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.

On Jan 29, 6:03*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.

Just guessing, but perhaps the smaller cabin size handles the larger
differential pressure reqiuired better than a big cabin. The extra
expense (and weight) to reinforce a large cabin (ie. heavy jet size)
may not be worth it.

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

--Dan

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.

Cheers

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?

Ramapriya

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.


Weight is a consideration. Even when riding along in Lears, we started
off in the mid 30's. As we burned off fuel, we could efficiently climb,
in stages.. and our final cruising altitude was around 43-45,000 feet.

My PIC told me that if he tried to push the climb any harder, he simply
burned fuel at a faster rate with a poor return on the investment. I was
cabin crew, not front office, but it was still a kick listening to the
airliners trading bumpy ride reports in the FL 300's and we chime in
with smooth rides in the FL400's.. knowing they wont be able to get there.

I'm sure cabin differential is a factor as well. Higher pressurization
differentials require a more robust pressure vessel, which weighs more.
Its a trade-off at the design stage. Flying too high would raise the
cabin altitude too high, despite pressurization, and require oxygen for
the crew and or cabin.

just my 2 cents
Dave

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

Dan > wrote in news:de91fd98-be3f-4ccb-bef2-79e2ec0dc076
@s13g2000prd.googlegroups.com:

> On Jan 29, 6:03*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.
>
> Just guessing, but perhaps the smaller cabin size handles the larger
> differential pressure reqiuired better than a big cabin. The extra
> expense (and weight) to reinforce a large cabin (ie. heavy jet size)
> may not be worth it.

Nah, the reason the little ones can go so high is cause nobody minds if
they do!
They're not constrained by revenue considerations and can have fighter jet
type wings and other shapes to allow good buffet margins up there. You
couldn't get a 747 up that high without buffeting it out of the sky unless
it were empty and out of gas!
The pressurisation wouldn't be able for 510 in a 747 because they woulnd't
make it any tougher than they needed to.
I can't see anyone allowing a pax airplane up above 430 anytime soon for
the simple reason a rapid blowout would kill a hefty percentage of the
people on board.
Even 430 isn't going to be pretty. Anything above 350, in fact, is going to
hurt some people pretty bad.
Until a manufacturer comes up with a technology that ensures a greater
margin of safety above 430 you won't see an airliner certified above that.


Bertie

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

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?

Ramapriya

D Ramapriya > wrote in
:

> 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. Not yet, anyway.


Bertie

On Jan 30, 2:33 pm, Bertie the Bunyip > wrote:
> D Ramapriya > wrote :
>
>
>
> > 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, 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

Remember the Concorde?

From Winipedia:

delta-winged ("OG delta wing") aircraft with four powerful Olympus
engines based on those originally developed for the Avro Vulcan
strategic bomber. The engines were jointly built by Rolls-Royce and
SNECMA. Concorde was the first civil airliner to have an analogue fly-
by-wire flight control system. It also employed a trademark droop
snoot lowering nose section for visibility on approach.

These and other features permitted Concorde to have an average cruise
speed of Mach 2.02 (about 2,140 km/h or 1,330 mph) with a maximum
cruise altitude of 18,300 metres (60,000 feet), more than twice the
speed of conventional aircraft. The average landing speed was a
relatively high 298 km/h (185 mph, 160 knots).
On Jan 29, 8:03 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.

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".

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.

Oh - Hey Bertie, any TCAS system ever hooked up to feed autoflight? I
can't think of any.

D Ramapriya > wrote in
:

> 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.


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.
>


You're talking straight out of your ass.


Bertie

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.
>
> Oh - Hey Bertie, any TCAS system ever hooked up to feed autoflight? I
> can't think of any.
>

Jesus. you wouldn't want that at the moment. there will probably come a
time, but this guy is just spouting **** he;s read in Flight International
with no understanding of what's going on.


Bertie

if the plane can go higher vs. the plane being commanded to go higher are
two different things.

"D Ramapriya" > wrote in message
...
> On Jan 30, 2:33 pm, Bertie the Bunyip > wrote:
>> D Ramapriya > wrote
>> :
>>
>>
>>
>> > 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, 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

On Wed, 30 Jan 2008 12:19:58 +0000 (UTC), Bertie the Bunyip >
wrote:

>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.
>>
>> Oh - Hey Bertie, any TCAS system ever hooked up to feed autoflight? I
>> can't think of any.
>>
>
>Jesus. you wouldn't want that at the moment. there will probably come a
>time, but this guy is just spouting **** he;s read in Flight International
>with no understanding of what's going on.

Yea, I figured that. I didn't know if there was something special in
the 380, but I couldn't think of any product where TCAS would jump in
and override the MCP.....

Peter Clark > wrote in
:

> On Wed, 30 Jan 2008 12:19:58 +0000 (UTC), Bertie the Bunyip >
> wrote:
>
>>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.
>>>
>>> Oh - Hey Bertie, any TCAS system ever hooked up to feed autoflight?
>>> I can't think of any.
>>>
>>
>>Jesus. you wouldn't want that at the moment. there will probably come
>>a time, but this guy is just spouting **** he;s read in Flight
>>International with no understanding of what's going on.
>
> Yea, I figured that. I didn't know if there was something special in
> the 380, but I couldn't think of any product where TCAS would jump in
> and override the MCP.....

No, and in fact we're required to disconnect everything, including the
autopilot to ensure we stay outside of the TCAS "doghouses" which are
red boxes that apear on the flight director. We just pitch the airplane
out of them. The autothrotles aren't considered to be up to the task
either. ( sorry don't know if you nw this, just for th ebenifit of
anyone who's wondering wtf we're talking about.)

Berti
>

On Jan 30, 3:48*pm, Bertie the Bunyip > wrote:
> D Ramapriya > wrote :
>
> > 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 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.
>
> You're talking straight out of your ass.
>
> Bertie


Very old hat... http://tinyurl.com/jfwe6.

Ramapriya

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.

Gig 601XL Builder > wrote in
:

> 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.
>

Hehe.
Bertie

Bertie the Bunyip wrote:
> Gig 601XL Builder > wrote in
> :
>
>> 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.
>>
>
> Hehe.
> Bertie


But it was the coolest flight I've ever taken commercial. First, I was
only 13 at the time and I got to sit in the jump seat for about 30
minutes including the supersonic transition. And while it was pretty
much a non-event it would have been hard to prove that to a 13 year old
would be pilot.

Gig 601XL Builder > wrote in
:

> Bertie the Bunyip wrote:
>> Gig 601XL Builder > wrote in
>> :
>>
>>> 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.
>>>
>>
>> Hehe.
>> Bertie
>
>
> But it was the coolest flight I've ever taken commercial. First, I was
> only 13 at the time and I got to sit in the jump seat for about 30
> minutes including the supersonic transition. And while it was pretty
> much a non-event it would have been hard to prove that to a 13 year
old
> would be pilot.
>

Cool. I'd like to have flown it. Who wouldn't?
I have no idea how they got around the various de-pressursation issues.
If there had been a rapid depressurisation at that altitude, well,
oxygen masks wouldn't have saved anyone. I used to know an ex FE on one,
but i never got to ask him much about it.


Bertie

Hi,

In article >,
Bertie the > wrote:
> Cool. I'd like to have flown it. Who wouldn't?
> I have no idea how they got around the various de-pressursation issues.
> If there had been a rapid depressurisation at that altitude, well,
> oxygen masks wouldn't have saved anyone. I used to know an ex FE on one,
> but i never got to ask him much about it.

You could ask Anthony. It was in one of the versions of MSFS but not in the
more recent ones.

Perhaps it was unreliable at that altitude so they removed it? :)

Andy

Andy Hawkins > wrote in
:

> Hi,
>
> In article >,
> Bertie the > wrote:
>> Cool. I'd like to have flown it. Who wouldn't?
>> I have no idea how they got around the various de-pressursation
>> issues. If there had been a rapid depressurisation at that altitude,
>> well, oxygen masks wouldn't have saved anyone. I used to know an ex
>> FE on one, but i never got to ask him much about it.
>
> You could ask Anthony. It was in one of the versions of MSFS but not
> in the more recent ones.
>
> Perhaps it was unreliable at that altitude so they removed it? :)


Yes, must strive for ultimate reality!


Bertie

"Dan" > wrote

Just guessing, but perhaps the smaller cabin size handles the larger
differential pressure reqiuired better than a big cabin. The extra
expense (and weight) to reinforce a large cabin (ie. heavy jet size)
may not be worth it.

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

I would think it is primarily an economic decision. More fuel to climb
higher, justified only if you can stay that high for a very long time.

Then it also could be the narrowing of the range of speed in "coffin
corner."

Perhaps a real ATP will enlighten us. That isn't me! <g>
--
Jim in NC

"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

> They're not constrained by revenue considerations and can have fighter jet
> type wings and other shapes to allow good buffet margins up there. You
> couldn't get a 747 up that high without buffeting it out of the sky unless
> it were empty and out of gas!

Is this buffeting related to slow flight? I now remember reading
somewhere, maybe in stick and rudder that large jets do not want to
risk flying very high up at a low airspeed because of the possibility
of an inadvertent stall during turbulence (not sure how much
turbulence exists at FL600 though).

On Jan 30, 11:44*pm, D Ramapriya > wrote:
> On Jan 30, 2:33 pm, Bertie the Bunyip > wrote:
>
>
>
> > D Ramapriya > wrote :
>
> > > 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, 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.

No, I think you are confused. Altitude is _not_ commanded, Only
thrust and aoa (CL) are commanded flight variables. The plane always
adopts an altitude where lift=weight. The lift is set by the point
where thrust equals drag, the latter set by airspeed, density and CL.
So once you have climbed to maximum altitude (for given fuel burn) you
will gradually drift up as fuel burns. If the max fuel burn is set by
range (e.g. across pacific) or engine performance I think it follows
that max (and/or best cruise) altitude is set by weight OK?

You might command an AP to go to max altitude but if the plane is too
heavy it won't get there and will fly along in a climb attitude (and
maybe even stall at high altitude) until enough fuel has burnt off to
allow it to get there.

Cheers

wrote in
:

>
>> They're not constrained by revenue considerations and can have
>> fighter jet type wings and other shapes to allow good buffet margins
>> up there. You couldn't get a 747 up that high without buffeting it
>> out of the sky unless it were empty and out of gas!
>
> Is this buffeting related to slow flight? I now remember reading
> somewhere, maybe in stick and rudder that large jets do not want to
> risk flying very high up at a low airspeed because of the possibility
> of an inadvertent stall during turbulence (not sure how much
> turbulence exists at FL600 though).


Well, actually it;s low and high. When the air going over a wing that's
traveling close to supersonic is accelerated futher by the action of the
wing, it goes supersonic over the wing. When you go too fast, max mach, you
get a loss of lift. When you go too slow, you accelerate the air over the
top of wing as well due to increased angle of attack. If you load the wing
up with weight or G (same thing as far as the wing is concerned) same thing
happens. The air buffeting from the shock wave is similar to a stall ( some
sources call it a stall) and loss of control and altitude results. Recovery
can be difficult, though not impossible. There are a number of other facors
at play here, but that's the meat of it.

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
:

>
>> They're not constrained by revenue considerations and can have
>> fighter jet type wings and other shapes to allow good buffet margins
>> up there. You couldn't get a 747 up that high without buffeting it
>> out of the sky unless it were empty and out of gas!
>
> Is this buffeting related to slow flight? I now remember reading
> somewhere, maybe in stick and rudder that large jets do not want to
> risk flying very high up at a low airspeed because of the possibility
> of an inadvertent stall during turbulence (not sure how much
> turbulence exists at FL600 though).
>
>
>

You can google the Advisory Circular AC 61-107a and it has a pretty good
dscription of what's going on. I can't read it at the moment because my
adobe is fuxored.


Bertie

WingFlaps > wrote in
:

> On Jan 30, 11:44*pm, D Ramapriya > wrote:
>> On Jan 30, 2:33 pm, Bertie the Bunyip > wrote:
>>
>>
>>
>> > D Ramapriya > wrote
>> > innews:24252c28-895a-44da-bd25
> :
>>
>> > > 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, 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.
>
> No, I think you are confused. Altitude is _not_ commanded, Only
> thrust and aoa (CL) are commanded flight variables. The plane always
> adopts an altitude where lift=weight. The lift is set by the point
> where thrust equals drag, the latter set by airspeed, density and CL.
> So once you have climbed to maximum altitude (for given fuel burn) you
> will gradually drift up as fuel burns. If the max fuel burn is set by
> range (e.g. across pacific) or engine performance I think it follows
> that max (and/or best cruise) altitude is set by weight OK?
>
> You might command an AP to go to max altitude but if the plane is too
> heavy it won't get there and will fly along in a climb attitude (and
> maybe even stall at high altitude) until enough fuel has burnt off to
> allow it to get there.
>

No. Max altitude as defined here is not performance limited, but mach
buffet limited. Though what you are saying is correct if you ignore this
factor.
The airplane ( well, most modern jets) will happily climb way above it's
max altitude as defind by mach buffet. We're frequenty still doing aover
1,000 FPM when we get there.

Bertie


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

On Jan 31, 2:38*am, Bob Moore > wrote:
> 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.
>
> 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.
>
> Below copied from the web:
>
> Cruise
> One cannot continue climbing for long because as the altitude increases
> at a given speed the CL increases. Speeding up would reduce CL, but this
> is limited by Mach number constraints or engine power.

Hi Bob,

I think this introduces compressibility. As I understand it, normally
CL is not considered a function of speed or altitude and it greatly
complicates the calculation of max theoretical altitude (ultimately
set by air separation and not simply weight). For example, during re-
entry the shuttle still has lift=weight but I think she's flying in a
fully stalled condition. Only later when air density is higher can she
actually fly "normally". Of course I doubt that I will ever have the
pleasure of flying so fast or high that compressibility becomes an
issue...

Cheers

"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

On Jan 31, 7:25*am, "Morgans" > wrote:
> "Dan" > wrote
>
> Just guessing, but perhaps the smaller cabin size handles the larger
> differential pressure reqiuired better than a big cabin. *The extra
> expense (and weight) to reinforce a large cabin (ie. heavy jet size)
> may not be worth it.

Absolutely! A narrow tube is better at resisting pressure according to
the law of Laplace.

Cheers

On Jan 31, 10:14*am, Bertie the Bunyip > wrote:
> WingFlaps > wrote :
>
>
>
> > On Jan 30, 11:44*pm, D Ramapriya > wrote:
> >> On Jan 30, 2:33 pm, Bertie the Bunyip > wrote:
>
> >> > D Ramapriya > wrote
> >> > innews:24252c28-895a-44da-bd25
> > :
>
> >> > > 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, 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.
>
> > No, I think you are confused. *Altitude is _not_ commanded, Only
> > thrust and aoa (CL) are commanded flight variables. The plane always
> > adopts an altitude where lift=weight. The lift is set by the point
> > where thrust equals drag, the latter set by airspeed, density and CL.
> > So once you have climbed to maximum altitude (for given fuel burn) you
> > will gradually drift up as fuel burns. If the max fuel burn is set by
> > range (e.g. across pacific) or engine performance I think it follows
> > that max (and/or best cruise) altitude is set by weight OK?
>
> > You might command an AP to go to max altitude but if the plane is too
> > heavy it won't get there and will fly along in a climb attitude (and
> > maybe even stall at high altitude) until enough fuel has burnt off to
> > allow it to get there.
>
> No. Max altitude as defined here is not performance limited, but mach
> buffet limited. Though what you are saying is correct if you ignore this
> factor.
> The airplane ( well, most modern jets) will happily climb way above it's
> max altitude as defind by mach buffet. We're frequenty still doing aover
> 1,000 FPM when we get there.
>
> Bertie

Yes. I was avoiding the compressibility problem for simplicity/
clarity. Damn you jet jockeys!

Cheers

"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.

WingFlaps > wrote in
:

> On Jan 31, 10:14*am, Bertie the Bunyip > wrote:
>> WingFlaps > wrote
>> innews:2fa7e74d-5402-4557-a5f7-72d42
> :
>>
>>
>>
>> > On Jan 30, 11:44*pm, D Ramapriya > wrote:
>> >> On Jan 30, 2:33 pm, Bertie the Bunyip > wrote:
>>
>> >> > D Ramapriya > wrote
>> >> > innews:24252c28-895a-44da-bd25
>> > :
>>
>> >> > > 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, 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.
>>
>> > No, I think you are confused. *Altitude is _not_ commanded, Only
>> > thrust and aoa (CL) are commanded flight variables. The plane
>> > always adopts an altitude where lift=weight. The lift is set by the
>> > point where thrust equals drag, the latter set by airspeed, density
>> > and CL. So once you have climbed to maximum altitude (for given
>> > fuel burn) you will gradually drift up as fuel burns. If the max
>> > fuel burn is set by range (e.g. across pacific) or engine
>> > performance I think it follows that max (and/or best cruise)
>> > altitude is set by weight OK?
>>
>> > You might command an AP to go to max altitude but if the plane is
>> > too heavy it won't get there and will fly along in a climb attitude
>> > (and maybe even stall at high altitude) until enough fuel has burnt
>> > off to allow it to get there.
>>
>> No. Max altitude as defined here is not performance limited, but mach
>> buffet limited. Though what you are saying is correct if you ignore
>> this factor.
>> The airplane ( well, most modern jets) will happily climb way above
>> it's max altitude as defind by mach buffet. We're frequenty still
>> doing aover 1,000 FPM when we get there.
>>
>> Bertie
>
> Yes. I was avoiding the compressibility problem for simplicity/
> clarity. Damn you jet jockeys!
>

Yeah, and you're right, but it's never why we stop the climb. in some of
the old, relatively breathless, airplanes, it would be a factor though.
I used to fly a 727-200 with tiny engines ( JT8D-7) and that ran out of
steam long before you got to max or even optimum altitude. Mind you, it
had huge margins anyway. One of the fastest civil jets ever, after
Concorde and the Convairs.


Bertie

>
> Well, actually it;s low and high. When the air going over a wing that's
> traveling close to supersonic is accelerated futher by the action of the
> wing, it goes supersonic over the wing. When you go too fast, max mach, you
> get a loss of lift. When you go too slow, you accelerate the air over the
> top of wing as well due to increased angle of attack. If you load the wing
> up with weight or G (same thing as far as the wing is concerned) same thing
> happens. The air buffeting from the shock wave is similar to a stall ( some
> sources call it a stall) and loss of control and altitude results. Recovery
> can be difficult, though not impossible. There are a number of other facors
> at play here, but that's the meat of it.

Pretty cool information I must say.. thanks! I guess its a whole
different world from my puny little cessna 150 ;)

wrote in
:

>
>>
>> Well, actually it;s low and high. When the air going over a wing
>> that's traveling close to supersonic is accelerated futher by the
>> action of the wing, it goes supersonic over the wing. When you go too
>> fast, max mach, you get a loss of lift. When you go too slow, you
>> accelerate the air over the top of wing as well due to increased
>> angle of attack. If you load the wing up with weight or G (same thing
>> as far as the wing is concerned) same thing happens. The air
>> buffeting from the shock wave is similar to a stall ( some sources
>> call it a stall) and loss of control and altitude results. Recovery
>> can be difficult, though not impossible. There are a number of other
>> facors at play here, but that's the meat of it.
>
> Pretty cool information I must say.. thanks! I guess its a whole
> different world from my puny little cessna 150 ;)
>

Your 150 would be affected by this if you got it up high enough!

Even turboprops are affected to a lesser degree when they get up around
20,000 plus. Dash 8s and ATRs and such. Malibus, and those single
turboprops probably woudl be as well. Straight wing airplanes are more
affected than swept wing airplanes. Lots of hot homebuilts have mach issues
if they get up high enough, too.

Bertie

On Wed, 30 Jan 2008 22:32:09 +0000 (UTC), Bertie the Bunyip >
wrote:

>Even turboprops are affected to a lesser degree when they get up around
>20,000 plus. Dash 8s and ATRs and such. Malibus, and those single
>turboprops probably woudl be as well. Straight wing airplanes are more
>affected than swept wing airplanes. Lots of hot homebuilts have mach issues
>if they get up high enough, too.

The Malibu has FL250 as max certified and Vne of 188 KIAS and the
Meridian has a Vmo of 188 KIAS and a certified ceiling of FL300 (I
don't know of any RVSM certified tho, so generally they're FL280 and
under). Starting to work up into that realm I'm interested, is that
really fast enough to have coffin corner issues, or would that kind of
speed with a Vs1 of 79 KIAS have large enough margins? TBM700/850 I
could understand, they're significantly faster....

Peter Clark > wrote in
:

> On Wed, 30 Jan 2008 22:32:09 +0000 (UTC), Bertie the Bunyip >
> wrote:
>
>>Even turboprops are affected to a lesser degree when they get up
>>around 20,000 plus. Dash 8s and ATRs and such. Malibus, and those
>>single turboprops probably woudl be as well. Straight wing airplanes
>>are more affected than swept wing airplanes. Lots of hot homebuilts
>>have mach issues if they get up high enough, too.
>
> The Malibu has FL250 as max certified and Vne of 188 KIAS and the
> Meridian has a Vmo of 188 KIAS and a certified ceiling of FL300 (I
> don't know of any RVSM certified tho, so generally they're FL280 and
> under). Starting to work up into that realm I'm interested, is that
> really fast enough to have coffin corner issues, or would that kind of
> speed with a Vs1 of 79 KIAS have large enough margins? TBM700/850 I
> could understand, they're significantly faster....
>

Yeah, they'd both be affected, but to a fairly minor degree as the
operational speeds are relatively low. 188 would true out a bit under
300 at FL300 which would be a bit under mach.5. It depends on what sort
of airfoil you have, but I'm guessing it's not a big fat clark Y so I'd
say that would be well below any real max mach issues.
It's all about how fast the air over the wing is going and it's not too
much of a stretch to accelerate the air enough to get a buffet. Loading
up the wing either by manuevering or turbulence penetration could induce
a buffet, but it probably would be the least of your worries if you were
in that situation anyway. If you got it wel over red lin, though, I
could see a mach number of .6 or more being an issue, alright.
It's worthwhile being aware of if you're going up that high, though. Key
things to remember are to fly the airplane smoothly and avoid turbulence
.. Light stuff is fine, even moderate isn't going to cause you any
troubles either, but it's a sucker's bet to try and climb over a CB,
the other thing to consider is the higher you go, the tighter the
margins are, so best not to try slow flight. Also, if it does get
violently turbulent, your margins increase as you descend. so what you
want to do is to get to your VA and descend carefully.
If there's an upper mach limit that;s lower than your VMo Piper should
publish it as a MMo and you'd have a mach meter combined with your ASI.

I think you're right, the TBM would almost certainly be affected,
though.

Funny, I thought those Malibus were a lot faster than that. There were a
few lost in the early days weren't there? . Structural?

Bertie

> A couple of reasons..........

<Big Snip of great stuff>

Thank you, Bob, for delivering an excellent, thorough, and precise
explanation by an acknowledged and legitimate expert in a pleasant,
non-confrontational way.

It's so...refreshing!

:-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

"Jay Honeck" > wrote in news:Kb8oj.8850$yE1.23
@attbi_s21:

>> A couple of reasons..........
>
> <Big Snip of great stuff>
>
> Thank you, Bob, for delivering an excellent, thorough, and precise
> explanation by an acknowledged and legitimate expert in a pleasant,
> non-confrontational way.
>
> It's so...refreshing!
>
>:-)



Unlike your crap.


Bertie

On Wed, 30 Jan 2008 23:13:42 +0000 (UTC), Bertie the Bunyip >
wrote:


>Yeah, they'd both be affected, but to ... <snip useful analysis>
>If there's an upper mach limit that;s lower than your VMo Piper should
>publish it as a MMo and you'd have a mach meter combined with your ASI.

Yea, they don't have Mmo or a machmeter in the Meridian. It does have
a real low Va though (right around 130KIAS at max gross if memory
serves, don't have my cheatsheet handy). It's a long, pretty thin
wing (43').

>I think you're right, the TBM would almost certainly be affected,
>though.

They also have a published Mmo and machmeter.

>Funny, I thought those Malibus were a lot faster than that. There were a
>few lost in the early days weren't there? . Structural?

Yea, after a few broke up the FAA did a complete recertification
review. After the dust settled, they found the aircraft was well
within certifciation criterion, and that nearly all the breakups were
associated with convective activity and blamed pilot decision making.
The initial and recurring training courses were modified. Seems like
it was the first round of doing something like they did with the MU2
but this didn't get to the level of being a SFAR.

I remember learning recently in A&P school that 36,000 ft. is the
optimum altitude for long-range cruising. At approx 36,000 the temp.
stops falling & remains constant but pressure still decreases
resulting in a rate-of-thrust decrease that's more rapid at higher
altitudes than approx. 36,000.

Ricky

writes:

> 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?

One important reason is restrictions on the time within which they must return
to an altitude that doesn't require pressurization in the event of a sudden
loss of cabin pressure. They have to be able to get to that safe altitude
within a certain number of minutes without overspeeding the aircraft.

Also, the higher the altitude at cruise, the greater the pressure differential
in the pressurization cycle, and the greater the wear and tear on the airframe
in consequence. Pressurization cycles are one of the limiting factors on
airframe lifetimes.

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

Mxsmanic > wrote in
:

> writes:
>
>> 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?
>
> One important reason is restrictions on the time within which they
> must return to an altitude that doesn't require pressurization in the
> event of a sudden loss of cabin pressure. They have to be able to get
> to that safe altitude within a certain number of minutes without
> overspeeding the aircraft.
>
> Also, the higher the altitude at cruise, the greater the pressure
> differential in the pressurization cycle, and the greater the wear and
> tear on the airframe in consequence. Pressurization cycles are one of
> the limiting factors on airframe lifetimes.
>

No a factor in limiting the altitude, fjuktard.

Bertie

Ricky > wrote in news:d853bc93-6705-4f74-bc06-
:

>
> I remember learning recently in A&P school that 36,000 ft. is the
> optimum altitude for long-range cruising. At approx 36,000 the temp.
> stops falling & remains constant but pressure still decreases
> resulting in a rate-of-thrust decrease that's more rapid at higher
> altitudes than approx. 36,000.
>

Hmmm, it is true that the temp stops decreasing around there. (It's called
the Tropopause) but i never thought of it in terms of thrust like that
before. Rate of climb does get a little iffy up that high!


Bertie