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max. recommended power setting with peak EGT?

Jumbo

Well Known Member
Folks,

I have read the post of Sig600 re ´LOP or ROP, which do you run?´ and the 4-chaptered John Deakin ´Where Should I Run My Engine?´ document.

However I still need your advice on what is the max. recommended power setting when flying peak EGT or just on the LOP side.

My set up is a RV-4 with a Lyco O-320 E2D, 8.50:1 pistons (160 HP), standard RV air intake with the standard carburator heat (and a carburator) plus a Sensenich metal prop (70CM6S9-79). I run mostly 98 Octane (ROZ) ethanol-free Mogas (the 98 ROZ is ca. 94 after the US standard) with a ca. 20 US gals top up with Avgas every 3rd or 4th refill. I don´t have a fuel flow meter and no 4-way engine monitor however I do have a MAP gauge next to the RPM gauge and a single channel CHT and EGT.

The engine is at ca. 650 SMOH (first overhaul in 1996 on a 1980 hrs engine) and it ran with no issues with the leaning method of ´lean until the engine runs rough and than push mixture in that the engine runs smooth again - all at less than 70% power´ mostly on US (car) Mogas in Alabama.

If I fly peak EGT at 60% power or 50° ROP at 65% power I see CHT in the low 300° F range (just above 300° F ) and peak EGT is between 1350° F to 1425° F max. - if you like read my post ´RV-4 Performance: O-320, Sensenich Metal Prop´ (www.vansairforce.com/community/showthread.php?t=78637). I actually can run the engine ca. 20°F LOP on the one-way EGT gauge until it runs rough.

I do not intend to enhance my engine instruments really and my mission is ´go fast however as efficient as possible´ so I would like to run as lean as I can however I´d still like to get decent power. Therefore my question ´what is the max. recommended power setting when flying peak EGT or just on the LOP side.´

Deakin says it is 60% however I get from other posts like from ´Ironflight´ that ´The four-cylinder Lycs are just not the same as the turbo-charged big engines in the Bonanzas and 210's (the real target audience for Deakin and GAMI). I DO agree with Deakin on most all points, but I am just not that worried about the O-360's we fly normally aspirated.´

So - can I run with 65% power (ie. 21" MAP and 2400 RPM) with the method ´lean until the engine runs rough and than push mixture in that the engine just runs smooth again´ or even at 70% (ie. 21.5" MAP and 2500 RPM)?

With the Europe fuel prices of ca. 13 USD per gal my target power setting would be 65% actually (however at PEAK EGT or as lean as possible which is at just LOP knowing for one cylinder only with my single channel EGT gauge).

Advice welcome, Heinz
 
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that is a valid question

Paul

thanks for your comment. I actually DON´T know as you pointed out rightly - I just know that ONE cylinder peaks and than goes LOP for about 20°F at 60% power until roughness kicks in (partial throttle of course due to fixed prop and carb heat OFF).

Therefore I am after some more opinions re the question I have raised - can I run 65% power without hurting anything at PEAK EGT or at (maybe) just LOP knowing for one cylinder only in my set up? Or would YOU run YOUR O-320 engine at 65% power with a single probe EGT gauge the way ´lean until the engine runs rough and than push mixture in that the engine just runs smooth again´?

I know some will say: get a 4 channel EGT/CHT and a fuel flow meter or a proper EIS which is a valid point indeed ... however not an option right now and I suppose I would run the engine the same way anyway WITH an EIS.

Just as a reminder: my set up is a RV-4 with a Lyco O-320 E2D, 8.50:1 pistons (160 HP), standard RV air intake with the standard carburator heat (and a carburator) plus a Sensenich metal prop (70CM6S9-79). I run mostly 98 Octane (ROZ) ethanol-free Mogas (the 98 ROZ is ca. 94 after the US standard) with a ca. 20 US gals top up with Avgas every 3rd or 4th refill. I don´t have a fuel flow meter and no 4-way engine monitor however I do have a MAP gauge next to the RPM gauge and a single channel CHT and EGT.


Thanks, Heinz
 
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consult POH of similar-engined airplanes

You might consider consulting the pilot operating handbook of some airplanes with similar engines. I believe the Cessna POH for the C-152 and C-172 both include leaning procedure as you describe (lean until rough, then richen until smooth). I don't know if they set an altitude limit or RPM limit for doing this procedure that would suggest a percent power, but it is worth a look.
 
found the L y c o m i n g F l y e r

Steve,

in the brochure L y c o m i n g F l y e r I found hints re the question. It talks about LIMITATIONS OF POWER AT PEAK EGT and says: ´Lycoming allows leaning to peak EGT at 75% power and below on our direct-drive normally aspirated engines.´

When they cover BEST ECONOMY MIXTURE (TCM says: ´Best economy mixture as it relates to the EGT system begins at peak.´) vs. BEST POWER MIXTURE they as well say ´Again, we repeat that maximum leaning (peak EGT) does not damage an engine at the engine manufacturer’s recommended cruise power.´

Well, if that is true I should be able to run 65% power with described method of ´lean until the engine runs rough and than push mixture in that the engine just runs smooth again´ and I will note the EGT gauge ..... however having read the Deakin publication ´Where Should I Run My Engine´ I am just not sure.

So what I would like to do is the ´target EGT climb´ and in cruise set a ´45´ number for 65% power (if you add the 1st 2 digits from the RPM plus the MAP ´45´ results to 65% power when being ROP) and than lean using the ´Deakin big mixture swoop´ right until the engine stumbles and than enrich JUST to the point where I JUST get the engine running without too much roughness. If I enrich any further I should get to peak EGT (from the lean side however) - I have done that and that is exactly what happens.

That should give me between 150 - 160 kts TAS depending on ALTs between 4000 - 8000 FT with fuel flows between 26 - 27 LPH or around 7 GPH and with which I´d be VERY happy with.

The only question is: IS THIS ACCEPTABLE OR DOES THIS HURT THE ENGINE?


What do you think?


Still uncertain, Heinz
 
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Heinz,

Lycoming allows leaning to Best Economy (Peak EGT) for 75% power and below however they also say:

For maximum service life, maintain the following recommended limits for continuous cruise operation:
(a) Engine Power Setting - 65% of rated or less.
(b) Cylinder head temperatures - 400°F. or below.
(c) Oil temperature - 165°F. - 220°F.

This is for continuous cruise operations which I understand includes both Best Power and Best Economy mixture settings.

I usually operate my 0 320 (carb) at Best Economy (manually leaned to rough then in to just acceptably smooth) at around 55% power but I will cruise up to 65% at Best Economy if I am in a hurry. I have a 4 probe EGT and have found that manually leaning as above usually has all cylinders near peak with some LOP.

As a guide to power you could use the graph on page 3-22 of the Lycoming 0 320 Operators Manual to give you FF and RPM for 65% power at Best Econony. This graph is for the injected engine but your carb engine would produce similar (perhaps slightly less) power for the given FF/RPM. For example leaned to Best Economy, 2400 rpm and 29 l/h would give 65% power regardless of altitude (obviously assumes accurate FF and RPM gauges).

Fin
9A
 
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so there is hope ...

Fin,

thanks for that indeed - and there seems to be hope for me that I can operate the engine safely and for longevity as I actually envisage.

I as well I have found this document of Electronics International Inc. : www.buy-ei.com/Information/Pilots Manual.pdf. Sorry if I now hijack my own post however I would like to share this with you and give everyone a good read when coming back after the break - lol.

Let me copy/paste some stuff EI says and than let me make some conclusions - re which I will ask for your feedback.

EI say they did a survey targeted at maintenance shops that performed engine maintenance on a regular basis and performed top overhauls. They called most shops advertising in trade magazines or flyers.

The survey was conducted as an open forum and started by asking two questions: “When you were called upon to perform unscheduled maintenance on an aircraft engine, what was the problem, and what do you think caused it?” These questions resulted in a lengthy conversation that covered everything from manufacturing defects to problems caused by pilot operation. EI limited the results of this survey to engine problems which a pilot caused or contributed to.

The results of the EI Survey as per EI is that one hundred percent of the shops reported that excessive EGTs and/or CHTs cause engine damage on a regular basis. Following is a list of some of the problems they reported:
* Sticky valves due to excessive heat, causing oil to bake onto the valve stems.
* Burnt exhaust valves caused by excessive heat and/or sticky valves.
* Extensive exhaust valve guide wear due to heat. Also, guide wear allows the hot exhaust gasses to leak up between the valve stems and the valve guides, causing the valves to stick.
* Excessive ring wear caused by detonation and/or excessive heat. Ring wear can cause the rings to leak. This can foul the plugs due to excessive oil in the cylinders. Also, compression can drop and the oil may turn black quicker than normal.
* Cracks and heat damage to the ring lands caused by detonation.
* Cracks in the cylinder heads around the exhaust ports, injector ports and spark plugs caused by excessive heat and/or detonation.
* Every year some shops see holes burned in the top of the pistons, bent or broken valves, broken rings, and damage to the piston pins, main bearings or connecting rods.

Later the document discusses the relationship between the exhaust valve life and the sum of the EGT and CHT which is shown in the figure below. Both the EGT and the CHT has a direct affect on the exhaust valve temperature according to EI. If the EGT goes up, the CHT must come down to keep the exhaust valve at the same temperature.

When establishing a leaning technique EI says we must take into consideration the effects of EGTs and CHTs on the exhaust valves. We do know that the higher the EGT+CHT sum, the shorter the life of the valve and EI use this as graph:

9vf6zt.png



Than the doc discusses these leaning methods:

The “Peak EGT” Leaning Method:
Set the mixture so the leanest cylinder operates at peak EGT. At this mixture setting the EGTs will be 100°F hotter than the “Best Power” leaning method”. This method results in the highest temperature on the exhaust valves and heat damage could become an issue. The engine will produce approximately 4% less power and the fuel consumption will be approximately 14% lower than with the “100°F Rich-of-Peak (ROP) Leaning Method.” The CHTs will be near there highest.

The “Lean-of-Peak (LOP)” Leaning Method:
Set the mixture so the richest cylinder operates at 30-80°F lean of peak EGT. At this mixture setting the CHTs will be the coolest and the EGT will be 20-70°F hotter than the “100°F Rich-of-Peak (ROP) Leaning Method” . This method results in reasonably cool exhaust valve temperatures. The engine will produce approximately 7+% less power and the fuel consumption will be 20+% lower than with the “Best Power” leaning method.”

The “LOP with Power Recovery” Leaning Method:
This method is not recommended unless a detonation survey to AC 33.47-1 has been performed, the result show a safe operating area exits lean of peak for the power levels you plan on using and FAA approval has been obtained. Set the mixture so the richest cylinder operates at 30-80°F lean of peak EGT. Increase the manifold pressure by 1.25" Hg to recover 5% of the power loss (.25" Hg per %H.P.). It is important the richest cylinder is not allowed to drift within 30°F of peak EGT (refer to the detonation survey for your engine). It must remain at LOP operation.

This graph shows what conclusion EI draws fom it:

dvofbs.png

With:
(1) When leaning to the engine manufacturer’s recommended power requirements, the chance of detonation is low.
(2) If your CHT’s are below 400°F, this leaning method is NOT a disadvantage.
(3) If your engine does not have a tendency to develop cabon deposits, this leaning method is NOT a disadvantage.
(4) If your engine has a wide fuel/air distribution between cylinders, some cylinders may be operating near peak EGT. If the EGT + CHT is under 1825°F, this leaning method is NOT a disadvantage.
(5) If your engine has a wide fuel/air distribution between cylinders, some cylinders may be operating near peak CHT. If the CHT is below 400°F, this leaning method is NOT a disadvantage.
(6) This method is not recommended unless a detonation survey to AC 33.47-1 has been performed, the result show a safe operating area exits lean of peak for the power levels you plan on using and FAA approval has been obtained. The following data is for an engine with a well balanced fuel/air distribution between cylinders.

I will now tell you what I plan to do to achive my goal and why - I am open for your comments and shoot me down if you feel like you would like do so as this will be good for my safety!

My aim is to do the ´target EGT climb´ and in cruise set a ´45´ number for 65% power and than lean with the ´Deakin big mixture swoop´ right until the engine stumbles and than enrich JUST to the point where I JUST get the engine running without too much roughness. I than should be at somewhere less than 65% power however with some clyinders up to 20°F LOP and some near peak. That should give me between 150 - 160 kts TAS depending on ALTs between 4000 - 8000 FT with fuel flows between 26 - 27 LPH or around 7 GPH and with which I´d be VERY happy with.

AND I must be doing all right as I would
* certainly be below 75% power up to Lycoming allows peak EGT in cruise
* actually use max. 65% (or less) power I am bang on the ´long engine life´ power setting suggestion
* be close to 60% power Deakin should OK this and
* be cruising at a sum of EGT and CHT around 1750°F in my installation (certainly below 1825°F) I am below the EI maximum (don´t like their CHT’s are up to 400°F as a limit as my limit is 325°F in cruise which I can keep easliy).

I should be doing fine ?! So what do YOU think??

Anyway I will be doing some test flights and I will note the MAP, RPM, EGT, CHT and speeds and will report back ... however it will take a little time as we are at the beginning of the winter here now.

Becoming more certain, Heinz
P.S. Sorry if this post bothers people with a vast knowledge on LOP/ROP etc. - I just don´t have this know how and I´d be glad for your input ...
 
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