On 29-Dec-2004, Helen Woods wrote:

In defense of 6 cylinders, many are older low compression ones like mine
which means one can burn auto fuel. Asuming one has an airport with
auto fuel available the cost difference is about $1/gallon which at 9g/h
leads to a savings of $16,200 over an 1800h TBO period. This pays for
the cost of the overhaul.

But then again, most 6 cyl engines (with the exception of the old Cont.
O-300) burn a lot more than 9 gph at typical cruise settings. Also, most
low compression engines are carbureted, with lower efficiency than injected
engines of similar power. For example, hourly fuel burn of a Lyc. O-360
(180 hp carbureted) is very close to that of their IO-360 (200 hp injected)
at equal percentage power settings.

Helen's main point is a good one, though. With fuel prices soaring,
efficiency, or possibly the ability to use cheaper autogas, is a big issue
for total operating cost. This is particularly true for well-utilized
airplanes where fixed costs (insurance, hangar/tiedown rental, etc) are a
smaller fraction of total cost.

Another factor in relative efficiency is retractable vs fixed gear. A 200
hp 4-place retractable will have about the same speed as a 240 hp 4-place
fixed gear plane. Think Arrow vs Dakota or Cardinal RG vs C-182. In
cruise, the RG will probably burn about 3 gph less than the FG. At 150
hours/year and $3.00/gal, that's $1,350/year. Much, much more than the
extra cost of maintenance likely required for the RG and possibly slightly
higher insurance premiums. So you end up saving money with the RG, as long
as you remember to lower the gear for landing!

--
-Elliott Drucker