Jump to content

Optimal CHT


Tommy

Recommended Posts

With GAMI, my new engine can go quite lean and run without missing a beat. I am quite fortunate to be able to run the CHTs as low as 310-320 across the board. 

Questions

1) is there such a thing as 'too lean.'?

2) is there such a thing as optimal CHTs? Is 320 too low?

Thanks guys!

Link to comment
Share on other sites

Quick answers: no and no.

Too lean only means slower speed and less fuel burn so you be the judge of when your too "slow".

Optimal CHT are temps below 400. After that temp you logarithmically increase fatigue, wear and changes in metallurgy.

Below 400 you don't get significantly better, so 320 in my book is as good as 380. But no one can argue that cooler is better. There is a point where it's too cool, but you'll never see that in the air.

Good job on LOP, what engine?

Link to comment
Share on other sites

Below 280'ish you begin to lose the ability to break down the lead blow through.  Pipeline flyers that fly low, slow, in the winter can experience this.  Probably not much of an issue for Mooney operations but yes you can get too cold with effort.  

Link to comment
Share on other sites

At lower altitudes the °LOP can get really interesting...

A sign of how well balanced the intake system is.  If you get to about 90°F LOP before the engine shuts off, this is pretty good.

Note: this was on my first IO550...  °LOP available is affected by MAP and DA I am guessing...

My willingness to go deep LOP at 10k' is pretty limited.

Best regards,

-a-

Link to comment
Share on other sites

PV,  

what is the altitude you would be able to restart at without the TC operating?

This sounds like one of those questions like the comfort level of running a tank dry in flight.

Restoring air flow is more of a challenge than restoring fuel flow.  FF comes back with the flip of a pump switch.

There is an LOP thread for TC'd Mooneys (or two or three) that is an interesting read.

Best regards,

-a-

Edited by carusoam
Link to comment
Share on other sites

1 minute ago, carusoam said:

PV,  

what is the altitude you would be able to restart at without the TC operating?

This sounds like one of those questions like the comfort level of running a tank dry in flight.

Restoring air flow is more of a challenge than restoring fuel flow.  FF comes back with the flip of a pump switch.

Best regards,

-a-

Dunno, don't want to find out :D

I think I have read in the mid teens on the t360, t520 I don't know. I also don't k ow if I could crank the prop out of feather. I've done it on twins but usually with the luxury of a bit more airspeed to help get it windmilling

Maybe if it stumbles you can fatten it up in time, again idk.

Link to comment
Share on other sites

Anyone run lop up in the flight levels? I'd like to try it but I'm a bit worried about putting the fire out and not getting it lit again. I think our spread is .2 so it should run pretty smooth.


Especially at flight levels. I've written extensively about LOP ops, and learned much from the work of George Braly and the team at GAMI. I'm not a religious LOP guy, when I want to go fast I'll run it rich but if I have a nice push in the tail, I'll nearly always lean back, especially when high. A good balance between ROP and LOP ops does a great job in keeping things clean and saving fuel.

A GAMI spread of .2GPH is excellent. On my Bravo I got it to .3 or slightly better.

Go give it a try. You won't put the fire out.
  • Like 1
Link to comment
Share on other sites

4 minutes ago, carusoam said:

Oooooh...  Very Rocket specific question on that....

Try a search on (Rocket LOP Erik) see if anything falls out...

Best regards,

-a-

I think I have read some of his posts.

Other than the prop it shouldn't be any different from a bravo in operation. I hope.

Link to comment
Share on other sites

10 hours ago, M20F said:

Below 280'ish you begin to lose the ability to break down the lead blow through.  Pipeline flyers that fly low, slow, in the winter can experience this.  Probably not much of an issue for Mooney operations but yes you can get too cold with effort.  

That's the only thing I've seen about minimum temps. The lead scavenging agent in fuel needs 250F IIRC. 

Link to comment
Share on other sites

5 minutes ago, DVA said:

 


Especially at flight levels. I've written extensively about LOP ops, and learned much from the work of George Braly and the team at GAMI. I'm not a religious LOP guy, when I want to go fast I'll run it rich but if I have a nice push in the tail, I'll nearly always lean back, especially when high. A good balance between ROP and LOP ops does a great job in keeping things clean and saving fuel.

A GAMI spread of .2GPH is excellent. On my Bravo I got it to .3 or slightly better.

Go give it a try. You won't put the fire out.

 

Thanks, I've tried it in the mid to high teens but haven't had the nerve higher :) thanks for the input.

I'm not way into it either, I'll burn 20gph to go fast over 15 to go 15 knots slower. It's not that much in the grand scheme but it would be nice as you say with a tailwind to squeeze out max range. I don't like to run the snail that hot, my partner will run it 1600+ which is allowed but not a good idea in my opinion.

Link to comment
Share on other sites

About the part related directly to the Rocket's full feathering Prop...

The Prop is controlled by oil pressure.  Oil pressure is generated by a gear pump in the prop's governor.  As long as the prop is turning, it generates it's own pressure to keep turning...

If the engine were to stop turning, the prop oil pressure would be dumped, the blades would feather...

Restart would probably then involve using the starter to get the engine turning below the altitude where the mixture would work...

This sounds complex like a process engineer's kind of realm.  The POH update from the STC probably has a more simple procedure to follow.

restarting a non turning Rocket engine from high altitude may involve...

0) getting down to the recommended altitude for restart to occur.  (Related to the compression ratio of the engine)

1) setting the mixture for the low level MP available?

2) using the starter to initially turn the engine, or point the nose more down hill?

3) using the fuel pump to ensure fuel flow?

4) making mixture adjustments (or sweep) as the TC comes alive?

5) losing an induction hose or getting a significant leak is the reason to practice this type of activity. Turbos can also fail... this is one of the reasons TN'd engines with a CR closer to an NA engine are becoming more popular.

PP thinking out loud. Not a mechanic or CFI, very little TC experience...

Best regards,

-a-

Edited by carusoam
Link to comment
Share on other sites

From a BSFC starts to increase again around 60°LOP, so I would say that is too lean if your goal is harnesing the most energy from every gallon of fuel.  From an engine health standpoint, if the plus are staying clean then they are hot enough (of course you can't know this in real time and must inspect to see how they look).  I find that my angle valve IO360 runs quite cool just past peak at higher altitude on the deck 30-50LOP produces more than acceptable CHTs.

Link to comment
Share on other sites

If you have a good engine analyzer that can output the data, I can't recommend the Savvy Analysis folks high enough. They have a great online tool that allows you to input your data and do your own analysis free of charge...but if you want their expert insight, it's only $129/year and they will help you tweak and tune to your heart's content.

Here is a link to a recent flight during which I did their Analysis Profile, which includes three ROP-LOP cycles and then a LOP mag test. It's interesting data, but I'm also doing this to test out to see if this link actually works!

https://www.savvyanalysis.com/flight/1823020/0e94c1d9-db6b-4eb4-8b67-4f964cb084f9

I know I can get to it, but I'd like to see if others can as well, so let me know. Thanks.

  • Like 1
Link to comment
Share on other sites

3 hours ago, Jeff_S said:

If you have a good engine analyzer that can output the data, I can't recommend the Savvy Analysis folks high enough. They have a great online tool that allows you to input your data and do your own analysis free of charge...but if you want their expert insight, it's only $129/year and they will help you tweak and tune to your heart's content.

Here is a link to a recent flight during which I did their Analysis Profile, which includes three ROP-LOP cycles and then a LOP mag test. It's interesting data, but I'm also doing this to test out to see if this link actually works!

https://www.savvyanalysis.com/flight/1823020/0e94c1d9-db6b-4eb4-8b67-4f964cb084f9

I know I can get to it, but I'd like to see if others can as well, so let me know. Thanks.

How come you have a TIT on your monitor? Is that the original EGT probe? I always have been curious between the difference of the 2. Your CHT temps are very similar to mine. 1 & 6 always way cooler than the rest. 5 the hottest even after the pixie hole. 

Link to comment
Share on other sites

The TIT is the "7th" probe which is actually at the confluence of the left-side exhaust manifold. It's the probe that actually feeds the single EGT readout in the main view of the G1000. It is usually about 100° hotter than the individual probes. If I had the Acclaim then this would really would be the TIT...I guess they just left it there in the Ovation for consistency with the G1000 models.

  • Like 1
Link to comment
Share on other sites

4 hours ago, Jeff_S said:

Here is a link to a recent flight during which I did their Analysis Profile, which includes three ROP-LOP cycles and then a LOP mag test. It's interesting data, but I'm also doing this to test out to see if this link actually works!

Linked worked perfect. Lots of good data points. What is your normal GAMI spread? Fuel flow looks good across the checks. Seems more of an airflow/cooling for the temp differences at your cylinders. Interested in what Savvy had to say for this flight. I'm a turbine guy and am still learning recip with these new data tools. Thanks for posting. 

Edited by Garryowen
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.