Mixture Control

[Jaime P]

The School I have been teaching for many years teach to have the student lean 0ne inch back and there has never been a problem with the engine ever. Over the week I had a conversation with some instructors who believe in teaching mixture back until rough running a then enrichen. I usely show them the proper way after they have some hours under there belt. Would like to get some opinions.
JAIME

 

[Ed Guthrie]

The School I have been teaching for many years teach to have the student lean 0ne inch back and there has never been a problem with the engine ever. Over the week I had a conversation with some instructors who believe in teaching mixture back until rough running a then enrichen. I usely show them the proper way after they have some hours under there belt. Would like to get some opinions.
JAIME

IMO, primacy--teach the student the correct way the first time.

 

[Dean]

I was taught to turn out slowly until engine starts to run ruff, then turn 1&1/4 turns back in. This ends up being 1" out.

 

[EdFred]

I was taught to turn out slowly until engine starts to run ruff, then turn 1&1/4 turns back in. This ends up being 1" out.

That 1" is gonna depends on altitude however. I don't have the verniers in mine, but there's definitely a difference in mixture contol location between leaning at 3000' and leaning at 10000'.

 

[James_Dean]

What does the POH say?


James Dean

 

[Dean]

That 1" is gonna depends on altitude however. I don't have the verniers in mine, but there's definitely a difference in mixture contol location between leaning at 3000' and leaning at 10000'.

Ok, Being from the Mid-West, I spend most of my time under 5000', so I lean at 3000' and thats it. For you high flyers, what altitudes do you lean at, say every 3000' or every 2000' ? The highest I have been was 8500' and that was just for a short time. (It took longer to get there in the 150 than I stayed there)

 

[Let'sgoflying!]

I think the problem is, if one can say there is a problem, is that the flight schools/cfi's are pretty busy teaching students the basics of aircraft control and they are looking for a safe ROT to teach the students on how to manage the red knob so you get these mixture controls with sharpie marks on them and suggestions like a half inch out etc. And I completely understand how a student has plenty on their plate. Unfortunately I think the ball gets dropped and often, no one goes back and says, 'OK lets spend an hour learing how this works and how to operate this properly'.

 

[James_Dean]

Ok, Being from the Mid-West, I spend most of my time under 5000', so I lean at 3000' and thats it. For you high flyers, what altitudes do you lean at, say every 3000' or every 2000' ? The highest I have been was 8500' and that was just for a short time. (It took longer to get there in the 150 than I stayed there)

Dean,

I usually fly between 8k and 10k in my Saratoga. I note the EGT's on the takeoff roll and at 500 ft. I lean every thousand feet in the climb to keep the EGT's around what they were at 500 ft. This technique reduces time to climb by several minutes, and saves quite a bit of fuel. I will run richer if need be to keep CHT's inline(under 385), but have only had to do this on days where ambient was 80 degrees+.


James Dean

 

[fgcason]

When I was learning down at sea level we initially left the knob full rich in the Cherokee. (summer, Pennsylvania, 1403 MSL, big long runway on a minimal obstruction mountain top) My CFI was a very much know your homework before showing up kind of guy. Very early on we had a discussion on aircraft systems. It's been a while but as I recall, the discussion went something like this: "This is the mixture. This is how it works and this is what it does yadda yadda. It's not super critical down here because____. However at high DA it's very important because ____" and on and on. It was a 5 minute discussion for the Red Knob 101 class. RK102 came later. You get the idea. He made it very clear from day one that it was a very important consideration however adjustment wasn't always needed and made sure I knew why we put it where we did under any given situation.

IMHO: Do not teach switch and lever positions. Teach why they need to be set where they are even if the student is in over their head a little bit then go over it in more detail when they quit breathing through the top of their head. That way the student doesn't get into a 'it goes here, next item' mindset. I say this because rote memorization motor skills to pull 1" out may be fine at one specific place in one specific airplane but 3-4-5 years from now that same pilot might be sitting at 10,000+ DA and reach over, pull 1 inch "because that's what we do by default with that knob based on the first 50 hours of training even though it does other stuff too" without thinking and end up in the trees..or worse.

As for what altitude I start considering adjusting the mixture: I don't bother with MSL. I work off density altitude since that's what the engine thinks the plane is operating at. On more than one occasion I adjusted the mixture for max power at 500 MSL on a really hot summer day. It gets adjusted as needed during the climb and after stabilizing in cruise.

My two marbles worth anyway...

 

[Lance F]

Ditto Eggman's technique. I monitor the EGT gauge in climb and try to keep it at 700dC, an easy point on the factory analog gauge to watch. I do this on a workload permitting basis, so this adjustment may get tweeked more or sometimes less often than every 1000'.

I think an instructor that leaves the mixture explanation to "pull it out 1 inch" is doing his/her student a disservice. (or perhaps the instructor doesn't have the training to give a proper technical explanation )

 

[gismo]

Ok, Being from the Mid-West, I spend most of my time under 5000', so I lean at 3000' and thats it. For you high flyers, what altitudes do you lean at, say every 3000' or every 2000' ? The highest I have been was 8500' and that was just for a short time. (It took longer to get there in the 150 than I stayed there)

There's no altitude cutoff for leaning during cruise and book fuel consumption rates are based on proper leaning no matter what altitude you cruise at. The lean above 3000/5000 thing was supposed to apply to climbs only. And with proper instrumentation you can lean in the climb from about 2000 DA if you want.

To answer your question, during a climb I adjust the mixture every 1000 ft if I'm not busy but there are times when I change more than 3000 ft without touching the mixtures. Whenever I level off I spend some time setting the mixture but that amount of time depends on how long I expect to stay at that particular altitude and how busy I am with other stuff.

 

[EdFred]

Ok, Being from the Mid-West, I spend most of my time under 5000', so I lean at 3000' and thats it. For you high flyers, what altitudes do you lean at, say every 3000' or every 2000' ? The highest I have been was 8500' and that was just for a short time. (It took longer to get there in the 150 than I stayed there)

Michigan isn't in the Midwest?

My best altitude for speed in the Cherokee is around 8000. If I'm going anywhere that takes over 30 minutes, I'm getting up to 8k. Of course, it only takes me about 8 minutes or so to get to 8k now.
Like the other guys, I tend to lean about every 1000 feet or so.

 

[Tom-D]

When I climb trying to acheave the highest I can get, I use the VSI as a best power meter.

I advance the throttle to wide open, trim to climb speed, and lean, I lean to see what best climb is, I leave it at that setting until it reads "0" again. and then lean again.

During cruise I set power, (1950 RPM) and lean for best speed.(@1950) lean and watch for rise in RPM, reset power, lean and reset power.

Remember my old radial runs 2050 wide open at sea level. but the principal works on any fixed pitch, non turboed engine.

This is how I got to 14,300' with the old F24 coming home across the Rockies Casper direct Pocatello.

The pic is the contental divide

 

[poadeleted20]

The School I have been teaching for many years teach to have the student lean 0ne inch back and there has never been a problem with the engine ever.

Since the proper setting for mixture varies with a wide range of parameters including air density and power setting, a "one size fits all" approach is inappropriate.

Over the week I had a conversation with some instructors who believe in teaching mixture back until rough running a then enrichen. I usely show them the proper way after they have some hours under there belt.

I'm not sure why you think their way is not "the proper way," since it is exactly what Lycoming recommends for nonturbocharged engines in cruse at 75% power or less.

Would like to get some opinions.

Not sure whether any "opinons" are needed, but Lycoming has a lot of good guidance on leaning their engines on their web site. Try these pages for reference...

Lycoming Key Reprints (Operation)
Lycoming Service Instruction 1094D
Lycoming Service Letters 185, 192, and 197

 

[jesse]

Eh. I never really fly anything with a fancy engine monitor like many of you here, so it's pretty basic as to what can be done.

On the ground after startup I usually lean right away, to the point to where the engine is barely running. When the engine is producing almost NO power, no damage can be done by this. One thing that is fairly important if you are going to do this, lean SO aggressively to where if you applied full power the engine would die. The reason for this is to make sure that you don't have it way lean and then takeoff full power like that, as that could cause damage. So either don't lean at all, or lean to the point to where it barely runs on the ground.

I generally just go full rich for takeoff after that.

On a hot day, a heavy airplane, or a ...very short "runway".. I will lean for peak power before takeoff, It MAY make the difference that might save your @#@$.

Per Lycoming in cruise I generally lean until a slight roughness, and then enrichen until the engine is smooth. (Best Economy)...For I am poor. I'd rather get there slower (build more flight time) and save some money all at the same time.

 

[Jaime P]

This is all great its amazing how many factor can be talk about I personally like the 1 inch back in the beginning and after more understand takes place then teach the proper way which work out to be 1 inch anyway. Thank everybody and Capt.Ron thanks for the tech info.
Jaime

 

[poadeleted20]

...then teach the proper way which work out to be 1 inch anyway.

While 1 inch may be right in some very limited set of conditions, it's not based on any engineering or performance basis. For that reason, I do not think it should be taught as a technique. That's like teaching students only to fly 65 KIAS on final regardless of conditions, configuration, or weight. If we instructors don't teach our students how to operate the aircraft properly based on conditions, we're setting them up for trouble both on practical tests and in real flying.

 

[Lance F]

Eh. I never really fly anything with a fancy engine monitor like many of you here, so it's pretty basic as to what can be done.

On the ground after startup I usually lean right away, to the point to where the engine is barely running.

If I may be allowed to amplify this a bit...You can optimize a lot of leaning without a fancy engine monitor.

Proper on the ground leaning is important to prevent plug fouling. This is being optimized at high EGTs. As long as you have at least one EGT probe just lean to the max EGT at about 1000 to 1100 rpm. You'll find that this mixture will increase the rpm about 20 or 30 rpm. So even if you don't have one EGT probe you can lean on the ground using your tach to find this little rpm rise. If you lean past this point, than EGTs go back down lessening the temps at the plugs (and probably also the ability to taxi )

Also if you have just one EGT you can use this to lean as you climb. Just note the position of this gauge at full TO power at 500' and keep it in that range for the rest of the climb.

 

[NC Pilot]

If I may be allowed to amplify this a bit...You can optimize a lot of leaning without a fancy engine monitor.

Proper on the ground leaning is important to prevent plug fouling. This is being optimized at high EGTs. As long as you have at least one EGT probe just lean to the max EGT at about 1000 to 1100 rpm. You'll find that this mixture will increase the rpm about 20 or 30 rpm. So even if you don't have one EGT probe you can lean on the ground using your tach to find this little rpm rise. If you lean past this point, than EGTs go back down lessening the temps at the plugs (and probably also the ability to taxi )

Also if you have just one EGT you can use this to lean as you climb. Just note the position of this gauge at full TO power at 500' and keep it in that range for the rest of the climb.

Great information Lance. John Deakin wrote several excellent articles on engine operation that are really informative:

http://www.avweb.com/news/columns/182179-1.html
http://www.avweb.com/news/columns/182176-1.html
http://www.avweb.com/news/columns/182583-1.html
http://www.avweb.com/news/columns/183094-1.html

Should be required reading for all CFI's.

 

[AirBaker]

Just out of curiousity, are the students being taught Lean of Peak and Rich of Peak? Or is this just 'leaning'?

 

[ejensen]

Just out of curiousity, are the students being taught Lean of Peak and Rich of Peak? Or is this just 'leaning'?

Doesn't sound like they are being taught anything but pull the red knob out 1" in cruise.

 

[Bill]

Doesn't sound like they are being taught anything but pull the red knob out 1" in cruise.

It IS amazing how many different things are taught and used. My PP guy taught me to lean in cruise, and his quote was "I'll teach you how to lean per the POH for this aircraft. After you get your PP, you'll probably read and experiement with how to lean, but during your training we'll do it per the POH."

 

[SkyHog]

Out here, starting altitude is 5800 feet on standard and higher temperature days. That means leaning before takeoff, and then usually every 1000 feet or so also. Seems I'm always adjusting the mixture.

No vernier knobs on the Cherokee, so its a bit harder than it was on the Skyhawk I used to rent. On it, I'd just pull back to rough, then 2 full twists to engine smoothness. In the Cherokee, I pull back to roughness and then slowly push back in until smoothness.

I'm also very new to this whole flying gig.

 

[Let'sgoflying!]

Just out of curiousity, are the students being taught Lean of Peak and Rich of Peak? Or is this just 'leaning'?

Well it used to be that most students learned on someone else's airplane, and it being a sensitive topic for airplane owners -with engines being worth 20K and fuel at 4$- such that I have heard owners give very specific instructions to renters and students (although it kind of undermines both the 'training the right way thingy', and the pilot in command thing). However I understand the owner's viewpoint;I have also seen happily broken-in engines come back from a flight smoking and needing all new valves, wouldn't you like to be that owner?
It is not the easiest thing to teach in flying and they are trying to dumb it down with idiot-proof rules of thumb, may not work.

 

[Lance F]

Just out of curiousity, are the students being taught Lean of Peak and Rich of Peak? Or is this just 'leaning'?

If the students are properly taught what "peak" is then LOP and ROP are pretty easy concepts. I'm afraid that too many instructors don't know and/or don't teach the concept of "peak"...and that's too bad.

 

[Jaime P]

I believe that a student in the early stage dose not fully understand what happen went running lean for to long. The planes I train in have no EGT, CHT. But everyone is right do it right from beginning proper leaning and keep reinforce it until they understand fully is the way go. Great Subject

 

[Ken Ibold]

If the students are properly taught what "peak" is then LOP and ROP are pretty easy concepts. I'm afraid that too many instructors don't know and/or don't teach the concept of "peak"...and that's too bad.

I think the case in many flight schools is that many of the airplanes are not very well instrumented, and in that case I would think it wise to err on the side of too rich. And those schools that use newer airplanes with good engine instrumentation have an institutional inertia that harks back to the trainers built in the 70s.

From the flight school's standpoint, fuel and spark plug cleanings are cheaper than top overhauls.

 

[poadeleted20]

In a nonturbocharged fixed pitch prop installation (typical light trainer), you will have a seriously rough runner before you can hurt the engine by leaning in cruise. Leaning in the climb and on takeoff is another story, because in some cases you can exceed CHT limits before you reach roughness, but above 5000 DA, leaning to peak RPM is necessary to achieve anything close to book performance. Also, a single-cylinder EGT is only likely to get you in trouble if the cylinders are not flow-matched -- it may give you a false sense of security if one of the non-instrumented cylinders beats the instrumented one to the lean side of peak.

 

[Lance F]

I think an instructor that leaves the mixture explanation to "pull it out 1 inch" is doing his/her student a disservice. (or perhaps the instructor doesn't have the training to give a proper technical explanation )

Are you allowed to quote yourself?

Anyway, my point isn't about the instrumentation that is or isn't in typical trainers. When the student pilot gets that rating, he/she can jump into a pretty wide range of aircraft/engine combinations.

If the student pilot hasn't been taught what "peak" means or proper ways to lean, then engine damage can occur and OWTs are perpetuated.

Just because 1" out works ok at 3000' in a C150 operating at a near sea level airport doesn't mean the student shouldn't be taught a lot more.

 

[Lance F]

...it may give you a false sense of security if one of the non-instrumented cylinders beats the instrumented one to the lean side of peak.

That's backwards. The false sense of security would be when the instrumented cylinder goes LOP first and non-instrumented remain on the rich side. It's the cylinder on the lean side of peak that's least likely to be damaged. That one will be cooler and cleaner.

 

[Let'sgoflying!]

Did someone say they fly an a/c with no CHT?
Is that

 

[gismo]

I think the case in many flight schools is that many of the airplanes are not very well instrumented, and in that case I would think it wise to err on the side of too rich. And those schools that use newer airplanes with good engine instrumentation have an institutional inertia that harks back to the trainers built in the 70s.

From the flight school's standpoint, fuel and spark plug cleanings are cheaper than top overhauls.

When I first trained (in the late 70's) there was no EGT gauge and almost no instruction WRT the red knob beyond pull it out to stop the engine.

 

[gismo]

I think the case in many flight schools is that many of the airplanes are not very well instrumented, and in that case I would think it wise to err on the side of too rich. And those schools that use newer airplanes with good engine instrumentation have an institutional inertia that harks back to the trainers built in the 70s.

From the flight school's standpoint, fuel and spark plug cleanings are cheaper than top overhauls.

When I first trained (in the late 70's) there was no EGT gauge and almost no instruction WRT the red knob beyond pull it out to stop the engine. I suspect that part of the issue is that there's not much in the PPL PTS about mixture control other than the applicant being required to recite a little about what a mixture control does (duh! controls the mixture).

You'd think that at least on the commercial checkride an applicant would be required to demonstrate proper leaning in climbs and cruise as well as explain what mixture/power/CHT conditions are harmful to the engine. That way the CFI's would have to be taught something correct about mixture control.

 

[gismo]

Did someone say they fly an a/c with no CHT?
Is that

I do. It doesn't have a mixture control either FWIW.

 

[jesse]

Eh. I never really fly anything with a fancy engine monitor like many of you here, so it's pretty basic as to what can be done.

On the ground after startup I usually lean right away, to the point to where the engine is barely running. When the engine is producing almost NO power, no damage can be done by this. One thing that is fairly important if you are going to do this, lean SO aggressively to where if you applied full power the engine would die. The reason for this is to make sure that you don't have it way lean and then takeoff full power like that, as that could cause damage. So either don't lean at all, or lean to the point to where it barely runs on the ground.

I generally just go full rich for takeoff after that.

On a hot day, a heavy airplane, or a ...very short "runway".. I will lean for peak power before takeoff, It MAY make the difference that might save your @#@$.

Per Lycoming in cruise I generally lean until a slight roughness, and then enrichen until the engine is smooth. (Best Economy)...For I am poor. I'd rather get there slower (build more flight time) and save some money all at the same time.

Just curious if I wrote anything there that is terribly wrong? I don't really think so.

Someone must have thought so though with their negative reputation point:
"Wow, you're an A&P now too, with all your engine knowledge. You don't know everything, and much less than everyone you are preaching to."

 

[Missa]

Just curious if I wrote anything there that is terribly wrong? I don't really think so.

No, what you wrote way fairly the same as what my instructor first taught me about leaning.

Someone must have thought so though with their negative reputation point:
"Wow, you're an A&P now too, with all your engine knowledge. You don't know everything, and much less than everyone you are preaching to."

Wow, that's just wrong. You didn't sound like you were preaching just answering the question of what you were taught on mixture contol. Too bad we don't know who that is or I would join you in returning the negiative to them for being rude!

Missa

 

[ejensen]

It IS amazing how many different things are taught and used. My PP guy taught me to lean in cruise, and his quote was "I'll teach you how to lean per the POH for this aircraft. After you get your PP, you'll probably read and experiement with how to lean, but during your training we'll do it per the POH."

Sounds like you had a reasonable instructor. Learning to fly at 5000', I was taught leaning on the first takeoff. Method depended on the available instrumentation but you leaned and knew why from day one. Always ROP though. Have learned much more as and owner with an engine monitor.

 

[poadeleted20]

...it may give you a false sense of security if one of the non-instrumented cylinders beats the instrumented one to the lean side of peak.

That's backwards. The false sense of security would be when the instrumented cylinder goes LOP first and non-instrumented remain on the rich side. It's the cylinder on the lean side of peak that's least likely to be damaged. That one will be cooler and cleaner.

Ummm....I think the last part is what I was saying -- the instrumented cylinder (falsely) says you're OK while the non-instrumented cylinder is toasting itself because it's been leaned too far. In the case where "the instrumented cylinder goes LOP first and non-instrumented remain on the rich side," all you do is use more gas than you have to.

 

[poadeleted20]

When I first trained (in the late 70's) there was no EGT gauge and almost no instruction WRT the red knob beyond pull it out to stop the engine.

I was trained the same way in the late 60's, although running O-200's on 80/87 did reduce the penalty for not leaning aggressively. Even today, it is, alas, pretty typical.

 

[AirBaker]

Ummm....I think the last part is what I was saying -- the instrumented cylinder (falsely) says you're OK while the non-instrumented cylinder is toasting itself because it's been leaned too far. In the case where "the instrumented cylinder goes LOP first and non-instrumented remain on the rich side," all you do is use more gas than you have to.

Ron,
I'm not sure if that is completely correct. (Or I'm just reading that wrong). The Temperature/Mixture curve is pretty steep on the lean side and much more 'flat' on the rich side. The temperatures drop off in a hurry on the lean side. If you've got any cylinders that haven't gone over peak, they probably running WAY too close to peak for their own good.