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ROP v. LOP


jlunseth

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Huh - so I shouldn't worry about 250-260?  That is what I was getting for example yesterday with OAT about 15 or 20 at 8k on a short run to get my son from college for the weekend.

It can get a lot colder around here and that was the first time I did LOP this winter.  Actually that is the lowest I have dared - I haven't even tried LOP when it is truly arctic cold out since I have been worried to even go there - I bet it would be a lot lower.

 

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1 hour ago, jetdriven said:

 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. 

Throttle back!? You must be going really low. What about impact of different RPM?

Carson's speed can actually vary with weight and by a lot. In a 201 it is 118kias at gross weight and as little as 108kias when you're lightest. So you either take a small speed boost as you burn off fuel or slow down and improve efficiency. What do you do in the airliners when you shed weight? Do you take the speed increase or power back usually?

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On 2/18/2017 at 8:28 AM, aviatoreb said:

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?

If the plugs remain clean at those temps, you should be fine.  I have to ask how cold is the OAT when you see 250 at cruise power? I run my bird WOT in the winter at negative DAs; even with OATs in the teens, at those settings my coldest CHT will stay above 280. Why not just pick a setting a little closer to peak.  Given the same CHT when ROP or LOP, the LOP setting will be a kinder setting. 

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OK, I'm gonna ask a stupid question, and probably stir this up even more, but I'm new to my Mooney and just getting to the point where I can consider this kind of stuff...

I just finished my "insurance required" checkout, and while I occasionally looked at temps, I was a lot more obsessed with altitude, airspeed, etc.  Now that I have a little breathing space, I've started doing some reading and research.  From what I've read, it APPEARS that LOP was originally discouraged for two reasons: older aircraft only had one CHT gauge, and the cylinders weren't "tuned" so that the temps were the same in all the cylinders.  So in those cases, it would have been possible to lean the one cylinder you could see, but still have the other 5 running hot.  My 231 has the JP gauge, so that I can see all 6 cylinders, and I have Gami injectors, so all of my cylinders are within a few degrees of each other.  That being the case, I've been able to lean it out quite a bit, and keep all the cylinders "cool enough" but also achieving a considerable reduction in fuel burn.  So, I'm quickly becoming a LOP guy.  Am I missing anything? 

Apologies for stirring this up.

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1 minute ago, DMJones said:

OK, I'm gonna ask a stupid question, and probably stir this up even more, but I'm new to my Mooney and just getting to the point where I can consider this kind of stuff...

I just finished my "insurance required" checkout, and while I occasionally looked at temps, I was a lot more obsessed with altitude, airspeed, etc.  Now that I have a little breathing space, I've started doing some reading and research.  From what I've read, it APPEARS that LOP was originally discouraged for two reasons: older aircraft only had one CHT gauge, and the cylinders weren't "tuned" so that the temps were the same in all the cylinders.  So in those cases, it would have been possible to lean the one cylinder you could see, but still have the other 5 running hot.  My 231 has the JP gauge, so that I can see all 6 cylinders, and I have Gami injectors, so all of my cylinders are within a few degrees of each other.  That being the case, I've been able to lean it out quite a bit, and keep all the cylinders "cool enough" but also achieving a considerable reduction in fuel burn.  So, I'm quickly becoming a LOP guy.  Am I missing anything? 

Apologies for stirring this up.

Sounds like you have a handle on it.  If you haven't already found these, I'd recommend looking at a few of the articles by John Deakin found at Pelican's Perch

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4 hours ago, aviatoreb said:

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?

Hi Erik.  I just wrote some stuff on this on another thread so I will just summarize.  There are warnings all over the POH for my 231 about operating below 250 CHT or 100 OT.  The gist of it is that full power settings should not be used, rather a lower power setting should be used to warm the engine before applying full power.  The question is why?  And on that I have not found anyone who can tell me why the cylinders would need to be protected from <250 operating temps.  If the temp on one or two of my cylinders sneaks a little low I don't worry alot about it.  However, both your engine and mine rely on oil flow through the turbo bearings to both cool and lubricate, so I do worry about <100 dF oil, and will go ROP or to peak if necessary to avoid it.  The third issue is engine compartment temp.  I have experienced air/oil separator freeze up by not getting and keeping the compartment temp up, and that relies on all the radiant heat sources in the compartment including the cylinders.  There are other devices in the compartment that need some heat also.  What about the brake master?  How well does a vacuum pump work at 0 dF, etc.  I install an oil cooler block for winter and take it out when spring comes.  I also have the cowl flaps adjusted to fully close in winter, and to trail in summer.  And I don't let the OT fall below 100 dF.  If all of the cylinders get down below 250, that would worry me also, but my cylinders are not very evenly cooled so there are always some warmer ones.

Edited by jlunseth
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5 minutes ago, jlunseth said:

Hi Erik.  I just wrote some stuff on this on another thread so I will just summarize.  There are warnings all over the POH for my 231 about operating below 250 CHT or 100 OT.  The gist of it is that full power settings should not be used, rather a lower power setting should be used to warm the engine before applying full power.  The question is why?  And on that I have not found anyone who can tell me why the cylinders would need to be protected from >250 operating temps.  If the temp on one or two of my cylinders sneaks a little low I don't worry alot about it.  However, both your engine and mine rely on oil flow through the turbo bearings to both cool and lubricate, so I do worry about >100 dF oil, and will go ROP or to peak if necessary to avoid it.  The third issue is engine compartment temp.  I have experienced air/oil separator freeze up by not getting and keeping the compartment temp up, and that relies on all the radiant heat sources in the compartment including the cylinders.  There are other devices in the compartment that need some heat also.  What about the brake master?  How well does a vacuum pump work at 0 dF, etc.  I install an oil cooler block for winter and take it out when spring comes.  I also have the cowl flaps adjusted to fully close in winter, and to trail in summer.  And I don't let the OT fall below 100 dF.  If all of the cylinders get down below 250, that would worry me also, but my cylinders are not very evenly cooled so there are always some warmer ones.

My uncle flies a c401 for 30 years and he says because of the turbo, he must run hotter than a NA engine to keep carbon deposits from building.  Not sure how true this is.  

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The lead scavenging additive doesn't work well at lower temperatures:

http://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/technical-talk/techart-18-30071600.html

 

It explains why we idle at 1000rpm, why cylinders need to be warm, why we do should do run ups (it's not just for testing the magnetos), lots of good stuff.

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Browncbr, the usual "carbon deposit" issue is carbon on the plugs that reduces or closes the plug gap.  Hotter temps might help, but the real culprit is running too rich especially during ground ops.  Tell your uncle there is no way he can hurt the engine by running it too lean on the ground, and he should lean it out as far as possible for taxi, etc.  Actually, the best way to do it is to watch the "lean rise."  An idling engine that is too rich will increase RPM's when it is leaned out, up to a point, and after that the RPM's will start to fall again on the lean side.  For ground ops it is best to lean to the peak of that lean rise or just a little past it.  Typically the lean rise is an increase of about 75 RPMs.  Go too far past it though and in idle conditions it is possible to starve the engine, causing it to shut down.  It doesn't hurt the engine, it is just a pain because it needs to be restarted.

LOP reduces carbon/lead build up quite well.  

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3 hours ago, DMJones said:

OK, I'm gonna ask a stupid question, and probably stir this up even more, but I'm new to my Mooney and just getting to the point where I can consider this kind of stuff...

I just finished my "insurance required" checkout, and while I occasionally looked at temps, I was a lot more obsessed with altitude, airspeed, etc.  Now that I have a little breathing space, I've started doing some reading and research.  From what I've read, it APPEARS that LOP was originally discouraged for two reasons: older aircraft only had one CHT gauge, and the cylinders weren't "tuned" so that the temps were the same in all the cylinders.  So in those cases, it would have been possible to lean the one cylinder you could see, but still have the other 5 running hot.  My 231 has the JP gauge, so that I can see all 6 cylinders, and I have Gami injectors, so all of my cylinders are within a few degrees of each other.  That being the case, I've been able to lean it out quite a bit, and keep all the cylinders "cool enough" but also achieving a considerable reduction in fuel burn.  So, I'm quickly becoming a LOP guy.  Am I missing anything? 

Apologies for stirring this up.

You sort of have a handle on it.  "Tuned" injectors are injectors that are matched to each cylinder's airflow and also compensate for any fuel they get from upstream injectors (Continental engines only). The goal is to have them all peak at the same time which is to say at the same(ish) fuel flow (conforming engine). That makes for a smooth running engine throughout the usable mixture spectrum.  CHTs within a few temps degrees of one another is great, but not necessary or even possible in all applications.  This is because mixture is not the only driver of CHT. All other things being equal, minor changes in airflow under the cowl can have a huge effect on CHTs.  I say all of this because you should no that it is entirely possible to have even CHTs or even EGTs or both and still have an engine with uneven fuel distribution that runs lousy LOP. 

Running on the lean side of peak requires that your engine run like 4 or 6 (or 8 if your name is Clarence) single cylinder engines running in tight formation around one crankshaft, temperature in degrees has nothing to do with it.

I think Lycoming was against it for two reasons.  1) Back when they started saying it, most airplanes were not well instrumented and 2) They dont' check fuel distribution in test cell to ensure conforming F/A ratios. 95% of their NA engines run beautifully LOP without tuned injectors.

Continental has been much more progressive in embracing LOP ops. Whats interesting is that the Continental intake design is prone to uneven fuel distribution. Most stock Contis don't run very well LOP and require Gamis to balance the inherent imbalance created by the intake.

Good luck, be careful and don't set power with raw EGT numbers at least not until you know your engine really well.

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5 hours ago, jlunseth said:

Browncbr, the usual "carbon deposit" issue is carbon on the plugs that reduces or closes the plug gap.  Hotter temps might help, but the real culprit is running too rich especially during ground ops.  Tell your uncle there is no way he can hurt the engine by running it too lean on the ground, and he should lean it out as far as possible for taxi, etc.  Actually, the best way to do it is to watch the "lean rise."  An idling engine that is too rich will increase RPM's when it is leaned out, up to a point, and after that the RPM's will start to fall again on the lean side.  For ground ops it is best to lean to the peak of that lean rise or just a little past it.  Typically the lean rise is an increase of about 75 RPMs.  Go too far past it though and in idle conditions it is possible to starve the engine, causing it to shut down.  It doesn't hurt the engine, it is just a pain because it needs to be restarted.

LOP reduces carbon/lead build up quite well.  

I agree, which is why I do exactly as you described, but he is 76 years old and isn't going to change.  He can keep popping jugs until he quits flying, but I sure as hell cant win an argument with him on anything. Haha

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6 hours ago, teejayevans said:

The lead scavenging additive doesn't work well at lower temperatures:

http://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/technical-talk/techart-18-30071600.html

 

It explains why we idle at 1000rpm, why cylinders need to be warm, why we do should do run ups (it's not just for testing the magnetos), lots of good stuff.

We idle at 1000RPM to keep the cams wet. 

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Some review......   The minimum temps on CHTs...

Lead Bromide reaction.  Which is mentioned in the Shell document posted above.  But that temp is more EGT and well above our usual CHTs...

Clearences between the piston and cylinder in cold temps are pretty tight and warnings about warming the engine after start and before run-up because of the cylinder choke....

There is a lot written about LOP for TC'd engines around here.  The K has many MS authors.  The Bravo has very few in comparison.  The Bravo's air intake is far from curvy and balanced enough for wide acceptance of LOP.

Air intakes get 'tuned' to produce close to identical air flow in each cylinder.

Fuel injectors Get 'balanced' to produce close to identical fuel flow in each cylinder.

in lieu of curvy balanced air intakes, like on an IO550, an IO360 can put proper injectors in the engine to match the air flow that exists...

six cylinders are slightly more of a challenge to put curvy intakes on.

Best regards,

-a-

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Just to squirt some more lighter fluid on to the fire:

It just occurred to me that running an engine LOP produces almost no CO so it is safer to run LOP and better for the planet!

And if you are flying along and your CO monitor goes off, switching to LOP will almost completely eliminate the risk.

CO.PNG

Edited by N201MKTurbo
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42 minutes ago, N201MKTurbo said:

Just to squirt some more lighter fluid on to the fire:

It just occurred to me that running an engine LOP produces almost no CO so it is safer to run LOP and better for the planet!

And if you are flying along and your CO monitor goes off, switching to LOP will almost completely eliminate the risk.

CO.PNG

True about CO but it produces more in the way of NOx.

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AFR%20vs%20emissions.jpg

This is probably a little better graph.  You can see that CO drops to a very low level but it's practically impossible to get much below 0.5%.  CO isn't particularly bad for the environment.  CO2 and NOx are worse. 

From a chemistry standpoint the relatively high levels of NOx generated by LOP operations have always been my biggest concern.  NOx in the presence of heat and water will form nitric and nitrous acids which are corrosive.  It's hard to know what impact that might have on the exhaust system and engine. 

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On 2/18/2017 at 8:28 AM, aviatoreb said:

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?

 

Mike Busch has answered this question. No such thing as too cold. Colder is better.

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24 minutes ago, Raptor05121 said:

Mike Busch has answered this question. No such thing as too cold. Colder is better.

Do you have a link to where he said that?  Here's where he talks about potential problems with running in the mid 200s for extended periods. 

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

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