mixture Mixture change with Throttle Reduction??

[Mark942]

My CFII insists that I add fuel flow (move the Red knob in) as I reduce MP at level flight during the "Slow Down" phase to get slow enough to drop the gear on an approach.  Level flight at 4000 MSL, (LOP at cruise but he says that doesn't matter).  This doesn't seem correct.  I am at the same density altitude, not starting down yet.  Opinions please, and references to actual data or expert's articles such as Mike at Savvy articles would be really appreciated.

Thanks,

-mark

[Browncbr1]

That sounds silly.

the only time I push in mixture is to keep from getting too deep LOP on descent.   

Edited March 3, 2022 by Browncbr1

[EricJ]

The only practicality I can think of is that it gets ahead of the leaning that'll happen as you descend.    I'm constantly having to remind myself to bump the mixture up during long descents.

 

[David Lloyd]

For injected engines, as long as it is rich enough to respond to the throttle I don’t see it matters.

For carbureted engines, some have a throttle enrichment valve that comes into play near full throttle. If you’re running one of those at full throttle, lop, and pull power for descent, you will suddenly have a very lean mixture. Once again, if rich enough to respond….  

Not sure if all carb’ed engines have a throttle enrichment valve.

[EricJ]

3 minutes ago, David Lloyd said:

For injected engines, as long as it is rich enough to respond to the throttle I don’t see it matters.

For carbureted engines, some have a throttle enrichment valve that comes into play near full throttle. If you’re running one of those at full throttle, lop, and pull power for descent, you will suddenly have a very lean mixture. Once again, if rich enough to respond….  

Not sure if all carb’ed engines have a throttle enrichment valve.

Most do, and ironically it is called the "economizer system", and it's why carburetors generally shouldn't be cruised at full throttle.    Fuel Injection likes to be cruised WOT, carburetors not so much. 

[smwash02]

If I'm understanding correctly, you're referring to when you're in level flight at pattern altitude?

I go full rich in the pattern to prepare for if I have to go-around. I aim to do this when I'm in a place where if the mixture change kills the engine, I can make the runway easily.

Edited March 3, 2022 by smwash02

[201er]

1 hour ago, Mark942 said:

My CFII insists that I add fuel flow (move the Red knob in) as I reduce MP at level flight during the "Slow Down" phase to get slow enough to drop the gear on an approach.  Level flight at 4000 MSL, (LOP at cruise but he says that doesn't matter).  This doesn't seem correct.  I am at the same density altitude, not starting down yet.  Opinions please, and references to actual data or expert's articles such as Mike at Savvy articles would be really appreciated.

Thanks,

-mark

It’s the opposite. If you’re LOP in cruise and you reduce throttle, you’re enriching the mixture and likely no longer LOP. You should reduce mixture (move red knob out) if you want to make an economy descent and stay slow LOP.

[carusoam]

+3 Check in with your CFII to find out what he meant, or why he would do that…

Something got lost in translation…

Slowing down to drop the gear… essentially you are preparing to land…

For simplicity… go 100°F ROP… or 200°F ROP… easier to ignore as you continue to descend in a low power mode…

 

 

 

For NA planes… descending from altitude, the mixture drifts leaner as you descend….

Each time you change a power setting, the mixture should be considered…

Since power is in a continuous flux during the descent…

When LOP, you can ignore it until you feel like resetting it…

When ROP, you can ignore it until you feel like resetting it… 

If your EGT gauge has a white box or a blue box… this makes resetting on the descent/ascent a breeze…. 

This is possible because the power level is generally less than 65%bhp or Vne will be the next issue…
 

With MP changing 1” every 1k’….  How often did the CFII recommend changing the MP and/or mixture?

Did he have a procedure for setting the descent rate as well?  Like always 500fpm?

 

PP thoughts only, not a CFI…

Best regards,

-a-

[PT20J]

12 hours ago, 201er said:

It’s the opposite. If you’re LOP in cruise and you reduce throttle, you’re enriching the mixture and likely no longer LOP. You should reduce mixture (move red knob out) if you want to make an economy descent and stay slow LOP.

The throttle controls the airflow through the servo and the servo meters fuel according to the airflow at the air/fuel ratio set by the mixture control. Why would reducing the throttle (at constant altitude) richen the mixture?

[FlyingDude]

During descent I keep adjusting throttle to maintain constant MAP. That way the engine power % doesn't change. I assume LOP/ROP setting doesn't change, either...

During the final 5 min of the flight, after I level for downwind and drop gear, I go full rich. Fuel flow indicates very low values already, so I don't care about fuel economy. It's also ready for a go-around...

In IFR flight, when I configure for landing before IAF, I find the peak egt and stay there. I push full mixture at FAF or when established, so that it's ready for going missed...

That's me. 

[FlyingDude]

48 minutes ago, PT20J said:

The throttle controls the airflow through the servo and the servo meters fuel according to the airflow at the air/fuel ratio set by the mixture control. Why would reducing the throttle (at constant altitude) richen the mixture?

Very good point... But aren't you supposed to readjust the mixture every time you change throttle & rpm (ie go with a new power setting)? Are there different types of fuel meters out there?

[PT20J]

4 minutes ago, FlyingDude said:

Very good point... But aren't you supposed to readjust the mixture every time you go with a new power setting? Are there different types of fuel meters out there?

The old Bendix Stromberg pressure carburetors (on which the RSA design is based) had auto rich and auto lean positions and you could just park the mixture there at any throttle setting in cruise. I’ve never tried it on the RSA, but an interesting test would be to set say 75% power and lean to peak and mark the mixture control position with a sharpie and then reduce the throttle to 65% and find peak again and see if the mixture control is at about the same position.

Skip

[Mark942]

I want to thank everyone for your insights.  Just to clarify, I was on an IFR approach prior to reaching the FAF.  Time to slow down, drop the gear and get configured for the decent in a stable approach.  I had been in cruise LOP with an injected IO-360-A1A.  My CFI says it doesn't matter ROP or LOP but that any change in throttle needs to be proceeded by an appropriate change in mixture.  Since I'm not changing altitude I don't think it is proper to mess with the mixture until I am ready to begin decent.  I usually wait until established on the Final Approach before I go Mixture and Prop full forward.

22 hours ago, PT20J said:

The throttle controls the airflow through the servo and the servo meters fuel according to the airflow at the air/fuel ratio set by the mixture control. Why would reducing the throttle (at constant altitude) richen the mixture?

So, I guess I agree with PT20J and that was my point in asking for other opinions.  Does anyone know of any published articles from someone such as Mike at Savvy or someone who can add "Science" and "Fuel Servo" knowledge to the discussion??

Thanks,

-mark

[carusoam]

Standard practice…

Changing power setting… equals trimming the fuel mixture….

How critical it is, time wise, depends on if the power change is moving the mixture towards the red box or away… based on the changes you are making…

Descending LOP… mixture is going leaner, and further away from the red box….

Descending ROP… mixture is going leaner, towards the red box…

 

By the time you are starting the approach procedure… anywhere near Sea Level…. You are OK to be full rich….

Since you are below 65%bhp… any mixture chosen will still be outside of the red box….

 

 

So… technically, the CFII has made a good point… change power, in the right order, just because… then adjust the mixture, just because….

When you do this often enough… you probably have a few things memorized… and the ability to use the engine monitor becomes second nature…

 

See if you can get a copy of the MAPA procedures… attending one of their classes is usually the way to get one…

The MAPA procedures are written specifically for Mooneys and Mooney engines….

 

Most of the logic comes from getting the most speed… or efficiency….

Efficiency during the descent is not as critical as during cruise… descent is only a few minutes compared to the cruise segment…

So it’s not a sin if you go full rich… 

 

PP thoughts only, not a CFI…

-a-

[PT20J]

53 minutes ago, Mark942 said:

I want to thank everyone for your insights.  Just to clarify, I was on an IFR approach prior to reaching the FAF.  Time to slow down, drop the gear and get configured for the decent in a stable approach.  I had been in cruise LOP with an injected IO-360-A1A.  My CFI says it doesn't matter ROP or LOP but that any change in throttle needs to be proceeded by an appropriate change in mixture.  Since I'm not changing altitude I don't think it is proper to mess with the mixture until I am ready to begin decent.  I usually wait until established on the Final Approach before I go Mixture and Prop full forward.

So, I guess I agree with PT20J and that was my point in asking for other opinions.  Does anyone know of any published articles from someone such as Mike at Savvy or someone who can add "Science" and "Fuel Servo" knowledge to the discussion??

Thanks,

-mark

Here’s a pretty in-depth article by John Deakin https://www.avweb.com/features_old/pelicans-perch-18mixture-magic/

Here’s the RSA Training ManuaL

15-812_b.pdf

[carusoam]

1 minute ago, PT20J said:

Here’s a pretty in-depth article by John Deakin https://www.avweb.com/features_old/pelicans-perch-18mixture-magic/

Here’s the RSA Training Manual

15-812_b.pdfUnavailable

15-812_b.pdf 3.08 MB · 0 downloads

Something shows unavailable… for some reason…

-a-

[PT20J]

1 minute ago, carusoam said:

Something shows unavailable… for some reason…

-a-

Thanks, Anthony. Not sure what happened, but I think it's fixed now.

[FlyingDude]

8 hours ago, carusoam said:

Descending LOP… mixture is going leaner, and further away from the red box….

Descending ROP… mixture is going leaner, towards the red box…

Not if you keep constant MAP and RPM. So if you don't touch prop and keep adjusting throttle, then LOP/Rop point won't move...

8 hours ago, carusoam said:

So it’s not a sin if you go full rich… 

There was one Mike Busch webinar where he says that full rich is like pulling the choke in a small engine: too much fuel, bad combustion and fouled plugs. It's on YouTube.

 

[carusoam]

7 hours ago, FlyingDude said:

 

There was one Mike Busch webinar where he says that full rich is like pulling the choke in a small engine: too much fuel, bad combustion and fouled plugs. It's on YouTube.

 

I am still having some difficulty describing this one… 

When learning to fly… we used 3k’ msl as the buffer for leaning the engine in the climb…

Below that… it was always kept full rich.

It certainly isn’t optimal…. And above that altitude… it would be like pulling the choke…. 
 

In the O1… we have the blue box on the ship’s calibrated EGT gauge… really helpful for adjusting the mixture quickly during climb/descent…

 

Of course a blue box on a calibrated EGT gauge isn’t a requirement…. It can be done on a more simple EGT gauge as well… 

The O1’s blue box indicates 2-300°F below peak… a range that lets thousands of feet of altitude change before having to adjust it again… 

note: On the other end of the calibrated EGT gauge is a calibrated hole location… (nice to have)  the IO550s get 7 EGT sensors….

 

When doing approaches… especially multiple approaches and hand flying, like in training…. The cognitive overload limit is often really close by…

Being able to set the mixture in a safe place quickly can really help simplify this part of the process…

A quick look at your EGT, and you see the needle is about to fall out of the blue box… a quick turn of the red knob, puts it right back in…

 

It really helps to know how much of a turn of the red knob makes the needle move… 100°F

 

PP thoughts only, not a CFI… and I probably still missed a point or two…  

Best regards,

-a-

 

 

 

[Mark942]

Thanks to everyone for the continued input.  Let me restate my basic question.  My CFII stated that a change in Throttle setting needs to be preceded by a change in mixture.  LEVEL flight.  Only trying to speed up or in my case, slow down.  No change in altitude (DA).  After reading through the link and pdf posted by PT20J, I am even more convinced that the job of the fuel servo is to maintain the fuel/air ratio with changes in throttle/air speed (ram air).

Am I missing something??  IF maintaining a constant altitude and only making a power change via throttle position, do I need to adjust the mixture to maintain the same fuel/air ratio (EGT and CHT as indicators).

Thanks,

-mark

[Austintatious]

36 minutes ago, Mark942 said:

Thanks to everyone for the continued input.  Let me restate my basic question.  My CFII stated that a change in Throttle setting needs to be preceded by a change in mixture.  LEVEL flight.  Only trying to speed up or in my case, slow down.  No change in altitude (DA).  After reading through the link and pdf posted by PT20J, I am even more convinced that the job of the fuel servo is to maintain the fuel/air ratio with changes in throttle/air speed (ram air).

Am I missing something??  IF maintaining a constant altitude and only making a power change via throttle position, do I need to adjust the mixture to maintain the same fuel/air ratio (EGT and CHT as indicators).

Thanks,

-mark

I was reading through this thread and still I cannot see a reason why one would need to adjust the mixture during descent with reduced power.  My aircraft is Turbo so perhaps it is different. 

I do see a need to tweek the mixture if you are maintaining altitude but changing speeds.  Specifically if you are increasing speed (increasing power)  You may be pushing the power up beyond a percentage value where no leaning is allowed with the mixture control.  If reducing speed the only reason to do it is to save more fuel or go from ROP to LOP or visa versa.

I mean if you are leaned out appropriately in cruise and pull the power back to descend, I cannot imagine that you will have any issues, unless you find yourself in a situation where you need to go around with full power.  In that case, failing to push the mixture in could be anything from sorta bad to real bad.

I always increase power from right to left ( Mixture > prop > throttle)

I decrease power from left to right (Throttle, prop, mix )

In either case, you can stop your progress through those three steps with no issues... EXE:  running 33/25 @ 20 GPH ... I can reduce the throttle only and be fine.  Or lets say i am running  25/25 @ 17 GPH and start the increasing power order... I can increase the mix to 20 GPH and stop there with no issues (other than burning more gas than I need)

 

Edited March 6, 2022 by Austintatious

[KLRDMD]

On 3/3/2022 at 8:07 AM, Mark942 said:

My CFII insists that I add fuel flow (move the Red knob in) as I reduce MP at level flight during the "Slow Down" phase to get slow enough to drop the gear on an approach.  Level flight at 4000 MSL, (LOP at cruise but he says that doesn't matter).  This doesn't seem correct.  I am at the same density altitude, not starting down yet.  Opinions please, and references to actual data or expert's articles such as Mike at Savvy articles would be really appreciated.

There is zero instruction in engine management in the flight instructor curriculum. This proves it.

[FlyingDude]

On 3/5/2022 at 2:39 PM, carusoam said:

When learning to fly… we used 3k’ msl as the buffer for leaning the engine in the climb

That's from Cessna POH.  Tells you to lean for take-off at DA > 3000.  (I recall, don't have it at hand.)

 

On 3/5/2022 at 2:39 PM, carusoam said:

PP thoughts only, not a CFI

CFI is not god...  I'm a CFI, and CFI ticket shows you know how to teach.  CFI has commercial (or higher) level knowledge and pretty much parrots what he was taught.  

And "right rudder".  CFI shouts "right rudder" A LOT.  

I was taught to re-adjust mixture every time I made "power changes", which involves throttle and/or rpm changes, even at level flight.  I did not know that throttle changes wouldn't require mixture changes due to automatic maintenance of mixture ratio...  Learned something new  

[carusoam]

Our fuel injector systems are pretty good at keeping things constant…

As long as their internal diaphragm is working correctly…

There is some nice detail provided by the fuel injector companies for how the system works…. Probably good to quote that document if using their logic… the drawing is a bit complex… but not impossible to understand… tough to memorize…

Since MP and Prop both change %power…. A mixture adjustment is expected for either….

If the mixture was automatically adjusted…. I bet the machine owner would check the mixture, because he could….  

 

My JPI has the fast acting EGT probes… it is a pretty quick check… using LF (Lean Find)

My ship’s EGT gauge has a calibrated blue box… it is pretty easy to keep in a safe place when too busy with flying the plane…

My plan A… is usually descending LOP… where things get more lean, traveling away from the red box in the descent…

At lower altitudes… my engine would run 100°F LOP… giving plenty of time to make adjustments before it would go silent…

 

Hmmmmm…

Guess we could prove something by staying level and pulling the throttle back… watch the EGT…

The raw EGT number probably declines…. As the volume of exhaust is decreasing….

Does it stay 100°F ROP… the way it was before the throttle change?

Looks like I am always checking the status of my mixture after every touch of the knobs… then hanging out in the blue box ROP when checking the knobs isn’t feasible… while MP + RPM/100 exceeds 65%bhp… (aka MAPA numbers)

It may take defining what a blue box for your machine and instruments require…

PP thoughts only…

Best regards,

-a-