New owner leaning question

[ZachP]

Hi all,

 

 I just purchase a very nice 1978 M20C. While I haven't posted I have lurked around the forums and found a lot of useful information that made my decision easier. 

 

 Today I had my first working ( not flight training check out) flight. I had a problem with some serious roughness during runup.

I called my mechanic and he talked me through a full power mag burn off (mag 1 was dropping 200 rpm).  After that he told me to have a very low taxi lean setting. Flight went well from then on.  Except I couldn't lean down to a fuel flow of 10.5 gph like I could the last 7 hours during my checkout flights. It wanted to run at 11.5 gph. I have a Shaden fuel flow meter.

 

I am curious about leaning on the C. I have done some reading here and online and there seems to be debate about how to/if you can lean the carbureted engine. I don't want to break my new engine. 

 

Thoughts?

[carusoam]

Fuel flow and engine monitors are helpful devices...

In carbureted Cs...

Leaning...yes.

LOP...unlikely.

My C used to like collecting lead BBs in the lower plugs.

Welcome aboard...

Best regards,

-a-

[Hector]

We probably need a bit more info to see what is going on. At a minimum give us altitude and power setting you were using while trying to lean at cruise. I have a C and I lean aggressively for all ground ops and very rarely have issues with plug fouling. I just came back from Key West and at 8000 with full throttle (22 inches) and 2400RPM my JPI 730 was showing 9.1 GPH just rich of peak.

[DS1980]

Yes, a carb engine can be ran LOP, usually with the aid of carb heat to help in atomization of the fuel. Depending on who you talk to, you will have different answers on the percentage of success. Mike Busch tends to think most carb engines can be run LOP if you really experiment with it. Some other people that have done it many times will give you around a 30% chance of success. The bottom line is this:

1.) It's OK to run ROP if you RUN RICH ENOUGH

2.) It's OK to run LOP, if you RUN LEAN ENOUGH

Also, if you're at 60% power (some say 65%-I'm staying conservative) or below, you just aren't generating enough ICP (Internal Cylinder Pressure) to hurt anything, so keep the power low and you won't hurt anything experimenting with LOP. The worst thing that will happen to your engine is that it will say, "Nope, I can't run LOP. Sorry, I tried."

Experiment with it. A great poll would be how many people with carb engines have one that can run LOP.

 

Hector, since you operate at the higher altitudes, have you tried LOP?

[philipneeper]

i have a 78 c as well. also the same issue, when leaning she will run really rough and likes 11 gph ish. curious to learn some new techniques! btw what serial # do you have, curious thats all.

Hi all,

 

 I just purchase a very nice 1978 M20C. While I haven't posted I have lurked around the forums and found a lot of useful information that made my decision easier. 

 

 Today I had my first working ( not flight training check out) flight. I had a problem with some serious roughness during runup.

I called my mechanic and he talked me through a full power mag burn off (mag 1 was dropping 200 rpm).  After that he told me to have a very low taxi lean setting. Flight went well from then on.  Except I couldn't lean down to a fuel flow of 10.5 gph like I could the last 7 hours during my checkout flights. It wanted to run at 11.5 gph. I have a Shaden fuel flow meter.

 

I am curious about leaning on the C. I have done some reading here and online and there seems to be debate about how to/if you can lean the carbureted engine. I don't want to break my new engine. 

 

Thoughts?

[Rwsavory]

For carb engines during cruise, Mike Busch recommends leaning until the onset of roughness and then enrich just enough for the engine to run smoothly.   For climb he recommends to start leaning at 3,000.    I have used this technique lately with good results.  I average about 10 gallons an hour when cruising at 7,000 and above, about 21-22 inches and 2300 RPM.  Our fuel flow is higher at higher RPM.  I don't have a fuel flow meter, so this was measured over several longer trips.

[John Pleisse]

Your leaning can vary based on density altitude. A whole gallon? Not sure.

 

A fouled mag/plug doesn't happen from just one over-rich event, it would be running rich as a matter of course. That kind of plug fouling is usually from disuse.

 

It is likely the two are separate issues and not a cause and effect, in unison.

[N33GG]

Welcome to the world of C-Models! 

 

My 68 C is equiped with an engine monitor, tracking CHT and EGT for all four cylinders.  I also have an accurate fuel flow monitor.  I fly ROP, and that is every cylinder ROP. 

 

If I only used the engine rough, and then rich to smooth mixture setting technique, I would probably be flying at about 10 gph cruise.  However, watching the engine monitor, cylinders 1,2 & 4 become ROP at about 10 gph, while cylinder #3 is lean and does not peak or begin to be ROP until about 10.7 - 11 gph.  There is no roughness with this one cylinder LOP, but monitors don't lie. 

 

So my usual cruise at altitude is full throttle, 2400 rpm, and fuel flow is right at 11gph.

 

If I am at lower altitudes and pull back power to 23"/2300 rpm (or 23 squared), fuel flow settles down to about 9.5 gph, and the cylinders are much better behaved, all four with more similar response to leaning.

 

I have flown lots of planes with carbureted engines, even owned several, with and without engine monitors.  I have used the lean until rough, and then rich to smooth mixture setting without any known problems.  When I have the monitor available, I keep every cylinder rich of peak.  I consider the behavior and performance of my 68 C to be very normal.

 

I have flown lots of planes with injected engines, even owned several.  Injected engines tend to be pretty uniform with each cylinder peaking at about the same time, at least much more so than carbureted engines.  GAMI engines or other tuned injector systems especially get everything even.   

 

Carbureted engines can have very different cylinder behavior than injected engines.  If you have one that behaves very uniform, consider yourself lucky. 

 

Intentional LOP in a plane with a carburetor is not for me. 

[N33GG]

And yes, aggressive leaning on the ground during taxi or mags will be very rough.  Just don't forget to go full rich before applying take off power!

[DonMuncy]

If you lean it really well for taxi, if you should forget, it won't matter, as it will falter when you advance the throttle.

[Hank]

I always lean my C on the ground. That habit burned me in a recent Cessna flight [i often make 1 or 2 each year], as I leaned the mixture after landing and had to coast off the runway with light braking, pump the primer a couple of times and crank her back up. Since then, I've looked at my quadrant and the red lever is pulled back more than halfway--she still gets enough fuel to taxi without coughing.

 

Don't forget to go Full Rich for runup! Afterwards, I lean again to back-taxi for departure [we don't have a parallel taxiway at home], turn around, Full Rich, Full Prop then Full Throttle and off we go.

 

If it's rough at runup, I advance throttle to 2000 RPM and lean her a little bit for an RPM rise, hold it there for 60 seconds by the yoke clock, back off throttle, Full Rich, back to 1700 RPM and the mags are usually good. Since leaning aggressively on the ground became a habit, I have less roughness on mag checks, usually right before it's time to pull and clean the plugs anyway.

 

I don't have fuel flow, and don't have panel space to install one. My experiments with LOP have been uniformly dismal—lean to peak and slightly rough, pull some carb heat, play with red lever, still rough. Yes, I have a carb temp gauge and have tried various ranges from 5-20ºC temp increase with similar results. Carb heat off, red lever forward, she smooths right down. I made some notes [still in the plane] on my weekend trip to the beach of power settings, OAT, altitude & setting, IAS, etc. I'll try to remember to get them on Saturday if you're interested. I like 50ºF ROP, it works for me, and the Advanced guys with injected engines can pay to upgrade my O-360 to an IO-360 before I will listen to them yell at me. [i think my Carb Temp gauge was added later since it's in ºC while EGT and OAT are in ºF.]

 

My "normal" power varies by altitude:

<~4000 msl     23"/2300

~4000-~6500  22"/2400

>7000             2500 & (WOT - enough to make the MP needle move)

And there's always the MAPA PPP "by the numbers" formula:  MP + RPM = 46 gives 65% power; every three above/below 46 adds/subtracts another 10% for those times you can't/don't want to look in the book or are at an in-between altitude [my Manual has tables every 2500'].

 

Pulling the prop back to 2500 usually gets MP back almost to where it was. Coming home at 10,000 msl my Owner's Manual shows WOT = 20.2", with the next listing at 20" which is where I was [20"/2500]. Normal leaning was about 5 mph Indicated faster than peak [133-135 mph vs. 128-130], and we won't discuss groundspeed.

[ZachP]

Thanks all. I have to check on what the serial number is for you phil. I have been using a way too rich taxi "lean" as I learned yesterday. My flight was at 7500' throttle full forward 2500rpm and lean the mixture back till either EGT peaked or engine ran rough. seemed like the roughness won out and so I went with 25-50 degrees rich of that to smooth it out. I got the 11.5 gph on the Shaden. I believe I was at 22" MP, but don't quote me. TAS was ~138kts into a 7 kt headwind. 

 

Do you all think a engine monitor system like the JPI series is worth the cost over the above technique or is it just mental masterbation?

[takair]

Are you sure the fuel flow is properly calibrated? May want to check on some cross country flights. Many installers don't take the time to fine tune them. You may also want to have your intake manifolds checked for air leaks. EGT is typically installed in the hottest/first to peak cylinder. If you have a leak, you may have another peaking first and causing roughness. Engine analyzer is great to have, but you can certainly fly without one if the engine is set up right.

[N33GG]

If you have a monitor, it is hard not to look at it and worry about small things.  I like them more on injected engines than carbureted ones, as the carburetor causes more erratic things to worry over.  Engine shops have told me they chase a lot of phantom problems due to engine monitors on both types of engines.  Some pilots and mechanics swear by them.  They are essential equipment if you want to run LOP.

 

If you have only seen monitors on injected engines, it can be a bit of a shock and even alarming the first time you look at one monitoring a carbureted engine! 

 

Of all the flying I have done in both injected planes and carbureted planes, with and without monitors, I have never had a problem that a monitor would have solved.  Maybe I am lucky.  Techniques are there for operating both types of engines, with and without monitors.  After all, you still have the other engine instruments, just not every cylinder.

 

All that being said, I like having the monitor to keep an eye on my engine.  It is simply more data and information that I can decide what to do with. 

 

I do wish they were not quite so expensive.  Not a big deal if you are flying an Ovation, but a significant percentage of the price of a typical C Model, or other small carbureted aircraft.

 

FWIW...

[aaronk25]

Some good advise above. The only time a engine needs to be full rich is for take off up to what ever altitude you start to lean at.......That's the one and only time. Lean aggressively on ground and lean during run up, right on the edge of roughness. Going full rich during run up is 1960s and your not doing your engine or your wallet any favors. Besides if you truly have a mag timing/internal issue the rich mixture can mask the problem.

My point is that if you don't lean aggressively durning the run up you need to do some studying and update your engine mgt techniques.

Mike busch....leaning 101

[carusoam]

If you can afford an engine monitor, get one...

Used, new, analog or digital...

It should be able to identify a stuck valve better and do other unusual detective work.

Like an AOA indicator... Nobody needs one. Everyone is likely better off with one....

Best regards,

-a-

[Hector]

Yes, a carb engine can be ran LOP, usually with the aid of carb heat to help in atomization of the fuel. Depending on who you talk to, you will have different answers on the percentage of success. Mike Busch tends to think most carb engines can be run LOP if you really experiment with it. Some other people that have done it many times will give you around a 30% chance of success. The bottom line is this: 1.) It's OK to run ROP if you RUN RICH ENOUGH 2.) It's OK to run LOP, if you RUN LEAN ENOUGH Also, if you're at 60% power (some say 65%-I'm staying conservative) or below, you just aren't generating enough ICP (Internal Cylinder Pressure) to hurt anything, so keep the power low and you won't hurt anything experimenting with LOP. The worst thing that will happen to your engine is that it will say, "Nope, I can't run LOP. Sorry, I tried." Experiment with it. A great poll would be how many people with carb engines have one that can run LOP. Hector, since you operate at the higher altitudes, have you tried LOP?

I have not tried but intend to do so shortly. I typically cruise high and so I lean to about 20 degrees rich of peak. If I try to lean beyond peak the engine lets me know its not happy, but I have not tried to use carb heat or pull slightly back from WOT to see if I can push it further. I've been meaning to give it try and now that I have installed a JPI 730 (less than two months ago) I can finally do this correctly.

[carusoam]

The JPI results should be interesting. It will give a clear picture about how your fuel distribution works...

Is there a method of adjusting the fuel distribution in the carb?

Good luck!

You may find some interesting results because there are not many Cs that have been loved enough to get a JPI or FF instrumentation.

Best regards,

-a-

[DS1980]

For carb engines during cruise, Mike Busch recommends leaning until the onset of roughness and then enrich just enough for the engine to run smoothly.   For climb he recommends to start leaning at 3,000.    I have used this technique lately with good results.

If you got this information from his Basic Leaning class offered through the EAA, he was referring to fuel injected engines with balanced fuel injectors, although he didn't specify this. This method with a carb engine puts you right in the middle of the red fin, which leads to the highest ICPs (40-50 degrees ROP). The reason a carb engine runs rough is because you have gone past the power curve on the rich side of peak which is pretty shallow and are nearing peak EGT or even on the lean side a tad, where the power curve drops off dramatically and a small difference in fuel distribution between cylinders will be felt as roughness. Enriching to smoothness is going to either put you near peak EGT or best power, both which are unkind to the engine.  I would encourage you to revisit this method. However, specifically for you, with running at 22 inches and 2300 RPM, I have you running about 63% power (my math might be wrong), which is right on the border of whether or not you are producing enough power to hurt anything at any setting. If this method is only used for this "low power cruise," well done! I just wanted to clarify that this shouldn't be done in just any cruise setting.

On the other hand, if using this method with an injected engine, the advise is quite genius. What he is saying is to lean to the onset of roughness, which will take you through LOP and through best economy mixtures. The reason the engine will run rough now with balanced injectors is because the mixture is getting too lean to burn. Enriching it just enough will bring you back close to best economy, which is the whole idea of LOP (besides being kind to the engine.)

 

Please understand my intentions with this post, as I am not trying to be "that guy on the forum" or criticize piloting technique, as in this case N5687Q is in good hands. I had the fortune of having a fellow (friends with Mike Busch in fact) as my CFI for a few years that understands this stuff at the molecular level. In no way am I an expert, I just hang out with them. And something about a Holiday Inn Express.....

 

Hector-pilot report expected soon!!!

[Cruiser]

Some common but TOTALLY incorrect statements related to ROP vs LOP operations.

 

50°F LOP is hotter than 50°F ROP

You will burn up your engine if you run too lean

Carb engines cannot be run LOP

LOP requires an engine monitor

LOP will void your warranty

running as far LOP as possible is best 

just slow down running ROP is the same as running LOP

you must take a course to be trained before running LOP

LOP is too complicated for the average pilot to do properly

 

any more? added your favorites here.

[aaronk25]

According to a well known upper midwest MSC, under new ownership....."running lean of peak will wear out a set of cylinders on a J inside of 100 hours". .....the stupidity continues with the following statement "camguard is no good the last plane I changed oil on that had cam guard in it all the cam guard drained first out of the quick drain"......to be followed up with the dumbest statement I have ever heard especially coming from a MSC owner "LOP doesn't save any gas when you take into account you go slower".....ok wait this guy said one more hillarious comment "a Bravo won't run LOP because the engine is balanced so perfectly that it will only run ROP" .............. I couldn't get my plane out of there fast enough! I mean this guy was actually turning wrenches on my plane! Scary!

[Hank]

Aaron, the A&P certification is about working on airplanes, not operating them. Do you take advice on driving from the neighborhood mechanic? Or do you avoid him because he drives differently than you? I'd go to a mechanic based on his reputation for trouble shooting and wrenching, not for his flying knowledge or lack thereof.

[aaronk25]

Understand.....but then if there is no correlation between common sense knowledge and A&P certification then why did my plane leave their shop with both mags timed 5 degrees off, a lose coil inside of the mag, way to much grease in the mag which lead to grease migrating into the distributor cap, a loose alternator, a non overhauled prop governor when it was logged as overhauled which wasn't realized immediately because despite a promise to return the log books to me a week after picking up my plane it took 4 months.......I could go on and on but in a effort not to detract from original post ill refrain.

Point is if a mechanic sounds like a he shouldn't be working on weed eater engines, don't let him touch your plane.

[Rwsavory]

If you got this information from his Basic Leaning class offered through the EAA, he was referring to fuel injected engines with balanced fuel injectors, although he didn't specify this. This method with a carb engine puts you right in the middle of the red fin, which leads to the highest ICPs (40-50 degrees ROP). The reason a carb engine runs rough is because you have gone past the power curve on the rich side of peak which is pretty shallow and are nearing peak EGT or even on the lean side a tad, where the power curve drops off dramatically and a small difference in fuel distribution between cylinders will be felt as roughness. Enriching to smoothness is going to either put you near peak EGT or best power, both which are unkind to the engine. I would encourage you to revisit this method. However, specifically for you, with running at 22 inches and 2300 RPM, I have you running about 63% power (my math might be wrong), which is right on the border of whether or not you are producing enough power to hurt anything at any setting. If this method is only used for this "low power cruise," well done! I just wanted to clarify that this shouldn't be done in just any cruise setting.

On the other hand, if using this method with an injected engine, the advise is quite genius. What he is saying is to lean to the onset of roughness, which will take you through LOP and through best economy mixtures. The reason the engine will run rough now with balanced injectors is because the mixture is getting too lean to burn. Enriching it just enough will bring you back close to best economy, which is the whole idea of LOP (besides being kind to the engine.)

Please understand my intentions with this post, as I am not trying to be "that guy on the forum" or criticize piloting technique, as in this case N5687Q is in good hands. I had the fortune of having a fellow (friends with Mike Busch in fact) as my CFI for a few years that understands this stuff at the molecular level. In no way am I an expert, I just hang out with them. And something about a Holiday Inn Express.....

Hector-pilot report expected soon!!!

Thanks for the feedback, but I am quite sure this is Busch's advice for operating carb engines during cruise as stated in both his basic and advanced leaning webinars. He says it puts you a best economy mixture on LOP. Go to minute mark 37:00 here: http://www.eaavideo.org/video.aspx?v=2534345030001

According to my POH (if that can be trusted) 22" and 2300 RPM at 7500 feet gives me 72% power. We are usually above standard temp down here, so that figure is probably a little high most of the time.

I lean a little bit during climb above 3,000 feet but still keep it well ROP according to my EGT.

Also, from Busch's 2008 Avweb article:

I fly a Cessna 172 with no CHT or EGT or fuel flow instrumentation. How should I lean my engine?

After stabilizing in cruise and reducing power to the desired cruise RPM, slowly lean the mixture until you feel the onset of perceptible engine roughness. Then slowly richen just to the point that the roughness goes away. With your limited instrumentation, that's the best you can do ... and it's not a bad technique. Having said that, I would strongly recommend that you consider installing a digital engine monitor in your airplane. To my way of thinking, having an engine monitor is even more important in a four-cylinder, single-engine airplane than it is in six-cylinder single or a twin. If you fly a four-cylinder single and you lose a cylinder in flight, you don't have much left. See you next month.

And don't worry, I don't think you are "that guy." I appreciate all of the advice I can get.

Cheers and happy flying.

[DS1980]

A thought on roughness--Lets take a simple single cylinder engine. A single cylinder engine will not run "rough." It will operate just fine throughout all of the mixture settings between too rich to burn and too lean to burn. So now lets take a 4 cylinder Lycoming. Why does it run rough? Because the cylinders are producing different amounts of HP compared to their neighbors. Where does this happen? It's not going to happen well on the rich side of peak where the power curve is flat, because a difference in fuel distribution is not going to give a big difference in HP. When we get near peak EGT and go on the lean side, the power curve drops off, so a small difference in fuel distribution will have a large effect on HP produced. So the most important question here is: Where does a correctly tuned carb engine run rough? And the answer is "somewhere near peak EGT or going into LOP operation."

 

 

 

Thanks for the feedback, but I am quite sure this is Busch's advice for operating carb engines during cruise as stated in both his basic and advanced leaning webinars. He says it puts you a best economy mixture on LOP.---Please acknowledge that he doesn't specify what engine he is talking about, and that's where the confusion is coming from. I have attached for better viewing the red fin graph  that I use as my profile photo. Now while this isn't a cover-all graph for all engines, the physics working inside aircraft engines is pretty much the same. Lets say you're cruising at 5000 feet. Where does leaning to roughness (which is usually somewhere near peak EGT since we are now dealing with a power curve that is more steep and therefore a small difference in fuel distribution will be felt as roughness), and then enriching to smoothness put the engine? Right back where the engine will run smooth, but will have horrible CHTs and ICPs-50 degrees ROP.

 

According to my POH (if that can be trusted) 22" and 2300 RPM at 7500 feet gives me 72% power. I told you my math is horrid. Even more of a reason to revisit this method.

I lean a little bit during climb above 3,000 feet but still keep it well ROP according to my EGT. How much more rich? Remember the #1 rule to engine management: It's OK to run ROP if you run rich enough, and same is true for LOP.

Also, from Busch's 2008 Avweb article:

I fly a Cessna 172 with no CHT or EGT or fuel flow instrumentation. How should I lean my engine?

After stabilizing in cruise and reducing power to the desired cruise RPM, slowly lean the mixture until you feel the onset of perceptible engine roughness. Then slowly richen just to the point that the roughness goes away. With your limited instrumentation, that's the best you can do ... and it's not a bad technique. Having said that, I would strongly recommend that you consider installing a digital engine monitor in your airplane. To my way of thinking, having an engine monitor is even more important in a four-cylinder, single-engine airplane than it is in six-cylinder single or a twin. If you fly a four-cylinder single and you lose a cylinder in flight, you don't have much left. See you next month. The key phrase here is "stabilized in cruise and REDUCING POWER." How much power does an engine in cruise, at altitude, with a power reduction produce? Mike is betting on somewhere around 65% power. Granted, this puts the engine in the red fin, but the red fin isn't just one color, as running in the center is more harmful than running on the outskirts. And because the 172 has no EGT, leaning to roughness is the only way to know kind-of where the mixture is. He also says "that's the best you can do." He means for this engine installation, which is borderline unacceptable.  Installing the engine monitor would open that pilot's eyes to what's going on in the engine, and I bet once he got a real look at his CHTs, he would enrichen a little more. Ask Mike Busch where you should run your engine with the best engine monitor on the planet and he will answer, "Whatever keeps your CHTs happy." Remember this is a function of physics and metallurgy. Running at 50 degrees ROP is the worst place to be at.

And don't worry, I don't think you are "that guy." I appreciate all of the advice I can get. And I will add, the fact that you are asking these questions puts you at the top 10% of pilots. I don't mean to seem egocentric, but we have a higher percentage of people on this forum that "get it." Must be a Mooney thing!! I was introduced to LOP about 5 years ago in a Cirrus and didn't like it until my CFI friend exercised my demons. Understanding the red fin graph should be mandatory for getting a pilot certificate.

 

Good discussion!!

Hector-Seriously man, do you need a better excuse to get out flying than to see if you can run LOP? Where is the Pirep??