CHTs too cold?

[N201MKTurbo]

So, @201er stated that he gets lass heat while LOP, and @PTK says it is all about EGTs and the EGTs are higher while LOP.

While this is unquestionably true, is there more to it than that?

Maybe so, maybe not. EGTs measure temperature, not heat. Heat is a complex subject with all that latent and sensible stuff. I think it deserves a bit more investigation.

Way above my paygrade. Are there any chemists/physicists on board that would like to chime in?

[Little Dipper]

With all the time you guys are spending watching CHT and EGT are  you spending any time looking out  the window and flying the plane?   Just wondering.   

 

[PT20J]

Just now, Little Dipper said:

With all the time you guys are spending watching CHT and EGT are  you spending any time looking out  the window and flying the plane?   Just wondering.   

 

....And all the glass on the panel -- don't forget to stare at that!

Of course, with an autopilot to fly, and TAWS and ADS-B traffic to warn you if you are about to hit anything, who needs windows? 

[r0ckst4r]

2 hours ago, M20S Driver said:

I did something similar after listening to Mike Busch's webinar.  I am targeting 330+ in Cruise.  This works fine in ROP but LOP is a challenge for a couple of cylinders that stay below 330.

I am a bit uncomfortable going to 360.  I am sure we will hear from guru's on this topic

Speaking specifically on the IO550g, Continental recommends CHT between 360-400 in cruise.  The reasons for keeping the CHT in that range were discussed earlier in the thread however it seems that by consensus that keeping it colder than that range is not a problem unless it is quite a bit lower. 

[PT20J]

This might be of interest:

Camguard-Parts-1-to-3.pdf

[carusoam]

2 hours ago, r0ckst4r said:

Speaking specifically on the IO550g, Continental recommends CHT between 360-400 in cruise.  The reasons for keeping the CHT in that range were discussed earlier in the thread however it seems that by consensus that keeping it colder than that range is not a problem unless it is quite a bit lower. 

if you read Bryan Lloyd’s explanation of why 370°F CHT is optimal... that is interesting...

If you read the The APS guy’s take on lean anywhere you want when below 65% bhp... you are good to go...

If you decide to lean 50°F LOP at altitude... I ask why you are flying a Mooney?

We have two choices...

• Speed 
• Efficiency

At 50°F LOP... the gasoline is fully burned before it leaves the cylinder... and you have really good efficiency...

Of course some of that extra efficiency is coming from flying slower...

If you select an altitude that limits your NA engine to 65% or less bhp... you can run at peak, or a little less than peak... convert all the gas to power... and fly your fastest... while efficiently using all your fuel.

Keeping CHTs below 380°F is a general standard used for long cylinder life... temps above this start to weaken the aluminum cylinder’s strength. So the wear rate increases marginally with every degree warmer.... Still safe to fly up to the redline... just the wear rate is increased...

In the cold... you may see CHTs dip below 300°F pretty easily...

One thing to keep your eye on... as covered in Skip’s article above is the temperature that LL reacts and leaves the engine with the exhaust... Too cold, you may be building a lead shot collection... see if you can find that temp... it may be down near 220°F...

If your CHTs are too low for your comfort... so will your cabin heat... feel free to go ROP...

Just don’t think that going 50°F LOP is somehow better for you or your engine... unless efficiency is your thing...

If efficiency is your thing... Vz is a really interesting topic... 

We have a few efficiencies...  that some MSers strive for... not all MSers... and not all the time....

• Burning 100% of the gasoline and turning it to power...
• Getting the most Nmpg
• Not using up the cylinders before TBO...

PP thoughts only, not a CFI...

Seeing if @CFII (Bryan Lloyd) is around...

Best regards,

-a-

[M20S Driver]

2 hours ago, r0ckst4r said:

Speaking specifically on the IO550g, Continental recommends CHT between 360-400 in cruise.  The reasons for keeping the CHT in that range were discussed earlier in the thread however it seems that by consensus that keeping it colder than that range is not a problem unless it is quite a bit lower. 

My CHT spread is about 35 deg, so I set the coldest one to 330 deg ROP and hottest one is around 365 to 370 deg.  With 20-40 deg LOP, I would be lucky to make it over 320 deg on the coldest cylinder at 65% power.

 

Here is my favorite part of the PT20J's article:

Hot Side: Run your engine hard, at least occasionally, 65-75% ROP or LOP enough to just stay out of the GAMI ‘Red Box’ (www.advancedpilot.com/redbox.html) and Cylinder Head Temperatures (CHTs) below 400°F. These will maximize combustion temperatures and minimize lead deposit build-up on your exhaust valve stems. The ideal range for CHTs is from 325°F-380°F. A lower CHT is fine if you are at a higher power setting.

[PT20J]

I usually cruise my little IO-360 at peak EGT and max. CHT of about 380 F. I live out in the west and often cruise 10 - 12K feet. Once I get my Surefly working, I expect to get about the same performance slightly LOP. Down low, I often use 2500/24" and 20 F LOP. (Probably 2400/25" would be a better choice).

I don't ever think about red boxes: It makes my head hurt. As an engineer (electrical, not mechanical -- but I did take thermodynamics) I find the idea that Lycoming and Continental engineers don't know how to operate their engines offensive. I think both companies have long track records of good engineering -- excepting a few inevitable goofs along the way. As for assertions that we now know more than was known when these engines were designed, I invite anyone with an interest to search the NASA Technical Reports Server for old NACA reports from the 1930's and 40's -- everything that has been stated in the last twenty years about engine operation was researched and understood back then. Especially interesting is NACA-TN-772. At 75% power and below, with CHTs below 400F, I'm convinced that my little Lycoming four banger will live long and prosper.

Skip

 

 

[r0ckst4r]

@PT20Janother great article

@carusoam Yes, I think I didn't articulate myself well.  At first like most newer pilots I was sticking to the POH but now based on what I've been reading for a while now I've gone to running much closer to peak EGTs and keeping the CHTs closer to the 360-400 operating range.  I'm just glad I'm not alone (and not crazy)

[carusoam]

For sure.... you’re not alone...   

At MS, your never alone...  even in the middle of the night...

But, you and all your flying friends are nuts... 

The POH for the O is pretty good...

At 300 plus pages or so, it covers LOP in a few columns of the power chart... just a hint of what is available to you... it is hidden with the standard words ‘best power’ and ‘best something else...’

It is really helpful to get the insight of the APS guys, and the engine knowledge of the Savvy guys...

For the coolest insight of operating the IO550, speaking with Bob Minnis Author of the 310hp STC is really cool... @StevenL757 is often in contact with Bob... I spoke with Bob when OHing my engine... My friend @Cris recommended the conversation after I flew his Screamin’ Eagle...

Man time flys at Mooney speeds... 

PP thoughts only, not a mechanic...

Best regards,

-a-

[StevenL757]

On 3/10/2014 at 7:21 PM, Cruiser said:

I was reviewing my recent flights and see that my CHTs have been running around 300°F and even lower in cruise. About 60% power and LOP of course.

On a flight at 9000' cruise OAT of -2°F the temperatures were

C1   C2   C3  C4  C5   C6

287 290 294 313 318 300  Avg

335 332 339 357 366 356 Max (in climb)

Is this too cold for extended cruise time say of two hour or so?

I checked with both Brian Kendrick and Bob Minnis on this.  These are perfectly normal temps.  You’re ok as long as they don’t get below 250 in cruise for any length of time.  During extreme cold weather ops, you’ll likely see them going below that briefly on approach and landing, but they’ll typically warm up again prior to shutdown due to the tight cowling.

[carusoam]

If not sure who Brian Kendrick is...

He gets mentioned while demonstrating the O3 to Flying Magazine...

https://www.flyingmag.com/pilot-reports/pistons/mooney-ovation3/

-a-

[Davidv]

8 hours ago, carusoam said:

If not sure who Brian Kendrick is...

He gets mentioned while demonstrating the O3 to Flying Magazine...

https://www.flyingmag.com/pilot-reports/pistons/mooney-ovation3/

-a-

He’s an extremely meticulous Mooney mechanic who used to run the factory service center.  Very nice guy and if you take your Mooney to him no stone will be left unturned.  Some people like this, some not so much (leave with more Mooney and less money).

[aviatoreb]

10 hours ago, StevenL757 said:

I checked with both Brian Kendrick and Bob Minnis on this.  These are perfectly normal temps.  You’re ok as long as they don’t get below 250 in cruise for any length of time.  During extreme cold weather ops, you’ll likely see them going below that briefly on approach and landing, but they’ll typically warm up again prior to shutdown due to the tight cowling.

What happens at 250 degrees that makes that the threshold number?

[StevenL757]

2 hours ago, aviatoreb said:

What happens at 250 degrees that makes that the threshold number?

Nothing specific that I'm aware of, but Bob may have other input...he's unavailable until the afternoon.  On the IO550 though, it's the bottom of the green arc, which I typically try to avoid.

[tmo]

I believe the lead scavenging agents need a certain temperature to work well, if the head is too cold, lead gets stuck places where it shouldn't.

[r0ckst4r]

I think WHAT happens has been already eloquently discussed earlier in the thread and the question posed (I'm assuming) is why 250 was chosen as the magic number.

The only answer I have seen thus far is what was just posted and that is because it is the lower limit on the green arc on our CHT gauge 

[carusoam]

Expect the lead scavenging temp occurs at and above the beginning of the green arc...

See what Mr. Minnis says, then check with the MS chemists... for the lead bromide reaction...

 

This gives us some hints, with regards to EGTs... but not so much for CHTs where the deposits typically occur...

https://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/technical-talk/techart-18-30071600.html

 

PP thoughts only, not a mechanic... or chemist...

Best regards,

-a-

[GeeBee]

I thought of this thread today. I left KABR where the surface temp this morning was M13 C, 7 F. I climbed to 11,000 to grab a piece of a monster tail wind. So there I was sitting in my R, WOT, 2400 RPM, 12.3 gph at 50 LOP doing 210 knots. It sure was nice but I could not hold her. Two cylinders were at 253 and going down. I elected to go closer to peak and got the temps up to about 260. So I started messing with it and even at 50 ROP I could not reach 300. Having an "optimal temp" is not too optimal when you have to throw buckets of fuel to get there.

 

[carusoam]

GB,  increasing RPM will give a few more flames per minute into the same system... raising temps some more... more useful heat, same cooling...

Would need to verify how much, but directionally it is the right idea...

Best regards,

-a-

[PT20J]

Wonder what the head temps were for water cooled auto engines back when mogas had lots of lead?

[larrynimmo]

Just now, PT20J said:

Wonder what the head temps were for water cooled auto engines back when mogas had lots of lead?

My thoughts exactly!

[GeeBee]

Raising RPM yes, but I only had 100 left. I don't think that will do it. 

I can tell you this. I just came off a cylinder break in with mineral oil and the difference between mineral oil and Aeroshell 15W-50 is huge on head temps. You can see it from takeoff to touch down. I saw differentials of up to 30 degrees. Then again, if you do a little course "finger tribology" on the two grasping a screwdriver dipped in them, you will feel the difference.

 

[jaylw314]

EGT - the average temp of exhaust gases

CHT - the temp of the metal cylinder head

Neither is what we really want to know, which is the (average) temperature of the spark plug head and valves.  That's where the temp needs to be adequate to scavenge lead-- you don't get lead deposits in the cylinder head or the exhaust pipes.  I suspect that a cold CHT due to fantastic cooling probably does not significantly reduce this temp at typical cruise powers.  Otherwise, Cirrus's and other planes with effective air cooling would be falling out of the sky left and right every winter in the upper Midwest and Canada, right?

[r0ckst4r]

I don't know about you guys but what I get from all this is as long as my CHT is below 360 I'm leaning to peak EGT and getting as many knots as I can for my fuel.