[VRB_20kt]

What is this 75% power that you shouldn’t lean above?

Leaning is about setting up the correct mixture - whatever the power setting. You’ll potentially get more power if you do it right.

[Paul_Sengupta]

the requirement is never lean above 75 % power.

That's folklore too. It's an ok response for general light aircraft flying, but it's too much of a generalisation. Below 75% (Lycoming...Continental say 65% I think...or the other way round) it doesn't matter what you do with the mixture, you're not going to hurt the engine, you can lean to peak EGT (around the stoichiometric ratio) and you're not going to get it hot enough to cause problems.

However above 65% or 75% you can still lean, but you have to either lean it so that you still have fuel cooling the engine (a certain number of degree rich of peak EGT) or you have an excess of air cooling the engine (a certain number of degrees lean of peak EGT, though this is usually fairly easy as it's usually the leanest it'll go without vibrating itself silly). Either way the CHTs will come down from where they would at peak EGT.

In fact my Bulldog POH says that after initial sea level take off, you can bring the mixture back while still operating full power in the climb in order to save fuel, though keeping it quite rich to enhance cooling.

[caverill]

In a rush to depart Biggin Hill I put in the QFE rather than QNH, but had it wrong and almost busted London TMA but was saved by SkyDemon. I hate QFE and love an instrument approach staying on QNH

[TrickyWoo]

This has been a very interesting read on the fuel economy front.

Of 3 FIs on my LAPL, one was an airline pilot and he did say very early on about leaning a bit to save £ and then remember the M on downwind. The other two didn't mention it and neither did the ground school far as I can recall.

I'm now in a syndicate and we run full too. And these are v experienced pilots.

OTHA I read a whole book called Mike Busch on Engines (US) and there's tons (or indeed tonnes) about LOP and ROP etc. And it made sense.

Is it worth persevering to change 'bad habits' now before they become engrained and save a few quid over the years? Is it even a large difference? What percentage would even basic engine management on a PA28 140 be for example?

(Same goes re QFE - I do it in the day as it's what I was taught but on a night flying course it was QNH and nowt else. Perhaps time to learn better behaviours now)

TW

[GrahamB]

@TrickyWoo FWIW I have fuel flow meter in my AA5 with a similar engine to your Cherokee. I save about 5-6 litres per hour by leaning in the cruise. Over a tenner an hour saved just by careful use of the mixture control is worth having.

I lean as far as it will go in every phase of flight, on the ground and even in the climb - I do have CHT/EGT probes on every cylinder, so I can keep an eye on things. I’ve never had a fluffed up plug and the engine is nice and clean inside, even after 1400 hours.

[Paul_Sengupta]

I would assume my consumption in the 'dog would be over 40 litres an hour unleaned. Leaned, it's about 30 litres an hour, so about 33% more fuel consumed if unleaned.

[Flyin'Dutch']

Leaning is not just about saving money.

It is also about looking after your engine and on making sure that the aeroplane performes according to 'The Book' especially when it comes to performance and range.

Half to a whole gallon per hour 'saved' on a long trip is going to be the difference between making it to the destination or not, as planned.

[TopCat]

What's your fuel consumption, @GrahamB ? I get reliably about 26 l/hr cruising at 2200rpm (which gives me 105 KIAS on a cold day, about 98 if it's hot). That includes initial climb and descent - I can't calculate an accurate enroute value, but I typically cruise climb and descend, so (waves arms) I'm assuming the bits right at each end more or less cancel.

[Rob P]

The 108hp Lycoming on the PA22 Colt consumed 5 litres/hr more on full rich than simply leaned. Over a tenner an hour difference, and better for the engine.

I have no idea what the 180 on the RV would burn at fully rich in the cruise, I have never done it. First action at top of climb is to lean. (Also for taxi to help prevent the plugs leading-up).

Rob P

[TopCat]

First action at top of climb is to lean. (Also for taxi to help prevent the plugs leading-up).

Yes, same here.

Hoiking out the mixture knob is immediately after flaps up on vacating the runway. It always amazes me that it only has another 1/3 inch or so of travel to ICO, and that leaves ample power for driving around on the grass.

[riverrock]

Leaned on the ground reduces contamination on the plugs also - and so long as you are at low power, no thermal management issues.

I go rich when lower airflow / higher power - ie climbing - to help with cooling, and also when I might need power in a hurry (so before landing - part of my before landing checks - or doing aeros). Other than that - lean till its rough then enrichen it in a bit.

Worth noting that you may have to lean to maintain power when high or your engine wont produce full power.

[Flyin'Dutch']

@TopCat Is that an O-320 @ 140 bhp?

[GrahamB]

What's your fuel consumption, @GrahamB ? I get reliably about 26 l/hr cruising at 2200rpm (which gives me 105 KIAS on a cold day, about 98 if it's hot). That includes initial climb and descent - I can't calculate an accurate enroute value, but I typically cruise climb and descend, so (waves arms) I'm assuming the bits right at each end more or less cancel.

With the 0320 and the HC STC I get c.26lph for 105KTAS at whatever altitude I happen to cruise at, and 29 lph for 110KTAS (with the G5 setup I get an accurate TAS displayed).

[Flyin'Dutch']

Just goes to show what an efficient airframe it is.

[TopCat]

@TopCat Is that an O-320 @ 140 bhp?

It's an O-320 E2G.

Nominally 150 hp, but with a high-compression STC like @GrahamB's.

Anecdotally that makes it about 160 hp, but there's nothing in the performance numbers to reflect that officially.

I've never had anything else to compare it with, so I don't know how much difference it makes in practice. It's a very popular STC in the Grumman community though.

The obvious downside being that 100 octane fuel is required. Hopefully the 100UL will be available and approved by the time 100LL is phased out, assuming I'm still flying by then.