Leaning... not something I have been doing!
Join Date: Mar 2007
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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?
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?
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.
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.
Join Date: Jun 2003
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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.
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.
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
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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.
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.
