Advanced leaning - Mike Busch

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astaib
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Advanced leaning - Mike Busch

Post by astaib »

Hello,

As I have problem to keep low CHT temperature (especially on cylinder #1), and because I’m currently reading the last book of Mike Busch “Engines”, I tried today to apply the advanced leaning method and to be LOP as MB is recommending. But the value of fuel flow is really lower than what the POH is recommending. With the following settings I achieve cool CHT (even cylinder #1, what I never get with a ROP leaning), but with 7.5 gallon per hour at 2000ft/ 2200RPM/ 26,8 PA. With this I get:
Cylinder 1:344
Cylinder 2:380
Cylinder 3:352
Cylinder 4:344
With an EGT maxi at 1485.
OAT: 15 C
QNH: 1030

Then I applied the parameters of the POH (ROP): 10.5 at 2000ft/2200 RPM/26,8 PA
But I get:
Cylinder #1:400
Cylinder #2:386
Cylinder #3:368
Cylinder #4:368
EGT: 1440 (maxi)
The speed is 5 to 8 knots faster then.

What do you think about the “aggressive” leaning? And what about being LOP ?

I then use the VM1000 to detect the peak EGT, and I found out the following value: 7.4 / 7.6 (1490F).

Thank for helping me.

Arnaud.
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Re: Advanced leaning - Mike Busch

Post by blsewardjr »

Arnaud- I fly LOP in my 2003 DA. My understanding is that the POH best economy fuel flow setting is calculated on the basis of peak (maximum) EGT for a particular RPM/MP/altitude combination so LOP fuel flow for the same combination would be less than the POH (and the power would be less). Most of the time I use around 7.5-7.7gph to produce around 62-64% power with the RPM/MP set to 65%. (The formula I use, which is true only for LOP operations, is %power = 14.9 * (gph)/180.) You appear to be running at around 75% power based on your reported RPM/MP and altitude. See this article by Mike Busch on how pilots need to be much more careful running LOP (and ROP) at 75% versus 65% --https://www.savvyaviation.com/wp-conten ... ed-fin.pdf
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Re: Advanced leaning - Mike Busch

Post by astaib »

Hello,

This is exactly this article (he copied/pasted it and made a chapter in the book) that I followed to make my "tests".
He also said somewhere in the book that there is a ratio that "define" if an engine can be operate at 75% with LOP.
This ratio is HP/cubic. If the result is close to 0,5 OK for 75%, if close to 0,6 better to operate at 65% and less.

Mine is a 180 HP/ IO360, then the ration is 0,5 (180/360), I assume that it can be operate at 75% with LOP fuel flow.

I'm a bit lost to be honest!

Thanks for your experiences.

Arnaud.
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Re: Advanced leaning - Mike Busch

Post by Torkell »

Hi Arnaud,

The numbers you are getting following Mike Busch' advice prove that he is indeed correct. It is similar to what I experience. You can fly LOP up to 75 %, as long as you don't experience excessive vibration (due to different mixtures and hence uneven horsepower distribution across cylinders). If you do, you might consider installing GAMIjectors (STC available, even for EASA aircraft). In fact, you might wanna do a GAMI lean test in any case, since the CHT on cylinder #2 actually increases, while the other three are decreasing when you are reducing fuel flow. While CHT cannot be used to judge mixture distribution across cylinders, the fact that there is an outlier is a good reason to do a GAMI lean test.

You can read about the test here http://www.gami.com/gamijectors/leantest.php.

With LOP operation (I have GAMIjectors installed), I typically get a cruise speed at 70 % power of 135 KTAS (fuel flow 7,9 GPH) at 5.000 ft. You can see an example from the attached screen grab, where RPM is 2410 rpm, MAP is 24,55", altitude is 5000 ft MSL and OAT is 15 degrees Celsius.
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Figures at LOP 2410 rpm / 24.55" MAP
Figures at LOP 2410 rpm / 24.55" MAP
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Re: Advanced leaning - Mike Busch

Post by Derek »

Does anyone know if LOP operation can apply to a da20 as well? DA20 manual only specifies rop operation. Sounds like it would be better to run lop and save fuel.
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Re: Advanced leaning - Mike Busch

Post by Colin »

Engine manufacturers argue against LOP. If you are above 5,000 feet you can't hurt the engine trying.
Colin Summers, PP Multi-Engine IFR, ~3,000hrs
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Re: Advanced leaning - Mike Busch

Post by astaib »

Hello,

I discussed with the shop where my engine was overhauled and they advised me to be very carefull with LOP as it will make the engine run hotter and risk for exaust valve to burn. I answered them that it is not hotter regarding CHT, but they explained me that the valve guide won't be correctly lubrificated, etc...

I don't know if it's a coincidence or not, but I just received today the new oil analysis report after 23 hours engine time (half time in LOP cruise), and Blackstone advise me that nickel is a little bit higher and told me that it can be a wear of the exaust valve guide?

Summary:
ROP and risk for exaust valve burning or LOP and risk for valve guide wear, that will lead to exaust valve failure anyway...

To be honest, I'm lost and I don't know what I will do!

Arnaud.
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Re: Advanced leaning - Mike Busch

Post by Torkell »

Hi Arnaud,

According to Mike Busch, low CHT is more important in keeping the valves cool than EGT, since the valve seat (connection between the valve an cylinder head when the valve is closed) is the primary point for heat transfer between the valve and cylinder head. Furthermore, I find it hard to understand how a richer mixture would somehow "lubricate" the valve guide.

In my experience, workshops in Europe are not very familiar with the ins and outs of LOP operations. Rather, some workshops I have discussed the topic with would happily attribute any engine issue to LOP and the use of unleaded (UL91 avgas) fuel.

The best expert advice I have come across is SavvyMX, a maintenance management company for general aviation aircraft (Mike Busch' own enterprise). While it is impractical for us in Europe to be managed by a company operating with a 10 hrs time difference, SavvyMX also offers a "Q&A" service. For USD 350 pr year, you can ask for a second opinion regarding all aspects of maintenance. They are very familiar with LOP operations, on condition maintenance, etc. I am using them myself and have had good advice in the past.

As for your latest oil analysis, you may well have a valve guide issue. It is in my opinion more likely that this is attributed to your high cruise CHTs than LOP operations. If we trust Mike Busch, a modern aircraft with efficient cooling should not go above 380F during cruise. This ought to be addressed, and the GAMI lean test could be a place to start (as well as investigating the baffle).

A final point: Have you done Lycoming SB388C / SI1425A recently? These documents specify a procedure to verify valve guide wear.

All the best,

Torkell

PS: I have flown LOP for four years, and my oil analysis shows absolutely no excessive metals.
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Re: Advanced leaning - Mike Busch

Post by astaib »

Hi Torkell,

Thank you very much for your message.
My engine was overhauled in 2017, so I guess that SB388C has been done.

I don't have GAMInjectors on my Lycoming so I guess that I cannot make the GAMI test, then I only have the VM1000 that is not recording the values...

The point on the baffle is interresting because my seals are dead and will be changed in the coming months as well as the baffle for cylinder #1 (I want to install the arizona baffle with a wider air intake).

Regarding the Saavy company, I think that I will go for a subscribtion, but as the data of my engine cannot tbe dump and that I already have the feedback of blackstone when I perfom some oil analysis, I'm not sure of the added value.
Especially in the case when their advices will be differents than my mechanics... In one hand, I'm sure than Savvy will have a very good experience, but in the other hand I don't want to loose the confidence that I have with my mechnic...

Not easy to dela with...

Arnaud.
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Re: Advanced leaning - Mike Busch

Post by Torkell »

Hi again,

You can indeed do the GAMI lean test without recording (you need to record manually). Also, GAMIjectors are not required to do this test.

The added value of SavvyMX is substantial, regardless of whether you can dump data into their system or not. For instance, they can provide second opinions on any aspect where the maintenance facility draws a costly conclusion, which they may or may not have good reasons to. They also have lots of experience in interpreting oil analysis. I would hope that your maintenance facility sees the value of a second opinion on complicated matters, too.

Out of curiosity: Did the baffle issue show up a while after the overhaul? Or was the problem overlooked by those who installed the overhauled engine?

All the best,

Torkell
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