To lean or NOT to lean?

[dirkdj]

I can only concur with White Bear.

The mixture control must be considered a FLIGHT control, if you don't learn to use it properly you could go down, regardless of elevator position.

Reading Deakin's columns should be required for piston engine pilots.

[IO540]

Like people post pictures from their trips, why don't we post pictures of our EDM700 data?

I can contribute about 400 of them ...

The bottom line, however, is that some of us have decent planes with the engine instrumentation so we can see what is going on. The majority of UK PPLs are operating within the self fly hire scene and those planes will never have any of that. The school has made a business decision to blow away extra 30% on fuel, for knocking say 100F off their CHTs. The renter pays for it through an inflated "wet" rate.

[LowNSlow]

I usually lean to the left when turning to port, lean to the right when turning starboard and lean on anything I can find when I come out of the pub.

[Chimbu chuckles]

Many years ago I got chipped by a company training pilot for leaning in cruise at 1500' during a line check...he was most adamant that the aircraft manual, BN2-300, said no leaning below 3000'...as someone alluded to above...and he was WRONG.

What the BN2 flight manual said was do not lean in CLIMB below 3000'. And what that is based on is 75% power.

Takeoff and climb from sea level on an ISA day at MCP and you will be at 75% power at around 3000', where you should then lean on climb for best power unless you want to drown your engine in fuel and spend a lot longer climbing. Admittedly the average PPL will never notice the difference because he rarely climbs high enough...but believe me it makes a huge difference when climbing high on a hot day...we routinely climbed higher than 12000' at ISA+20 to pass through mountain passes between valley systems full of short, rough, steep bush strips at elevations of between 3500-8000' (ISA+20). We went for mths never operating at density altitudes low enough to see 24 inches MP on takeoff...let alone 29.6...and yes leaning on takeoff was as routine as scratching your balls while watching TV.

I own a normally aspirated 1970 A36 and it's fitted with an IO550B, Gamijectors and most importantly an EDM700...and Deakin and I are on first names, he's a terribly nice and knowledgable fella.

My POH has all the guff you see in your POHs about leaning for peak EGT (best economy) and 50 ROP(best pwr) and it's straight out BS.

These POHs are written by the airframe manufacturer not the engine manufacturer...they are written by humans who don't understand the science and are written to make the aeroplane look good....it's that simple.

The reason why 95% of engine don't make TBO is because they are operated via a combination of the POH, ignorance and legend.

It's an absolute fact that of you run an engine 50-80 degrees ROP you are operating at peak CHT..on my engine it's around 70 ROP...the EDM 700 has a download feature and I have downloaded a flight and graphed it as John does in his articles..in fact I will see if I can put them up here for you to see.

Ok here's some raw data....fuel flows down the left are actually in 1 liter/hr increments even though I have recorded it in GPH.

The figures at the very bottom eg 78LOP are how Lean of peak I was when I started to experience some roughness and terminated the flight test.

http://www.fototime.com/{5BB6EE5E-50...B}/picture.JPG

In the graphed version of the above raw data you see that all EGTs rise together, peak together and fall down the lean side of peak together. The CHTs are a little harder to pick in terms of where they actually peak....it's a long steady peak rather than a spike type peak...probably if I fiddled with the graph boundaries and squeezed it it might look better...cannot be bothered though. What it does do show what balanced injectors actually do

http://www.fototime.com/{77704DF6-76...5}/picture.JPG

[IO540]

Yes that's how it should be. All peaking within 0.1GPH; very good.

Unfortunately, there are just two kinds of people in flying: those that have already been converted, and those that will never be converted

[Chimbu chuckles]

What it also shows is I need new baffles....Liquid air ones designed to lower cylinder 2, 4 and 6 CHTs especially so all the CHTs end up being very close to the rest rather than some 50F hotter. I also need to replace the 'shark gill' cheek plates with 'louvre' type to increase delta P. The later is actually part of the IO550B upgrade mod that the previous owners never bothered to do

io540 there is a third group...those flying carburetted engines

[Say again s l o w l y]

Jeez, I know we are supposed to try and operate our machines as well as we can, but this is all a bit OTT!

Many people here say that operating a machine as the book says is unlikely to get you to TBO, I'm sorry but B*LL*CKS. I have only ever had one machine not reach TBO and that was due to one cylinder deciding to exit engine left due to a manufacturing flaw.

If the engines we currently use had a bit more modern design in them, then all of this would be redundant. A good well mapped ECU should do all of this for you, why leave it to the most fallible part of the equipment? ie. Us.

We don't blow away 30% of our fuel, our PPL customers do that for us. I would far rather they leaned properly and saved some fuel, but most haven't been taught properly how to do it.............. We always try, but there does seem to be a lot of resistance to moving the red knob incase of damage. When people fly with me they are encouraged to do it. Away from my prying eyes, there is little I can do.

People seem to delight in saying the POH is wrong and what would the a/c manufacturer know about engines. I would bet they know a damn sight more than most pilots and since we all love banging on about how the POH is so important, why is it suddenly a load of rubbish?

Without fancy pants digital monitoring, it is impossible to see what is really going on, so operating per the POH is all you can do. So for those without the benefit of this tuff, if the POH is wrong, tell me how it should be operated?

[Chimbu chuckles]

Yes they are WRONG...because they tell you to operate the engine in such a way that, if you're above about 65% power, you WILL heat damage the cylinders. Over time the cylinders oval because of repeated high temps, the pistons don't so you get increased cylinder wear and low compression leading to top overhaul.

Interestingly enough years ago, way before the current technology was available, we used to get to TBO too....mostly because at the extremely high DAs we were operating at we were operating them correctly by fluke...combined with flying them hard all day every day....by pure luck we were at or below 65% pwr more often than not because of operating at high DAs...at 65% pwr and below you can do whatever you want with the mixture and you will never see high enough temps to do damage.

The original fit triplex gauge on my Bonanza is actually reading one of the lower CHTs so if that was all I had and I operated as per the POH 3 of my cylinders could be continously over 400F and if I was operating with the one I have info on around 380-400F, which is in the green band therefore 'OK', 3 of my cylinders would be, unknown to me, up around 450F...which is still in the green band.

You might say so what...it's in the green band....under 460F which is the limitation as per the POH...but if you look at Deakins article on Mixture you will see a graph from Pratt & Whitney that shows quite clearly that at temps much over 400F the cylinder metal is permanently weakened...and there we are, right back to top overhauls again.

There is a reason why, over many years, owners and 'experienced' pilots have grown wary of the red knob...because they followed recommended procedures, for the most part, and engines typically needed top overhauls around 500-800hrs before TBO....more often than not.

Typically the compressions of two or three cylinders drop and owners make the mistake of changing ALL the cylinders...reasoning that if those 2 or 3 are stuffed the others can't be far behind...WRONG! They most likely are the cooler running cylinders and have not been exposed to temps over 400F....I would hate to think how many cylinders have been changed for no good reason.

I cannot think of a single Ops manual/POH in ANY of the piston engine aircraft I have flown over 3500 hrs sitting between or behind 300hp/6 cylinder Continentals and Lycomings that does NOT recommend leaning at 75% power and below to peak EGT for best economy or 50 ROP for best power...that ENTIRE recommended mixture range is deadly for cylinders at power settings much over 65%.

That list includes every Cessna and Piper SE aircraft in production post 1970, Helio Couriers, Pitts, Bonanza, Baron,Bn2,Aerostar, Queenairs, C310, 402, 404, Twin Commanche, Partenavia...and a few more I can't remember.

[dirkdj]

Chimbu,

I agree 100% with you. Old wives tales get repeated again and again.
Deakins articles are an absolute goldmine for those who want to spend some time reading them. I have known John for over 10 years on the old Avsig forum and he is absolutely straight. The famous APS course is now available on-line and it is a great opportunity for those that cant spare the time or the money to go to Ada.

I have given a lecture on engine operation in the local flying club (they invited me). Maybe 5 of 50 were really listening. Very sad.

Maybe we can develop a secret handshake..

[Fuji Abound]

Chimbu - I am not sure if I am missing your point?

I agree an engine should ideally be leaned in all circumstances appropriate to the power setting and height (or change in).

I am still concerned that many are tempted to lean to achieve the "perfect" setting without infact having the monitoring equipment with which to properly ensure CHTs are not being exceeded.

The fact of the matter is most aircraft sadly dont even have a single EGT gauge never mind a CHT gauge or anything more sophisticated.

Get it wrong and there is every possibility of exceeding CHT limits. Forget to adjust the settings (as many pilots are susceptible) and again CHT limits may be exceeded.

Hence my earlier view that unless you have the equipment to monitor CHTs and the discipline the review the settings every time you change the power settings run rich of lean. It may not be ideal but you are less likely to exceed CHTs. I am not aware that by running rich of lean you will cause any other damage to the engine.

[White Bear]

Fuji,
I developed the following rules for my self when I rented that IMHO would give me the best fuel economy, and do no damage to the engine.

If the aircraft you fly:
1. Does not have effective temperature monitoring eqpt.
2. Does not have a wobbly prop.
3. Does not have fuel injection.
Following initial climb out reduce rpm’s to 23-2400, then lean until the engine runs rough, then enrich until it runs smoothly.
Do this each time you change the throttle setting, or attitude.
In the initial climb stay full rich.
In cruise climb lean above 3000ft.

Given 1, 2 & 3 above, it is unlikely the engine will run at or above 75% power in a leaned condition.
To paraphrase Deakin , with power settings below 75% whatever you do with the mixture control will not hurt the engine.
Regards,
White Bear.

Edited to add that I also leaned aggressively on the ground prior to departure and immediately following arrival.

[dirkdj]

There are several factors that will destroy your cylinders before even getting to the cruise part of the flight:

- the full rich mixture setting not being rich enough on take-off power and the subsequent power reduction on initial climb. This power reduction (commonly to 25"/2500rpm) closes the fuel enrichment valve and will drive the CHT even higher. During a steady climb at full throttle, the CHT should stabilize. If it increases, your full rich is not rich enough and the mechanic should be asked to set it richer.

- during the climb, power will start to fall due to density altitude increasing and gradual leaning can be started by observing the target EGT. Leaving it full rich will rob power.

- proper baffling is essential.

[Chimbu chuckles]

Fuji A and SAS,

It is my strongly held view that 'fancy pants digital' technology should be mandated for all 'big bore' IO engines, along with appropriate instruction on it's use and the internal workings of piston engines.

But that won't happen.

That being the case I would recommend the following.

On climb;

Set MCP on takeoff and do NOT touch it again on climb until 3000' or leveling off. By that I mean follow the POH. IO470/520/550s for instance have MCP of 'full throttle/2700RPM/full rich(at sea level). Setting 25/25 at 1000' after takeoff is bad for your engine and reduces performance at the worst possible time....Some parts of the EU mandate prop governers be set at 2500 RPM for noise pollution reasons. That is the only reason an IO 520/550 has that limitation.

If climbing significantly higher than 3000' lean to about 120 degrees ROP passing 3000' and then give the mixture about a 1/3 twist leaner every 1000' or so after that....keeping an eye on your CHT/EGT of course...enrichen if you get roughness until it's smooth again...watch the EGT each time you twist...sooner or later...probably around 9000' you will see it decrease which means you are LOP...probably a typical engine won't do that AND run smoothly, so enrichen a bit and then leave it...it's about as good as you'll get. Be aware that once you are up around 7000' your available % pwr is getting well below 75% so you really cannot hurt the engine.

High speed cruise;

Obtain from the POH the MP/RPM combination that they suggest equates to 75% power...but do not lean further than 80F ROP EGT.

Long range cruise;

Obtain from the POH the MP/RPM combination that they suggest equates to 65% pwr and lean the mixture to peak EGT...or as close as you can get while maintaining smooth running...might be around 25F ROP.

The oldest aeroplane (aside from various vintage biplanes etc) I have flown is a 1956 C180 that belongs to a mate and now resides in the UK, G-BTSM...once upon a time it was P2 (PNG registered). It has an EGT gauge...surely aeroplanes not fitted with at least an EGT gauge are a rare thing these days?

It, of course, is not IO but merely O so all bets are essentially off. The fuel air ratios in most non injected engines are so random that all you can do is lean to rough running and enrichen for smooth running...but the same 65-75% power considerations should be observed imho.

In the old days when I was flying IO and TSIO twins for a living we would not lean them below, from memory, 60-80F ROP for the IO engines and about 100F ROP for the TSIO engines...and we had few problems with the IO engines...TSIO engines tend to eat cylinders almost no matter what you do.

I also lean brutally on the ground as soon as it settles down in idle after starting on my aeroplane...it completely stops 'morning sickness' (fouled plugs). But you must develope a habit of going 'Mixture, pitch and power' as you begin each takeoff lest you forget and try to takeoff with a lean mixture. Another way to avoid that very damaging possibility is to lean so brutally on taxi that it dies when you try and increase throttle on that takeoff without going full rich. That is called a lean mixture cutout...too much air/not enough fuel.

[IO540]

Sounds reasonable to me.

I think the majority of UK's GA fleet has no engine temperature monitoring. Some have a useless CHT gauge. One IR instructor I flew with recently told me to go by the oil temperature gauge...

The price paid for lack of instrumentation is the need for ultra conservative fuel practices.

I too lean on the ground, to the point where the engine starts to pack up. No way could one get airborne with that in error - in fact one can't even taxi on grass with it.

[justinmg]

I have heard that the hottest cylinder can be identified, and the probe moved to it (for simple CHT installs). Would this not give most of the required info, as you would never go leaner than that one cylinder dictates???
I understand it wont give you shock cooling warnings like a JPI, but good engine handling should avoid most of that.

[Chimbu chuckles]

The probe in simple installations should be on the hottest cylinder...and yes it would give you 'most of the required info'.

However it doesn't give all the info...and the hottest cylinder can change due to local airflow effects in different phases of flight...not to mention over time as other things impacting cooling change...like baffles wear out etc.

Instruments like the EDM 700 and their competitors really should be considered essential by aircraft owners...I am at a loss to understand why there is such resistance to installing them...they are not THAT expensive and pay for themselves in a VERY short time frame just on fuel saved let alone engine wear etc.

When I last flew my mate's C180 in the UK late last year (the first time I had flown that one since the late 80s) I was surprised to see them not leaning at all. The reasoning was that it was a waste of time etc on the reletively short low level flights they typically did. I explained some of the issues and for the flights we did on that day I leaned appropriately at all times...including after start and taxiing etc.

We flew three sectors from their farm strip north of WW to IOW, back to WW for fuel and back to their farm strip....never above 2000'. Leaning the mixture gave smoother running and saved almost 20 liters/hr that day over what they considered normal...at GBP1.40/liter!!!! Do the math...it was a HUGE % of what they charge themselves to fly the aircraft.

Twas a wonderfull day...been a long while since I'd flown a Cessna taildragger, let alone that one...I think I'd last flown a C180 in the late 90s...can still do a nice 3 pointer on grass

Shock cooling is a bit of a myth as well.

[IO540]

"I am at a loss to understand why there is such resistance to installing them"

Most of UK GA is just managing, scraping out the bottom of the barrel, that's why.

It's also probably not worth doing on a carb engine. You pay less for the plane but you then pay for ever by having to pour extra fuel into it. Same with fixed landing gear; lower purchase price and extra 20% or so on the juice, for ever after.

If you could buy an EDM700, mail order from the USA, and install it yourself, you would get the job done for about half the price.

[Say again s l o w l y]

What sort of money would an analyser like that cost, fully fitted in the U.K? For example on a conti IO360.

[mm_flynn]

Originally Posted by Fuji Abound

Whilst I appreciate automotive engines are in many ways different animals they do bring home the extreme danger of operating an engine at peak fuel mixture efficiency unless you can be absolutely certain you can monitor and control all the factors that might just mean the engine has become over lean,

Fuji,
In the comment above, does 'over lean' mean closer to stochiametric than plan (on the rich side) or does it mean leaner than stochiametric (broadly Lean of Peak EGT in aviation speak). I always had the impression (as an uneducated bystander) that high performance auto engines where designed to run well ROP to get as much power as possible out of the small displacement without burning up/over pressuring and to lean out to stochiametric at lower power settings.
I would love to understand a bit more about what you have learned in the auto-engine space. My experience is all in aeroengines and I run it just the same as IO540 (LOP with fancy engine analyser and some trend analysis on the downloaded data)

[IO540]

SAS

Obviously you need to get a quote from an avionics shop but in 2002 I paid about 3.5k+VAT for an EDM700 installation, factory fitted. Engine was an IO540 (as you may guess ) The actual instrument costs a disgustingly small fraction of this amount; you could buy it mail order with an 8130-3 form but then you need someone willing to put it in just on the labour charge.

I can see, one day when I get old, dumping all this "IFR capability" nonsense and flying a permit plane, and doing all the work myself. I envy those people who fly some carbon fibre/kevlar plane at 140kt IAS on half the fuel I use and can put in their own non-TSO avionics...

MMF

I don't think car engine management is directly applicable to the old Lycos because car engines are water cooled so you can always get the heat out of everywhere. Whereas these old designs are very economical with where the metal is (for low weight) which is why we have to watch it. Car engines also vary the ignition timing, which is a huge advantage in controlling detonation etc. FADEC would do a lot in the old engines (not in terms of cruise efficiency but in terms of easier management) but until it is certified... even then I would be wary, having seen the absolutely cr*p design and build quality prevalent in GA avionics. Even Thielert have not been able to make it reliable. I suppose two completely redundant ECUs, magneto-powered, would be OK.