Does cruise altitude matter?

(Ben Jackson) wrote in news:fmLZc.105358$Fg5.1951@attbi_s53:

For a non-turbocharged piston airplane, does cruise altitude really
matter? I made a complicated spreadsheet which produces a fairly simple
answer: Unless you climb way above your critical altitude, trip time
and fuel burn don't vary much at all. Over a 500nm trip, it only takes
about 4% longer to fly at 3000MSL instead of 7000 (approximately critical
altitude) and 7% longer if you go clear up to 13000. For my plane that's
a difference of about 7-15 minutes out of 3+ hours.

How high does your critical altitude have to be (due to turbocharging
or jet/turbine) before it really starts to matter what your cruising
altitude is?


How are you factoring wind into your spreadsheet? I have tried the same on
DUATS and came to the same conclusion as you. The difference is pretty
minimal in most cases, except when there is an inversion layer with a high
speed flow above it. In that case, it makes sense to climb up to catch that
flow (or stay below if you are going against it). I found that in most
cases the difference in enroute time is less than 5 minutes even for trips
as long as 3 hours.