Max Service ceiling for commercial airplanes

D Ramapriya wrote in
:

On Jan 30, 3:48*pm, Bertie the Bunyip wrote:
D Ramapriya wrote
innews:2690baef-0857-4600-a0c5-4
:

On Jan 30, 2:33 pm, Bertie the Bunyip wrote:
D Ramapriya wrote
innews:24252c28-895a-44da-bd25-







m:

On Jan 30, 2:08 pm, Bertie the Bunyip wrote:
D Ramapriya wrote in
news:2ff47125-cffd-4909-b028-
:

On Jan 30, 8:41 am, WingFlaps wrote:
On Jan 30, 2:03 pm, wrote:

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.

Could be due to weight? When you fly across the Pacific the
plane can only get higher as fuel is burned.

Get higher? I thought that's what the continual small
adjustments effected by the trim wheels do to preclude,
especially with the AutoPilot engaged?

Huh?

Bertie

I meant to say that the AP will ensure that you keep flying at
the programmed altitude (through trim and throttle changes)
instead of letting the plane go higher with diminishing weight.
Have I missed something?

We get cleared to an altitude and have to hold that altitude to
avoid running into other airplanes. The autopilot does not just go
where it pleases.

My point exactly,

No, it wasn't. you said that the AP will ensure that you keep flying
at the programmed altitude throught trim and throttle changes.
It won't.


So the AP's FD Altitude Controls do what?


The FD and the autopilot are two different things.


Bertie

Bob Moore wrote in
46.128:

wrote
Also why do large aircraft fly much lower than
their service ceilings? I assume they would be
even more efficient if they flew close to service
ceilings on long haul flights.

A couple of reasons...........First, something known as "Optimum
Altitude". As an aircraft climbs, its true airspeed (Mach Number)
increases, and at high Mach Numbers, there is a rapid increase in
Drag. This results in a higher fuel burn at cruise altitudes above
Optimum Altitude. So as the aircraft climbs above optimum, there
is an increase in fuel burn and a decrease in buffet boundry margins.
At the aircraft's maximum altitude, there is literly NO buffet boundry
margin, ie. Mach buffet equals Stall buffet equals Coffin Corner.

Actually, at max, you still have your margin, whatever that may be,1.4,
1.25 or whatever, unless you go right up past that to the point where
you get low and high speed buffet at the same time. It's not the high
mach number increasing the drag. .80 is .80 whether you are at 260 or
410. The drag past optimum comes from the incipient buffet caused by the
increasing mach of the air accelerating around the wing due to the
increasing alpha. Splitting hairs, I know..

Second, time for an Emergency Descent. FAR 25.841 (copied below)
limits the maximum useable altitude. The B-707 that I flew for 17
years was limited to FL410 just due to the time required for the idle
power,gear down, speed brakes extended, max gear extended speed
descent,
while the Air Force flew them to FL420.

We don't put the gear down for a blowout anymore. Don't know why. The
gear doors are even less limiting than they used to be...


Bertie

On Jan 30, 6:11*pm, Bertie the Bunyip wrote:
D Ramapriya wrote :


We get cleared to an altitude and have to hold that altitude to
avoid running into other airplanes. The autopilot does not just go
where it pleases.

My point exactly,

No, it wasn't. you said that the AP will ensure that you keep flying
at the programmed altitude throught trim and throttle changes.
It won't.

So the AP's FD Altitude Controls do what?

The FD and the autopilot are two different things.

Bertie


Fair enough but I was talking (loosely, admittedly) of what the AFDS
commands and gets done.

Ramapriya

D Ramapriya wrote in
:

On Jan 30, 6:11*pm, Bertie the Bunyip wrote:
D Ramapriya wrote
innews:d6cd3158-6cb0-4ffd-927c-5
:


We get cleared to an altitude and have to hold that altitude to
avoid running into other airplanes. The autopilot does not just
go where it pleases.

My point exactly,

No, it wasn't. you said that the AP will ensure that you keep
flying at the programmed altitude throught trim and throttle
changes. It won't.

So the AP's FD Altitude Controls do what?

The FD and the autopilot are two different things.

Bertie


Fair enough but I was talking (loosely, admittedly) of what the AFDS
commands and gets done.


Uh, no you weren't


You were talking about what you imagine they do based on what you've
read in the latest issue of "Take Off!"

Get the litle Spitfire finished yet?

Bertie

Dan wrote:

I've been on commercial flights up to FL410, and (I beleive) FL430.
These were long-haul international flights.

--Dan

I've been on a commercial flight that was at ~FL600.

On Jan 30, 6:36*pm, Bertie the Bunyip wrote:
D Ramapriya wrote :





On Jan 30, 6:11*pm, Bertie the Bunyip wrote:
D Ramapriya wrote
innews:d6cd3158-6cb0-4ffd-927c-5
:

We get cleared to an altitude and have to hold that altitude to
avoid running into other airplanes. The autopilot does not just
go where it pleases.

My point exactly,

No, it wasn't. you said that the AP will ensure that you keep
flying at the programmed altitude throught trim and throttle
changes. It won't.

So the AP's FD Altitude Controls do what?

The FD and the autopilot are two different things.

Bertie

Fair enough but I was talking (loosely, admittedly) of what the AFDS
commands and gets done.

Uh, no you weren't

You were talking about what you imagine they do based on what you've
read in the latest issue of "Take Off!"

Get the litle Spitfire finished yet?

Bertie


Try and stop projecting, Bertie.

Ramapriya

D Ramapriya wrote in
:

On Jan 30, 6:36*pm, Bertie the Bunyip wrote:
D Ramapriya wrote
innews:efc9979a-39c2-404c-8460-9
:





On Jan 30, 6:11*pm, Bertie the Bunyip wrote:
D Ramapriya wrote
innews:d6cd3158-6cb0-4ffd-927c-5
:

We get cleared to an altitude and have to hold that altitude
to avoid running into other airplanes. The autopilot does
not just go where it pleases.

My point exactly,

No, it wasn't. you said that the AP will ensure that you keep
flying at the programmed altitude throught trim and throttle
changes. It won't.

So the AP's FD Altitude Controls do what?

The FD and the autopilot are two different things.

Bertie

Fair enough but I was talking (loosely, admittedly) of what the
AFDS commands and gets done.

Uh, no you weren't

You were talking about what you imagine they do based on what you've
read in the latest issue of "Take Off!"

Get the litle Spitfire finished yet?

Bertie


Try and stop projecting, Bertie.

Yeah, an IKYABWAI poast.


That'll fool 'em.

Bertie

Clark wrote in news:Xns9A354D69FC171ch2uswestnet@
64.209.0.90:

Peter Clark wrote in
:

On Wed, 30 Jan 2008 02:44:29 -0800 (PST), D Ramapriya
wrote:


My point exactly, in response to WingFlaps' "When you fly across the
Pacific the plane can only get higher as fuel is burned".

The AP will anon go where it pleases too on the next-generation
'Buses, albeit in exceptional circumstances. From what I've read, if
there's a TCAS warning, the decision will be taken out of the pilots'
hands and the AP will command as needed to avoid a collision.

Ramapriya

Google "step climb".

better yet, google cruise climb


Different thing altogether.


It;'s a speed selected to optimise the climb in order to get a speed that
will give you a better performance, whether that be time point to point, or
fuel economy. IOW you sacrifice a tiny bit of your ROC in order to get a
disproportianate increase in speed. Works in anything to some extent or
another.

Bertie

Gig 601XL Builder wrote in news:13q134hrfmbhv24
@news.supernews.com:

Dan wrote:

I've been on commercial flights up to FL410, and (I beleive) FL430.
These were long-haul international flights.

--Dan

I've been on a commercial flight that was at ~FL600.


Not technically commercial since it didn't make money!

You were on a socialist flight!

Bertie

Bertie the Bunyip wrote:
Gig 601XL Builder wrote in news:13q134hrfmbhv24
@news.supernews.com:

Dan wrote:

I've been on commercial flights up to FL410, and (I beleive) FL430.
These were long-haul international flights.

--Dan
I've been on a commercial flight that was at ~FL600.


Not technically commercial since it didn't make money!

You were on a socialist flight!

Bertie


Good point.