Mixture leaning question.

[steve181]

Your cruising along at 6000 feet for example in a standard Cessna 172 with a fixed pitch propeller, you've leaned the mixture. You decide to climb to 8000 feet at full power.

Before you go through to full power to begin the climb do you?

A: Fully richen the mixture to help cool the engine during the climb, & keep it fully rich until you are cruising again at 8000 feet?
B: Climb without adjusting the mixture?

I'm not sure on this because at 6000 feet the air temperate will be cold (0°C assuming the surface temperature is around 18°C) so enriching the mixture to assist with cooling would be overkill? So I'm swaying more towards option B but want your thoughts.

Cheers.

[Horatio Leafblower]

1/. Read the aircraft flight manual
2/. Read the aircraft flight manual
3/. Read the aircraft flight manual

...and 4/. if all else fails, in the example you have given, go full rich before applying full power.... please.

[steve181]

The aircraft's flight manual is 30 years old mate, it's an artifact of a time long ago. Everything aviation related has changed considerably in 30 years so when it comes to things like this I'd rather have a modern answer to my question.

Climbing with full power on a leaned mixture above say 6000 feet is not a death sentence for the engine as far as I'm aware? Actually I'll just expand on that; of course to play it completely safe always have the mixture full rich when climbing at full power regardless of altitude. My question is; is there any leeway with this situation?

[RadioSaigon]

Originally Posted by Steve181

Climbing with full power on a leaned mixture above say 6000 feet is not a death sentence for the engine as far as I'm aware?

Absolutely not. If it were, I would have personally contributed massively to the balance sheets of both Teledyne Continental and Textron Lycoming. To the best of my knowledge, I haven't.

One thing you may want to consider: on a C-172 and many other light singles, there is a little-known "feature" called (rather clumsily) full-throttle auto-rich. As the name implies, when the throttle is forward to the firewall, your mixture is automatically advanced. A very good reason to not go charging around all over the place at full throttle IMO -as one Hunter Valley instructor tried to get me to do in his C-172 not so long ago... wonder if he's figured out why I don't fly there any more... anyways: if you are inclined to prove this to yourself, hop into your 172, set your mixture via the EGT -at a reduced throttle setting obviously, then when you're ready, advance your throttle to the firewall whilst keeping an eye on your EGT. That should be ample evidence of the accuracy of my assertion.

To run your engine at max RPM (and probably very close to max MP) without engaging this auto-rich, you'll find you need to back the throttle off to about 1cm from the firewall.

...and for those of you "AFM is Gospel" bible-bashers, I challenge you to find anywhere in your AFM that this full-throttle auto-rich is even mentioned

If you like, prove it to yourselves too -if you dare. No engine damage can result from this; indeed the only "damage" likely is to your belief and faith in the veracity of your AFM...

[Corkey McFuz]

Well look, as with skinning a cat, there are also a million different ways of flying / operating an aircraft, - right down to the very basics and everybody thinks their way is right.

My self, I would richen it up, not full rich that is pointless and overkill, mind you, really you're not going to do any more harm than pouring a little more avgas down a drain, at that height anyway.
But I wouldn't leave it where it is.

I agree about your comment about the flight manual. The reality is, for the most part they are written by lawyers, for lawyers. Simply for arse saving.
And yes, a lot has changed in the years since the product was new and they didn't know that much about it themselves (be it engine, aircraft whatever) and a lot of new improvements, practices etc has been learnt since.

Find John Deakin's Pelican's Perch on avweb, there are some very good articles there which may help.

[boltz]

If you read the manual, you will find it states the following: (C172N)

En Route Climb
1. Airspeed -- 70-85 KIAS
2. Throttle -- FULL OPEN
3. Mixture -- RICH (above 3000ft, LEAN to obtain maximum RPM)

So there's your answer

[bushy]

C172 is modern, but it's flight manual is not?????

You should have the correct flight manual for the particular aircraft you fly. If you don't, then don't fly it. If you do then fly it within the limits that are defined in the flight manual including any supplements that it may have.
And you should use a rich mixture if you are going to use high power, but you may not be able to get high power in a 172 engine at 6000 feet. It will more likely run rough due to being too rich. If it does, then you can lean it intil it runs smoothly. Check your flight manual and/or the engine makers manual. Even if they are old, as long as they apply to the particular machine you have.

[bentleg]

If you read the manual, you will find it states the following: (C172N)

En Route Climb
1. Airspeed -- 70-85 KIAS
2. Throttle -- FULL OPEN
3. Mixture -- RICH (above 3000ft, LEAN to obtain maximum RPM)

So there's your answer

C172R (fuel injected, so potentially different to C172N)
En Route Climb
The mixture should be full rich below 3000 feet and may be leaned above 3000 feet for smoother operation, or to obtain maximum RPM.

[RadioSaigon]

None so blind as those that don't want to learn...

If you fly a normally aspirated, carburetted, fixed-pitch single, it'll take you about a minute at normal cruise settings to see where I'm coming from. Who knows, the few litres of fuel you save yourself by utilising a little knowledge, may one day be the difference...

I rest my case. Play on, kiddies.

[AerocatS2A]

RadioSaigon, if it's possible to lean for smooth operation and/or max RPM at full throttle then your "full throttle/auto-rich" is not working as you think, if it is a feature at all. I think I'd rather fly the manual than believe something someone told me on some internet message board somewhere.

[Peter Fanelli]

The aircraft's flight manual is 30 years old mate, it's an artifact of a time long ago. Everything aviation related has changed considerably in 30 years so when it comes to things like this I'd rather have a modern answer to my question.

You know I think that might just be the most ridiculous thing I've ever read on this forum.

You are of course correct, when flying your 30 year old 172, it's engine and procedures are outdated. Suggest you read up on operating procedures for the modern diesel engines in the DA-42 and use those procedures instead of the obviously old procedures applicable to the 172.

What a dick head.

If you owned a Model T Ford, would you operate it the way it has to be operated or would you treat it like a Falcon?
Maybe you'd try to drift it.

[muffman]

In an old 172 with a carby I would be reluctant to lean the mixture during climb even as per the flight manual unless you were experiencing rough running, which seems unlikely at the sorts of altitudes one would normally fly them.

In the newer fuel injected 172s I would lean as per the flight manual procedure which says above 3000ft providing it is equipped with an all-cylinder monitor (which the new ones are).

If you don't have fuel injection and an all-cylinder monitor, my advice is just burn the extra fuel and put up with the slight performance loss until you're at a cruise power setting.

[steve181]

Peter Fanelli read what I said again; "when it comes to things like this" i.e. mixture leaning. I NEVER said the flight manual was irrelevant or void as a whole because of it's age. Don't take what I said out of context because now you've wasted my time explaining myself.

I would never go against things like fuel consumption, W&B figures, max speeds etc BUT in my opinion things like mixture leaning procedures can be open for debate.

If you ASSUME you make an ass out of you & me!

At the end of the day if there is a general consensus about my original question I'll confirm it with my instructor & go from there. Or if people feel strongly that I consult the flight manual only & ignore any information or advice that has been developed over the last 30 years regarding leaning then I'll go with that also. This is why I asked my original question because I wasn't certain of the answer. It's better that I understand something clearly because I took the time to ask than just guess my way through things ... fatal in an aviation setting.

[Avgas172]

Oh Dear, Thats why I love my 1964 'H' Model, it just tells me what it wants to do, and everything is slowly.

[ZEEBEE]

Your cruising along at 6000 feet for example in a standard Cessna 172 with a fixed pitch propeller, you've leaned the mixture. You decide to climb to 8000 feet at full power.

A C172 climbing from 6000 ft ???
Are you kidding me ?
Seriously though, I've always erred on the side of caution and leaned above 5000 ft until the engine is running smoothly again.

Leaning for max RPM is dangerous (IMO) because now you're running the engine at peak egt (albeit at low power, after all how much power can a normally aspirated O300 or O320 produce at these DA's?) .

Running excess rich may be considered safe, but NOT when it's likely to foul plugs and wash away lubricating oil from the upper cylinder area.

As for auto-rich....I've heard of it but not since the DC-3 era.
Certainly, my O-360 doesn't have it. (just as well too!)

[Brian Abraham]

The aircraft's flight manual is 30 years old mate, it's an artifact of a time long ago. Everything aviation related has changed considerably in 30 years so when it comes to things like this I'd rather have a modern answer to my question.

The thing that has changed considerably over the last 30 years has been the LOSS of knowledge as to how to operate piston engines. We no longer have the experience of the old timers who operated BIG fire breathing pistons as a living to pass on the lessons. And there is no difference in basics whether it be a Continental O-200 or a turbo compound Wright R-3350. Instructors these days, because of their youth and lack of experience (no fault of theirs, they were probably taught by an individual of the same background), are usually the purveyor of old wives tales, and not of wisdom. Leaning is a subject that is only rivalled by the downwind turn in its ability to generate a heated discussion.

Leaning for max RPM is dangerous (IMO) because now you're running the engine at peak egt (albeit at low power

A broad statement that requires qualification. It depends, and a reading of the below mentioned John Deakin will give an education in where/when you can operate at peak, and even lean of peak. Whether the engine is direct drive, fixed pitch, CSU, float carb, pressure carb, fuel injection, turbo/super charged, has EGT, or new multi probe monitor are some factors that bear on the specific operating details. Lycoming are quite specific in allowing operation at peak when operating below 75%, but they direct you to the flight manual for aircraft specific procedures.

There is no better person to read and follow on leaning than John Deakin. The index to his articles is here "Pelican's Perch" Index

[Oktas8]

Auto-rich and economiser

John Deakin's articles are fantastic aren't they? I've learned quite a lot by reading his posts.

On another note:

One thing you may want to consider: on a C-172 and many other light singles, there is a little-known "feature" called (rather clumsily) full-throttle auto-rich. As the name implies, when the throttle is forward to the firewall, your mixture is automatically advanced to full-rich.

No, this is not true. You are thinking of the economiser function, which does enrich the fuel-air mixture at full throttle. It doesn't fully enrich the mixture, it simply adds a little more fuel in addition to the "normal" fuel jet in the carburettor or fuel distribution manifold. This is to provide extra fuel for cooling at sea-level full power.

When taxiing, it is possible to aggressively lean the mixture so the engine is just barely running at 1000rpm (or 1200 rpm, or whatever). If you advance to full throttle the engine stops. This would not happen if there was an auto-rich device.

The original question? I'd go for answer "c". Slightly enrich the mixture according to how much I'm increasing the throttle setting from cruise to full. Continue to lean during the climb i.a.w. that dodgy old collection of old wives' tales called the flight manual. When arriving at TOC, re-lean the mixture according to how much I reduce throttle setting from climb to cruise.

Regards to all,
O8

[frigatebird]

'64 - H model? Thought they were '67 - the last of the 0-300 six cylinders.

[RadioSaigon]

mea culpa

On re-reading my post I must confess to a poor choice of language, leading to some subsequent posters assuming the feature I speak of as taking your mixture to full rich with the throttle firewalled -not my belief (or intention) at all. Such an attribute could be potentially fatal, leading to an excessively over-rich mixture and subsequent engine shut-down. Simply stated, that was the context within which it was explained to me all those years ago when I first noticed the behaviour and set about polling other pilots and engineers for why; even though I understood clearly it did not take the mixture to full-rich, I didn't modify the language in my own mind.

Rather my intention is to highlight an attribute that dramatically enrichens the mixture with the throttle all the way forward. The evidence of this can be easily established by anyone in a 172, as outlined previously. Keep an eye on your EGT as you slide the throttle in -it'll head straight towards the bottom of the scale! Not a feature I would consider an "economiser" at all Oktas8 -quite the opposite in fact.

Were I to enrich the mixture prior to selecting climb-power, I would be looking for a drop of in the region of around 100deg, rather than the several hundred degrees drop your "ecomomiser" causes. To me, the effect is excessive and counter-productive, which IMO is very relevant to the question originally posted by Steve181 (BTW -the 181 is another aicraft that has a similar attribute, as does its stable-mate, the 161).

Far be it from me to suggest that anyone accept anything they read here as gospel AerocatS2A -I wouldn't; without supporting evidence. My posts direct people towards information not contained in their AFM (a very poor document IMO, as evidenced by my previous posts in other threads... probably best not to reignite that debate here) with the intention of at a minimum raising awareness, encouraging debate and hopefully inspiring more than a little curiousity and thoughtful knowledge-seeking. Are you up for it???

Simply throwing "read the AFM" at me or any other serious querant in here is IMO a cop-out of the worst kind. It reeks of someone that doesn't care enough to thoroughly know their aircraft. That is not a personal criticism directed at any specific individual either, rather a criticism of both the authors and publishers of those poor documents -and those that do behave as if the words written in their AFM will absolve them of all responsibility, should their actions or inactions lead to all turning to custard.

It is my belief that going to full throttle before initiating a climb in a 172 will alone more than sufficiently enrichen your mixture to counter the loss of airflow cooling within your engine. Any additional manual mixture enrichment is IMO excessive and counter-productive. My preferred method of achieving this is to manually enrich the mixture the desired amount myself, then advance the throttle to max RPM (and presumably MP) whilst keeping the throttle below any additional "automatic" enrichment.

[AVIATOR1982]

Please please please please read the frickin flight manual, it really is irrelevant how old it is, it is there for a reason and anybody even thinking of flying any airplane without knowing the thing from cover to cover should not be in the air....(of course this is just my opinion so feel free to kill yourself at your own will).