"Ben Jackson" wrote in message
news:fmLZc.105358$Fg5.1951@attbi_s53...
For a non-turbocharged piston airplane, does cruise altitude really
matter?

Well, according to the numbers you've provided, it makes between a 4% and 7%
difference. Whether that "matters" is up to each pilot, of course.

As George says, there's more to picking a cruise altitude than airspeed. At
the very least, groundspeed is an issue, and total trip time will be
affected by routing, which may be affected by cruise altitude.

Airspeed is not a very common priority for non-turbocharged airplanes with
respect to cruise altitude.

[...]
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?

The right question to ask is "how long does a trip need to be?" Assuming no
wind, you will always go faster climbing higher in a turbocharged airplane,
until reaching your critical altitude. The only question is how long you
need to fly at that faster speed to make up the time spent climbing. And
that depends on the airplane, and the loading for that day (factors that
affect the time to climb).

But again, there are other issues, and especially in a turbocharged
aircraft, it's unusual to find a no wind situation when you get to the
altitudes where the turbo is really helping.

In my turbocharged airplane, I fly as high as seems practical for the length
of the trip. Local flights, often only 30-45 minutes long, I rarely get
above 2000' AGL. For a long cross-country of 2-4 hours in length (I try to
avoid longer flights, as my bladder protests too much ), I will climb to
anywhere between 10,000' and 16,000', depending on the length of the trip,
winds aloft, whether I have to spend a portion of the trip underneath Class
B airspace (limiting my climb), and a number of other factors.

Pete