Fred,
Verrrry interrrresting! On a pleasure flight yesterday, I wanted to
get a certain data point for LOP and ROP at reduced power. Here is what it
looked like in the style you used.
I was at 4400 MSL (6210 Dalt), 22.7" MAP, 2330 RPM (maybe 65% power????) in
an auto pilot managed flight (similar to your 4K numbers). @50 LOP, 5.8
gph and 169 KTAS (3.43g/100nm). @100 ROP, 7.9 gph and 181 KTAS
(4.36g/100nm). A 7% increase in speed cost a 27% increase in fuel
consumption. Much like the ROP comparison you gave.
Maybe I will go after more data points - but only on real trips as the
costs are not worth getting "experimental" support for the truth as we know
it (see emboldened, slanted and underlined text below).
Grayhawk
In a message dated 7/12/2008 4:13:00 P.M. Central Daylight Time,
fredmoreno@optusnet.com.au writes:
I took the best (least scatter,
most consistent) sets of runs for my typical cruise conditions (8500 Feet,
55-65% power,50F lean of peak) and then compared to the Cessna/Columbia 350
performance tables from the pilots operating handbook that was once available
at the Columbia web site. I found that if I multiplied the
Columbia 350 speed by 1.27, I got a very good fit over the
full speed range I have examined.
I then plotted the modified
Columbia figures and with an Excel spread sheet I generated
tables and then curves for gallons/100 nautical miles as a measure of fuel
economy. I argue that this provides the best measure of comparative
operating costs, better than miles per gallon which distorts the
presentation. Here are the results.
.................
These curves support
previous suggestions for economical flying: fly slower, fly higher, and fly lean
of peak.
...............
But the cost of cranking it up to
75% and running rich of peak is +20% in cost while gaining only about +6% in
speed. Or, if you like, it costs 20% more to arrive 3.6 minutes sooner for
each hour of flight.