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Lean Range Test Results

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alpinelakespilot2000

Well Known Member
I'd appreciate comments on a lean range test I did today. I have done it previously, but had not been able to do it WOT (as it should properly be done) until I had my prop repitched. It has been repitched and here are my results:

Test conditions:
WOT
8000' MSL
~9500' DA
-Made 4 runs, starting at full rich and taking about 6-8 minutes to slowly lean until all 4 cylinders peaked. Then went to full rich, allowed temps to stabilize, repeated the process 4 times.

Average EGT delta between full rich EGT and peak EGT:
Cylinder #1: 173.3F
Cylinder #2: 107.8F
Cylinder #3: 251.0F
Cylinder #4: 229.8F

The order in which each cylinder reached peak was always 2-1-4-3 and the standard deviation for each cylinder on all four runs above was within +/- 10F, so I'm pretty sure I got some accurate averages.

Average fuel flow delta from first peak to last peak was 1.14gph so, as expected, running LOP is tough, though I will experiment with some carb heat to see if that helps.

My main concern, especially given how high up I was, #2 seems to be running really lean (and that cylinder does generally run hot relative to the others) but anything else I can take from these numbers and/or should do or check for?

Thanks.
 
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What are the actual CHTs? That's the most important number for engine long term health. Carbureted engine is going to be tough to get an even spread.
 
Carb Heat

Steve,

Try a few levels of carb heat - I can really influence the mixture using varying levels of carb heat.

Also try the throttle a bit off the WOT stop.

Good luck - I can get my O-320 to run quite well LOP
 
Thanks Pete. I m thinking the backing off the throttle a bit is key. I ran the same lean range test with the throttle backed off a bit and my lean ranges were exactly the opposite. The front two were the richest and the back two the leanest. Go figure. Actually I've learned to go back and forth between WOT and partial throttle in my climbs to deal with temps due to those front and back cylinders heating up and cooling opposite of each other. Not sure that this is the best way to handle it, but it sort of works.

My Dynon says i can get LOP, but just barely. Will start experimenting with some carb heat too.
 
Sig600 said:
What are the actual CHTs? That's the most important number for engine long term health. Carbureted engine is going to be tough to get an even spread.
Click to expand...
Usually I don't have trouble keeping cruise temps below 380 or so, but WOT climb, even at 500fpm, on a quick turn around can get #2 up into the 400s or low 410s pretty quickly. Otherwise I have to manage climb temps by alternating b/w WOT and partial throttle to keep climb temps below 400 in the summer. See post above responding to Pete.
 
Mike Busch talks about using carb heat in his book, pick up a copy. Quick read lots of valuable info.

Some things I'd look at for climb temps...
Fuel flow at take off, are you getting enough fuel?
Baffle sealing, how good are they? Are you losing air anywhere?

DanH? He's pretty smart on this stuff.
 
alpinelakespilot2000 said:
Average EGT delta between full rich EGT and peak EGT:
Cylinder #1: 173.3F
Cylinder #2: 107.8F
Cylinder #3: 251.0F
Cylinder #4: 229.8F
Click to expand...

I ran the same lean range test with the throttle backed off a bit and my lean ranges were exactly the opposite. The front two were the richest and the back two the leanest.
Click to expand...

But was the delta between cyls as large? Some other cylinder only has a ~100 degree rich-to-peak with the new throttle position?
 
alpinelakespilot2000 said:
I'd appreciate comments on a lean range test I did today. I have done it previously, but had not been able to do it WOT (as it should properly be done) until I had my prop repitched. It has been repitched and here are my results:

Test conditions:
WOT
8000' MSL
~9500' DA
-Made 4 runs, starting at full rich and taking about 6-8 minutes to slowly lean until all 4 cylinders peaked. Then went to full rich, allowed temps to stabilize, repeated the process 4 times.

Average EGT delta between full rich EGT and peak EGT:
Cylinder #1: 173.3F
Cylinder #2: 107.8F
Cylinder #3: 251.0F
Cylinder #4: 229.8F

The order in which each cylinder reached peak was always 2-1-4-3 and the standard deviation for each cylinder on all four runs above was within +/- 10F, so I'm pretty sure I got some accurate averages.

Average fuel flow delta from first peak to last peak was 1.14gph so, as expected, running LOP is tough, though I will experiment with some carb heat to see if that helps.

My main concern, especially given how high up I was, #2 seems to be running really lean (and that cylinder does generally run hot relative to the others) but anything else I can take from these numbers and/or should do or check for?

Thanks.
Click to expand...
I will reinforce what Sig600 referred to when he asked about the CHT's. Information about EGT temps is valuable when initiating the LOP process and when you reach the LOP point but what really matters once you get to the point of running LOP are the CHT temps. CHT temps may or may not be in lock step together in a carbed engine but if they are well below 400 DEG during LOP operations your engine will be working fine. Pay attention to what the CHT readings are during LOP cruise settings and let us know what they show after your next test flight.
 
RVbySDI said:
I will reinforce what Sig600 referred to when he asked about the CHT's. Information about EGT temps is valuable when initiating the LOP process and when you reach the LOP point but what really matters once you get to the point of running LOP are the CHT temps. CHT temps may or may not be in lock step together in a carbed engine but if they are well below 400 DEG during LOP operations your engine will be working fine. Pay attention to what the CHT readings are during LOP cruise settings and let us know what they show after your next test flight.
Click to expand...

Thanks for the input. In general, I pay almost no attention to EGTs operationally outside of LOP ops and for checking ignition health. Accordingly, I know CHT's matter much more than EGT but the CHT's are only secondary to what I'm interested in here and why I posted the initial question. I do, in fact, have some CHTs that run hotter than I like, but one of the reasons this may be the case is because I have one or more cylinder running really lean. That's why I ran Mike Busch's lean range test to see if a lean cylinder might be the cause of my high CHT. If I can fix that, then maybe the CHT issue will take care of itself. (???)
 
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DanH said:
But was the delta between cyls as large? Some other cylinder only has a ~100 degree rich-to-peak with the new throttle position?
Click to expand...

Thanks Dan. Yes, it was. The highlighted red below is the a test I ran last year before my prop got repitched allowing me to go WOT for the test. At that time, not realizing I was supposed to do the test WOT, I did it at partial power and ended up very concerned about the lean (and hot) #3 and #4 cylinders. Full thread here: http://www.vansairforce.com/community/showthread.php?t=101743&highlight=lean+range
In the process of tracking down some high temps, I did a lean test through Mike Busch's Savvy Analysis Program. The lean range for my four cylinders are:
1-205F
2-222F
3-68F
4-62F
Test was conducted at 6000 ft at about 60-65% power, starting from full rich, then leaning until each EGT peaks.
I still get these same numbers, more or less now when I run the test at less than full throttle.

I may be wrong, but this wide disparity between what the lean ranges are from WOT (#1 and #2 very lean) to what they are at reduced power setting (#3 and #4 lean) leads me to believe that at least some of my CHT problem is a fuel distribution one rather than primarily one of my baffles (admittedly probably not perfect and that I continue to work on) or a possible induction leak which I've tried very hard, with no avail, to detect. Is there any possible truth to this?
 
alpinelakespilot2000 said:
Thanks for the input. Actually the CHT's are only secondary to what I'm interested in here. I do, in fact, have some CHTs that run hotter than I like, but one of the reasons this may be the case is because I have one or more cylinder running really lean. That's why I ran Mike Busch's lean range test to see if a lean cylinder might be the cause of my high CHT. If I can fix that, then maybe the CHT issue will take care of itself.
Click to expand...
This is exactly why it is important to monitor the CHT readings during LOP operations more so than the EGT readings. So, I am not quite following why you would consider the CHT readings as 'secondary' to what you are looking at. You are there and I am not, so if the EGT's are helpful to you more so than the CHT's then I am sure you will figure things out. Let us know what you find out.
 
RVbySDI said:
This is exactly why it is important to monitor the CHT readings during LOP operations more so than the EGT readings. So, I am not quite following why you would consider the CHT readings as 'secondary' to what you are looking at. You are there and I am not, so if the EGT's are helpful to you more so than the CHT's then I am sure you will figure things out. Let us know what you find out.
Click to expand...
I agree with you, Steve, that long term, CHTs are what I am most interested in controlling. Short term, to identify lean cylinders, Mike Busch's lean range test uses EGTs. That's why the EGTs are primary to me at the moment. Thanks again for your thoughts.
 
alpinelakespilot2000 said:
Thanks Dan. Yes, it was.......

1-205F
2-222F
3-68F
4-62F
Test was conducted at 6000 ft at about 60-65% power, starting from full rich, then leaning until each EGT peaks.[/COLOR]
I still get these same numbers, more or less now when I run the test at less than full throttle.
Click to expand...

Wow.

I may be wrong, but this wide disparity between what the lean ranges are from WOT (#1 and #2 very lean) to what they are at reduced power setting (#3 and #4 lean) leads me to believe that at least some of my CHT problem is a fuel distribution one rather than primarily one of my baffles (admittedly probably not perfect and that I continue to work on) or a possible induction leak which I've tried very hard, with no avail, to detect. Is there any possible truth to this?
Click to expand...

In the immortal words of Sir Arthur Conan Doyle....

Maybe Pete and Alex will jump in here. I for one had no idea carbed fuel distribution was this screwy.
 
DanH said:
I for one had no idea carbed fuel distribution was this screwy.
Click to expand...

Yep, nothing unusual about a 200F+ spread on carbed Lycomings. Assuming port flow and CR is near equal, the only big remaining variable is mixture distribution. Fuel injection typically gives far less spread without resorting to heating the charge or fiddling with throttle plate angle.
 
Screwy - Very....

My distribution was a mess until I started to play around liberally with carb heat. It is second nature now to set power, lean to a known fuel flow, then tweak the carb heat to even up the CHTs. I can move the carb heat knob and watch the mixture being steered with the rising and falling EGTs. Move the knob to cool a CHT.

MY CHTs were very even until I Hortonized my #3 cyl with an air chute.....now it is my coolest......Thanks Dan......

I have a CS prop and run EI with touch of advance that seems to make LOP ops smoother at the settings where I run.

I just noticed the pics of my original analysis are expired in that thread - I will try to update and post them here. I have a powerpoint as well.


DanH said:
Wow.



In the immortal words of Sir Arthur Conan Doyle....

Maybe Pete and Alex will jump in here. I for one had no idea carbed fuel distribution was this screwy.
Click to expand...
 
RVbySDI said:
This is exactly why it is important to monitor the CHT readings during LOP operations more so than the EGT readings. So, I am not quite following why you would consider the CHT readings as 'secondary' to what you are looking at. You are there and I am not, so if the EGT's are helpful to you more so than the CHT's then I am sure you will figure things out. Let us know what you find out.
Click to expand...

I think what he's trying to point out is the uneven distribution to each cylinder which is measured by EGT.

Until engine monitors came along over the last few years we probably never really cared that it was so uneven, but now that we have electronic ignition and a whole lot more data for fine tuning we're seeing just how much variable there is in a carbed engine. Once the fuel/air mix leaves the carb, it's at the mercy of the fluid dynamics of the intake system. Some guys just get lucky, others have big challenges like this.
 
Thanks Sig, yes, I did see where he was concerned about the differences in temperatures between cylinders. I think that is an inherent situation with carbed engines that is difficult to compensate for. That fact is one of the multiple reasons I went the fuel injection route. In my case with fuel injection, EGT's are within ~20 deg of each other while CHT's range <10 deg from each other when running LOP. The even distribution of fuel using fuel injection makes those tight spreads possible.
 
Mixture

Try wrapping the #2 intake pipe with exhaust insulation material. There have been some reports that this will richen the mixture, at least slightly.
 
Link to Graphs

Here is a link to some slides Alex and I presented to the Twin Cities Builder's group.

They show the results of FI and Carb testing to validate LOP ops.

Carb heat has been working for 7 years to get me LOP - I really think EI and a bit of advance helps as well.
 
Engine efficiency vs air frame efficiency

petehowell said:
Here is a link to some slides Alex and I presented to the Twin Cities Builder's group.

They show the results of FI and Carb testing to validate LOP ops.

Carb heat has been working for 7 years to get me LOP - I really think EI and a bit of advance helps as well.
Click to expand...

Great data Pete! It is always interesting to study the data. I was wondering how the integrated picture looked on trip cost. Looks like the air frame efficiencies outweigh the fuel gain efficiencies from running LOP. Slowing 10 Kts saves $7.15 per hour and adds 4 minutes per hour to the trip time.

MPG Delta Delta Delta
GPH IAS INM/gal minutes Gal cost ($5.5/Gal)
6.9 143 20.7 6.29 -1.5 -$8.25
7.1 148 20.8 4.05 -1.3 -$7.15
7.5 151 20.1 2.78 -0.9 -$4.95
7.7 152 19.7 2.37 -0.7 -$3.85
7.9 153 19.4 1.96 -0.5 -$2.75
8 156 19.5 0.77 -0.4 -$2.20
8.2 157 19.1 0.38 -0.2 -$1.10
8.4 158 18.8 0.00 0 $0.00
8.6 157 18.3 0.38 0.2 $1.10
8.8 157 17.8 0.38 0.4 $2.20
9 158 17.6 0.00 0.6 $3.30
9.1 158 17.4 0.00 0.7 $3.85
9.3 158 17.0 0.00 0.9 $4.95

INM/gal - Indicated nautical miles / gal

So I guess the message is if you are really cheap, slow down and enjoy the view. :D If you have time to burn, minimum cost should be at maximum glide distance velocity.
 
Mogas

Just to spice things up, or throw gas on the flames, run LOP on mogas! My O-320 loves it, and it really makes the cost go down. As always YMMV......

Wow - I just reread that and feel a bit ashamed, but I am leaving it.

Kudos to Alex on the analysis - he taught me what I know about the topic.


BenNabors said:
Great data Pete! It is always interesting to study the data. I was wondering how the integrated picture looked on trip cost. Looks like the air frame efficiencies outweigh the fuel gain efficiencies from running LOP. Slowing 10 Kts saves $7.15 per hour and adds 4 minutes per hour to the trip time.

MPG Delta Delta Delta
GPH IAS INM/gal minutes Gal cost ($5.5/Gal)
6.9 143 20.7 6.29 -1.5 -$8.25
7.1 148 20.8 4.05 -1.3 -$7.15
7.5 151 20.1 2.78 -0.9 -$4.95
7.7 152 19.7 2.37 -0.7 -$3.85
7.9 153 19.4 1.96 -0.5 -$2.75
8 156 19.5 0.77 -0.4 -$2.20
8.2 157 19.1 0.38 -0.2 -$1.10
8.4 158 18.8 0.00 0 $0.00
8.6 157 18.3 0.38 0.2 $1.10
8.8 157 17.8 0.38 0.4 $2.20
9 158 17.6 0.00 0.6 $3.30
9.1 158 17.4 0.00 0.7 $3.85
9.3 158 17.0 0.00 0.9 $4.95

INM/gal - Indicated nautical miles / gal

So I guess the message is if you are really cheap, slow down and enjoy the view. :D If you have time to burn, minimum cost should be at maximum glide distance velocity.
Click to expand...
 
petehowell said:
Steve,

Try a few levels of carb heat - I can really influence the mixture using varying levels of carb heat.

Also try the throttle a bit off the WOT stop.

Good luck - I can get my O-320 to run quite well LOP
Click to expand...
Thanks for the replies everyone. I'm starting to think that I don't really have any major problems other than very poor distribution. I think I have a plan, though.

First, I'll try some baffle chutes (per DanH and Michael) on cylinders #2 and #3 to try to address climb CHTs that are not as low as I'd like.

Second, I'll work on experimenting with throttle position and carb heat to improve my cruise distribution. Pete: I'm trying to set up a methodical approach for this. Do you have any suggestions for how much of each I might expect to need to try? How do you "measure" how much you use?

Thanks again.
 
BenNabors said:
Great data Pete!
MPG Delta Delta Delta
GPH IAS INM/gal minutes Gal cost ($5.5/Gal)
6.9 143 20.7 6.29 -1.5 -$8.25

So I guess the message is if you are really cheap, slow down and enjoy the view. :D If you have time to burn, minimum cost should be at maximum glide distance velocity.
Click to expand...

Interesting numbers, I was up the other day and had this performance.
6.2GPH 144 IAS 23.2 INM/gal

RV7 IO-360-C1E6( slightly modified)

Are these numbers realable between different aircraft? Most likely not, with errors in calibration. It's still nice to see mileage better than what my GMC gets!

I am quite sure a rocket leaned out beside me will be burning less than that, as has been proven every time we fly together.
 
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