Picking Optimal Altitudes

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

when I plan a flight against the wind (like a few days ago comming back from
phoenix) I go with the altitude that gives me the best ground speed.
On my way back from phoenix at 8500 ft I had a GS of 130 kts, I had to go to
10500 for terrain and my GS went down to 117 kts., so I jumped back down to
8500 when I had the chance.

Turbo airplanes take advantage of the thinner air up high is why they can go
faster then normally aspirated planes. you maintain your full 200 HP up to a
DA of 12,000 ft. So 12000 ft is where you start to lose horse power but the
air is thinner allowing you a better TAS and if you play the winds right,
some really good ground speeds. stay low if you have a head wind, get up
high when you have a tail wind.

Sometimes, the wind down low will be higher then say around 10,000 or 12000
ft or about the same. If there is not much difference in the winds, I would
select the higher altitude because of the thinnner air. Also you dont use as
much fuel up high.


"O. Sami Saydjari" wrote:

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

I travel about 8-10 thousand into the wind and 14-20 with the wind. I agree.
Usually the headwind increases faster than TAS with altitude. I travel 8-10
for safety--glide distance.



"Jeff" wrote in message
...
when I plan a flight against the wind (like a few days ago comming back
from
phoenix) I go with the altitude that gives me the best ground speed.
On my way back from phoenix at 8500 ft I had a GS of 130 kts, I had to go
to
10500 for terrain and my GS went down to 117 kts., so I jumped back down
to
8500 when I had the chance.

Turbo airplanes take advantage of the thinner air up high is why they can
go
faster then normally aspirated planes. you maintain your full 200 HP up to
a
DA of 12,000 ft. So 12000 ft is where you start to lose horse power but
the
air is thinner allowing you a better TAS and if you play the winds right,
some really good ground speeds. stay low if you have a head wind, get up
high when you have a tail wind.

Sometimes, the wind down low will be higher then say around 10,000 or
12000
ft or about the same. If there is not much difference in the winds, I
would
select the higher altitude because of the thinnner air. Also you dont use
as
much fuel up high.


"O. Sami Saydjari" wrote:

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

"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?

The 2 kts per 1000 feet seems about right. The speed increase is due
to the fact that the turbo allows the engine to maintain power output
at a much higher elevation than a normally aspirated engine. The
increased power output coupled with thinner air allows the plane to go
faster.

Generally speaking, the winds above 10k are out of the west, and can
be strong enough to negate the speed advantage of the turbo. On these
trips, it makes sense to fly lower. Going Eastbound, you will
generally want to fly high to take advantage of both the high TAS and
the large tailwinds.

There are exceptions however, so you need to look at the forecast and
PIREP'ed winds aloft as part of your flightplanning to decide whether
or not it makes sense to climb high.

However, you will find many times that having a turbo and oxygen are a
great advantage no matter what the winds aloft. Just last week, I was
on top of a rising cloud layer at 10,000 in my Cherokee, a smooth ride
and in the sun. (The clouds were ~9kft thick at my location.)
However, as I traveled North, I was to pass a weak cold front, and the
temps were already dropping. I considered climbing higher, but had
visions of my Cherokee struggling to outclimb iceladen clouds, and of
course the hypoxia issues as one continues climb... I ended up
descending and flew 2 hrs in bumpy, rainy IMC. Not much fun, but I
kept the OAT above zero and made it to my destination no problems.

If I had turbo and oxygen, I would have zipped up to 12,14,16,
whatever it took to clear the clouds, enjoyed a smooth ride home in
the sun, and an easy descent in the better weather at my destination.

-Nathan

"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?

You need to run the performance charts against some actual weather. Use
ADDS for wind and everything else. Up wind and downwind are completely
different exercises. Every day is different but patterns will quickly
develop with experience. The turbo changes things a bit. Hit the books
with some actual weather.

In article , "O. Sami Saydjari"
writes:

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?


Yes, but it is generally smoother up higher.

Chuck

In a previous article, said:
When planning a flight against the wind, how to you pick the best
altitude when trying to minimize flight time?

Since Santa was good to me and I now have the complete Sporty's Air Facts
on DVD, I've now seen Richard Collins say several times that he chooses
his altitude based on finding a smoother ride rather than a faster trip.
Of course, he's got a pressurized and turbo charged P-210, so he's got a
lot more choice of altitude than I do.


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kindled, flamed and, on occasion, extinguished and mourned." -deCadmus

Lazy people (like me) ask their computer. FlightStar from Jepp has an
"optimize altitude" function that is pretty handy. Once it has downloaded
DUATs weather it will display groundspeed and fuel burn for all altitudes
and highlight the optimal flight level.

"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

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

McGregor wrote:
: Lazy people (like me) ask their computer. FlightStar from Jepp has an
: "optimize altitude" function that is pretty handy. Once it has downloaded
: DUATs weather it will display groundspeed and fuel burn for all altitudes
: and highlight the optimal flight level.

Although I can do it by hand, I find it much more convenient to have DUATS do
it for me. Since I fly a non-turbo'd Cherokee, I'm effectively relegated to 10kft or
less. A quick check of winds aloft, and maybe two or three altitudes with DUATS flight
planner (it corrects for current wind) and see where I end up. On the fly, I pretty
much figure I need about 5 kt difference in wind to counteract a 2000' climb/descent.
Unfortunately, the nicer the weather (this time of year in particular), the higher the
pressure and bigger the headwind for a westly flight is. Even skimming the trees at
1000' AGL doesn't usually help, so I end up climbing for smoothness and happy engine at
6-10k.

-Cory


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