"Ben Jackson" wrote:

I think we're comparing different numbers. If your spreadsheet uses the
same times as your logbooks (engine start to engine stop) and your trips
average 2 hours of which about .3 is at low/no power (taxi, landing),
then your total number is about 17% lower (2 / (2 - 0.3)) than the
instantaneous reading you'd get in cruise, which Jay is reading off of
his EDM-700. Your 11.3 GPH would be closer to 13.3 GPH on an engine
analyzer. The shorter your average trip, the higher the actual burn
would be.

I didn't say how my spreadsheet comes up with the numbers it does, but in
fact it does not use the same times as my pilot logbook. My stated fuel
burn is per tach hour, which in my case usually works out to be uncannily
close to actual flight time, takeoff to touchdown.

Sure, I burn a little less in taxi, but I burn a little more in climb. Most
of my trip is in cruise, probably closer to 3 hours on average, so whatever
is happening there should mostly determine my results. The rest of the time
seems to average out for typical X/C work. I feel pretty good about the
number 11.3 -- that's what I use in the Hayward Air Race and it gives me
excellent results (which I have so far managed to waste by making other
stupid mistakes). My POH even says that 2300 RPM and 21" MP at 8000' should
give me 66% power on 11.2 GPH.

I've also done the exercise of taking off from PAO with full tanks (88 gal),
then flying four hours to HIO whereupon I dip my tanks and find that I've
got 42 gallons left in there. So there's just no way I could be burning 13
GPH for any sustained period of time in cruise; if I had an engine monitor
that said so, it would have to be lying.

The difference between my economy and O-470 powered C182s and Jay's
Pathfinder probably has a lot to do with having well-balanced fuel injectors
rather than a carburetor. If he's running 50+ ROP, and I'm running right at
peak or a little on the lean side, that's going to cost him an extra gallon
or two per hour. Then consider the fact that Jay probably doesn't cruise at
11,000 between Iowa City and Racine like I have to between Medford and
Redding.

In conclusion, I think it's a mistake to dismiss the IO-540 on the new
Cessnas as an insignificant update to the type. The O-470 was a good
engine, but the IO-540 rocks. It's easier to manage and more efficient.