Leaning... not something I have been doing!

[bigfoot01]

... Relative newby - 70 hrs on PA28/C150/C152. I was interested while reading the other 10000' thread the bit about leaning. Most of my flying has been done under/around 3000'. Recently I took part in a fly away and did a cruise at FL45. I was lucky that my passenger was a rather cool instructor. While trundling along, he said was I going to lean the engine. Having not thought of this (probably makes me a bad person!) I said I stated I generally don't bother leaning, as it doesn't make any difference to me in terms of cost, and most of my flying isn't really relevant to this. He observed that the fuel might become more valuable in case of a diversion/planning failure and also leaning provides a performance advantage, as the unburnt fuel has a cooling effect.

Having thought about this, I clearly should have leaned the engine at FL45, even by my own thinking, but picking up the point that was raised in 10000, I wonder if I should be leaning on my flights regardless of height.

I am assuming that when climbing fuel fully rich is the right way to go also!

Hey ho still living and learning

[maxdrypower]

That is correct matey , One shouldnt just be leaning based on height . Aircraft use fuel at all altitudes and power settings ,your paying for that fuel so you really want to to use as little as possible . As I said I lean as soon as I am in the cruise , even if that is 1000ft leaving the zone . As part of your checks prior to a climb or descent or a change in power setting always select micxture fully rich . This is vital becaue if you put full throttle in with the engine leaned you run the risk of detonation(I thinkit is ) and possible engine damage. Im afraid d I am notgreat at putting down facts and figures and I dont have abook to hand , Im sure someone will clarify but imho lean lean lean like I say your paying for it . I gave the example of the g1000 172 that cruises at 11-12gph lean it at 1000ft to 8 gph if you on a nav trip of several hours then that is a significant saving and like your instructor said , more fuel if it all goes wrong. Flying schools in my experience dont lean , that fuel cost is put down on your bill .

This is the leaning protocol from my aircraft group it may help

A few common myths about leaning are detailed and countered as follows:-

Myth:- You shouldn't lean below 3000ft

Answer:- The aircraft flight manual clearly states that you should lean at any altitude when using less than 75 percent power. It then goes on to say that you can even lean off when using full power if you are above 3000ft. So the 3000ft thing is only applicable to full power operation, not cruise power.


Myth:- If you forget to richen up in the descent it will damage your engine

Answer:- No it won't if you are not using more than 75 percent power which you wouldn't be using in the descent anyway. All that might happen is that if you have the mixture leaned for optimum power at high altitude and forget to richen as you descend, you may not get the power you want as you level off because the mixture will be too lean to provide enough power. Simple remedy, when you notice this lack of power, richen up.


Myth:- If you lean too much by mistake your engine will stop


Answer:- Richen up again and guess what, it will start again. The engine never fully stops, it windmills, as soon as you richen up it starts again right away. I'll demo this to anyone who wants to see it!


So in summary a few too many bar room flyers over the years have made the whole populus of real pilots afraid of the big red knob. Result, club aircraft that cost you £150+ per hour to fly.

We have aircraft which cost you £45, £60 and £65 per hour to fly because we lean off and save £14 per hour in fuel, all have a healthier and happier engine and bank balance. (We charge our hourly rates based on the flight manual published fuel burn for each aircraft which is for optimum mixtures. We only charge cost price so if it costs us more it ends up having to cost you more)

Now to the main point of this training post, how we do it!

As a slightly over cautious approach we have a little policy to only lean when in the cruise. We don't complicate the issue by saying that you can lean off in the climb above 3000 ft and you don't need to fully richen in the descent etc. So:-

1:- Lean off only when established in the cruise at cruise RPM (which is less than 75 percent power so you can lean at all levels)

2:- When climbing or descending, always remember to go full rich. (Never forget this, one time only can damage an engine)

3:- After changing levels, re-lean for the new altitude

4:- Circuit details or manoeuvres such as stalls or steep turns etc, always use full rich


In aircraft without a fuel flow gauge, use the rpm fall away method of leaning which is as follows:-

Set cruise power, maintain level flight and lean off until a noticeable drop in RPM occurrs. (RPM will fluctuate slightly on fixed pitch propellers as you fly along through up and down drafts or turbulence so you are looking for a definite leaning related drop)

Once the drop has occurred, advance the mixture towards rich until the cruise RPM is restored

Thats it!



It's as simple as that

8 Gallons per hour is a good fuel flow at low levels typical of which we usually fly around at. You can use the RPM fall away method described above if you prefer and if you go higher, (5000ft plus) you are better off using that method because 8 GPH will be too rich. You will get a lower fuel burn the higher you go.

It wouldn't be uncommon that as you go to these higher levels and try to maintain power as you climb, that you would get more power if you do lean off a little even under full power and of course once you level off you may find you need full throttle to maintain your cruise power. If that is the case, full thottle does not mean full power so you can still lean off using the RPM fall away method.

Full throttle is what you are asking for. Full power is what you get only if the air pressure permits, so as you get higher, full throttle can't give you full power even though you are asking for it which is why you can lean at high throttle settings when you get to high altitude.


The main point to keep it simple is ALWAYS remember to richen up when climbing or descending and always lean off in the cruise

I hope you have found this informative and useful. If we all adopt good leaning procedures we can all help to keep it low cost for all.

[Comanche250]

On the other hand would it not be sensible to relate to the POH for the a/c you are flying? Take for instance a C150, below 5000' leaning is not permitted. I agree leaning the bigger engines is sensible and is also recommended, but it boils down to a/c specifics.
"also leaning provides a performance advantage, as the unburnt fuel has a cooling effect."
How is that possible when there is less fuel being entered into the cylinders and the fuel that is in there is being burnt more efficiently? Watch the EGT's when you lean off, they go up, not down!
C250

[maxdrypower]

Comanche , Ive edited my post with bits and bobs , But yeh you are right the POH is the ultimate authority

[Comanche250]

Yeah I posted before you changed yours, couldnt have put it better myself :ok:

[Established Localiser]

Isn't it a shame that many instructors do not teach the art of Leaning to students.
I dont ever remember during training any teachings on leaning apart from a quick chat about it.
maxdrypower that was a well put answer to the origional post. :ok:
POH is the ultimate guide to a particular aircraft however I still think that basic common knowledge of Leaning should be taught during training.
EL

[bigfoot01]

...my C152 at FL45?

[maxdrypower]

No If you were in the climb and levellled off at 45 then leaned then yeh bang on correct. whenever you use less than 75% power . So you could have leaned if you had levelled off at 45 or 1000ft it doesnt matter , so long as you goto fully rich when you climb up again lean whenever you are cruising . If you can be bothered and have the means try doing a 2hr navex without leaning and fuel up at the other end then do the same route having leaned , and see the difference ion your fuel price , obviously this is not exact as conditions may be slgihtly different but you will notice some difference.
But again look at your POH . The protocol I gave was for a cessna 172 . Although we have 172' 152's and archers in our group and it the policy throughout . I dont fly the 152 so cannot say with accuracy what their POH says But an engine is an engine and it wont be much diferent

[stickandrudderman]

The Pa28 that I use occasionally has a sticker advising "lean for taxi"!
So proving that it's good to lean a lot more often than people realise.
(The reason for this is to reduce the chance of a fouled plug whilst taxiing)
So, what's your favourite colour?

[davidatter708]

Hang on a sec all the c152 at our club use 2400rpm to get a cruise of 90kts that is never below 75% power therefore do you never lean at whatever height. However as you go higher your rpm wont change but you will need to lean but then you are leaning when over 75% power.
I also take it full rich for aeros.
David

[Mark 1]

Take for instance a C150, below 5000' leaning is not permitted.

Not true.

I think you will find that leaning at FULL POWER below 5000' is not permitted.
Below 75% power, leaning is recommended at any altitude. Especially if you want to achieve published performance and fuel consumption, and avoid fouled spark plugs.
Of course it should not be at the expense of exceeding any other engine limitation.

[maxdrypower]

I couldnt say for a 152 as I dont fly them , but Im sure they can be leaned , I would suggest a quick trip to the POH would clear that one up

Blue , no , ARGGGGGGGGGGHHHHHHHHHHHHHH

[Comanche250]

Mark 1, From the C150 POH and I quote...'The mixture control must NOT be used below 5000'. No where does it mention anything about full or 75% power.

C250

[davidatter708]

The F152/II POH states that
"The mixture control must not be used below 2000ft. Above 2000ft the mixture may beleaned by using the vernier control until maximum RPM is obtained with fixed throttle, and then the contol is pushed forward "full Rich" until RPm starts to decrease. The mixture should be readjusted for each change in power, altitute or carb heat. When climbing the mixture should be full rich unless the engine runs rough due to too rich a mixture. Full rich should alwaysd be used at power settings in excess on 75%.

What I dont get is at standard temp the chart says 2400rpm is 101kts
2300 is 96kts and 2200 91kts now the red line is at 2550 so this is no where near 75% however in the graph 2400rpm is 75%bhp so is this 75% business done on rpm or bhp??
Dave

[maxdrypower]

Now I have to say Im lost I can save fuel but this is above me . You will probably get half a dozen different pieces of advice here now . There must be a decent instructor whom you know who is an expert on 152's who can help , I however cannot

[davidatter708]

Thanks anyway It must be bhp otherwise the POH wouldnt tell you to lean at all.
Dave

[davidatter708]

Just found summin interesting in my POH it says that leaning should only be done above 5000ft and only used to smooth engine above that altitude. Therefore it sounds like it isnt to reduce fuel cost but only to make it non rough

[Mark 1]

C250

Fair enough, if that's what your manual says.
I'd be interested to know what model of C150 you got it from. There are quite a lot of different models, all with their own flight manuals.

[davidatter708]

The F152/II POH states that
"The mixture control must not be used below 2000ft
From an earlier post this might help
David

[IO540]

There is no engineering/technical basis for prohibiting leaning below X thousand feet. It's utter nonsense.

Which is not to say such an instruction doesn't appear in some handbook, or a school rule book.

Most instructors don't know anything about engine management anyway, so it won't get questioned by too many people.

Running full rich all the time keeps the engine cool (at the cost of about 30% extra fuel) which helps to protect it from gross abuse of the kind training / rental fleets get regularly. The standard "wet rental" business encourages abuse anyway.

Leaning is not a complicated subject but it's been done to death here so many times, and it can't be explained in a short piece of writing. I would suggest reading John Deakin at avweb.com as a starting point.

[nano404]

Can changing the prop pitch (when applicable) save fuel too?;) What happens if you lean below 2/5000 feet? Is there any effect or is it a just in case (you drop out the sky) safety measure?

[Dan Winterland]

I always used to teach leaning as part of Effects of Controls 2. Why? It was in the syllabus I was tought to use! But then I pointed to point out that Lycoming themselves mention that leaning below 5000' should not be necessary. Only ever lean in the climb to prevent rough running and in the cruise - with care.

Why? It's because to break down excess fuel into it's basic elements takes a lot of heat and this aids cooling. Excessive leaning leads to a hot engine and potential problems as a consequence. On one group I was a member of, one pilot used to lean a lot - probably because he did the groups books and wanted to save a bit of money. After he went on a week long trip where he had obviously been leaning a lot, we needed to change the engine. Not much of an economy there!

For effective leaning, A Cylinder Head Temp guage or even better, an Exhaust Gas Temp guage are required. Without these, leaning is guesswork so it's better to err on the safe side.

[IO540]

Prop RPM does affect efficiency (MPG, if you like) but it's not trivial.

Engine efficiency improves at lower RPM due to reduced friction and pumping losses - assuming the ignition is co-operating and not delivering the spark much too early. Our engines are fixed-timing and will be set up for cruise RPM.

Prop efficiency improves with higher RPM, so long as you don't get too close to mach 1 on the tips.

I have done measurements, with accurate equipment, and there is no consistent result in the 2200-2500 RPM range (IO540 engine). So I fly at the setting where the engine sounds best, which is 2400.

In extreme cases, such as maximising endurance in a hold, one uses very low RPM, say 1800, and a very low MP, say 18". This is about 40% power and I could hold for 12-15 hours like that, going along at about 110kt.

At altitude, above say 10,000ft, a non-turbo engine needs to be at full throttle anyway to get acceptable power, and higher RPM gets more air in so at these levels one flies at max (or close to max) RPM anyway.

[RatherBeFlying]

There's been the odd accident report where a C-150 or suchlike ran out of fuel short of the destination because the pilot used the POH fuel consumption figures, which are based on leaning, but did not lean in cruise -- ergo he ran out of gas:uhoh:

[IO540]

The truth is that the vast majority of spamcan pilots haven't got a clue what their flow rate really is.

I was horrified when I was doing my PPL about the practices that were going on, especially the way people relied on the tech log entries.

The industry gets away with it largely because no one person spends much time away in a given plane, and it isn't long before it gets topped off again. But if you let a load of fresh PPLs on a 3-4 hour trip to say France, a lot of them would run out of fuel. And those that don't would be doing a ridiculous number of fuel stops.