Mixture Rich or Best for ground ops

[N201MKTurbo]

2 hours ago, jaylw314 said:

That would make sense if the boost pump was off somewhere during the runup, right?  After all, the takeoff checklist does include turning off the boost pump at some point.  On takeoff, I'd much rather find out the engine runs with the boost pump off but not on, than finding out it runs with the boost bump on but not off.  The former I'll find out immediately and can abort.  The latter I will find out at a fairly inopportune time...

It’s a free country, you are free to cycle the boost pump any time you want.

[PT20J]

The primary failure mode of a mechanical fuel pump is a torn diaphragm in which case it just stops pumping. I don’t think it makes a lot of difference when you turn the boost pump on because you don’t know when the engine driven pump will fail. It’s just a good idea to have it on for takeoff so you have redundancy in case it fails at low altitude. 

Skip

[PT20J]

5 hours ago, Shadrach said:

Incidentally, a properly set up Lyc IO360 typically does not typically foul plugs even when ground run with the mixture full rich.

Good point. The ground leaning procedure came into vogue when 80 octane was phased out and smaller low compression engines had to burn 100LL that had a lot more lead than 80/87 and these engines started having lead fouling problems. The idea was to lean out the idle mixture to raise the temperature of the spark plugs so that the lead scavenger was more effective. The BY plugs were created to get the electrodes further exposed to combustion gasses for the same reason. It doesn‘t hurt to lean on the ground, but it may not have a lot of benefit for engines designed for 100 octane fuel. 

Skip

[Shadrach]

48 minutes ago, PT20J said:

The primary failure mode of a mechanical fuel pump is a torn diaphragm in which case it just stops pumping. I don’t think it makes a lot of difference when you turn the boost pump on because you don’t know when the engine driven pump will fail. It’s just a good idea to have it on for takeoff so you have redundancy in case it fails at low altitude. 

Skip

I’m pretty sure that I know of a pump that continued to function even with a torn diaphragm. It was a neighbor’s Cherokee six. The problem was revealed by the smell of raw fuel in the hangar which was dripping from cowl.

[PT20J]

32 minutes ago, Shadrach said:

I’m pretty sure that I know of a pump that continued to function even with a torn diaphragm. It was a neighbor’s Cherokee six. The problem was revealed by the smell of raw fuel in the hangar which was dripping from cowl.

The aviation pumps have two diaphragms with a space between that drains out a tube through a small orifice. If the main diaphragm ruptures, the secondary keeps pumping and some gas leaks out the drain tube restricted by the orifice to alert you to the condition.

Here's a great description of these pumps.

 

[Mooney-Shiner]

5 hours ago, jaylw314 said:

Wow, that's so odd.  Anyone know why they did that?

I thought you were in Ukraine because your handle looks like it starts with some of the airport identifiers I see in Digital Combat Simulator   I've been playing that a bit too much lately...

You are not wrong.  I'm Ukrainian-American, who lived in US for 22 years and serve in USMC. When I set up my account I mistook the  user name for the email (I'm not good in the computer things). Of course this is an email that I used back when I was 17 back in late 90-s (jeez!), and now using it for all unofficial business. All the Ukrainian tail numbers start with UR-.

[skykrawler]

The fact that your engine 'fouled the plugs' when you turned on the boost pump could mean that the boost pump is sucking air and introducing it into the fuel injector system.

 

[carusoam]

Summary…?

1) Testing the fuel pumps prior to flight is a good practice…

2) Running the electric fuel pump during the run-up, adds another variable…  with not much value added… post y2k…

3) Excess cooling on the ground vs. fouled plugs… skip the extra cooling, keep the plugs clean….

4) Deep leaning on the ground does lead to an engine stumble when going to full power…

5) Use caution when leaning on the ground… expecting a stumble if you forget to push the mixture…  

6) If you don’t use a deep enough lean… you may not get the stumble warning…

7) When leaning on the ground… it helps to be familiar with the FF for your ship… full rich is about 2X nicely leaned…

8) Some electric fuel pumps are not rated for continuous running… know which one you have.

9) Example… the IO550 uses the low boost pump on for cold weather starting…. Without it on, the engine dies from starvation during the first minute or so… until things warm up a bit…

10) Example… The IO550 uses 4gph during idle at 1krpm at full rich, about 2gph nicely leaned, less when deeply leaned…

11) Both our fuel pumps have the two diaphragms… and a drain between them…  unfortunately, it is hard to see the fuel draining from the cockpit… don’t forget to look for blue stains at the drain during the pre-flight…  getting a pump resealed is a quick, not so expensive, way to stop a pump from leaking down the drain….

12) MS has a few people that have backgrounds stemming from the Russia, Ukraine, and other nearby countries…

13) If for some reason, you would like to change your screen name… that is possible too.   

14) It is really helpful to have a FF monitor for knowing what is going on during the various phases of ground handling…

PP thoughts only, not a mechanic…

Best regards,

-a-

[N201MKTurbo]

I've never liked my middle name. I think I should change it to Mixture...

[0TreeLemur]

On 11/23/2021 at 9:25 PM, 201er said:

Oh another thing I learned is to taxi with the mixture as far back as possible without quitting. This way if you forget to push it back in for takeoff, you’ll stumble the engine when you advance the throttle rather than cause detonation.

and then some poo comes out....

[Hank]

5 hours ago, 0TreeLemur said:

and then some poo comes out....

Nah. I keep my C so lean that taxiing from the grass up onto pavement will make the engine sputter and threaten to shut off unless I richen up, and that's only about half throttle. No way would a takeoff happen . . . .

[Mooney-Shiner]

10 hours ago, skykrawler said:

The fact that your engine 'fouled the plugs' when you turned on the boost pump could mean that the boost pump is sucking air and introducing it into the fuel injector system.

 

This is an interesting note...

How an excess air in the fuel system causes overly rich solution and flooding my bottom spark plugs with fuel causing a misfire?

[Mooney-Shiner]

22 hours ago, PT20J said:

Good point. The ground leaning procedure came into vogue when 80 octane was phased out and smaller low compression engines had to burn 100LL that had a lot more lead than 80/87 and these engines started having lead fouling problems. The idea was to lean out the idle mixture to raise the temperature of the spark plugs so that the lead scavenger was more effective. The BY plugs were created to get the electrodes further exposed to combustion gasses for the same reason. It doesn‘t hurt to lean on the ground, but it may not have a lot of benefit for engines designed for 100 octane fuel. 

Skip

Thank you, PT20J.  This is an excellent explanation. I began wondering why would Lycoming built their IO-360 so inefficiently...Now I know that they built IO-360 with totally different fuel in mind. In totally unrelated note, makes me wonder if this means that low compression IO-360s are prime candidate for a regular car gas STC or just blanket use approval since they would be right at home with lower octane number of car or marine gas. 

Happy Thx-giving!

Edited November 26, 2021 by ukrsindicat@yahoo.com

[Mooney-Shiner]

9 hours ago, carusoam said:

14) It is really helpful to have a FF monitor for knowing what is going on during the various phases of ground handling…

-a-

Nice summary of PP thoughts only, A.

I totally forgot that I have JPI450 fuel flow scan. I wonder what GPH should I look for for my IO360A1A at taxi, runup, take off?

Happy Thx-giving!

Edited November 26, 2021 by ukrsindicat@yahoo.com

[Shadrach]

On 11/25/2021 at 7:28 PM, ukrsindicat@yahoo.com said:

Thank you, PT20J.  This is an excellent explanation. I began wondering why would Lycoming built their IO-360 so inefficiently...Now I know that they built IO-360 with totally different fuel in mind. In totally unrelated note, makes me wonder if this means that low compression IO-360s are prime candidate for a regular car gas STC or just blanket use approval since they would be right at home with lower octane number of car or marine gas. 

Happy Thx-giving!

You’ve misunderstood Skip’s comment. The IO360 is and always was designed to use 100LL. As I said in the comment Skip was quoting, Properly set up IO360s should not foul plugs even when ground run with the mixture full rich.  Skip’s comment was about the genesis of ground leaning and how it carried over to engines that may benefit from ground leaning but don’t really require it. The IO360 is one of those engines that does not.

Edited November 28, 2021 by Shadrach

[N201MKTurbo]

The idle mixture is a fickle thing. It has no altitude compensation. While it can be set up perfectly at your home drome, it doesn't mean it is right anywhere else. If you live in Flagstaff (7000 ft) and adjust it perfectly, it will be very lean if you go to the coast. 

[A64Pilot]

The funny thing is that a great many of the engines that could benefit from ground leaning like a Continental C-85 as they were designed for a min. 73 octane have a carburetor that often can’t be leaned, and yet they soldier on. It’s lead in excess of the fuel the engine was designed to be run on that causes fouling, it’s not the mixture, but excessive leaning can reduce the amount of lead of course.

There are a great many beliefs about these engines that simply are not requirements, and they have flown for a very long time without these special procedures and equipment without issue.

A few have made significant money by convincing people that the engine manufacturers are fools, people that would never consider operating their car or lawnmower in a manner inconsistent with the owners manual will do so with their airplane. 

[M20F]

Never lean on the ground, never had a fouled plug. 

[Shadrach]

3 hours ago, N201MKTurbo said:

The idle mixture is a fickle thing. It has no altitude compensation. While it can be set up perfectly at your home drome, it doesn't mean it is right anywhere else. If you live in Flagstaff (7000 ft) and adjust it perfectly, it will be very lean if you go to the coast. 

Prior to me operating this plane it was never leaned on the ground. My dad left it full rich for ground ops. He finally started leaning for high alt take offs after a puckering experience at Albuquerque on a hot day.  My dad flew this plane all over the continent and operated at fields of all elevations from Flagstaff to Mexico City to Albuquerque to Truckee to etc..fouled plugs were never a problem.

[RobertGary1]

If increasing throttle causes a rise in rpm more than a couple hundred you are too rich. I took that approach 20 years ago and not fouled a plug since. 

[RobertGary1]

11 minutes ago, Shadrach said:

Prior to me operating this plane it was never leaned on the ground. My dad left it full rich for ground ops. He finally started leaning for high alt take offs after a puckering experience at Albuquerque on a hot day.  My dad flew this plane all over the continent and operated at fields of all elevations from Flagstaff to Mexico City to Albuquerque to Truckee to etc..fouled plugs were never a problem.

In an injected plane? That seems difficult. Lycomings and even more contenentals don’t put out near full power at full rich and high da. A carb’d plane id believe. 

[Shadrach]

1 hour ago, RobertGary1 said:

In an injected plane? That seems difficult. Lycomings and even more contenentals don’t put out near full power at full rich and high da. A carb’d plane id believe. 

I know that and you know that, but in 1973, my dad was not very conscious of it. As I said, a puckering experience at ABQ jogged him into awareness. Warm day, high altitude and a well loaded plane made for a very uncomfortable departure. I was not yet born, so it was a cautionary tale that I’ve heard many times (Dad is 82 and probably tells the tale at least twice a year)…

[PT20J]

2 hours ago, RobertGary1 said:

In an injected plane? That seems difficult. Lycomings and even more contenentals don’t put out near full power at full rich and high da. A carb’d plane id believe. 

Shouldn't make a difference whether the engine is injected or carbureted. Both devices meter fuel based on airflow measured through a venturi. The problem is that the venturi measures volume and the engine requires a mixture based on mass. The fuel metering system is calibrated for standard sea level air density, but has no way to know that the same volume of air passing through the venturi at a higher altitude contains fewer air molecules, so we have to compensate manually by reducing the fuel flow with the mixture control.

Skip

[RobertGary1]

2 hours ago, PT20J said:

Shouldn't make a difference whether the engine is injected or carbureted. Both devices meter fuel based on airflow measured through a venturi. The problem is that the venturi measures volume and the engine requires a mixture based on mass. The fuel metering system is calibrated for standard sea level air density, but has no way to know that the same volume of air passing through the venturi at a higher altitude contains fewer air molecules, so we have to compensate manually by reducing the fuel flow with the mixture control.

Skip

Just my experience that the cont and Lycoming carb engines are far more forgiving taking off too rich.  
The worst are the turbo cont injected engines. I’ve seen them quit in the runup if too rich high density and that was on a factory delivery flight so I assume it was tuned better than the fleet. 

[Shadrach]

26 minutes ago, RobertGary1 said:

Just my experience that the cont and Lycoming carb engines are far more forgiving taking off too rich.  
The worst are the turbo cont injected engines. I’ve seen them quit in the runup if too rich high density and that was on a factory delivery flight so I assume it was tuned better than the fleet. 

In the case of Lycomings that might be because many are leaner than optimal at WOT under normal circumstances. The little Continentals do not love 100LL.