Mixture management

[guillaume78150]

On the Bonanza, on idling or taxiing, unless one lean the mixture, the spark plugs are quickly fouled. And when leaning, the RPM rises a bit.
On the Comanche, when leaning on taxiing, the engine cough and lose RPM. And plugs don't get fouled so easily.
Both engines are naturally aspirated and carbureted, why is that difference ?

[AKar]

This RPM rising while leaning is a proper consequence of leaning the mixture from "much too rich" (the idle mixture) to more or less so. You gain power doing that, other things constant. Practically, just about every one of these engines need to have their idle mixtures, with the knob full in, set at "much too rich" to allow for starting and reasonable cold idling.

In real life, excessively quick fouling of the spark plugs on ground with throttle full back and mixture full rich, generally (but not always) indicates, accordingly, excessively too rich idle mixture setting. In fact, a ballpark setting for a good idle mixture may be approximated by noting the very RPM gain when leaning from the full-rich. This is not adjustable from the cockpit but takes some action under the cowls.

-Esa

[fottip]

On the Bonanza, on idling or taxiing, unless one lean the mixture, the spark plugs are quickly fouled. And when leaning, the RPM rises a bit. On the Comanche, when leaning on taxiing, the engine cough and lose RPM. And plugs don't get fouled so easily. Both engines are naturally aspirated and carbureted, why is that difference ?

The answer already provided is correct as far as it goes.

In real life, it's always a good idea to lean a reciprocating engine on the ground, simply for good engine hygiene. And, in real life, some engines are notoriously prone to spark plug fouling and lead deposits elsewhere inside the engine, valves and valve stems, etc, more than others. Conversely, many can accommodate full-rich mixture during ground operations and suffer no adverse effects. It depends on the specific engine variant.

Another factor in the real life equation is that many airplane engines in service today were designed to run on the (now obsolete) 80/87 octane avgas. It was replaced in the late '90s due to EPA environmental concerns, by 100LL avgas, "LL" a misnomer for "low lead", misnomer because it actually contains MORE lead than the old 80/87 avgas it replaced. The increased tendency of 100LL avgas to foul engines lead to the availability of an additive called TCP, which acts as a lead scavenger to prevent lead fouling in engines. And the story doesn't end there - EPA has been trying to outlaw the current 100LL for the same reasons it outlawed 80/87 avgas, and the only reason it hasn't yet is because no one has come up with a viable alternative for the thousands of aircraft that depend on 100LL. If there were no more 100LL, with nothing to replace it, all those aircraft would be grounded.

I owned a Piper Cherokee 140 years ago, and I avoided the whole issue by installing an auxiliary gas tank and pump in the bed of my truck, and I refueled the plane myself using unleaded car gas from service stations, legalized with an STC I bought.

So that's some real world aviation plug fouling background. I don't know how faithfully modeled lead fouling in sims is. I DO know that coders who have no real-world experience in aviation sometimes tend to "over-simulate" things just because they can, and it screws up otherwise perfectly good simulations. One example that comes to mind is the Piper Cub, a tail dragger with a reputation for biting pilots who aren't adept on the rudders, especially on the ground. The result was a Cub simulation in early MSFS sims and P3D sims that was essentially unflyable, since they were so poorly modeled.

This was probably more information than you wanted, but I thought a little historical perspective might prove interesting. I spent enough money and time worrying about how best to maintain the real airplanes I owned for over 20 years, and now, I just disable all the simulated maintenance junk in the sim so nothing breaks - I don't want to be bothered with that again - I bought it to FLY!

[Scott - A2A]

On the Bonanza, on idling or taxiing, unless one lean the mixture, the spark plugs are quickly fouled. And when leaning, the RPM rises a bit.
On the Comanche, when leaning on taxiing, the engine cough and lose RPM. And plugs don't get fouled so easily.
Both engines are naturally aspirated and carbureted, why is that difference ?

The Bonanza we tested exhibited this behavior of increased RPM (as much as 100RPM if I recall correctly) with leaning. If you apply full power this lean the engine will sputter. From what we understood this was typical of the continental engine installed so we modeled it this way. Our Comanche doesn't exhibit this behavior, maybe just a tad of an increase of RPM with leaning mixture. They are completely different in this regard but the Accu-Sim counterparts reflect this behavior in both airplanes. I can't say why these are different other than it's just different mixtures due to different designs.

Scott.

[AKar]

What I could perhaps add to this, is that these are factors that are: adjustable, affected by many factors, and vary from individual airplane to the next.

Airplanes are operated differently and in different conditions. Hence, they tend to be maintained and adjusted differently. Further, what one owner/operator/mechanic finds acceptable, or preferable even, another might not. Third may not even realize there is an issue, sometimes even when there clearly is: "It has always done that." Some stuff is highly subjective, while some other stuff (like having wrong spark plugs installed!) is not.

Giving the big picture, Continental's fuel-injected engines are (supposedly) adjusted for their idle mixture setting so that a rise of 25 to 50 RPM is observed when leaning from the full-rich mixture with the engine ran at specified idle RPM, while still respecting idle fuel pressure specifications. Much higher rise than this indicates excessively rich idle mixture setting, while not getting noticeable rise at all tends to indicate too lean setting accordingly.

That's what the book says anyways, and while it is mostly sound starting point, we get into dirty little realities of life. Some engines tend to idle poorly when operated in very cold conditions. Those may benefit from a tad richer idle mixture, resulting in "excessive" idle rise during summer time (and perhaps associated issues with fouling, in particular if their idle RPM is adjusted too low at the same time). Some engines may tend to foul their plugs in way they are operated. They may benefit from a bit leaner idle mixture, though I'd be sure to have the idle RPM checked as well. Likewise, an aircraft flown primarily from, I don't know, Bogota perhaps, almost certainly gets adjusted for a way leaner idle mixture - in extreme cases, it may very well fail to fire up at sea level completely! The list goes on.

And of note, the above-mentioned rise of 25 to 50 RPM is checked at specified idle RPM, not at 1000 RPM or whatever they are usually warmed up at. The specified idle RPM for Continentals is typically, but not always, 600 RPM.

Both engines are naturally aspirated and carbureted, why is that difference ?

Oh, forgot on my previous post, Comanche has a carburetor, Bonanza is fuel-injected.

-Esa

[guillaume78150]

The Bonanza we tested exhibited this behavior of increased RPM (as much as 100RPM if I recall correctly) with leaning. If you apply full power this lean the engine will sputter. From what we understood this was typical of the continental engine installed so we modeled it this way. Our Comanche doesn't exhibit this behavior, maybe just a tad of an increase of RPM with leaning mixture. They are completely different in this regard but the Accu-Sim counterparts reflect this behavior in both airplanes. I can't say why these are different other than it's just different mixtures due to different designs.

Scott.

A2A made it right then !
Thanks Scott.

Both engines are naturally aspirated and carbureted, why is that difference ?

Oh, forgot on my previous post, Comanche has a carburetor, Bonanza is fuel-injected.

-Esa

I missed that indeed ! BTW, is that the reason why at, say 8000 feet, 20 inHg MP, 65% mixture and 2200 RPM, at an average speed of 150 kts, the Bonanza returns 10 gph when the Comanche 12 ?
Thanks.

[Tomas Linnet]

I owned a Piper Cherokee 140 years ago

I and I thought the Wright Brothers was the first ones....guess I was wrong

[MkIV Hvd]

I owned a Piper Cherokee 140 years ago

I and I thought the Wright Brothers was the first ones....guess I was wrong

Somebody had to......

[fottip]

I owned a Piper Cherokee 140 years ago

I and I thought the Wright Brothers was the first ones....guess I was wrong

Somebody had to......

"Somebody had to..." WHAT..EXACTLY, EINSTEIN?? What in hell is this crap?

What does this have to do with the "Wright Brothers", fer God's Sake? Are you so ignorant you don't even realize that Piper Cherokees are being flown today by the THOUSANDS. WORLDWIDE?? Your ignorance is profound.

Jeez...gotta' love it. Decades of personal REAL LIFE experience owning and maintaining airplanes, and offering advice, BASED ON THAT REAL LIFE EXPERIENCE, to people asking questions about SIMULATED airplanes, and what do I get? Trash posts from people who have ZERO real world experience, doing the usual internet commando number, and knowing they won't get called to account for their bullshit. YOU PEOPLE ARE LOSERS.

This is my LAST A2A forum post. You losers have proved to me you don't deserve any more REAL WORLD aviation wisdom and experience from me.

I completely understand your response will be fine, good riddance, proving that you have no appreciation of quality information in answer to the questions asked here. Is lack of quality information a good thing, you think? YOU be the judge. If you think action based on answers you get from your simmer peers who have no aviation experience is sufficient, good luck with that.

I'm outta' here. Life's too short.

Buh bye

[MkIV Hvd]

I and I thought the Wright Brothers was the first ones....guess I was wrong

Somebody had to......

"Somebody had to..." WHAT..EXACTLY, EINSTEIN?? What in hell is this crap? Are you so ignorant you don't even realize that Piper Cherokees are being flown today by the THOUSANDS. WORLDWIDE?? Your ignorance is profound.

I try to add some real world experience to the internet know-it-all bullshit we see here everywhere, and I get what? You clowns who don't know a damned throttle from a bottle, and you think it's "cool" to trash my posts. Who the hell ARE you losers? Get off the internet until you get a life and some understanding of the world around you.

Jeez...gotta' love it. Decades of personal REAL LIFE experience owning and maintaining airplanes, and offering advice, BASED ON THAT REAL LIFE EXPERIENCE, to people asking questions about SIMULATED airplanes, and what do I get? Trash posts from people who have ZERO real world experience, doing the usual internet commando number, and knowing they won't get called to account for their bullshit. YOU PEOPLE ARE LOSERS.

Well it was funny before...now it's hilarious!!
Dude, it was a joke...and to quote Taylor Swift, "You Need To Calm Down!" ... maybe grab a beer and see if you can find a sense of humour somewhere...

Btw...the post above was edited before I posted so I didn't know we were going to lose all the real world experience "fottip" brought to this forum full or RW pilots of all levels...sorry all.........

[fottip]

Well it was funny before...now it's hilarious!! Dude, it was a joke

No. What I originally posted was not a "joke".

You clowns can take it however you want, but it was a serious respoonse to a serious question.

Take it as a "joke" if you want, "Dude", but that just makes you a "joke".

DEAL WITH IT.

[Hook]

Well it was funny before...now it's hilarious!!

Pure gold. You couldn't make something like this up.

Hook

[Hook]

I DO know that coders who have no real-world experience in aviation sometimes tend to "over-simulate" things just because they can, and it screws up otherwise perfectly good simulations. One example that comes to mind is the Piper Cub, a tail dragger with a reputation for biting pilots who aren't adept on the rudders, especially on the ground. The result was a Cub simulation in early MSFS sims and P3D sims that was essentially unflyable, since they were so poorly modeled.

Hm. Who besides A2A made a Cub with that much detail?

...now, I just disable all the simulated maintenance junk in the sim so nothing breaks - I don't want to be bothered with that again - I bought it to FLY!

Sure, why not?

Hook

[AKar]

Both engines are naturally aspirated and carbureted, why is that difference ?

Oh, forgot on my previous post, Comanche has a carburetor, Bonanza is fuel-injected.

BTW, is that the reason why at, say 8000 feet, 20 inHg MP, 65% mixture and 2200 RPM, at an average speed of 150 kts, the Bonanza returns 10 gph when the Comanche 12 ?
Thanks.

It could be one factor. Carburetted engines tend to be somewhat less efficient. However, with that much difference I'd say they are ran at somewhat different mixture settings. Having the knob 65 % in does not necessarily tell much.

-Esa

[guillaume78150]

I understand. Thanks. The Bonanza is a bit more demanding, faster but the Comanche is more comfortable and relax to fly.
Two fine airplanes anyway.