Max Service ceiling for commercial airplanes

wrote in news:c3217254-afdf-40c0-b87a-
:

Out of curiosity I was wondering which civilian passenger airplanes
have the highest service ceilings? Wikipedia indicates that some
business jets have ceilings greater than 53000 ft or so while the 747
has only 43000 ft. Also why do large aircraft fly much lower than
their service ceilings? Usually I never see a large jet go beyond
37000 or so even on very long haul flights. I assume they would be
even more efficient if they flew close to service ceilings on long
haul flights.


AFAIK the new Bus has one of F430 as well. You can fly right up to the
service ceiling but the max allowable FL goes down with weight. THe buffet
margins become tighter when you are heavy and the max allowable altitude
goes down accordingly,. As you burn fuel you can go up in steps, so on a
long trip you might originally be limited to say, FL330 and then after an
hour or two your limit may rise enough that you can get to 350 and then
again to 370 and so on until you either get to max or its time to come
down. The performance computer (integrated into the FMS) gives you a
constant readout of the limit.
Also, it's not so clever to go up another 4,000 feet if you're going to
have another 100 knots on your nose! A typical rule of thumb tradeoff for
wind/altitude is about 7knots per 1,000 feet, though this isn't hard and
fast.We have tables for it or you can put some projected winds into the FMS
and ask the computer to do it for you.
Another factor is the distance travelled. It makes no sense to go to 410 on
a 200 mile trip. Having said that, the ideal fuel burn profile is close to
straight up and straight down on short trips. No level cruise. IOW, you
keep climbing until you intercept the descent profile and then come down.


Bertie

"Bertie the Bunyip" wrote

Another factor is the distance travelled. It makes no sense to go to 410
on
a 200 mile trip. Having said that, the ideal fuel burn profile is close to
straight up and straight down on short trips. No level cruise. IOW, you
keep climbing until you intercept the descent profile and then come down.

Yep, I've been on flights like that. Kinda' strange.

What percentage of power are the engines normally running, on the "coming
down" portion of a flight like that?
--
Jim in NC

"Morgans" wrote in
:


"Bertie the Bunyip" wrote

Another factor is the distance travelled. It makes no sense to go to
410 on
a 200 mile trip. Having said that, the ideal fuel burn profile is
close to straight up and straight down on short trips. No level
cruise. IOW, you keep climbing until you intercept the descent
profile and then come down.

Yep, I've been on flights like that. Kinda' strange.

What percentage of power are the engines normally running, on the
"coming down" portion of a flight like that?

Idle, Right back to the stop is the ideal as far as you can safely do it.
You're supposed ot have the power up to stabilised approach power by about
1,000', bu tit's almost impossible not to touch the taps before then
because of ATC.

Bertie

Morgans writes:

What percentage of power are the engines normally running, on the "coming
down" portion of a flight like that?

Flight idle.

Mxsmanic wrote in
:

Morgans writes:

What percentage of power are the engines normally running, on the
"coming down" portion of a flight like that?

Flight idle.


And what's that, wannabe boi?

Bertie

AFAIK the new Bus has one of F430 as well. You can fly right up to the
service ceiling but the max allowable FL goes down with weight. THe buffet
margins become tighter when you are heavy and the max allowable altitude
goes down accordingly,. As you burn fuel you can go up in steps, so on a
long trip you might originally be limited to say, FL330 and then after an
hour or two your limit may rise enough that you can get to 350 and then
again to 370 and so on until you either get to max or its time to come
down. The performance computer (integrated into the FMS) gives you a
constant readout of the limit.

I see.. that actually explains what I saw on a Cathay flight across
the Pacific last year. It appeared to level off at 35 but when I
checked 6-7 hrs or so later (on the moving map) we were at 40. At the
time I thought the climb rate beyond 35 must be very slow but I think
its to do with weight as you explained.

Also, it's not so clever to go up another 4,000 feet if you're going to
have another 100 knots on your nose! A typical rule of thumb tradeoff for
wind/altitude is about 7knots per 1,000 feet, though this isn't hard and
fast.We have tables for it or you can put some projected winds into the FMS
and ask the computer to do it for you.
Another factor is the distance travelled. It makes no sense to go to 410 on
a 200 mile trip. Having said that, the ideal fuel burn profile is close to
straight up and straight down on short trips. No level cruise. IOW, you
keep climbing until you intercept the descent profile and then come down.

Bertie

wrote in
:



AFAIK the new Bus has one of F430 as well. You can fly right up to
the service ceiling but the max allowable FL goes down with weight.
THe buffet margins become tighter when you are heavy and the max
allowable altitude goes down accordingly,. As you burn fuel you can
go up in steps, so on a long trip you might originally be limited to
say, FL330 and then after an hour or two your limit may rise enough
that you can get to 350 and then again to 370 and so on until you
either get to max or its time to come down. The performance computer
(integrated into the FMS) gives you a constant readout of the limit.

I see.. that actually explains what I saw on a Cathay flight across
the Pacific last year. It appeared to level off at 35 but when I
checked 6-7 hrs or so later (on the moving map) we were at 40. At the
time I thought the climb rate beyond 35 must be very slow but I think
its to do with weight as you explained.


Yeah, that sounds like what they were doing. That'd be a typical sort of
step climb. They were probably at 370 for a while in between as well. The
rate was probaly not too bad. It's still worthwhile to go up for the sake
of an hour or two up there. A lot of fuel would be saved.


Bertie

"Bertie the Bunyip" wrote in message
.. .
wrote in news:c3217254-afdf-40c0-b87a-
:

Out of curiosity I was wondering which civilian passenger airplanes

snip

Also, it's not so clever to go up another 4,000 feet if you're going to
have another 100 knots on your nose! A typical rule of thumb tradeoff for
wind/altitude is about 7knots per 1,000 feet, though this isn't hard and
fast.We have tables for it or you can put some projected winds into the
FMS
and ask the computer to do it for you.

In the Lear we sometimes found you could climb out of the headwind. With
the 100kts on the nose at FL350, we could go to FL430 and get out of half of
it.(Westbound Winter)


Another factor is the distance travelled. It makes no sense to go to 410
on
a 200 mile trip. Having said that, the ideal fuel burn profile is close to
straight up and straight down on short trips. No level cruise. IOW, you
keep climbing until you intercept the descent profile and then come down.


The old Lears, did exactly that. They had enough thrust to go direct to
FL450 at gross, and burned so much fuel it was worth while to get high and
keep it there until you had to come down. Rule of thumb was trip distance in
tens of miles times 2 for the cruise altitude. 200nm=40,000, we would file
for 41.


Al G

"Al G" wrote in
:


"Bertie the Bunyip" wrote in message
.. .
wrote in news:c3217254-afdf-40c0-b87a-
:

Out of curiosity I was wondering which civilian passenger airplanes

snip

Also, it's not so clever to go up another 4,000 feet if you're going
to have another 100 knots on your nose! A typical rule of thumb
tradeoff for wind/altitude is about 7knots per 1,000 feet, though
this isn't hard and fast.We have tables for it or you can put some
projected winds into the FMS
and ask the computer to do it for you.

In the Lear we sometimes found you could climb out of the
headwind. With
the 100kts on the nose at FL350, we could go to FL430 and get out of
half of it.(Westbound Winter)

Yeah, we hardly ever get on top of a jetstream unless it;s very low.
Alos, we'd be wary of even trying in case we hit the cold side CAt near
our margin.


Another factor is the distance travelled. It makes no sense to go to
410 on
a 200 mile trip. Having said that, the ideal fuel burn profile is
close to straight up and straight down on short trips. No level
cruise. IOW, you keep climbing until you intercept the descent
profile and then come down.


The old Lears, did exactly that. They had enough thrust to go
direct to
FL450 at gross, and burned so much fuel it was worth while to get high
and keep it there until you had to come down. Rule of thumb was trip
distance in tens of miles times 2 for the cruise altitude.
200nm=40,000, we would file for 41.


More importantly, you had the buffet margins. We could also go to that
altitude if power were the issue, but at max gross, we're limited to
about 350 initially.