Mixture rich on approach?

[Rykymus]

Lotta opinions but it really only matters what the POH says.

Blindly following the POH is the same as blindly following your CFI. You're assuming that the POH, which may have been written decades ago and never updated in the face of changing knowledge, has safety and/or engine longevity as it's goal. Likely, it's concern is more about liability and making money. (ie: Let's get that engine in for OH/Replacement before TBO)

I would agree, however, that if in doubt, follow the POH. As for me, I'll figure out what works in MY best interests, and for me, that's safety and engine longevity. (Which also adds to safety.) I lean for best RPM at any (DA) altitude, and I aggressively lean during taxi. My POH says to keep it full rich below 5,000 ft, but I start leaning at 2,000 and see an increase of at least 100-200 rpm, and much better climb performance.

 

[Checkout_my_Six]

Agreed....

I never take off full rich....and I fly a turbo charged engine. I monitor fuel flow, TIT, and CHTs...and use that info to decide fuel flow required with a given power setting.

 

[MAKG1]

remember....they are referencing a "density altitude"....not AGL or MSL. Big difference folks.

...and regardless you can't harm your engine by over leaning when the power settings are lower than 70-75%.

Yeah, it sure does seem like some people have been missing that point.

Locally, DA has been at least 2000 above pressure altitude here, over the past few days. Been hot as hell. That's not enough to lean for takeoff in a Cessna, but it's getting close.

 

[Pilawt]

Blindly following the POH is the same as blindly following your CFI.

My POH devotes about the same amount of text to leaning as it does to crosswind landings. Both concepts are a little more involved than can be covered in one paragraph. Imagine a CFI sending a student out in a crosswind with no instruction other than "read the manual!"

 

[denverpilot]

Blindly following the POH is the same as blindly following your CFI. You're assuming that the POH, which may have been written decades ago and never updated in the face of changing knowledge, has safety and/or engine longevity as it's goal. Likely, it's concern is more about liability and making money. (ie: Let's get that engine in for OH/Replacement before TBO)

That whole statement was fine until that last line. Assuming an aircraft manufacturer was purposely trying to burn up engines pre-TBO back in the day, is kinda silly. They weren't cheap to repair back then, any more than they are now.

 

[Caramon13]

Blindly following the POH is the same as blindly following your CFI. .

Disagree . Blindly following the POH is NOT the same as blindly following a CFI. The POH is an authoritative guide with tested parameters and is FAA approved. If you follow the POH, regardless of what someone tells you, you are flying the plane according to FAA approved, manufacturer approved techniques. Go outside of that and you become a test pilot. TBO is a recommendation, not a mandate.

My POH devotes about the same amount of text to leaning as it does to crosswind landings. Both concepts are a little more involved than can be covered in one paragraph. Imagine a CFI sending a student out in a crosswind with no instruction other than "read the manual!"

It's not supposed to be a "how to". You don't become a pilot by reading the POH. What it DOES do is tell you how to safely operate the airplane. Crosswind tolerance is different than crosswind technique.

 

[blueskyMD]

+2 on the yes. I don't go full rich unless I'm going around. Only takes a nano-second to do it. Same with the prop. I usually leave it at cruise setting unless I need a steeper descent. It all goes forward on a missed. I know there are a lot of Mike Busch haters on here but that's how he operates his twin cessna and his engine's are more than double TBO.

This

 

[Dan Thomas]

Handling the mixture knob is too much responsibility for me

You might be kidding (I hope you are), but that statement nails the problem. There is too little understanding by students and CFIs and a lot of pilots as to what the mixture control does, what the engine's requirements are regarding mixture at various power settings, DAs, and so on. Too many folks get taught "full-rich" or "leaned for cruise" with nothing in between, and no education beyond that. Older POHs don't do any better, either. Regulations were a lot slacker.

Trying to take off full rich on a high-DA day is going to get you eventually, either with increased maintenance costs or maybe an accident. Failing to enrich as you glide from considerable altitude on a cold day could result in a dead engine that you don't notice until it's too late, and even enriching might not make it happy. It's too cold. Until computers take over all this stuff, like they have in cars, we need to know how to handle the engine.

There are some carbs that run much richer than others, even the same model of carb on the same model of engine. Consistency is really poor, and you might find that what you did with your old engine might not work well at all with the new one. And some engines are fitted with carbs that are deliberately made to run pretty rich, like the HA-6 on the O-540J3C5D in the R182. If you try to manage that one like the carbed 172, you're in for some difficulty. Even in the runup you'll get huge mag drops if you don't lean it.

 

[CC268]

You might be kidding (I hope you are), but that statement nails the problem. There is too little understanding by students and CFIs and a lot of pilots as to what the mixture control does, what the engine's requirements are regarding mixture at various power settings, DAs, and so on. Too many folks get taught "full-rich" or "leaned for cruise" with nothing in between, and no education beyond that. Older POHs don't do any better, either. Regulations were a lot slacker.

Trying to take off full rich on a high-DA day is going to get you eventually, either with increased maintenance costs or maybe an accident. Failing to enrich as you glide from considerable altitude on a cold day could result in a dead engine that you don't notice until it's too late, and even enriching might not make it happy. It's too cold. Until computers take over all this stuff, like they have in cars, we need to know how to handle the engine.

There are some carbs that run much richer than others, even the same model of carb on the same model of engine. Consistency is really poor, and you might find that what you did with your old engine might not work well at all with the new one. And some engines are fitted with carbs that are deliberately made to run pretty rich, like the HA-6 on the O-540J3C5D in the R182. If you try to manage that one like the carbed 172, you're in for some difficulty. Even in the runup you'll get huge mag drops if you don't lean it.

I don't take this forum too seriously so don't take me too seriously! But thanks for the info it is always useful. I think I do a pretty good job with the mixture knob and was taught quite well from my instructors.

 

[Pilawt]

It's not supposed to be a "how to". You don't become a pilot by reading the POH. What it DOES do is tell you how to safely operate the airplane. Crosswind tolerance is different than crosswind technique.

The short paragraph on leaning in Section 4 of the Cessna POH is a technique. It is an arbitrary, abbreviated, bumper-sticker, one-size-fits-all technique that ignores any number of variables but uses a minimum of words. It is a different technique from that in the Lycoming manual, which in turn is a different technique from that in manuals for Piper aircraft with the identical engine.

Maybe it's a good idea to understand how leaning actually works and what it does.

Limitations are in Section 2 of the aircraft POH.

 

[danhagan]

Just flew with a pilot who on approach I asked him didn't he want to go full rich before landing? He said no, he'd just firewall it along with throttle and prop if we needed to go around. Does anyone else do this?

Not me, I have a secret "check" that occurs in the downwind (see below) ...

My first few lessons he showed me how to lean for altitude after the run-up. Then someone burned up the valves in the 152. After that he decided to change the app on his planes.

That pilot needs to learn how to use the red knob ....

You might be kidding (I hope you are), but that statement nails the problem. There is too little understanding by students and CFIs and a lot of pilots as to what the mixture control does,

Ding ding ding WINNER!

Read three pages and haven't seen it yet, but you all know what the "M" stand for in GUMPS, right?

I don't think my engine would last with several of the pilots here. At a high DA field, I have to lean for max RPM at take off. Because it is a close cowled Tiger, I have to watch temps in the climb and enrichen to cool *and* sometimes level off to cool the CHTs if they get out of hand. Once at cruise, I lean again (usually at 10,500 or 11, 500). During descent I'll enrichen slightly, and in the downwind at the destination I will lean for landing (stumble then enrichen). Biggest risk will be if the mix cable ever breaks.

 

[Caramon13]

The short paragraph on leaning in Section 4 of the Cessna POH is a technique. It is an arbitrary, abbreviated, bumper-sticker, one-size-fits-all technique that ignores any number of variables but uses a minimum of words. It is a different technique from that in the Lycoming manual, which in turn is a different technique from that in manuals for Piper aircraft with the identical engine.

Maybe it's a good idea to understand how leaning actually works and what it does.

Limitations are in Section 2 of the aircraft POH.

Yup, I'd agree with the bolded statement . And that would be where a CFI comes in, or if you are more self-sufficient any number of informative websites. Or you can buy a plane with a Fadec engine .

 

[flyingcheesehead]

Great post, Dan!

Failing to enrich as you glide from considerable altitude on a cold day could result in a dead engine that you don't notice until it's too late, and even enriching might not make it happy. It's too cold.

I don't normally enrich in the descent, since I'm pulling the throttle back and keeping a relatively constant MP, but I have noticed that in cold weather that doesn't seem to work as well, with the engine (IO-550) getting a bit rough after a long descent unless I richen it up a bit. Why is this different in cold weather?

And some engines are fitted with carbs that are deliberately made to run pretty rich, like the HA-6 on the O-540J3C5D in the R182.

Interesting. We've noticed that we burn closer to 15gph on the R182 than the 13gph we got on the straight-leg 182, and it's difficult to lean it even close to 13gph without roughness. Would sure love to know what we can do to make that better!

 

[Checkout_my_Six]

Interesting. We've noticed that we burn closer to 15gph on the R182 than the 13gph we got on the straight-leg 182, and it's difficult to lean it even close to 13gph without roughness. Would sure love to know what we can do to make that better!

1. check your plugs....and make sure the resistance is within spec. (5,000 ohms or less) and that they are clean and gapped correctly. If not change over to Tempest fine wires.
2. check your fuel distribution and determine if the cylinders are leaning in sync. If not make injector adjustments....use GAMI injectors?
3. verify timing is correct per the TCDS
4. verify you don't have any induction leaks...your A&P should know how to do this
5. check your spark plug wires for damage and leakage.

those are a few things to check....there might be a few additional things that could affect it.

 

[Tarheelpilot]

Ignore Mike at your own peril.

I'm not a big fan of the guy, but on matters of engine management, he's right.

.

Most of the time he is correct or at least has good ideas. At the end of the day if someone has advice that is contradictory to the recommendations of the manufacturer or TC holder then I ignore the self proclaimed experts advice. Where mikes musings are helpful is filling in the blanks and developing best practices where the manufacturer has no guidance.

 

[flyingcheesehead]

2. check your fuel distribution and determine if the cylinders are leaning in sync. If not make injector adjustments....use GAMI injectors?

On a carbureted engine?

 

[Checkout_my_Six]

On a carbureted engine?

why would you have injectors on a carb'd engine?

btw...there are a few tricks to get a carb'd engine to run smoother lean. Like, using carb heat (just a smig - cracked) to better atomize the fuel....make sure the throttle is wide open (better turbulent flow off the butterfly valve for mixing)....and use airspeed as an indicator (lean for best power - highest airspeed- then lean 2-3 kts/mph lower from max speed for best economy speed). I'd lean like that running 75% Hp or 7,000 feet DA or more. That setup will yield -30 deg on the lean side.

 

[flyingcheesehead]

Most of the time he is correct or at least has good ideas. At the end of the day if someone has advice that is contradictory to the recommendations of the manufacturer or TC holder then I ignore the self proclaimed experts advice. Where mikes musings are helpful is filling in the blanks and developing best practices where the manufacturer has no guidance.

Except he (and Deakin) specifically show exactly how, and more importantly why, the manufacturer's guidance isn't good for your engine. The manufacturers are still generally making recommendations in line with what has been recommended since these engines were certified shortly after WWII. Today, technology allows us to better measure what is going on inside the engine and a lot of work has been done on that by third parties (mostly Deakin/Braly/Busch) and it turns out that we know better ways of doing things now than we did 70 years ago.

The manufacturers have no motivation to make better recommendations, especially if it means they sell fewer parts. Most companies don't set out to prove themselves wrong - Bad for PR.

 

[flyingcheesehead]

why would you have injectors on a carb'd engine?

That's why I asked! You said it.

I'm hoping @Dan Thomas can explain more about that particular carb and why it's so dang rich. I wish I were that rich!

 

[Dan Thomas]

That's why I asked! You said it.

I'm hoping @Dan Thomas can explain more about that particular carb and why it's so dang rich. I wish I were that rich!

I called Precision Aeromotive about that carb (before Volare took over the line). They told me that Lycoming had specified the fuel flows they wanted for that engine in the R182, and that it indeed was really rich and we just had to deal with it. It was bad on warm days at our 3000' AGL airport, and would stumble and belch when the carb heat was applied. The solution was to lean it until it was doing what it should. So we'd lean it for runup if the mag drops were too big. We'd lean it on downwind if it stumbled. Just got to use the knob, that's all.

One student saw black smoke behind the airplane when climbing through 7000'. He was using full rich as per POH and got all worried. Somehow, he hadn't been trained well enough on mixture controlling.

When we replaced the engine in that airplane it came with a new HA-6 that would not let the engine idle properly no matter what we did with it. Pop and bang and cough and miss on several cylinders. It wasn't atomizing the idle fuel properly at all. The intake plenum on the J3C5D is on the back of the engine, and the horizontal-draft HA-6 feeds into it. The plenum divides six ways to the cylinders. The poor atomization was throwing large fuel droplets that hit the forward plenum wall and flowed down and would get sucked into the cylinders fed off the bottom of the plenum, and they'd get way too rich at idle and would stop firing. Foul the plugs, too. At higher power settings it ran better. Ordered another carb on warranty and got an interim bill for $8800 for that carb! About eight years ago, that was. Nearly nine thousand dollars for a carb that doesn't work as well as the carb off a '65 Ford. Go figure. The replacement behaved itself, but a little later an emergency SB came out on it and I had to take it off. Again. http://msacarbs.com/pdf/SB-18_A 031511.pdf

 

[midlifeflyer]

Blindly following the POH is the same as blindly following your CFI. You're assuming that the POH, which may have been written decades ago and never updated in the face of changing knowledge, has safety and/or engine longevity as it's goal. Likely, it's concern is more about liability and making money. (ie: Let's get that engine in for OH/Replacement before TBO)

I would agree, however, that if in doubt, follow the POH. As for me, I'll figure out what works in MY best interests, and for me, that's safety and engine longevity. (Which also adds to safety.) I lean for best RPM at any (DA) altitude, and I aggressively lean during taxi. My POH says to keep it full rich below 5,000 ft, but I start leaning at 2,000 and see an increase of at least 100-200 rpm, and much better climb performance.

The problem in this area is that most POH say full rich for takeoff and landing. I know people who have corresponded with manufacturers suggesting "mixture RICH" new change to "mixture AS REQUIRED" to no avail. Even the POH can be wrong.

 

[flyingcheesehead]

Y'know, I've always just thought of this as a "whatever works" issue, but after reading the thread and thinking about it some more, I'm going to change to always adjusting the mixture prior to landing.

Why? Well, I do go out west sometimes, so there's a chance I could be at a high-DA airport and need to go around. In that situation, the "three-lever shove" is a bad idea. If the mixture/prop are already adjusted prior to landing, it's a throttle-only go-around, regardless of where you are. Consistency is a good thing.

 

[dell30rb]

Full rich (altitude considerations of course) and props full forward on final. You never know when you'll need everything she's got.

Ever try to suddenly go full throttle at 1-2000 ft on an engine that's set for LOP cruise at 6-7,000 ft? Won't work on many GA piston engines. It will bog down.

 

[Dan Thomas]

Great post, Dan!



I don't normally enrich in the descent, since I'm pulling the throttle back and keeping a relatively constant MP, but I have noticed that in cold weather that doesn't seem to work as well, with the engine (IO-550) getting a bit rough after a long descent unless I richen it up a bit. Why is this different in cold weather?

Cold air doesn't vaporize the fuel as well, and a cold engine needs more fuel to make it run. Your car's mileage goes down in cold weather because the computers have to feed it more at least until the engine warms up, and even then a low DA means denser air and therefore more fuel to get the fuel/air ratio right.

And, if I remember right, cold air has a larger density change per unit of altitude than warm air does.

 

[Checkout_my_Six]

and it's leaner cause it's "making" more power....with that fuel....vs. wasting.https://www.pilotsofamerica.com/community/find-new/posts

 

[Sac Arrow]

Full rich (altitude considerations of course) and props full forward on final. You never know when you'll need everything she's got.

Ever try to suddenly go full throttle at 1-2000 ft on an engine that's set for LOP cruise at 6-7,000 ft? Won't work on many GA piston engines. It will bog down.

More times than I can remember. It took me a while to figure out that when you are in the LOP regime, it's the mixture controlling the power, not the throttle.

 

[flyingcheesehead]

Cold air doesn't vaporize the fuel as well, and a cold engine needs more fuel to make it run.

True, but this is a warm engine, descending from cruise. I suppose it is cooling down on the way down, though.

even then a low DA means denser air and therefore more fuel to get the fuel/air ratio right.

Right, but shouldn't this already be compensated for by the fact that we leaned for cruise in cold air?

And, if I remember right, cold air has a larger density change per unit of altitude than warm air does.

That, plus the engine cooling, is likely it. The atmosphere is "shorter" in the winter. Since the air is more dense, and we don't magically have more air, the atmosphere takes up less volume. PV = nRT. Since T is shrinking, V shrinks too.

Thinking out loud: On a descent in the winter, the change in DA from the surface to a given PA is greater due to this atmospheric shrinking. Since MP would be a pressure, and the actual number of air molecules is also affected by density, the winter descent would increase the rate at which the fuel/air ratio is changing.

Interesting thread on this subject here too: http://www.pprune.org/tech-log/475540-manifold-pressure-altitude-effects.html

 

[Anthony]

I don't think my engine would last with several of the pilots here. At a high DA field, I have to lean for max RPM at take off. Because it is a close cowled Tiger, I have to watch temps in the climb and enrichen to cool *and* sometimes level off to cool the CHTs if they get out of hand. Once at cruise, I lean again (usually at 10,500 or 11, 500). During descent I'll enrichen slightly, and in the downwind at the destination I will lean for landing (stumble then enrichen). Biggest risk will be if the mix cable ever breaks.

It would be safe with me. I had my Tiger based in Colorado with actually a pretty low (for there) field elevation of 5,512 ft. But even before (and after) I lived there, I leaned from engine start to shutdown, except for those times, as you state that I needed extra cooling. In mid summer, with high temps, and high DA, I too had to do step climbs, but that was pretty rare, especially after I had my engine baffling re-worked. Having a four cyl. JPI engine analyzer helped, A LOT.

 

[danhagan]

It would be safe with me. I had my Tiger based in Colorado with actually a pretty low (for there) field elevation of 5,512 ft. But even before (and after) I lived there, I leaned from engine start to shutdown, except for those times, as you state that I needed extra cooling. In mid summer, with high temps, I too had to do step climbs, but that was pretty rare, especially after I had my engine baffling re-worked. Having a four cyl. JPI engine analyzer helped, A LOT.

I have an analyzer also, but like temps below 410* on the rear jugs (I start enrichening at 400*). With field elevation 4100 and desert heat, I'm usually nearing 400* just reaching pattern altitude. Baffling was done at FletchAir previously ... my only option is the Lopresi cowl which I don't want to do right now.