Picking Optimal Altitudes

Stan, It guess I was too lazy to try to compute the flight plan several
different ways. Your note, and one other made me dust off the math
knowledge and do some of that there fancy ciphering (hearing "weeeee
dogies" in the background...said with hillbilly accent, of course).

For a mythical plane that climbs 1000 fpm at 100 nm/hr and cruises at
150 nm/hr and a service ceiling of 20,000 ft. Comparing flight at 1000
ft agl versus 18,000 agl....for a 100nm trip one's tailwind would have
to be about 40nm better at 18,000 compared to 1000 ft. For a trip
distance of 200, the tailwind would only need ot be about 14nm/hr more
favorable. For a 700 mile trip (one that I will be making fairly
often), the winds only need to be about 3nm/hr more favorable.

Now, I just hope the mythical heater is powerful enough so that I do not
freeze my butt off at those altitudes.

-Sami

Stan Prevost wrote:
I generally run several flight plans at different altitudes, accounting for
the differences in true air speed, wind speeds, and time to climb and
descend. More often than not, I find that the extra time to climb uses up
the gains in TAS at altitude, and winds are the only factor that make a
significant difference. If the flight is long, say 3-4 hours, then the
climb can be worth it, but for less than a couple of hours, it usually is
not. I fly behind a turbocharged engine and have built-in oxygen, so I can
go anywhere up to 18-20K, but usually stay below 12K or so unless there is a
net advantage due to wind. I like to stay high enough to keep from having
to switch from centers to approach controls all the time and to get above
the haze layer for a smoother ride. But sometimes the high winds just force
you down into the turbulence and traffic at 3-4K.

Stan

"O. Sami Saydjari" wrote in message
...

When planning a flight against the wind, how to you pick the best
altitude when trying to minimize flight time?

If I read my performance charts correctly, my aircraft (Piper Turbo
Arrow III -- service ceiling 20,000 ft) seems to gain about 2 nts of
*true* airspeed for every 1000 feet you go up. Firstly, does that sound
about right to folks? I assume that this effect is from the decrease in
air friction at high altitudes (even though the prop also has less air
to "push on").

So, unless there is some other factor, I think this means that if the
winds increase at anything higher than 2 nts per 1000 feet, I am best
off staying at the Minimum Enroute Altitude. Is that right?

My experience thus far suggests that most of the time, the winds aloft
speed increase far faster then 2 nts per 1000 feet, so, in general, it
is unlikely that I will do much better than staying at the absolute
minimum altitude. Is that consistent with other folks' experience?

-Sami