Leaning

[funfly]

Am I correct in thinking that, in the cruise, leaning an engine (Lycoming) to any point less than the 'desired' point is better than not leaning at all?

[Fuji Abound]

:zzz: :zzz: :zzz:

This has been done to death recently. Worth using the "search" facility.


:)

[Confabulous]

fun,

Are you talking about the 'desired' point being the Lycoming specified leaning (50 degrees rich of peak EGT) or tuned leaning (50 degrees lean of peak EGT)?

Any leaning is good, but it really depends on the engine - injected engines tolerate vicious (aka GAMI tuned) leaning far better then carbed ones - the O540 vs the IO540 for instance

Speaking of IO540, I think he can explain this far better then I :E

[IO540]

A great deal has been said and written on this, but the best reference is John Deakin's articles which can be found at avweb.com (they keep moving about on there...)

The short answer to the original question is NO.

Both carburetted and fuel injected versions of the standard Lyco/Conti aircraft engines have their fuel metering set up so that when all 3 levers are fully forward at sea level the engine will develop its full rated power, and the mixture is then very rich, setting the engine operating point at about 125F rich of peak (ROP). This results in a lot of unburnt fuel, which gives cooler combustion.

It's done because these lightweight engines are poorly designed when it comes to removing excess heat, and their air/fuel flows to different cylinders are usually poorly balanced so one has to waste fuel to the cylinders with the richest mixture to avoid those with the leanest mixture not getting enough.

If you now start to lean the mixture (still at full throttle) the EGT starts to rise, the CHT will rise, but the engine won't be producing any more power. The worst point heat-wise is about 50F ROP.

If you continue leaning, to peak EGT, the fuel is being burnt with exactly the right amount of air and this is the most efficient operating point (actually it happens about 25F LOP (lean of peak) but it makes no practical difference). Lyco engines are in general authorised to run at peak EGT at 75% of rated power or lower only.

Then if you continue leaning into the LOP region, the power output is more or less proportional to the fuel flow rate. This is a good place to be. If the engine was really well set up (every cylinder getting the same amount of fuel etc) then you could just leave the throttle on full bore and use the mixture to control the power... in practice fuel and air flow imbalances cause excessive vibration and many engines can't run in the LOP region (this is where GAMI injectors come in; you buy a set matched to your particular engine).

That's the essence of it.

Getting back to the original question, if you lean to about 50F ROP and leave it there, with the throttle on full bore, climbing at Vx (i.e. not a lot of cooling) and let the CHT rise to 500F or so, you will probably get detonation and eventually knacker the engine. Detonation is not usually evident to the pilot - other than through a rapid rise in CHT. (Pre-ignition is evident but that's an altogether different thing.)

So, a "little leaning" is not a good idea. Best to climb with everything forward (as the POH says) to either

a) top of climb, or

b) to an altitude where the power will be below 75% (due to loss of air)

and then set the plane up for cruise and lean to peak EGT, or a little bit LOP if you can.

If your engine is poorly balanced and can't reach peak EGT without shaking too hard, then you are bit stuffed..... you have to run the engine with a very rich mixture.

On the plus side, Deaking suggests that one cannot achieve detonation unless the CHT is above about 450F and 75% power (this was a TIO540 test I think). This suggests that one isn't actually going to damage the engine by incorrect leaning at any "normal" cruise setting.

I fly an IO540 and do exactly as above; all 3 forward to TOC or to about 6000ft, then set 23/2300/LOP (10.5GPH) which is about 60-65% power, and just sit there. Leaning a little bit more if climbing higher, to maintain peak EGT.

[Islander2]

On the plus side, Deaking suggests that one cannot achieve detonation unless the CHT is above about 450F and 75% power (this was a TIO540 test I think). This suggests that one isn't actually going to damage the engine by incorrect leaning at any "normal" cruise setting

You're going to think I've got it in for you with recent posts, so please let me assure you this really is nothing personal.

But if you are going to quote Deakin's advice, I feel it's incumbent on you to get it correct!

Deakin is extremely outspoken in his belief that our engines, for longevity, should NOT be operated continuously (i.e. in the cruise) at anything like 450 degF CHT, or anything approaching 75% power unless (in that case) you are well, well away from peak CHT (i.e. well removed from circa 50 degF ROP EGT ... indeed, at 75% power the APS recommendation is to operate either richer than 140 degF ROP on the leanest cylinder or leaner than 30 degF LOP on the richest cylinder!). Even climbing at 450 degF CHT is a complete no-no for Deakin, although it is a value less than the 'Limitation' promulgated by both TCM and Lycoming (and therefore the Limit contained in our POHs).

His advice (in his Avweb articles, at the 2-day Advanced Pilot Engine Management Seminar in Ada and also in his on-line newsletters to APS graduates) is that 420 degF CHT is "an absolute-do-something-right-now redline", 400 degF is "a working limit ... engine monitors should be set to show/sound an alarm at this level", and that 380 degF should be "a working target which allows doing just about anything with a well set up engine".

Similarly, regarding power setting, he is dismissive of Lycoming's advice (to their publicly-demonstrated chagrin) that higher HP engines (especially the turbos) can be operated in the cruise (for reasonable TBO) at anything like 75% power if you are anywhere remotely in the region of peak CHT on any cylinder. He even believes that TCM's comparable figure of 65% may be on the high side, and strongly recommends a more conservative approach (for engines from either source) of 60-65% power.

Further, he is at pains to point out that, whilst anything other than light detonation is obviously disasterous for even short periods (and APS students get to watch the effects of a highly-instrumented test-rig engine being taken into light detonation ... so that's obviously not immediately catastrophic), you don't need simply to prevent detonation to achieve long cylinder lives and avoid premature (and potentially disasterous) failures. All it can take, he claims, to produce problems over a period of time is very high CHTs (i.e. >420 degF) resulting from very high internal combustion pressures due to mixture settings that are inappropriate for the other engine parameters.

You can agree or disagree with his advice (although it is based on ten plus years of hard data from the GAMI test rig). What you cannot reasonably do is to suggest this is actually not what he is saying!

[funfly]

:zzz: :zzz: :zzz: This has been done to death recently. Worth using the "search" facility.:)

Sorry, I didn't make myself very clear, I didn't mean to open the discussion on leaning again - my question was about one specific issue where I was looking for practical advice from people who know a lot more than I.

Situation:
I arrive at my cruise altitude, say 5,000, but still have 'things' to do before I get around to setting the mixture correctly.
Is there any point/harm/benefit in moving the mixture knob part way to where I know it will eventually go - will this be better/worse/waste of time than leaving it fully rich until I get around to leaning it by EGT?

Question:
Forget the theoretical leaning settings;
I the cruise is some leaning better than no leaning at all?

[Islander2]

In the cruise is some leaning better than no leaning at all?

Short answer, although already covered above ...

Unless you can confidently lean to a mixture setting that avoids dangerously-high internal cylinder pressures and temperatures, with the consequent risks of long-term engine damage or short-term engine failure due to thermal runaway and detonation (and this is a process that necessitates a multi-cylinder engine monitor), then:

a) NO, if you are at 'high' power settings;

b) NO, NO, NO, if you are at 'high' power settings on a big, turbo'd engine; or

c) DEFINITELY YES, if you are at 'low' power settings.

Determining what the relevant values are for 'high' and 'low' power is something that needs the long answer! Study the POH, study the engine manufacturer's operating manual for the model, then read Deakin from start to finish several times in an attempt to understand why the manufacturer's advice should be taken with a pinch of salt! :O

BTW, the APS course, which is truly excellent if you really want to understand this stuff, is now available on-line for those that don't have the time to travel to GAMI's facility in Ada. (Edited to say that, by taking the course on line you will miss the invaluable experience of 'playing' with the test-rig engine ... where you can establish different engine parameters such as power settings, magneto timing and fuel type, and watch the effect on individual cylinder ICPs, EGTs and CHTs).

[englishal]

Is there any point/harm/benefit in moving the mixture knob part way to where I know it will eventually go - will this be better/worse/waste of time than leaving it fully rich until I get around to leaning it by EGT?
Thats how I always lean. Reach the cruise and cruise power, pull the knob back a bit, do whatever I have to do then lean properly. In recent times, I click the "Engine button" on the right hand MFD, choose "lean assist" then bring the mixture back until the CHT graphics tell me I've reaced peak. Then advance it until I get a reading of 50F rich of peak. Makes hell of a difference actually, watching the fuel flow on the screen in a DA40 FF went from around 12 gals / hr to around 8 when correctly leaned at about 6000'.;)

[IO540]

Islander

I agree with you. It's a case of how much to write in response to a 1-liner, that's all.

I fly at 60-65% myself, with CHTs never above 430F and that is only short-term in climb. My normal cruise CHTs are about 350F, and often lower.

Funfly

There is no point in leaning a little bit initially. I would suggest the best way is to level off (trim forward on the elevator, trim off any rudder trim) until the target IAS is reached, and then bring back the MP to the target value, bring back the RPM to the target value, and then bring back the mixture to the peak-EGT or LOP point.

No point in half-fiddling with the mixture - even if it does no harm by the time you have brought the power back to a 60-65% cruise setting.

[dublinpilot]

The trouble with Deakin is that he tells us that if we don't have an engine monitor showing temps on each cylinder, then we can't use his techniques.

Probably a quite reasonable statement. But not much help to those of us with only a single EGT gauge. :hmm:

Of course this makes you think it might be better to not lean at all, use more fuel, but spare the engine.......but then you wind up fouling the plugs. Probably the only safe way to operate in this case, is to use power settings below 75%. According to Lycoming you can't damage with leaning below 75% power.

Just my uninformed thoughts.

dp

[Islander2]

.According to Lycoming you can't damage with leaning below 75% power.
That is, indeed, what Lycoming say.

But there's a HUGE amount of data now from GAMI's test-rig to say they're wrong - especially for the larger GA engines - and, since they've been putting out this 'advice' for so long, I guess backtracking is kinda awkward!

You pays your money, takes your choice. I fly behind a 300HP IO-550, and there is no way I would operate that anywhere approaching 75% HP with the mixture setting in Deakin's 'Red Box'.

Maybe I'm just gullible.:D There again, and interestingly, TCM's advice on their engines is that you are okay operating at any mixture setting at 65% and below. That's a peculiar difference between Lycoming's advice and TCM's, don't you think, given the engines are technically near identical!

[dublinpilot]

Agreed Islander.

I just find these threads very fustrating, as the two aircraft I fly don't have engine monitors.

One is fixed pitch (carb engine) and only engine gauges are rpm, oil temp & pressure. Other one is csp (fuel injected engine), and enginge gauges are MP, RPM, Oil pressure & temp, and single EGT.

Deakin who is always given as the great sage, says you can't use his advice because you don't have an engine monitor.

Everyone says you must lean, if you don't you'll fowl up the plugs.

But if you don't magically lean it correctly you'll damage the engine.

What is one to do? The POH isn't much help. It just says to lean, nothing more.

Seems like operating at low power settings is the only real safe way to operate the engine. Seems like a bit of a waste of an engine though, constantly using very low power settings.

All the advice that appears on pprune about engine leaning is geared to those with engine monitors, but unless I'm mistaken, most light aircraft don't have these. They tend to be the exception rather than the rule.

dp

[Say again s l o w l y]

Why does nobody give advice? Simply because the vast majority don't know!

How do you lean properly without the benefit of full engine monitoring kit? Follow the advice already given by Lycoming.
Lots of people will through up their arms and say "That's not what Deakin says...." but to be honest I'm not convinced about all of it.

I was involved with data collection on IC engines of all kinds from my days at Uni, and the results can be skewed in all sorts of ways. Especially if the customer has something to gain from a certain conclusion. i.e all the data comes from GAMI and they sell the stuff because Lycoming obviously have no idea what they are doing...... (According to these comments and results anyway.)

So, until someone comes up with a definative source on what to do on a bog-standard engine, then the manual is all we poor saps have to go on. Since I rarely see engines going pop or use too much fuel, then I'm certain the standard procedures seem to work O.K.

[IO540]

DP

There are two operating points (only) that can be easily set without instrumentation:

1) Full-rich

Fairly obvious how you do that one :O

2) Peak EGT

You lean until the engine RPM starts to drop off noticeably, and then go back (rich) a little bit. Verify that the carb heat lever still works as normal: a small RPM drop. Every Lyco-type aero engine I know of is authorised to run at peak EGT when below a certain power setting (65 or 75%).

So, in climb, use 1).

In cruise, set the power to or below 65% and use method 2).

How to get 65% or below? Look at the engine manual (which is likely to be a separate publicaton to the POH, or the info could be in the POH somewhere) and look up what power the engine is supposed to be developing at a given altitude and RPM (with a specified prop attached).

You will find that at a certain altitude, say 7000ft, it can't make 65% anyway, so if climbing to/above that altitude, the issue goes away. If below that altitude, you have to set the specified RPM when top of climb is reached.

I flew a PA28-161 recently for a couple of weeks and vaguely recall a page from the POH which would show max RPM of some 2600, and a 65% power RPM of something like 2300 at sea level.

That's the only way to do it. Top of climb, set the correct RPM and lean for peak EGT.

The case where you are stuffed is where the engine cannot make peak EGT without excessive vibration. I have no suggestions for that one.

[dublinpilot]

IO,

Thanks for that.

That's pretty much what I do do. Of course even having done this, one cylinder could be lean, one rich.......one 50F ROP.....(the danger area?).....etc etc... no way of knowing. I could be cooking one cylinder. Of course I could bring the power back to 60-65% as you suggest, then I could do as I like with the red lever.

But still......there doesn't seem to be a safe way of leaning an engine for 75% power, with the typically found engine instruments.

When I eventually can afford my own aircraft, it will have all the gizmos :}

dp

[englishal]

Not forgetting of course, if you have a TIT then you should lean using your TIT :}

[dublinpilot]

Ahh....don't go making a tit of yourself Al! :}


Sorry.....:O

[IO540]

there doesn't seem to be a safe way of leaning an engine for 75% power

That's correct, but that isn't what you do. You first adjust the power** to get say 65% power or less, and then you lean for peak EGT.

So the fact that one of the pots is 50F ROP and another is 25F ROP and another is at peak, etc, doesn't really matter. However, if three of them are as described, and another is at 50F LOP then the engine will shake itself to bits because while the first three will be developing similar power, the 4th one will be developing considerably less.

** with a fixed prop, with the power lever; with a CS prop, with the MP lever

There is the caveat with a climb to high levels e.g. 10k-15k feet when you have to lean during climb because the engine won't run full-rich at those levels; again this is not an issue because the power is so low due to the thin air.

[Islander2]

dublinpilot
I would wholeheartedly support IO540's suggested approach. You'll lose a little speed, but in the process be kind to your engine and save a not insubstantial amount on fuel costs.

IO540
See, we do agree sometimes.:D