ROP v. LOP

[Bob_Belville]

1 minute ago, 201er said:

That probably puts you close to Carson's speed and that's why it is so efficient.

I have not studied Carson's number recently but I think I was about the best range speed. I also had a head wind going wnw complicating the choices.

[mooniac15u]

12 hours ago, Greg_D said:

A guy posted a panel pic of his Ovation in cruise on FaceBook the other day.  He was ROP, burning over 16GPH and had cylinder head temps around 380.  I suggested he might want to try running LOP, not to save fuel, but to be nicer to the engine.  Hard to believe, but there are still naysayers out there.  One guy commented that the pictured EGT was high enough and that going LOP was "hotter".  

He also mentioned that the Mooney POH stated that LOP was not recommended.  Has anyone ever seen that in a Mooney POH?

Why are you worried about a CHT of 380?

[Bob - S50]

13 hours ago, jetdriven said:

You may be a little leaner than best economy. Somwhere near where you are, airspeed takes a tremendous hit for each .1 gph saved. Iirc it was around 25-35 ish LOP was the best efficiency before the massive drop. 

Agree.  From what I've read in John Deakin articles, the best brake specific fuel consumption happens about 30 LOP +/-.  Dependent on what percentage power you are using.  Once you are LOP, horsepower is essentially directly proportional to fuel flow until you get so lean that it affects the combustion process.  And for my 200 HP engine, a drop of about 1.3 GPH is a 10% decrease in power.  That will definitely result in a loss of airspeed.

If we were looking for maximum range (and which of us bought a Mooney for its range) we M20J owners would fly around about 30F LOP and about 88 KIAS.  Carson's number allows us to get the maximum increase in speed for the least amount of wasted gas.  In my Mooney that's about 116 KIAS.

[Greg_D]

I wouldn't be worried about a CHT of 380 while climbing in my plane as that's about normal on a warm day.  When LOP in cruise, I see anywhere between 300-325 on all cylinders.  And that was the point, LOP will allow you to run cooler CHTs.  

Of course, the always present member of the "flat earth society" tried to convince everyone that when running LOP you burn cylinders up because LOP produces infinitely hotter EGTs and therefore hotter CHTs.

[mooniac15u]

6 minutes ago, Greg_D said:

I wouldn't be worried about a CHT of 380 while climbing in my plane as that's about normal on a warm day.  When LOP in cruise, I see anywhere between 300-325 on all cylinders.  And that was the point, LOP will allow you to run cooler CHTs.  

Of course, the always present member of the "flat earth society" tried to convince everyone that when running LOP you burn cylinders up because LOP produces infinitely hotter EGTs and therefore hotter CHTs.

I understand that LOP will result in lower CHTs but I was wondering why you felt 380 was problematic. Is there some data that suggests 380 is bad?

[Greg_D]

Just now, mooniac15u said:

I understand that LOP will result in lower CHTs but I was wondering why you felt 380 was problematic. Is there some data that suggests 380 is bad?

Aluminum loses half its strength at 400 deg F.  380 is not that far from 400.  20 degrees seems like a safe margin of error on uncalibrated instruments.

CHT is a direct indication of internal cylinder pressure.  Lower ICP is better for the engine as far as longevity is concerned.  Cooler and cleaner is better.  Those are two of the key concepts taught at the APS seminars and also covered quite well by Mike Busch in his Savvy Aviator series.

[mooniac15u]

Just now, Greg_D said:

Aluminum loses half its strength at 400 deg F.  380 is not that far from 400.  20 degrees seems like a safe margin of error on uncalibrated instruments.

CHT is a direct indication of internal cylinder pressure.  Lower ICP is better for the engine as far as longevity is concerned.  Cooler and cleaner is better.  Those are two of the key concepts taught at the APS seminars and also covered quite well by Mike Busch in his Savvy Aviator series.

I am aware of why 400 is an issue. I was trying to understand why you thought 380 wasn't enough of a buffer when Mike Busch specifically says that's a reasonable value. 

http://www.avweb.com/news/savvyaviator/savvy_aviator_59_egt_cht_and_leaning-198162-1.html

 

 

[kmyfm20s]

8 minutes ago, mooniac15u said:

I am aware of why 400 is an issue. I was trying to understand why you thought 380 wasn't enough of a buffer when Mike Busch specifically says that's a reasonable value. 

http://www.avweb.com/news/savvyaviator/savvy_aviator_59_egt_cht_and_leaning-198162-1.html

 

 

I completely abide by the 380 as a good temp to try not to surpass but listening to the manufacture the cylinder are built with the fact that they loose significant strength with elevated temperatures. I think it is Bill Ross(?) that discussses this in one of his webinars from TCM.

[carusoam]

The flat earthers must have only had carbs and a single EGT that wasn't calibrated on a scale with numbers.  Lucky ones flew M20Cs.

LOP for that guy was confused with running close to peak because his carb took a lot of extra effort to run past peak.  Without MS, LOP means very lean before running rough.  In the flat earther's plane this is pretty close to peak...

They didn't lean during taxi either.  Collecting lead balls in the lower plugs minimizes the driving force to try anything new.

Convention covers a lot of the other issues.  400° vs 380°.  While selecting 380° I know the plug is sitting in a hole that is 50° hotter than the cht well.  Fortunately the guidance of 50% of initial strength is good enough.  The abrasion resistance is also important and will be dependant on tempurature too...

These are some observations I have had while reading everything around here...

MS is great for pointing out where facts can be found, and for sharing what works and doesn't work.

Best regards,

-a-

Edited February 17, 2017 by carusoam

[mooniac15u]

1 hour ago, kmyfm20s said:

I completely abide by the 380 as a good temp to try not to surpass but listening to the manufacture the cylinder are built with the fact that they loose significant strength with elevated temperatures. I think it is Bill Ross(?) that discussses this in one of his webinars from TCM.

Exactly.  One has to assume that the materials are up to the task when kept within normal operating conditions.  Are the ICPs such that 50% of the initial strength is insufficient?  Does anyone have actual data on this?

It seems clear that running cylinders at very high temperatures is bad for longevity.  Reducing CHTs should help with that, but at some point there is likely a diminishing return on further reduction of temperatures.  Is that 400 deg?  380 deg?

[carusoam]

There is a lower limit where the lead additive in 100LL isn't burned completely leaving it to deposit somewhere.

The O can easily see CHTs as low as 280°F in winter on the east coast...

I think that leaves us with a target range of 320° to 380°F if/when able...

Best regards,

-a-

[Bob - S50]

I think your CHT personal maximums are a matter of preference.

My POH says CHT green radial goes up to 450F.  Supposedly, Lycoming thinks the engine will make TBO as long as I keep the CHT at or below 450F.  I follow the 400F recommended by Busch.  That gives me a 50F margin.  At what point do you stop adding extra margin?  If 400F isn't good enough you use 380F.  If you really want to be safe you use 360F.  Maybe 340F would be even better.  Ambient would be even better (never start the engine).  In the summer when I'm cruising at 10,000' +/-, I'm always struggling to keep #3 CHT below 400F without needing to put the cowl flaps in the trailing position.  I usually do that by leaning a bit more.  However, when I hit a downdraft, the plane slows as it climbs through the air mass to maintain altitude.  The CHT climbs about 10F.  Then I hit the downdraft and the opposite happens.  I just keep it below 400F during those downdrafts and it ends up being right around 390F in level flight.

Purely personal preference of course.

[Shadrach]

6 hours ago, mooniac15u said:

I understand that LOP will result in lower CHTs but I was wondering why you felt 380 was problematic. Is there some data that suggests 380 is bad?

380 isn't problematic, but it's not a huge margin away from what is healthy.  Some applications have to live with those numbers.  If we're talking about an NA bird in cruise, I would be checking the baffling. 380 is the top of my summer time max performance climb CHT . If it goes much over that, I will change configuration.  

[Shadrach]

1 hour ago, Bob - S50 said:

I think your CHT personal maximums are a matter of preference.

My POH says CHT green radial goes up to 450F.  Supposedly, Lycoming thinks the engine will make TBO as long as I keep the CHT at or below 450F.  I follow the 400F recommended by Busch.  That gives me a 50F margin.  At what point do you stop adding extra margin?  If 400F isn't good enough you use 380F.  If you really want to be safe you use 360F.  Maybe 340F would be even better.  Ambient would be even better (never start the engine).  In the summer when I'm cruising at 10,000' +/-, I'm always struggling to keep #3 CHT below 400F without needing to put the cowl flaps in the trailing position.  I usually do that by leaning a bit more.  However, when I hit a downdraft, the plane slows as it climbs through the air mass to maintain altitude.  The CHT climbs about 10F.  Then I hit the downdraft and the opposite happens.  I just keep it below 400F during those downdrafts and it ends up being right around 390F in level flight.

Purely personal preference of course.

Margins should consider OAT.  If I saw 365 with an OAT of 12, I'd be concerned; 365 with an OAT of 90, not so much.

[Greg_D]

57 minutes ago, Shadrach said:

Margins should consider OAT.  If I saw 365 with an OAT of 12, I'd be concerned; 365 with an OAT of 90, not so much.

The picture I was referring to showed CHTs all around 380 deg, while in cruise, burning 16 GPH, with an OAT of 15 F.  That's too warm for me.  Probably not a bad number if ROP on a warm day.  He had the equipment and engine to do it better if he would just get some training and believe the science rather than the small crowd telling him that LOP operations would burn up his engine. 

And for the POH purists who claim everything that anyone needs to know about engines is contained in that document, most list 450 or 475 as the CHT redline.  That's just not good for the engine.

[jlunseth]

20 hours ago, kortopates said:

Ask him what is Best Economy mixture as defined by Engine manufacturers today and in modern POH's? 

Yes!  That is the chuckle.  I don't pay much attention to the fuel setting mixtures in my POH anymore, but I can't help but notice that for the most part, the "best economy" settings are my LOP setting.  The main difference is that the POH usually specifies a lower MP than I use, but when LOP, fuel flow dictates %HP, not MP.  So at the POH's best economy fuel setting and a higher MP, I am making the same power as the POH setting but at a somewhere greater "distance" from LOP, viz. more degrees lean from peak.

So basically, the best economy setting is LOP.

[RobertGary1]

20 hours ago, Greg_D said:

He also mentioned that the Mooney POH stated that LOP was not recommended.  Has anyone ever seen that in a Mooney POH?

Yes, from Lycoming...

" TEXTRON LYCOMING DOES NOT RECOMMEND OPERATING ON THE LEAN SIDE OF PEAK EGT."

https://www.lycoming.com/sites/default/files/Fuel Mixture Leaning Procedures.pdf

 

-robert

[Shadrach]

2 hours ago, Greg_D said:

The picture I was referring to showed CHTs all around 380 deg, while in cruise, burning 16 GPH, with an OAT of 15 F.  That's too warm for me.  Probably not a bad number if ROP on a warm day.  He had the equipment and engine to do it better if he would just get some training and believe the science rather than the small crowd telling him that LOP operations would burn up his engine. 

And for the POH purists who claim everything that anyone needs to know about engines is contained in that document, most list 450 or 475 as the CHT redline.  That's just not good for the engine.

Agreed. It would take a lot of heat to take CHTs to that level under those conditions. Not for me either.

[Greg_D]

1 minute ago, RobertGary1 said:

Yes, from Lycoming...

" TEXTRON LYCOMING DOES NOT RECOMMEND OPERATING ON THE LEAN SIDE OF PEAK EGT."

https://www.lycoming.com/sites/default/files/Fuel Mixture Leaning Procedures.pdf

 

-robert

I asked for a quote from a Mooney POH.  The link is to an old (1994) Lycoming service instruction, not a POH.  Lycoming has since revised their stance on LOP and in the interim admitted that while it was possible, that most pilots didn't possess the knowledge to do it properly.

Regardless, the picture I was commented on was from an Ovation with a Continental engine with LOP numbers clearly listed in the POH.

[kortopates]

11 minutes ago, RobertGary1 said:

Yes, from Lycoming...

" TEXTRON LYCOMING DOES NOT RECOMMEND OPERATING ON THE LEAN SIDE OF PEAK EGT."

https://www.lycoming.com/sites/default/files/Fuel Mixture Leaning Procedures.pdf

 

-robert

That was in the period of lycoming constantly contradicting themselves. Even in that very document, see their graph on the same page where they clearly show Best Economy Cruise is LOP! Even though they apparently don't want you fly best economy. (In truth, they draw it too close to peak for my taste, but we all know it moves closer to peak as % power reduces anyway so I am not going to worry about it.) 

[jlunseth]

Uh.  All I said was there is a seminar coming up.  

[Greg_D]

2 minutes ago, jlunseth said:

Uh.  All I said was there is a seminar coming up.  

Come on!  You know any topic with LOP in the subject is going to generate some heat

[jetdriven]

19 hours ago, Bob - S50 said:

Agree.  From what I've read in John Deakin articles, the best brake specific fuel consumption happens about 30 LOP +/-.  Dependent on what percentage power you are using.  Once you are LOP, horsepower is essentially directly proportional to fuel flow until you get so lean that it affects the combustion process.  And for my 200 HP engine, a drop of about 1.3 GPH is a 10% decrease in power.  That will definitely result in a loss of airspeed.

If we were looking for maximum range (and which of us bought a Mooney for its range) we M20J owners would fly around about 30F LOP and about 88 KIAS.  Carson's number allows us to get the maximum increase in speed for the least amount of wasted gas.  In my Mooney that's about 116 KIAS.

 I showed CNOE this, but we flew at two different speeds at 10gph LOP. One was about 10-15 knots faster. The 30 LOP setting was much faster The 90 LOP. Still running smooth. Still running cool.  10-15 knots faster for free at 30 LOP, this is with the throttle pulled back some too. Pull throttle back, go faster on same FF. Counterintuitave.   I don't think after about 30-5 LoP, that HP=FF directly. At least not on the lycoming IO-360.  

Carson didn't correctly assume  that engine efficiency would be less at lower power settings.  88 KIAS is a very low % of power and the engine won't produce, say, 60 HP on half the fuel flow as 120HP. Anyways I thought Carson speed was 1.23 x min l/d or around 123 KIAS. 

[aviatoreb]

Ok here is a question that seems important if I were to run LOP this time of year - which I don't - my engine seems as if it gets colder than I would like!  With coldest cylinders of 250 or 260 that seems too cold to me.  So in winter I am all ROP.  How cold is to cold to let your cylinders run?

[jetdriven]

Depends on who you talk to. But afaik there is no lower limit.  My neighbor across the way has a F33 Bonanza with the IO-470 (260hp) and the d'shanon liquid air baffles.  He runs 230-250 CHT all the time and his engine has 600 hours now, zero issues. Bill Cunningham, who built his motor, told him it's great don't mess with it. 

Edited February 18, 2017 by jetdriven