Mixture Control
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Mixture Control
Hello all.
Whilst reading over old threads I have encountered a few regarding different methods of mixture control. In my training (which is yet to finish, as I had to take a long life sabbatical until just recently) I was taught to lean the mixture either above 5000ft or on long cross country trips.
Now, I have just stumbled across a few threads about ground leaning, for instance. This is news to me. I'm fascinated and, as usual, want to know about it, what you do and other tips you may have.
Disclaimer: I know there have been a few threads about this over the years, but most are buried and I figured it's been long enough to do a RAFT check. (New acronym I've made up for "Re-animate a forum thread")
Whilst reading over old threads I have encountered a few regarding different methods of mixture control. In my training (which is yet to finish, as I had to take a long life sabbatical until just recently) I was taught to lean the mixture either above 5000ft or on long cross country trips.
Now, I have just stumbled across a few threads about ground leaning, for instance. This is news to me. I'm fascinated and, as usual, want to know about it, what you do and other tips you may have.
Disclaimer: I know there have been a few threads about this over the years, but most are buried and I figured it's been long enough to do a RAFT check. (New acronym I've made up for "Re-animate a forum thread")
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So, I'm interested in hearing from you folks too.
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Last weekend, we just finished the APS seminar in Kortrijk.
John Deakin was one of the teachers. You can search for his columns on engine management under 'Pelican's Perch'. There is very good information there, even for advanced pilots.
If you lean on the ground (highly recommended) you should lean far enough that there is no chance the engine will develop any more power without stumbling. There will be no chance that you take-off with just a little bit leaning (detrimental). You can lean at any altitude in cruise. At high power and when taking-off be sure to be rich enough.
John Deakin was one of the teachers. You can search for his columns on engine management under 'Pelican's Perch'. There is very good information there, even for advanced pilots.
If you lean on the ground (highly recommended) you should lean far enough that there is no chance the engine will develop any more power without stumbling. There will be no chance that you take-off with just a little bit leaning (detrimental). You can lean at any altitude in cruise. At high power and when taking-off be sure to be rich enough.
Problem with trying to lean the mixture correctly is usually a lack of information displayed in the cockpit.
An EGT gauge is very usefull.
However in older trainers they're either not installed or placarded inoperative. If working it's usually only hooked up to one exhaust stack and it may not be the hottest one.
It could have been installed on a random cylinder rather then the leanest one.
Yes, surprise, with carbureted engines they rarely run equal.
This has to do with intake plenum variations, carburetor design and so on.
An aftermarket engine monitor gadget should show you all cylinders.
Leaning for ground ops is a little easier.
For the usual 160-180 hp 4 cylinder : : after engine start run up to 1200-1300 rpm and start leaning.
Watch for initial rpm rise then a drop and a stumble. Lean for the rise.
You now have the correct setting for the max power setting you should need for taxiing. Unless you're operating off a potato field that is.
Also when going full power ( in the runup area!) the engine should stumble and die before reaching full power.
Problem with just arbitrarily pulling it back a little in the taxi is when you forget about it you may overheat a cylinder in the climb as the lean is not aggressive enough to prevent full power.
In the USA you're always taught to lean on the ground also.
An EGT gauge is very usefull.
However in older trainers they're either not installed or placarded inoperative. If working it's usually only hooked up to one exhaust stack and it may not be the hottest one.
It could have been installed on a random cylinder rather then the leanest one.
Yes, surprise, with carbureted engines they rarely run equal.
This has to do with intake plenum variations, carburetor design and so on.
An aftermarket engine monitor gadget should show you all cylinders.
Leaning for ground ops is a little easier.
For the usual 160-180 hp 4 cylinder : : after engine start run up to 1200-1300 rpm and start leaning.
Watch for initial rpm rise then a drop and a stumble. Lean for the rise.
You now have the correct setting for the max power setting you should need for taxiing. Unless you're operating off a potato field that is.
Also when going full power ( in the runup area!) the engine should stumble and die before reaching full power.
Problem with just arbitrarily pulling it back a little in the taxi is when you forget about it you may overheat a cylinder in the climb as the lean is not aggressive enough to prevent full power.
In the USA you're always taught to lean on the ground also.
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Leaning on the ground is not so much a fuel saving issue - as the fuel flow is low during near-idle the savings are really marginal - but more an issue of keeping the engine clean. An excessively rich mixture (full rich) leads to incomplete combustion and leaves residu (soot) on the spark plugs. If the cylinder temps are low this soot won't burn off and thus accumulates. This may cause the plugs to "foul": Not produce a spark. Not good. It may also lead to quicker oil contamination and maybe some other adverse effects.
This effect is increased the richer the mixture becomes. When the OAT is high and/or when the DA is high, this means the mass of air entering the cylinders is reduced, but the amount of fuel stays the same. Thus the mixture becomes even richer. As the UK rarely experiences high temperatures or high density altitudes, leaning on the ground is not all that important there. But in hot or high environments (I learned to fly in Florida) it's good practice to lean a bit. How much is a bit of guesswork: We just pulled the mixture knob back one inch (PA28) but there may be more sophisticated methods.
In any case, during your runup make sure you select full rich (unless the DA is so high that you need to takeoff with a reduced mixture for max performance) and make sure the RPM drop L/R is within the limits stated in the POH.
This effect is increased the richer the mixture becomes. When the OAT is high and/or when the DA is high, this means the mass of air entering the cylinders is reduced, but the amount of fuel stays the same. Thus the mixture becomes even richer. As the UK rarely experiences high temperatures or high density altitudes, leaning on the ground is not all that important there. But in hot or high environments (I learned to fly in Florida) it's good practice to lean a bit. How much is a bit of guesswork: We just pulled the mixture knob back one inch (PA28) but there may be more sophisticated methods.
In any case, during your runup make sure you select full rich (unless the DA is so high that you need to takeoff with a reduced mixture for max performance) and make sure the RPM drop L/R is within the limits stated in the POH.
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There's nothing I could really add that's already been said here, most manufacturers recommend leaning above a certain density altitude (note not indicated altitude!) although this is often to prevent ham-fisted pilots from running the engine too lean and causing damage. 3000' or 5000' is usually the quoted figure in my experience.
I was lucky and was taught leaning, just as well as a PA38 I used to fly years ago (which I learned on) used to have regular problems with plug fouling. If it was encountered usually running the engine at 1800-2000rpm then aggressively leaning the engine to the onset of rough running fro a few seconds was enough to clear the fouled plug. Not a good idea to do it too often though, 2 or 3 attempts and then shutdown and a call to the engineer to have a look. That did happen a few times, much to the chagrin of the CFI. Otherwise it wouldn't have been too good for the engine's life I'd imagine.
The aircraft I flew (and most others since) have only had EGT guages that were u/s anyway so I was taught to lean to pear RPM then enrichen slightly. Not the most accurate but enough to avoid damage with the limited info available. There was one PA28 that had a serviceable EGT but I was so used to the RPM method that I just used that anyway.
I was lucky and was taught leaning, just as well as a PA38 I used to fly years ago (which I learned on) used to have regular problems with plug fouling. If it was encountered usually running the engine at 1800-2000rpm then aggressively leaning the engine to the onset of rough running fro a few seconds was enough to clear the fouled plug. Not a good idea to do it too often though, 2 or 3 attempts and then shutdown and a call to the engineer to have a look. That did happen a few times, much to the chagrin of the CFI. Otherwise it wouldn't have been too good for the engine's life I'd imagine.
The aircraft I flew (and most others since) have only had EGT guages that were u/s anyway so I was taught to lean to pear RPM then enrichen slightly. Not the most accurate but enough to avoid damage with the limited info available. There was one PA28 that had a serviceable EGT but I was so used to the RPM method that I just used that anyway.
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There's nothing I could really add that's already been said here, most manufacturers recommend leaning above a certain density altitude (note not indicated altitude!) although this is often to prevent ham-fisted pilots from running the engine too lean and causing damage. 3000' or 5000' is usually the quoted figure in my experience.
So, in the cruise, lean at any altitude unless the POH explicitly says otherwise, and be sure that you're using the POH material that you've read in the intended flight regime.
Durden's is a good book - I am just about to start on the companion volume.
*I've written "(almost?)" in brackets since, as Durden says, it's what is in the POH that counts - not what is in any other document, and generic statements are often wrong for your particular situation.
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Its this (key) point that many don't understand (well said DaveW). The problem comes when trying to run the engine at high power settings (i.e. above cruise power) with a leaned mixture. If done correctly at cruise power or lower power settings there will be no issue at whatever density altitude.
I think many operators operate a "lean for taxi" procedure to avoid plug fouling (albeit on hard-standing). When taxiing on hard standing the engine's practically at idle in most cases so leaned almost to ICO mostly presents no problem.
But many (not all) FIs seem to teach PPLs to not touch the Big Red Lever unless starting or shutting down. Its a vital engine control and its usage should be fully taught and understood...
Edited to add - I only speak for NA engines with fixed-pitch props. I have no experience on Turbos nor with CS Props. From what I gather turbo engines are a rather different breed that require very careful handling procedures can differ significantly.
Last edited by TelsBoy; 28th Jun 2017 at 12:27. Reason: Addendum + daft spelling errors corrected
Temperatures will make or break a turbo piston engine.
Turbo Inlet Temperature is important as well as avoiding rapid temperature changes. EGT is controlled by the mixture control so turbo inlet temperature is controlled by the mixture controller.
With large piston engines and CS propellers careful throttle and mixture control is required to attempt to make it to TBO.
Turbo Inlet Temperature is important as well as avoiding rapid temperature changes. EGT is controlled by the mixture control so turbo inlet temperature is controlled by the mixture controller.
With large piston engines and CS propellers careful throttle and mixture control is required to attempt to make it to TBO.
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In flight, at 65% power or below, you cannot harm the engine with the mixture control. If you have an engine monitor, learn to use it.
If you have a carburetted engine, use of a bit of carb heat may even out the mixture enough to make it run lean of peak smoothly. If you have a fuel-injected engine, it may take some injector swapping (with the help of competent people) after doing Gami lean tests. My engine now runs smoothly LOP, the last straw was the change of spark plugs from Champion fine wire to Tempest.
The engine management and in particular the use of the mixture knob at PPL level is vastly underteached.
If you have a carburetted engine, use of a bit of carb heat may even out the mixture enough to make it run lean of peak smoothly. If you have a fuel-injected engine, it may take some injector swapping (with the help of competent people) after doing Gami lean tests. My engine now runs smoothly LOP, the last straw was the change of spark plugs from Champion fine wire to Tempest.
The engine management and in particular the use of the mixture knob at PPL level is vastly underteached.
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Hello all.
Whilst reading over old threads I have encountered a few regarding different methods of mixture control. In my training (which is yet to finish, as I had to take a long life sabbatical until just recently) I was taught to lean the mixture either above 5000ft or on long cross country trips.
Now, I have just stumbled across a few threads about ground leaning, for instance. This is news to me. I'm fascinated and, as usual, want to know about it, what you do and other tips you may have.
Disclaimer: I know there have been a few threads about this over the years, but most are buried and I figured it's been long enough to do a RAFT check. (New acronym I've made up for "Re-animate a forum thread")
Whilst reading over old threads I have encountered a few regarding different methods of mixture control. In my training (which is yet to finish, as I had to take a long life sabbatical until just recently) I was taught to lean the mixture either above 5000ft or on long cross country trips.
Now, I have just stumbled across a few threads about ground leaning, for instance. This is news to me. I'm fascinated and, as usual, want to know about it, what you do and other tips you may have.
Disclaimer: I know there have been a few threads about this over the years, but most are buried and I figured it's been long enough to do a RAFT check. (New acronym I've made up for "Re-animate a forum thread")
This all leads/has led to all the old wives tales pilots have been told. So far in this thread there has (as usual) been some good advice and some bad advice.
My suggestion is visit Pelican's Perch https://www.avweb.com/news/pelican/182146-1.html Articles 8, 18 and 19 are compulsory followed by 15 and 16 and any/all the rest John Deakin has written.
If you can find articles written by Walter Atkinson of https://www.advancedpilot.com/ then study them. You will be better informed listening to these two gentlemen than the OWT from young instructors.
If you are going to lean on the ground, then lean aggressively. This will assist in keeping the combustion temperature up and prevent full power being applied. One post mentioned the PA38. Most 4 cylinder Lycomings have their mags wired left mag to left top, right bottom and right mag to right top, left bottom. (Plugs, that is...) The O-235 in the PA38 had one mag wired to top plugs and the other to the bottom plugs. The bottom plugs would always foul. Lycoming brought out an SB to cure this; the problem is lead accumulation and not soot.
I have owned and RV-6 (IO-360) and RV-10 (IO-540) and would gladly demonstrate full throttle at sea level and 150F LOP. (91% power)
Tin hat, flak jacket, foxhole....
Last edited by Chuck Notyeager; 28th Jun 2017 at 17:56.
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Radial engines have perfect fuel and air distribution. Auto lean in big radial engines is 50 LOP.
Lycoming recommends cruise for best economy AT peak EGT, provided 75% power or less.
Below 75% power, no matter what you do with the red knob; you cannot damage the engine. So leaning for taxi, cannot damage the engine.
Air cooled engines have idle mixture set rich. This is so that it will idle when cold and accelerate after a glide approach. Leaning for taxi is advisable as long as you lean aggressively. You really do not want to go full throttle and be LOP as the engine might run nice and smoothly, but will not produce the power you need.
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Chuck,
I would recommend 65% as the limit below which you cannot damage the engine with the mixture knob. I fly both a NA Bonanza and a TN Bonanza, always LOP except for takeoff and climb.
I would recommend 65% as the limit below which you cannot damage the engine with the mixture knob. I fly both a NA Bonanza and a TN Bonanza, always LOP except for takeoff and climb.
I've never understood the "don't lean below x000 feet" thing. In my TR182 I lean for taxi, otherwise the plugs foul. The only time I fly full rich is for take off and the initial climb to 1000 feet or so. After that I lean to CHTs of 400 or less - maybe up to 410 on the hottest cylinders. Much easier with a full engine monitor. Flying full rich (22 gph) would be pretty catastrophic for both my bank account and range, as compared to 14.5 which is what I can normally do without problems.
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Thanks for the replies, all.
I'm bounding through Deakins' material with Pelican's Perch. Really fascinating stuff. He speaks highly of his GAMIjectors, which I've since read up on, as a segwayed note.
This is a practice I will encourage my instructors to teach, as deep as they dare. I want to get this in on the ground level, rather than discovering this some hundred hours into my license. Whilst I'm not afraid of that red lever (which isn't to say I don't respect it!) I also don't fully understand the art of it. Hence my post here.
Unfortunately, however, my trainer isn't equipped with EGT or CHT gauges, so I will be relying on the RPM and engine note to tell me all about leaning, for now. Thinking ahead, then, would it be wise of me to seek further dual training when I have access to an aircraft that does?
I'm bounding through Deakins' material with Pelican's Perch. Really fascinating stuff. He speaks highly of his GAMIjectors, which I've since read up on, as a segwayed note.
This is a practice I will encourage my instructors to teach, as deep as they dare. I want to get this in on the ground level, rather than discovering this some hundred hours into my license. Whilst I'm not afraid of that red lever (which isn't to say I don't respect it!) I also don't fully understand the art of it. Hence my post here.
Unfortunately, however, my trainer isn't equipped with EGT or CHT gauges, so I will be relying on the RPM and engine note to tell me all about leaning, for now. Thinking ahead, then, would it be wise of me to seek further dual training when I have access to an aircraft that does?
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I lean out when on the deck, and as soon as I leave the pattern, depending on what I'm planning on doing once I get to pattern altitude will determine weather I'm leaning for best power or best economy. The only time I'm full rich is on run-up and take off. The new plane has a four cylinder EGT monitor which is an excellent tool.
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I lean out when on the deck, and as soon as I leave the pattern, depending on what I'm planning on doing once I get to pattern altitude will determine weather I'm leaning for best power or best economy. The only time I'm full rich is on run-up and take off. The new plane has a four cylinder EGT monitor which is an excellent tool.
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Assume you are returning to land after a long flight at altitude; richen as necessary during descent to ensure smooth engine operation, then for approach and landing leave the mixture where it was because you should only be using low power. On short finals richen as required for a possible go around. (At sea level that would be full rich.)
With a basic trainer if you have less than 2500 RPM and less than full throttle, lean till engine runs rough then richen ONLY ENOUGH for smooth operation. If you have a fancy engine monitor then use this with Lean Assist.
You really cannot cause detonation in a low compression aircraft engine (8.5:1 or less) any rough running is unbalanced power pulses so smooth running is good.
Deakin will tell you; detonation can only happen in a very narrow band of power/fuel/air/BMEP and either a richer OR a leaner mixture will stop it.
Keep it safe out there
With a basic trainer if you have less than 2500 RPM and less than full throttle, lean till engine runs rough then richen ONLY ENOUGH for smooth operation. If you have a fancy engine monitor then use this with Lean Assist.
You really cannot cause detonation in a low compression aircraft engine (8.5:1 or less) any rough running is unbalanced power pulses so smooth running is good.
Deakin will tell you; detonation can only happen in a very narrow band of power/fuel/air/BMEP and either a richer OR a leaner mixture will stop it.
Keep it safe out there