UdoR wrote:
How can I fly at best speed, but staying out of the red box on the lean side? Because I, too, wouldn’t fly at, say, 90 or 100 kts knowing that I could fly at 150 or 160 kts indicated (or only when there is a reason to do so, like sightseeing). This is why I started to research on how to get there without “crossing to the rich side” (although the temptation is strong from the rich side and power it will give to you! :-) .
I think you will find the answer again in the POH. Basically, below say 75% Power all LOP will do is to decrease fuel flow and TAS by a small percentage. In practical matter, if you find out the most economical long range cruise from the POH and fly that regime LOP, you will see something a bit slower and economical almost parallel to the best economy setting. MPG will rise slightly, so will the range. But maybe more importanly, flying LOP according to John Deakin and many others will increase your engine life. And that is a big factor into economy.
There may be a second order benefit of LOP if you employ reduced RPM at the same time, so the leaner mixture gets burnt better, in our fixed ignition timing engines which have the timing optimised for the max power operating point (all 3 levers forward) without melting the cylinder heads 
Antonio wrote:
I do not think there is a significant MPG difference between actual peak EGT and 50LOP
Peter wrote:
It is way more than you get between peak EGT and any amount of LOP.
There should be no difference in MPG at all. Theoretically, it is the gas that produces power/thrust and if there is enough air to burn it all up, the resulting power is the same. At 50LOP the CHT might be cooler than at peak EGT.
When there is too much air, the combustion will be worse (one-sided, or incomplete, or rough) and the efficiency will drop again. So best efficiency is the stoichiometric combustion at peak EGT. You go below peak EGT to cool the cylinder by extra air, not to improve MPG.
(However, I cannot tell that I would see lower CHT when flying LOP than compared to flying peak EGT. Still investigating on that, though)
Mooney_Driver wrote:
Oh I think quite a few are very interested in efficiency, otherwise neither the Comanche nor the whole Mooney brand would never have been as successful as they were.
Mooney_Driver, good to have some input here, and no offense was intended by my post.
I achieve quite similar results from calculations for my plane, where speed surprisingly (for me) seems to be a negligible factor in relation to MPG. Therefore, reducing speed doesn’t help to improve MPG.
But to give an example, it does make a quite a difference whether flying LOP or ROP. And at least for my engine, I cannot fly LOP with higher power settings – and as far as I know or heard, this concerns literally any aircraft engine. So one decision is, will I fly LOP or will I fly ROP.
So – at least for me – the real question to be answered is: How can I fly at best speed, but staying out of the red box on the lean side? Because I, too, wouldn’t fly at, say, 90 or 100 kts knowing that I could fly at 150 or 160 kts indicated (or only when there is a reason to do so, like sightseeing). This is why I started to research on how to get there without “crossing to the rich side” (although the temptation is strong from the rich side and power it will give to you! :-) .
And as far as I can oversee this, two improvements to achieve this are: reduce RPM (which contributes to lower CHT, which is even more important than the resulting higher prop efficiency) and fly “on the step”. But so far I haven’t met lots of pilots who concern about this, or to put it the other way round: I wished it would concern more than it seems to do.
But enough written.
In fact, for the same power level, I do not think there is a significant MPG difference between actual peak EGT and 50LOP .
Peter wrote:
more than you get between peak EGT and any amount of LOP.
At power settings of 65% or higher, especially on TC aircraft, peak EGT is not a good proposition, so a fairer comparison is 100ROP vs 50LOP, and that is over 20% MPG delta
Yes; winds make a huge difference in piston GA. And another huge factor is range; if you can avoid a refuel stop you save enough time to rival a turboprop which had to stop.
Surely the most economic airspeed for an A-to-B flight uwill depend on head/tail wind component?
Posts about “the step” moved to thread about the step
I think, referring to my original post, 5% is well worth having. It is way more than you get between peak EGT and any amount of LOP.
Mooney_Driver wrote:
UdoR wrote:
I’m quite disappointed to see that so few pilots concern about efficiency.
Oh I think quite a few are very interested in efficiency
I agree…be it because of fuel costs, total operating costs, environmental or other reasons, a lot of us are interested in efficiency.
I just think that in a typical European flying environment, efficiency is much more driven by factors other than RPM as discussed above. Not least because as discussed not all the available RPM range is practical for a variety of type-specific reasons.
In my view the following factors play a bigger role than RPM in the trip efficiency, beyond mpg (ie fuel or other cost to go from A to B ) with a guess-number of resulting variability on a given flight all else being equal:
Of course they are influenced by flight rules, weather, aircraft type, loading, trip distance, tripgoals (sightseeing?), pilot-aircraft contractual relationship, etc…
A very interesting discussion , but it is diverting way beyond the OP into overall efficiency!
