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Question about LOP operation and HP %age

L

lr172

Well Known Member
I know that Lycoming doesn't recommend leaning below 75% and I suspect that may be conservative as well, at least when at lower loads (i.e. lower MAP's as seen with FP prop configs). I have been setting up at cruise in the 80% power area and then go LOP. That brings my % of HP down to 70-75% power once LOP. My question to the experts: Does this approach fall within the <75% power recommendation for safe performance? I have seen the detonation charts that Dan has posted and it seems that under square configurations showed no detonation potential. My typical cruise configurations are similar to 2600 & 23".

Thanks,

Larry
 
lr172 said:
I know that Lycoming doesn't recommend leaning below 75%.....
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Above 75%. To paraphrase, Lycoming's "Big 'Ole One Size Fits All Statement" says when below 75%, you can lean as you please.

Lycoming's statement was published in the days before they acknowledged LOP operations. In general, the pro-detonation region centers at about 25 ~ 50 ROP. They didn't want operators to go there at high power. We still don't.

However, it's possible to run LOP at well above 75%, with three caveats. (1) You have to pass through the pro-detonation zone to get to the LOP side, (2) when you do, you need to get really LOP, not just a little bit on the lean side of peak, and (3) that means actually finding peak is tricky.

I have seen the detonation charts that Dan has posted and it seems that under square configurations showed no detonation potential. My typical cruise configurations are similar to 2600 & 23".
Click to expand...

In general, I agree. However, remember that "safe" has more factors than just RPM and MP, notably compression ratio, CHT, intake air temperature, oil temperature, and ignition timing. Here's the thing....watch for adverse CHT indications, notably a rapid rise.
 
Mathematically and no other factors considered, 23" MP is 76.87% power.

Why push the envelope in this area, pull it back to 22", you can lean (according to Lycoming) to your hearts content.
 
A minor point in this particular instance, but any time you throttle the engine you are giving up VE. WOT is one of the keys to pulling good BSFC numbers.
 
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Toobuilder said:
A minor point in this particular instance, but any time you throttle the engine you are giving up VE. WOT is one of the keys to pulling good BSFC numbers.
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This is in part my desire for doing this. At 8000 and WOT, I am around 80% power and 2800 RPM. By going LOP and staying WOT, I drop to 2700 and 70-75% power with a good fuel flow.

Larry
 
Ok, so if you set 75% and lean to 50 lop you end up with about 65%.
If you now push the throttle to regain the 75% with a Bendix style FI can you assume you still have the same fuel/air ratio?
BTW, Dynon claims the % power reading is still good on the lean side of peak.
 
DanH said:
Above 75%. To paraphrase, Lycoming's "Big 'Ole One Size Fits All Statement" says when below 75%, you can lean as you please.

Lycoming's statement was published in the days before they acknowledged LOP operations. In general, the pro-detonation region centers at about 25 ~ 50 ROP. They didn't want operators to go there at high power. We still don't.

However, it's possible to run LOP at well above 75%, with three caveats. (1) You have to pass through the pro-detonation zone to get to the LOP side, (2) when you do, you need to get really LOP, not just a little bit on the lean side of peak, and (3) that means actually finding peak is tricky.

In general, I agree. However, remember that "safe" has more factors than just RPM and MP, notably compression ratio, CHT, intake air temperature, oil temperature, and ignition timing. Here's the thing....watch for adverse CHT indications, notably a rapid rise.
Click to expand...

Thanks Dan, this is helpful. Getting to the lean side is relatively easy, just by observing the power loss. I am developing a pretty good understanding of the RPM drop associated different LOP levels (I have a FP prop) at cruise power by observing EMS logs post flight. What do you consider "really LOP?"

Larry
 
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jimgreen said:
Ok, so if you set 75% and lean to 50 lop you end up with about 65%.
If you now push the throttle to regain the 75% with a Bendix style FI can you assume you still have the same fuel/air ratio?
BTW, Dynon claims the % power reading is still good on the lean side of peak.
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This is an approach that I considered as well to avoid the danger areas Dan discussed. It was my understanding that the mixture control was for absolute fuel flow, not relative. Therefore, just pushing the throttle in your example would force you leaner. However, I haven't installed my Bendix FI yet, so can't say with any authority. I know it works that way on a carb.

Larry
 
Larry,
Have you done a lean range test to figure out how lean each cylinder is running? Fuel distribution in an 0-320/360 can be REALLY screwy leaving one cylinder (or more) much leaner than the others and thus increasing that one cylinder's detonation potential, even when it appears that you are well ROP or LOP on the Dynon. I am in this situation so I am very careful about leaning unless I am absolutely certain I'm well below 75%. Am I being too conservative? I don't know what I don't know, so I don't know. Just something to check on yours if you haven't already. Hope this helps.
 
alpinelakespilot2000 said:
Larry,
Have you done a lean range test to figure out how lean each cylinder is running? Fuel distribution in an 0-320/360 can be REALLY screwy leaving one cylinder (or more) much leaner than the others and thus increasing that one cylinder's detonation potential, even when it appears that you are well ROP or LOP on the Dynon. I am in this situation so I am very careful about leaning unless I am absolutely certain I'm well below 75%. Am I being too conservative? I don't know what I don't know, so I don't know. Just something to check on yours if you haven't already. Hope this helps.
Click to expand...


My peaks are well grouped. 1/2 together and 3/4 together. They end up about 30-40* apart in cruise; I get a better distribution at WOT. This is all somewhat moot for me, as I have purchased a Bendix FI setup that will be going in over the next couple of weeks and should be able to get my peaks pretty close after tuning.
 
David-aviator said:
Mathematically and no other factors considered, 23" MP is 76.87% power.
Click to expand...

By that logic, you're at 100% power when on the ground and the engine is off. ;)

RPM is a primary factor in power too. So you can just run 29" at 2,000 RPM which is 75% power as well.

In reality, 22" at 2,400 RPM is about 66% power so you're giving up quite a bit.
 
Not how you do it?

lr172 said:
My peaks are well grouped. 1/2 together and 3/4 together. They end up about 30-40* apart in cruise; I get a better distribution at WOT. This is all somewhat moot for me, as I have purchased a Bendix FI setup that will be going in over the next couple of weeks and should be able to get my peaks pretty close after tuning.
Click to expand...

I'm rusty, but my recall says that the degrees EGT are not the correct way to know if they are peaking together. That's because each sensor's placement and the somewhat different characteristics of the pipe and even variations in the sensors can make this inaccurate. The recommended method as I understood it had to do with when they peak, not the EGT reading itself. There is lots of information about this from GAMI, Advanced Pilot and others.

I hope this helps.
 
lr172 said:
My peaks are well grouped. 1/2 together and 3/4 together. They end up about 30-40* apart in cruise; I get a better distribution at WOT. This is all somewhat moot for me, as I have purchased a Bendix FI setup that will be going in over the next couple of weeks and should be able to get my peaks pretty close after tuning.
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Peak EGT at the same fuel flow is the goal, *NOT* matched EGT's. The actual EGT value isn't important and we don't care if they all read the same. You want them to peak (at what ever number) at the same time relative to fuel flow.
Once LOP, use fuel flow formula to determine power. Fuel Flow * 15.9 / rated HP for % power.
Tim Andres
 
David-aviator said:
...and a good reason to have a CS prop...
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I guess then I shouldn't be flying LOP with my O-360 fixed pitch prop.

KLVJ%2Bto%2BSC86.jpg


As for how and when I run LOP, I only do it above 6500' DA and start leaning at 65% power, as indicated by the SkyView, and when down low I typically see it drop to about 55% power and less than 7 GPH, as seen in this photo:
20140420_190323.jpg
 
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lr172 said:
T What do you consider "really LOP?"
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Specific LOP numbers are hard to obtain. What is available says under worst-case conditions (short version: everything very hot) it is possible to get some light detonation as lean as 50 LOP at 2700 and 28.5 MP.

Given a parallel valve 320, normal temperatures, and 2600/23, I doubt you need worry. Do a big pull to the lean side, enrich slowly to find peak, then lean again to set whatever LOP you like. Finding peak from the lean side is generally safer, and you should notice if the CHT suddenly starts clicking up.

For the most part, worrying about percentage HP is a waste of time. For example, I can show you charts with no detonation at 2700/26.8, and plenty at 2400/28.6, a lower power percentage. it's all about where you set the three knobs, not the percentage indication on the EFIS.
 
Once at cruise speed and altitude I am full throttle, I pull back to lean. I always cruise full throttle and lean. Altitude does not matter to me. If I am maneuvering I keep it about 150 degrees ROP.
These engines when operating correctly and cool have a very small red box.
 
hevansrv7a said:
I'm rusty, but my recall says that the degrees EGT are not the correct way to know if they are peaking together. That's because each sensor's placement and the somewhat different characteristics of the pipe and even variations in the sensors can make this inaccurate. The recommended method as I understood it had to do with when they peak, not the EGT reading itself. There is lots of information about this from GAMI, Advanced Pilot and others.

I hope this helps.
Click to expand...

I meant that 1/2 peak at the same time, not temp, and 3/4 peak at the same time about 30-40* later, but relative degrees, not absolute (e.g. 1 peaks at 1370 and 3 peaks when 1 is at 1400)
 
DanH said:
Specific LOP numbers are hard to obtain. What is available says under worst-case conditions (short version: everything very hot) it is possible to get some light detonation as lean as 50 LOP at 2700 and 28.5 MP.

Given a parallel valve 320, normal temperatures, and 2600/23, I doubt you need worry. Do a big pull to the lean side, enrich slowly to find peak, then lean again to set whatever LOP you like. Finding peak from the lean side is generally safer, and you should notice if the CHT suddenly starts clicking up.

For the most part, worrying about percentage HP is a waste of time. For example, I can show you charts with no detonation at 2700/26.8, and plenty at 2400/28.6, a lower power percentage. it's all about where you set the three knobs, not the percentage indication on the EFIS.
Click to expand...

Thanks for the follow up. This is consistent with what I had thought based upon all of my research. I appreciate you and others posting lots of factual data to help draw these types of conclusions.

Larry
 
Trend wise

but not specific to the 360, leaner has greater detonation margin. Harder to ignite and much cooler all around.

This is a huge opportunity for a clever application of EFI (full control of throttle, ignition and A/F). Using higher Cr, retarded timing and lower MAP at lower altitudes and then opening up the pipes at altitude for an excellent BSFC. Liquid cooling would extend the benefits.

Remember the Conti liquid cooled engine that ran at 15:1 Cr? Flat rated from 0to 60,000.

Large multi-megawatt natural gas engines are lean burn, have outstanding overall thermal efficiency, (turbocharged etc.), highly boosted and BMEP equal or higher than diesels.

Sorry for the off topic.
 
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