If I increase the FF to 17.6 (85% power) CHTs overshoot 380 approaching 400 (til I lean again). I did (quick and dirty, so unreliable) lean test and EGTs peaked with a 19.1–19.8 FF (0.7 spread), though the peak EGTs ranged from 1614 (EGT3) to 1492 (EGT6) - spread of 122 (CHT3 383 CHT6 350). So I think the mixture / injectors are OK (assuming the lean test was OK).
Why are my CHTs so hot? =D
Why is the TIT spread so large? It seems that one side of the motor (CHT1, 3, 5) is hotter than the other side (CHT2, 4, 6) and this is backed up by the diff in TITs? Though EGTs (left vs right) seem to average the same (but maybe they’re affected less by cooling)?
Is the EGT spread of 96 normal? Does it indicate a problem in injectors / mixture? Or can it be because of cooling? (Does EGT spread reflect mixture imbalances or cooling more?)
Is the CHT spread of 41 normal? Does it indicate a problem of cooling? (Does it reflect cooling or mixture imbalances more?)
Why is cylinder 6 cold?
Why is cylinder 3 hot?
Can you guys sustain 85% cruise power? What fuel flow, OAT, altitude and CHTs? What’s a typical EGT at that setting?
Confirm that all (turbo) cirrus cruise numbers are LOP and you can’t operate 85% ROP because of the fuel flow restriction (no FF > 18)?
Why does the fuel flow restriction exist if you can go past the “red box”? Also, if I can climb full rich, why can’t i cruise full rich?
John - A lot of the COPA members don’t monitor the public side, but hopefully someone will chime in here. The member side does have a Turbo specific forum folder that talks in great detail about many of your questions. It’s worth the membership for that and many other conversations if you are not already a member.
Load your engine data at www.cirrusreports.com and become a Copa member and you will hear a solution.
But two things I can tell you. Your fuel flow spread at peak Egt is off. It should be a maximum of .5 gph, ideally lower. Have your fuel nozzles cleaned. You also need more air (manifold pressure) in your engine. Have it adjusted to 30". If it is still hot (cht), an increase in RPM will help.
Good luck
John - I don’t think any of the “spreads” are relevant - don’t obsess with those.
At that OAT at that altitude, you were in ISA+22 conditions - very hot. At that wimpy MP of 29.6, you just weren’t getting enough air for the fuel flow you were using, since the density of the air is low because of its temperature. IOW, you were running richer than ideal. At ISA+22, I’d be looking to get about 30.5 MAP if I could, and likely the max fuel flow usable would be about 17.3 or so, to keep CHT’s below 380.
I see you were running at 2550 RPM, which means you had the throttle open quite a bit, so that tells me that your absolute pressure controller needs to be adjusted to give you more MP in the summertime.
The Turbo will do a lot better in the high 'teens, too. I rarely fly as low as you were flying except on very short trips.
Now that you have joined COPA, see this post, and actually that whole thread will be of interest.
If you’d like to talk about operating your TN, you can call me at 805 448-8292.
I’d like to suggest John to read another thread on COPA which is very informative on how to operate our TN/T engines at max LOP power in relation to density altitude: critical altitude.
As for your excellent analysis, a higher MP is needed, I was wondering about the injectors, if the GAMI spread is 0.7 gal/h then maybe tuning the injectors would be a good idea. I hope John has the massive plugs as they will help with cooler CHTs.
Patrick
NB: Is not the T° ISA+16°C? I thought the T° lapse rate in ISA is 6.5°C/1000m.
Any Dr worth his weight will make you answer many questions before telling you bad news or good news.
Do you have any other engine data to post?
Has this situation been consistant since you owned the aircraft?
Any maintenance functions previous to the complaint?
Any maintenance functions trying to correct the complaint?
Have you ever done a GAMI fuel nozzle spread check?
How many hours on the aircraft engine? Magnetos since 500 inspection? last timing adjustment?
Have the fuel nozzles been cleaned lately?
but some comments on what can be gleaned from the data posted…
The TIT split is large not so large that you should have a problem with #3 CHT…but the split should be closer to 40 degrees with the right #2 above the left. EGT relationships will change based on the “Back pressure” of wastegate valve position…by the design nature of the installation some EGT’s will be different…1 low 2-3-4 higher, 5 low and 6 slightly higher than 5. TIT split is a result of position of the turbos on the exhaust manifold and wastegate valve clocking (Dictated by clearance inside the cowling)
Did you bump the power lever back and thus reduce MP/RPM when this excursion occurred? (Both drop…) if you retard the power lever when you see CHT’s rise when LOP you are increasing the mixture ratio…ICP (combustion pressure) and temperature follows (UP)
Please answer the questions above and upload more data.
I believe I did retard the power lever on the flight you inspected - after I level off, I set 29.6MP (as per the checklist).
The situation has been consistent with this aircraft. Unfortunately I’ve flown it only in the summer so I don’t yet know whether it’s an OAT issue. But I’ve seen reports of planes flying at 85% in high OATs.
I don’t manage the maintenance of this plane so I don’t know the details regarding what tests they’ve done and last time they cleaned nozzles, etc.
You’re right. I overlooked that he mentioned a 0.7 GPH GAMI spread. If that is indeed the spread, yes, by all means that is an issue that should be corrected.
I think the suggestion to have the TAT/GAMI guys and/or Jim B look at it is an excellent one.
Yes, it is closer to ISA + 16. I had quickly eyeballed a graph and my eyeballs ain’t what they used to be! According to this calculator, it would be between 16 and 17. (Of course, that’s based on the 1976 data and there has been inflation since then!)
Thanks a lot for the info. I managed to do a lean test and the spread looks good to me - 0.4 FF spread. I understand that <= 0.5 is the target? In fact, what is a good (normal?) value if I’m aiming to sustain 85% performance? Here’re the results (graph) of the lean test:
It’s not a rental. I don’t own it but I know the owner and it’s three of us flying it.
I’ll have to read up / check on the other items you posted (wastegates, etc.) to continue debugging. I should note that the right turbine in the aircraft got changed recently (it’s new) and I wonder whether that has to do with the much larger R TIT.
