I'm not sure. My dad gets sloppy rich with the mixture knob in our PA28 and scares me with worse-than-the-book-fuel-flows, lol. Getting 4gph in our c-150 was kind of normal, though nearly impossible in the 160hp warrior. On my best days, I could be off by .5 gph. 3.5gph was routinely doable in our 150 when me only at 170lbs and not full fuel.
I've read mike busch's arsenal of lean of peak, and then lycoming and continentals's take on it. I'm not even doing that. I've researched this stuff to about 6" thick of books worth. I've made plans for low alt and high alt flying for different gross weights for a dozen planes to prove my l/d max theory. I was never taught it. It all started one day when flying my 150 100nm in severe VFR. I could climb to 10k or 1k. What altitude to fly? I had all the variables to choose from! As a new private pilot, there were again more questions than answers.
Planes that have engine monitors have only shown me that lean of peak is not possible, or more efficient, unless the injectors are matched. AND even then, what 'the guys' don't tell us is cable creep, and injector change over time [usage] can bring the flow rates to 'unmatched' condition. Maintaining 20F of EGT is DIFFICULT AT BEST anyway. I will say it is worth it if it can be done. These operations typically record flight data - a good thing because it can change so quickly. Usually, these engine monitors allow for better leaning because we can see EQUAL cylinder stress [in the form of CHT being equal] because low power settings can't have too high an EGT, and we can put the knob anywhere. This is why we see constantly "lean below 65% power won't damage an engine" in many publicaitons... and this stands to reason because we know that we can pull that mixture as lean as possible on the ground during taxi and its only for the good.
anyway, back to our simple non-monitored plane: lean aggressively, and fly at L/D Max is all that I'm doing. I subtract speed for below gross weight accordingly. Derive how much by the planes data. If you can't figure it out, I read "Piloting to Max Performance" by Bjork. Good book. When the girlfriend is with me however, I keep it 3kts faster just to ensure the positive side of the curve and keep some speed. When flying at glide speed, the engine is slow enough that fuel burn lessens from published numbers. Its rare to see fuel flows published for the l/d max speed range. I still always use published fuel flow figures. lets stay safe now. I'm just overjoyed when I see 4 gal more in the tank at a fuel stop. Climbing for TAS does not pay unless climbing for a tailwind, both turbo and normally-aspirated. Turbo is closer anyway to economy when climbing. Each airplane will differ. Leaning w/out engine monitors is just done for smoothness and everything we've been taught. Except to the few about "do not lean below 5k'" which is totally wrong. Lean like all get out during descent because the plane richens during descent right? Leans while ascending? Keep those plugs clean!
I also pressure pattern fly and travel long distances. [search willaims best page and pm me for how] This won't affect gph, but does affect mpg and subsequently the transition of cash into logbook hours. This is a lost flying art. I fly it IFR too by just picking intersections. I fall in love with watching the gnd speed increast 3kts per 10deg turn for the entire flight. I often save 20min total one way flight time going to florida from tennessee [500nm]. 40% of the time, in reality, conditions dictate a normal direct route.
Carson speed: Before I found l/d max, I was told that this 1.3Vy is the way to go. Why? this is the speed on most general aviation planes figured to provide the most "bang for the buck" . Meaning, on the drag curve and fuel consumption graphs, the most speed comes out before drag increases exponentially. Its all exponential curves, and we have a wide range at L/D max to play with and a narrow one as drag increases with speed. Once 1.3Vy is exceeded, fuel flow increases and does not reward with as much value as the lower speed. This is almost an arbitrary speed because everyone is different.
Thanks to congress, I'm trying to increase hours for least amount of expense and go places. L/D max is best for me. If you want to fly in circles, we know that one speed of minimum sink is best, and its lower than glide speed.
I've heard of coking valves for low power settings. I'll dismiss this as an old wives tale. CHANGING THE OIL properly prevents this. I've overhauled our engines, and see what this does. Its not there. Lead damage is more threatening. Old oil breaks down around the 35+hrs mark of use, and when you see it on the stick all of a sudden drop [consumption] its time to change. don't add another quart and push it to 50hrs. Although I tell you while flying slow, I generally make it to 45-50hrs before seeing this consumption hit.
Hope this helps!
Andy <-- almost an A&P!
1100hrs in 15 years <--almost there airline job!
C-150 and PA-28 161 and 180 for time building in logbook.
P337T commercial flying
C-150 best on 50/50 mix mogas roughly [don't have it on the pa28s]
