Hi Ben

If you lived where I live, cruise altitude on almost any crosscountry
trip is based on altitude required to clear terrain.

That usually takes care of anything between 7500 and 11500ft.
After that, can we get a decent tailwind?
Can we dodge turbulence/weather?
Controlled airspace we usually fly over, or ask permission and fly
through.

So it all depends what you are calculating - time enroute , see tailwind.
Fuel burn? All I calc is that I have lots. I really don't see any great
monetary saving by selecting anything except tailwind, and I'm landing
in 2 - 3 hours anyway. That's as much as I want to handle in a 172
without a walk/washroom/coffee ion that order

HTH

Tony
--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE

In article fmLZc.105358$Fg5.1951@attbi_s53, (Ben Jackson)
wrote:

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?




--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE