine begins to run rough, push the mixture richer. Many people think of 50ºF rich of peak [two tick marks] as being bad for the engine, and would suggest running three or four tick marks richer than the peak EGT temperature.
• Both Rich of Peak [ROP] and Lean of Peak [LOP] are temperatures lower than the peak EGT temperature.
• You will not achieve the speed or range shown in the book unless you lean the mixture properly. What does your book suggest?

[Tommy]

By 50F, you mean one tick mark on my celcius EGT gauge, right?

Is it safe without sophisticated engine monitoring to run LOP? My engine can run 100F LOP smoothly and CHT temp within 380F does it mean that I can safely run 50F LOP.

[DS1980]

It should be running cooler than 380F at 100 LOP. That's REALLY lean. I would recommend getting a per-cylinder monitoring system. You can run LOP with your instrumentation, but you're really not going to get the big picture. Your engine seems to be quite capable of LOP, since you can go so lean and still be smooth. The key is that if it is running smoothly, as that indicates all your cylinders are producing the same power.

 

I have attached the red box. Inside the red area is where the engine is producing Internal Cylinder Pressures (ICPs) that from a metallurgy prospective are not good for an engine. Please notice that if you are running at 60% power or below, you cannot hurt the engine by experimenting. Now you can upset the engine by taking it to extremes, but you can't hurt it, so get into the POH and find your HP charts and determine what setting will put you at 60% or below.

 

Also, getting back to your temperatures. The "hot" issue at the moment, on the forum anyway, are weaknesses in the baffling of some engines since we are getting into summer. I would suggest taking a look at yours or having a mechanic (one that knows what they are looking for) take a look. As I said, 380F at 100 LOP is hot.

 

And about LOP: the entire point of LOP is to fly more efficiency. There are settings LOP that are more so than other. Best Efficiency, although not completely known, will be somewhere around 15-30 degrees LOP. Try to stay "richer" than 50 LOP and see what your temps are. You should be able to run here, although I am concerned your CHTs may be too high. As you mentioned, 380 should be a max.