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Trimeresurus
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Why do the A350s/787s cruise so high?

Wed Sep 09, 2020 7:48 pm

Whenever you filter by altitude on flightradar24, you see that 90% of planes cruising above FL400 are A350s and 787s(discounting small private jets). What is the reason for this?
 
GalaxyFlyer
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Re: Why do the A350s/787s cruise so high?

Wed Sep 09, 2020 8:14 pm

Saves fuel, light loads allow climb to F400 thru F430.
 
N965UW
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Re: Why do the A350s/787s cruise so high?

Wed Sep 09, 2020 9:19 pm

I've been under the impression that newer models such as the A350 and 787 are more aerodynamic than their predecessors. They take advantage of advances in aircraft design over the years. Their engines are more optimized to the frame. The wings provide more lift and were designed with stretches in mind, in contrast with aircraft that have high wing loadings (B764) or those that often operate heavy (B77W).

Even the older A330 can fly pretty high. The -200 was a shrink from the -300, which gives it great performance. US and later AA were notable for taking their 330s up high. Last summer I was on an AA A332 that had a decent pax load. Initial climb was to FL380 with a step to FL400. This was a regular practice. They even took their A333s up to FL380 regularly.

The A350 and 787 also operate with lower cabin altitudes. But I don't know if that has anything to do with it. Any airliner can maintain a set cabin alt up to its service ceiling.
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Starlionblue
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Re: Why do the A350s/787s cruise so high?

Wed Sep 09, 2020 11:39 pm

The 787 and A350 simply have better altitude performance than their predecessors. Flying higher gives lower fuel burn if you can get up there, so airlines take advantage. There are of course weight, wind and temperature dependencies, so every flight is different.

The 787 and A350 also have a higher service ceiling compared to 777 and A330.

N965UW wrote:
I've been under the impression that newer models such as the A350 and 787 are more aerodynamic than their predecessors. They take advantage of advances in aircraft design over the years. Their engines are more optimized to the frame. The wings provide more lift and were designed with stretches in mind, in contrast with aircraft that have high wing loadings (B764) or those that often operate heavy (B77W).

Even the older A330 can fly pretty high. The -200 was a shrink from the -300, which gives it great performance. US and later AA were notable for taking their 330s up high. Last summer I was on an AA A332 that had a decent pax load. Initial climb was to FL380 with a step to FL400. This was a regular practice. They even took their A333s up to FL380 regularly.

The A350 and 787 also operate with lower cabin altitudes. But I don't know if that has anything to do with it. Any airliner can maintain a set cabin alt up to its service ceiling.


The lower cabin altitude has little to do with the higher cruise altitude. Higher cruise altitude is possible based on wing and engine performance. Lower cabin altitude is possible based on materials that better withstand a higher differential pressure regularly.

Going up to FL380, or even FL410 in an A333 is no big deal. The A333 can fly 9 hours comfortably so if your sector is only 1-3 hours you will often go to FL400 right from the start.

The cabin altitude is not fixed up to the service ceiling. It varies somewhat depending on the cruise altitude, but never exceeds a maximum value.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
RJMAZ
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Re: Why do the A350s/787s cruise so high?

Thu Sep 10, 2020 7:17 am

Well nearly all of the A380 fleet is not operating and that also flies high.

The 777-300ER, the A321 are underwinged due to the multiple MTOW increases. All the freighter aircraft like MD-11 have smaller wings to fit code D gates.

With narrrowbody aircraft the passengers often exceed 25% of the takeoff weight resulting in them landing only 20% lighter than the takeoff weight While on a long haul widebody flight the passengers can be less than 10% of the takeoff weight. In the last hour of the flight with so much burnt the aircraft might be 35-40% below the takeoff weight. Being this light allows them to fly very high.
 
ELBOB
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Re: Why do the A350s/787s cruise so high?

Thu Sep 10, 2020 8:13 am

Starlionblue wrote:

The 787 and A350 also have a higher service ceiling compared to 777 and A330.



Not quite...

The A350, 787, 777 are all certificated to 43,100 ft

The A330 is certificated to 41,100ft, or 41,450 with a software option.
 
flipdewaf
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Re: Why do the A350s/787s cruise so high?

Thu Sep 10, 2020 8:19 am

ELBOB wrote:
Starlionblue wrote:

The 787 and A350 also have a higher service ceiling compared to 777 and A330.



Not quite...

The A350, 787, 777 are all certificated to 43,100 ft

The A330 is certificated to 41,100ft, or 41,450 with a software option.

A35K is 41,450 too.

Fred


Sent from my iPhone using Tapatalk
Image
 
VSMUT
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Re: Why do the A350s/787s cruise so high?

Thu Sep 10, 2020 9:02 am

RJMAZ wrote:
All the freighter aircraft like MD-11 have smaller wings to fit code D gates.


The MD-11 has small wings because it has a 1960s wing. The 767 has a small wing because it is a 1970s design built for medium-haul routes. The A330, 777 and 747 have big wings. Your point doesn't really hold water.
 
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JerseyFlyer
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Re: Why do the A350s/787s cruise so high?

Thu Sep 10, 2020 10:19 am

flipdewaf wrote:
ELBOB wrote:
Starlionblue wrote:

The 787 and A350 also have a higher service ceiling compared to 777 and A330.



Not quite...

The A350, 787, 777 are all certificated to 43,100 ft

The A330 is certificated to 41,100ft, or 41,450 with a software option.

A35K is 41,450 too.

Fred

Sent from my iPhone using Tapatalk


Given that ATC corridors are 1000ft apart, what is the benefit of 450ft? Just curious.
 
spacecadet
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Re: Why do the A350s/787s cruise so high?

Thu Sep 10, 2020 10:23 am

ELBOB wrote:
Starlionblue wrote:

The 787 and A350 also have a higher service ceiling compared to 777 and A330.



Not quite...

The A350, 787, 777 are all certificated to 43,100 ft


Service ceiling and maximum operating altitude are two different things. The FAA and EASA certify maximum operating altitude. Service ceiling varies with load and conditions but can be generally higher or lower for one aircraft relative to another with the same certificated maximum operating altitude.
I'm tired of being a wanna-be league bowler. I wanna be a league bowler!
 
unimproved
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Re: Why do the A350s/787s cruise so high?

Thu Sep 10, 2020 11:43 am

ELBOB wrote:
Starlionblue wrote:

The 787 and A350 also have a higher service ceiling compared to 777 and A330.



Not quite...

The A350, 787, 777 are all certificated to 43,100 ft

The A330 is certificated to 41,100ft, or 41,450 with a software option.

Certified is the max altitude in the best case scenario. The 787/A350 has a better wing design so it's easier to actually climb to that height.
 
744SPX
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Re: Why do the A350s/787s cruise so high?

Thu Sep 10, 2020 8:00 pm

The 747SP still has the lowest wing loading of any large passenger aircraft, with the 788 being the next closest.
 
RJMAZ
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Re: Why do the A350s/787s cruise so high?

Fri Sep 11, 2020 1:43 am

VSMUT wrote:
The MD-11 has small wings because it has a 1960s wing. The 767 has a small wing because it is a 1970s design built for medium-haul routes. The A330, 777 and 747 have big wings. Your point doesn't really hold water.

It is leakproof. I said underwinged. Not once did I use the word small wing or big wing. This comes down to the wingloading and span relative to the weight.

The 777-300ER has a smaller wing than the A350-900 yet the 777W has a much higher takeoff weight of 351t versus only 280t. The 777W is underwinged.

The 747-8 has a wing with 23% more area yet its MTOW is 60% higher than the A350-900. The 747-8 is underwinged.

The DC-10 and MD-11 was designed to fit code D gates it has nothing to do with them being old.
 
VSMUT
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Re: Why do the A350s/787s cruise so high?

Fri Sep 11, 2020 7:15 am

RJMAZ wrote:
VSMUT wrote:
The MD-11 has small wings because it has a 1960s wing. The 767 has a small wing because it is a 1970s design built for medium-haul routes. The A330, 777 and 747 have big wings. Your point doesn't really hold water.

It is leakproof. I said underwinged. Not once did I use the word small wing or big wing. This comes down to the wingloading and span relative to the weight.

The 777-300ER has a smaller wing than the A350-900 yet the 777W has a much higher takeoff weight of 351t versus only 280t. The 777W is underwinged.

The 747-8 has a wing with 23% more area yet its MTOW is 60% higher than the A350-900. The 747-8 is underwinged.

The DC-10 and MD-11 was designed to fit code D gates it has nothing to do with them being old.


You said:
RJMAZ wrote:
All the freighter aircraft like MD-11 have smaller wings to fit code D gates.


All freighter aircraft don't, not even all freighters in that size category. The A330-300P2F and 777F are evidence of the contrary. Further, the development history of the MD-11 is well known. It wasn't designed to fit code D gates. They just reused an old wing that happened to fit code D gates. It is no secret that they wanted to do a bigger wing for it. Economic woes prevented them from doing so.
 
RJMAZ
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Re: Why do the A350s/787s cruise so high?

Fri Sep 11, 2020 9:58 am

VSMUT wrote:
You said:
RJMAZ wrote:
All the freighter aircraft like MD-11 have smaller wings to fit code D gates.


All freighter aircraft don't, not even all freighters in that size category. The A330-300P2F and 777F are evidence of the contrary.
The 777F and 747-8 are not like the MD-11 to fit code D gates. They are the size above and I responded separately to the 777 by saying they are underwinged for their MTOW.


VSMUT wrote:
Further, the development history of the MD-11 is well known. It wasn't designed to fit code D gates. They just reused an old wing that happened to fit code D gates. It is no secret that they wanted to do a bigger wing for it. Economic woes prevented them from doing so.
No. Keeping within code D was a primary seller point of the MD-11. US airports had a huge number of these gates. The MD-11 freighter was offered at launch and it was a requirement that it met existing D gates at freight hubs
 
BigSaabowski
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Re: Why do the A350s/787s cruise so high?

Fri Sep 11, 2020 10:07 am

JerseyFlyer wrote:
flipdewaf wrote:
ELBOB wrote:

Not quite...

The A350, 787, 777 are all certificated to 43,100 ft

The A330 is certificated to 41,100ft, or 41,450 with a software option.

A35K is 41,450 too.

Fred

Sent from my iPhone using Tapatalk


Given that ATC corridors are 1000ft apart, what is the benefit of 450ft? Just curious.


41,100 is a valid cruise altitude in China: it equates to 12500 meters. Not sure about the other two.
 
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SheikhDjibouti
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Re: Why do the A350s/787s cruise so high?

Fri Sep 11, 2020 7:33 pm

744SPX wrote:
The 747SP still has the lowest wing loading of any large passenger aircraft, with the 788 being the next closest.

Care to share your actual numbers?

Wikipedia gives one set of data, a.net another.
And the differences are puzzling (and in some cases substantial)

The 788 looks good (even better than the 747SP !) at 4058 sq ft wing area, but not so good if it is 3501 sq ft.
So which is it?

And the A330neo blows both away ... if the numbers on wikipedia can be believed. I have my doubts.
Nothing to see here; move along please.
 
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ElroyJetson
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Re: Why do the A350s/787s cruise so high?

Sat Sep 12, 2020 2:43 am

The 787-10 is certified to 41,100 ft. The 788 and 789 and certified to 43,100 ft.


https://en.wikipedia.org/wiki/Boeing_787_Dreamliner
707 717 727 72S 737 733 737-700 747 757 753 767-300 764 A319 A320 DC-9-10 DC-9-30 DC-9-50, MD-82 MD-88 MD-90 DC-10-10 DC-10-40 F-100
 
Sokes
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Re: Why do the A350s/787s cruise so high?

Sun Sep 13, 2020 7:33 am

SheikhDjibouti wrote:
And the A330neo blows both away ... if the numbers on wikipedia can be believed. I have my doubts.

A330 has shared wing with A340 and less speed.
Neo wing grew even bigger.
Why to doubt low wing loading?
Why can't the world be a little bit more autistic?
 
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SheikhDjibouti
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Re: Why do the A350s/787s cruise so high?

Sun Sep 13, 2020 12:04 pm

SheikhDjibouti wrote:
744SPX wrote:
The 747SP still has the lowest wing loading of any large passenger aircraft, with the 788 being the next closest.

Care to share your actual numbers?
Sokes wrote:
SheikhDjibouti wrote:
And the A330neo blows both away ... if the numbers on wikipedia can be believed. I have my doubts.

A330 has shared wing with A340 and less speed.
Neo wing grew even bigger.
Why to doubt low wing loading?

Fair question; but why don't you have a look at the actual numbers for yourself?

The problem boils down to this;
I expected the highest wing loadings to be the somewhat notorious Russian ground-huggers; the Il-86 and Il-96.
Basically flying bricks that only gain altitude due to the curvature of the Earth.

It turns out that the A340-200/300 and DC-10-30/40 are in that group too.
Whilst the A340-500/600 and MD-11 are even worse than the Ilyushins :o
(and that hurts me because I really like the A340 aesthetically....)

The next highest group tends to be later developments of well known airframes, in each case where stretches and engine power increases have allowed a substantial increase to MTOW usually whilst retaining the original wing (¹). e.g. Boeing 767-300/400 especially ERs, Boeing 747-400 etc etc. A350-1000, Boeing 777X
(¹) some of these had minor tweaks to the wing

Then we come to the group with the lower wing loadings.
Boeing 747-100, A300B4, A350-900, Boeing 747SP, Boeing 787-8, Boeing 777-200 (not ER), and somewhat surprisingly DC-10-10 :o

But the absolute winners are A330neo and Boeing 767-200

So far, so obvious (mostly)
My concern is because the A330neo wing isn't just tweaked, it is a whopping 29% larger. That is unprecedented, and makes me doubt the figures.

Is the A330neo wing really 5010 sq ft / 465 m² ?
Does anybody have an aerial view showing A330-ceo and neo side by side, for comparison?

Now, having ruffled some feathers in another thread for questioning data sourced from the internet, let me say I am honestly looking for a definitive answer here. I gain no pleasure from disputing these numbers. :white:
Nothing to see here; move along please.
 
ElpinDAB
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Re: Why do the A350s/787s cruise so high?

Sun Sep 13, 2020 5:00 pm

SheikhDjibouti wrote:
SheikhDjibouti wrote:
744SPX wrote:
The 747SP still has the lowest wing loading of any large passenger aircraft, with the 788 being the next closest.

Care to share your actual numbers?
Sokes wrote:
A330 has shared wing with A340 and less speed.
Neo wing grew even bigger.
Why to doubt low wing loading?

Fair question; but why don't you have a look at the actual numbers for yourself?

The problem boils down to this;
I expected the highest wing loadings to be the somewhat notorious Russian ground-huggers; the Il-86 and Il-96.
Basically flying bricks that only gain altitude due to the curvature of the Earth.

It turns out that the A340-200/300 and DC-10-30/40 are in that group too.
Whilst the A340-500/600 and MD-11 are even worse than the Ilyushins :o
(and that hurts me because I really like the A340 aesthetically....)

The next highest group tends to be later developments of well known airframes, in each case where stretches and engine power increases have allowed a substantial increase to MTOW usually whilst retaining the original wing (¹). e.g. Boeing 767-300/400 especially ERs, Boeing 747-400 etc etc. A350-1000, Boeing 777X
(¹) some of these had minor tweaks to the wing

Then we come to the group with the lower wing loadings.
Boeing 747-100, A300B4, A350-900, Boeing 747SP, Boeing 787-8, Boeing 777-200 (not ER), and somewhat surprisingly DC-10-10 :o

But the absolute winners are A330neo and Boeing 767-200

So far, so obvious (mostly)
My concern is because the A330neo wing isn't just tweaked, it is a whopping 29% larger. That is unprecedented, and makes me doubt the figures.

Is the A330neo wing really 5010 sq ft / 465 m² ?
Does anybody have an aerial view showing A330-ceo and neo side by side, for comparison?

Now, having ruffled some feathers in another thread for questioning data sourced from the internet, let me say I am honestly looking for a definitive answer here. I gain no pleasure from disputing these numbers. :white:



I'm not sure where the numbers from Wikipedia come from or how valid they are, and it's good that you question them. But as far as the A330neo vs ceo wing, a gain of more than 1000sq ft does, at first glance, seem like a bit much for a 12ft span increase. However, looking at the Aspect Ratio (ratio between wingspan and mean cord) listed on wiki, the neo is 8.8 vs 10.06 for the ceo wing. While I don't remember reading about any increase in wing cord for the neo (usually articles and graphics just say something like "wing aerodynamic improvements", this decrease in AR implies that the cord has been lengthened, which would explain such a seemingly excessive increase in overall wing area for the A330neo over the ceo. As a side note, the A330neo also has a lower AR than the A340-500/600, which I know did, in fact, receive a modified wing with a cord extension.



Also, on your disappointment for the A340-200/300 high wing loading, remember that it was originally designed to be the air frame longer routes while the A330-200/300 was designed for longer routes. They share the same wing, so given the same thrust output and weight, they should theoretically have very similar climb performance with all engines operating. The advantage that the A340 has over the A330 is that for one engine inoperative scenarios, the A340 would have lost less excess thrust (excess thrust = thrust available for climb) than the A330 at the same weight. So, simply put, the A340 can operate at higher MTOW weights than the A330 because it is able to lose an engine and climb over an obstacle better than the A330 would be able to. So don't let the A340's higher wing loading at MTOW overshadow the aircraft's aesthetics for you 8-) The A340-200/300 of its time would have been a more capable aircraft than the A330 of the same model year.
 
ElpinDAB
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Re: Why do the A350s/787s cruise so high?

Sun Sep 13, 2020 5:45 pm

Back to the original topic, I think there is more to this than simply thrust to weight ratio and wing loading. As some posters have mentioned, overall aerodynamic efficiency and optimization has alot to do with cruise altitude and climb performance in the subsonic and transonic realm. And yes, new aircraft with composite wings and more aerodynamic fuselages can definitely gain a bit of climb and cruise performance. Especially in the upper 30's and lower 40's where airliners cruise, excess thrust is far less than it would be down low, so any advantages in other areas that are less tangible or more difficult to measure might explain alot of this. A newer engine such as the Trent X or GenX might be capable of producing greater thrust to higher altitudes and be optimized for the most efficient portion of flight envelope of their mated air frame than older engines, but I can't verify the validity of that statement. But also, I wouldn't doubt that certain things like wing design (aspect ratio optimized for cruise speed/altitude at weights that provide the most benefit to the majority of missions, cross section, laminar flow, etc.) have also been greatly enhanced by improved computing power in the design process that allows the same basic shape to be improved at levels beyond what is published to people who aren't employed by the contributing manufacturers themselves.

From personal experience, I will say that flying jets that are, on paper, the same model at the same weight in the same conditions, a brand new jet, less than a month or two old, will generally descend at 100-200fpm less than an older jet at idle thrust below 10,000ft. This implies a more aerodynamic air frame. Granted, there were a few other subtle improvements such as antennas integrated/moved, and better aerodynamic seals for different wing surfaces, but overall, the difference is subtly noticeable. Despite not being able to notice how that would translate to climb performance close to the edges of the operating envelope because of safety margins/adherence to operating procedures, I would absolutely say that the newer aircraft would be able to cruise higher and/or burn a little less fuel than the older aircraft, and not just because of gradual engine degradation over time.

Just to hammer-in the points of aerodynamic efficiency, I have re-positioned a couple of airliners with the landing gear down, and it's surprising how poor the climb performance becomes approaching 10,000ft and above. Far more of a difference than I would have guessed without seeing it first-hand. So, I'm sure that removing something as tiny as an antenna might measurably decrease climb performance approaching service ceiling, but not really enough for anybody to publish externally.

For me, that starts to put things into perspective when comparing the climb performance of airliners of various generations that might have similar wing loading and thrust to weight ratios.
 
GalaxyFlyer
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Re: Why do the A350s/787s cruise so high?

Sun Sep 13, 2020 7:03 pm

The C-5 had retracting landing lights ob each wingtip, old school that was. If you forgot to retract at 10,000’ (“Lights and speed” was the call), you’d find out at F280 or so when the climb basically stopped. Huge drag once Mach became a factor.

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