Not in response to Roger.
Took a better look yesterday. Altitude 9,000’; 76% power, 15.6GPH (LOP), 171KTAS
Plane is 2017 GTS, incl. FIKI & EVS.
15.6 gph at 9000’ is ROP.
I use 15.0 gph at 3500’ and lower altitudes. That is LOP. At 9000’, a fuel flow around 13.8 gph will be LOP.
Something is off here. Probably a miscommunication. An NA 22 at 9000 at ISA and 2550 RPM will need about 20gph to make 76% Power, at about 100dF ROP.
Robert’s numbers look like turbo LOP numbers; 15.6gph at 30 inches MP will get you about 76% in a T.
Robert,
Paul and Tom are correct. That looks more like a best power setting to me. Best power is the most power you can produce for a given altitude.
There’s just no way he’s getting 76% Power at 15.6gph at 9000 feet in an NA. He would need more like 20+gph.
So unless i am completely off base (which is possible), this is what i do… i am WOT, at 9k’, which is 75-76% of power, then i lean to 15.6GPH per the COPA FF Cart… i thought that was/is LOP? Do i misinterpret the chart?
Below from a slightly older flight - descending through 6.6k’; I will be flying down to MIA this coming week and will take some more pics at 9k’ with the power, FF settings.
IMG_0418.MOV (27.1 MB)
From the chart’s SR22 column and APS LOP formula for power: FF 15.7 x 14.9 (LOP constant) = 233.93 HP / 310 Max HP = 75.5% power.
It appears to indeed be a LOP setting to me…although I personally typically have not been flying LOP above 65-70% power.
By the time you level off at 9000, you should have already leaned (incrementally) to about 20 GPH (top of green fuel flow arc plus about a gallon per hour).
Your percent power at this point should be around 75.
If you then lean to about 25 - 50 degrees LOP, your percent power will drop to about 65%, and your full flow will be about 13.5 - 14gph.
15.6gph / 9000 feet / 76% power are simply an impossible combination of values.
One simple way to set a “safe” LOP cruise mixture is to aim for an average EGT of around 1400dF. Whatever your altitude, this temperature generally assures you are operating out of the red fin.
And now I apologize for exacerbating the thread creep…
Hey Tom,
I am leaning after the first 1000’ or so to the top of the green… then continue to do so as I climb…
I will take a clean, purpose made picture / video Tuesday when i am flying down to FL. I may be off, but i don’t believe i am.
Here one at 8k’ (and a heavy headwind).
https://drive.google.com/open?id=1U1yJcVdNmjzxFSot8xuGBXhGfsp_OAMS
Be careful. If you are indeed LOP that would be true, slow but true.
1400 EGT is also a ROP reading. Depends on the FF vs air available. One side of that is a 100 LOP. And the other is a 100 degrees ROP. Both look the same. But one is best power and one is a 100 LOP. Which BTW is probably, depending on the plane, significantly leaner than best economy.
Good point. I should’ve clarified 1400dF LOP…
True. Watching the video Robert is running 2670 RPM at 20 degrees F. That can explain high FF and being LOP. Plus since FF has to match density altitude at 20 F that is some dense air so it takes more fuel. I don’t usually fly in air that cold so I can’t estimate (and I am too lazy to calculate) it so it seems plausible he was LOP.
While that Does not hurt the engine it is loud and more vibration so I run WOT at lower RPM.
Video was useful.
Tom:
Robert is correct in what he is doing and has been taught well. You are making an assumption that is not always true. That is, you think you have to lean to at least 50 degrees LOP to operate. As your total power decays with altitude, you are out of the red fin totally at some point but usually above 8000 feet. At that point any fuel flow LOP is OK and Robert is finding the best one at 9000 feet and indeed he is at 73% power doing so. Higher up the best place to operate is at peak EGT. Horrors?? Have we not been told peak EGT is the worst place to operate the engine?? Not up that highe where your peak possible power( due to high DA) is less than 65-70%.
What Robert is merely doing is getting the best combination of power and efficiency out of his engine at a higher altitude. Good job Robert!
Good debate and good info. The below may just be my battle against boredom while in cruise so any comments are appreciated.
I typically experiment a bit with RPM settings as I tend to coax a couple more knots per hour by pulling it back just a bit…back less at higher altitudes (NA pilot so “high” is like 11k) and back more at lower altitudes. The prop does generate drag and it gets boring on a long 3 hour cruise :). Interestingly enough DA, etc do seem to impact this so I don’t use a prescribed setting. I start at about 2630 and ease up and down from there.
Brian, thanks. Glad to hear its OK. In fact, i used the COPA Lean of Peak operations guide you gracefully shared with me during one of our most recent flights.
A synopsis of that same document is here (page 3):
“When reaching your final cruise altitude, level off and leave everything alone until the airspeed stabilizes.
This seems to take a good 2-3 minutes in the Cirrus. Then position the power lever / RPM as follows:
2000’ … 2500 RPM (Max MP at 2500)
4000’ … 2600 RPM
6000’ or above… 2700 RPM
The IO-550 is perfectly happy running at 2700 RPM all day long. This is where a good noise- canceling
headset pays off! For running LOP, you generally want to be WOT: Wide Open Throttle (or as wide open as
the above RPM guide will place you).”
So flying at >6k’, my RPM should be, according to this doc, at 2700 RPM, which for me is 2670. THEN i lean to 15.7 per the table, which gets me to approx 75%, 170KTAS and hopefully (!) LoP.
Interesting discussion and thanks for posting. Does your fuel flow with the blue cyan “bifurcate” into a ROP and LOP setting? I just took delivery of a SR22 NA 2018 and it does that; but you have to pull the throttle back to 2500 RPMs area before it sets this picture up.
Based on what the Cirrus engine guys say at that power setting you aren’t “babying” the engine. They also do not buy into the operation of LOP at WOT as we know. Not surprising since that’s what Continental’s book says but it would seem to make some sense that running the engine at 2670 RPM would be considered running it pretty hard?
HI Brand, congrats on your 2018 G6!
Yes, you have to pull the power (and/or mixture) back to approx 76% for the cyan to show up. Its in the POH somewhere but do not have it handy.
You are assuming an awful lot about my rather innocuous comment there, Brian, in addition to reading into my comment things that were clearly not intended or stated.
I have spoken to Robert personally.
And now this thread needs to return to the OP’s intent.
Tom, Brian, I appreciate all the guidance you give to ‘us’ newbie cirrus drivers. I think we got it sorted out. Thx both for your excellent guiidance and interest to get to the bottom of it!