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LAXintl
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Airbus Decides On Lower Thrust Requirement On A350

Sat Sep 22, 2007 11:25 pm

I wonder if the trust reductions will hurt targeted performance and was partially driven due to the lack of flexibility without GE participating.

Quote:
Airbus Decides On Lower Thrust Requirement For A350
09/24/2007

Airbus has reached consensus on a lower thrust rating for the engines that will power the A350 twin-widebody as part of the process to refine the aircraft-maker's newest product offering.

The thrust level for the first-to-be-fielded A350-900 is now set at 83,000 lb., having previously been 87,000 lb said Gordon McConnell, chief program engineer. The thrust level has now been frozen and Rolls-Royce -- still the sole engine provider -- will work to that level.

Thrust levels for the -800, which will be introduced in mid-2014 a year after the initial version, is now 74,000 lb., rather than 75,000 lb. listed earlier. For the largest model, the -1000 set to enter service in late 2015, the rating is 92,000 lb.

Airbus is still interested in enlisting General Electric to join the program, but little progress appears to have been made in recent months.

Full strory; (subscription required)
http://www.aviationweek.com/publicat...+Lower+Thrust+Requirement+For+A350
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Lumberton
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RE: Airbus Decides On Lower Thrust Requirement On

Sat Sep 22, 2007 11:32 pm

The link you posted requires a log-in, but from the thrust level you cited it appears that the specification is now well within range of the GENx for the -800 and should be able to grow to the thrust required for the -900. Big week for the A350; composite frames and possibly soon a second engine?

[Edited 2007-09-22 16:38:10]
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Stitch
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sat Sep 22, 2007 11:41 pm

Quoting Laxintl (Thread starter):
I wonder if the trust reductions will hurt targeted performance and was partially driven due to the lack of flexibility without GE participating.

MTOWs grew significantly when they went from the A350 to the A350XWB and they have been creeping upwards by over 10,000lbs since on the A350-900 and A350-1000 since.

On the "bright side", this could mean they don't need as high an MTOW as they thought. Whether that is because they lowered MEW, the engines burn less fuel for they don't need to carry as much, or the wings are even more efficient then planned, I do not know.

On the dark side, it could mean that the engines can't scale as high as RR said they will and Airbus is being forced to lower MTOW to accommodate this, which could mean performance is being impacted.

However, it does help GE get closer, especially since a 787HGW will need at least 85,000lbs of thrust.
 
NAV20
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sat Sep 22, 2007 11:44 pm

Every design involves compromises. On the face of it, less power=lower speed. But it can also equal greater range for less fuel. And lighter weight (through the full-composite switch) might equal the same range/speed on the same amount of fuel.

Inclined to agree that Airbus has been forced by GE's reluctance to produce a new engine to design the aeroplane to suit available engines, instead of the other way round.

But one can still infer that the A350 remains largely a 'me too' response to the 787, rather than any sort of revolutionary design in its own right.
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 12:28 am

Quoting NAV20 (Reply 3):

Those thrust requirements are for Take-Off and as Stitch has summed up its either due to reduced TO drag. (You need more thrust than drag to climb! Therefore if the climb rate is fixed and TO drag does down then TO trust requirements go down.)

Or a better cruise L/D, lower MWE, or improved L/D. i.e. for a given range less fuel is required and they have adapted the airframe to new MWE/OWE, L/D and SFC coupled with reduced MTOW. I would say with 99.9% confidence that this is a very good sign for fuel burn.
 
777236ER
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 12:31 am

Quoting NAV20 (Reply 3):
less power=lower speed

Wrong.
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 12:40 am

Quoting Stitch (Reply 2):
On the "bright side", this could mean they don't need as high an MTOW as they thought. Whether that is because they lowered MEW, the engines burn less fuel for they don't need to carry as much, or the wings are even more efficient then planned, I do not know.

?It must be either the weights or the low speed lift or a combination of both. Fuel consumption would affect the weights, so it might be RR offering better fuel consumption from the engines than had been expected. And that might reinforce the old "newer engines argument" as far as GE are concerned.
 
ikramerica
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 12:47 am

Now I really have doubts that they can produce a 77W killer with 44k pounds less thrust. I just don't see it really being as capable as first claimed...
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777236ER
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 1:31 am

Quoting Ikramerica (Reply 7):
Now I really have doubts that they can produce a 77W killer with 44k pounds less thrust. I just don't see it really being as capable as first claimed...

Why not?
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Slovacek747
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 1:51 am

I agree. There is no way they can have 44K less pounds of thrust and still accomplish what the 77W can. We have made great strides in technology but the plane isn't going to be that light or that much better aerodynamically.

Slovacek747
 
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Stitch
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 1:53 am

Quoting Slovacek747 (Reply 9):
I agree. There is no way they can have 44K less pounds of thrust and still accomplish what the 77W can. We have made great strides in technology but the plane isn't going to be that light or that much better aerodynamically.

It is planned to be both significantly lighter (40t or more) and much better aerodynamically then the 777, so it will certainly not need nearly as much thrust.
 
caminito
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 1:53 am

I am surprised that these most important news did not induce (as by now!) a larger forum reply !!

If the article of Aviation Week contains other news as the stated in Reply 0, it would be really important to be able to read it, if not, I would
be grateful for some more details.

Quoting NAV20 (Reply 3):
But one can still infer that the A350 remains largely a 'me too' response to the 787, rather than any sort of revolutionary design in its own right.



Quoting Laxintl (Thread starter):
The thrust level has now been frozen and Rolls-Royce -- still the sole engine provider -- will work to that level.

This alone (the "me too") does not constitute a negative for the A350XWB, as Airbus itself has said that what they are doing will base as far as possible on the experience of Boeing with the B787, improved by the technology progress achieved during the 6 years time gap. For the customers, it is irrelevant who was the "inventor" !!

But what seems concerning are the ongoing conceptual changes (by no means simple details) of often"frozen" issues.
Only during this week it was disclosed:

- the fuselage was shifted from Alu to composite, except the crossbeams, which FOR NOW will remain metallic. Some observers still believe that Airbus finally will shift to barrels.
- the nose was shifted from intended composite to metal and also its configuration changed
- now, this reduction of engine trust

As all these and eventually still not disclosed changes are not spontaneous creations but obviously preceded by time consuming and engineer hour draining parallel studies, it is a fair assumption that the design progress reached must be far behind schedule. The original goal to achieve EIS mid-2013 certainly included a reasonable reserve for unforeseen events, but as Airbus was aware of the critical importance of the mdelivery dates referred to the B787 timing advantage, surly did not consider such changes as above more than 6 months after launch.
 
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 2:15 am

The reason I doubt the A350-1000 will really be a 1:1 replacement for the 77W in capability is that the A350F will carry less payload than the 777F for the same mission by 20%, but somehow the A350-1000 will be just as capable as the 77W and the A350R will be more capable than the the 772LR. There is a disconnect in the math there. Unless the 90t cargo numbers for the A350F are wrong?
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caminito
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 2:15 am

In my Reply 11 I wrote "Engine trust" instead of "thrust". Sorry !
 
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 2:35 am

Quoting Ikramerica (Reply 12):
Unless the 90t cargo numbers for the A350F are wrong?

Where are you getting your numbers from?
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WingedMigrator
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RE: Airbus Decides On Lower Thrust Requirement On

Sun Sep 23, 2007 3:21 am

Quoting Stitch (Reply 10):
It is planned to be both significantly lighter (40t or more)

MTOW of the A350-1000 is 295,000 kg. 777-300ER is 351,000 kg. That's a 56,000 kg difference, of for the metric challenged, that's 123,000 lbs, or over 60 short tons. Most of the difference is accounted for by the fact that more efficient engines allow a smaller fuel load for the same mission.

With 16% less weight than the 77W, you can discard 16% of the thrust right away. With 17% less weight per unit area of wing, you need 8% less velocity to lift the airplane (all other things being equal). Keeping field performance fixed, reaching 8% less velocity in a given distance allows you to cut thrust by another 17%.

Those cuts would take you from the 77W's 115 klbs per engine to just 80 klbs, but the A350-1000 is still spec'd much higher, at 93 klbs.

Quoting Ikramerica (Reply 7):
Now I really have doubts that they can produce a 77W killer with 44k pounds less thrust



Quoting Slovacek747 (Reply 9):
There is no way they can have 44K less pounds of thrust and still accomplish what the 77W can.

Simple physical relationships suggest that your doubts are unfounded... not only should the capability be similar, but the field performance should be better thanks to the much lower wing loading.

Furthermore, if you compare the A350-1000 to the 773ER, there is clearly room for an A350-1100 that would still be lighter and have a more lightly loaded wing than the 773ER... The A350 family appears to have ample growth potential left before running into limitations of pavement loading, field performance or engine thrust.
 
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 3:42 am

Quoting NAV20 (Reply 3):
Every design involves compromises. On the face of it, less power=lower speed.

With that logic, the 777-300ER should be the fastest aircraft in the world

Quoting NAV20 (Reply 3):
Inclined to agree that Airbus has been forced by GE's reluctance to produce a new engine to design the aeroplane to suit available engines, instead of the other way round.

On the contrary, the reason GE is not on board the A350XWB is because Airbus wouldn't compromise the design to suit the GEnx

Quoting HawkerCamm (Reply 4):
Or a better cruise L/D, lower MWE, or improved L/D. i.e. for a given range less fuel is required and they have adapted the airframe to new MWE/OWE, L/D and SFC coupled with reduced MTOW. I would say with 99.9% confidence that this is a very good sign for fuel burn.

 checkmark 

Quoting Caminito (Reply 11):
I am surprised that these most important news did not induce (as by now!) a larger forum reply !!

A 1.5 - 4.5% reduction in thrust isn't such important news in my opinion...

Quoting Ikramerica (Reply 12):
Unless the 90t cargo numbers for the A350F are wrong?

The 90t is simply a structural payload, more than that would require extra strengthening of the floor, i.e. more empty weight. It's an engineering choice and should not be used to make assumptions about the performance of a whole family of airplanes.
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dl767captain
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 3:57 am

if the MTOW goes up doesn't that mean the plane will be under powered. how does the A350 MTOW compare to the 787? lets do the A350-800 and 789 (basically same size)
 
EDDB
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 4:05 am

Quoting DL767captain (Reply 18):
if the MTOW goes up doesn't that mean the plane will be under powered

I don't exactly get what you mean by under powered... Either you make it in the air.... Or you don't!
Each plane has to show a certain climb performance in the one-engine-go-case! If it doesn't, it won't get certified...
 
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 5:00 am

Quoting WingedMigrator (Reply 16):
With 16% less weight than the 77W, you can discard 16% of the thrust right away. With 17% less weight per unit area of wing, you need 8% less velocity to lift the airplane (all other things being equal). Keeping field performance fixed, reaching 8% less velocity in a given distance allows you to cut thrust by another 17%.

Those cuts would take you from the 77W's 115 klbs per engine to just 80 klbs, but the A350-1000 is still spec'd much higher, at 93 klbs.

Straight to the point, as always  thumbsup .

The improvement in engine performance, if factored in at the beginning of the design process, can have a quite dramatic effect on overall efficiency.
As you say, the necessity to lift less fuel due to better SFC, of itself confers a further aerodynamic advantage, as lift drag is proportional to weight. Hence drag redcues on top of the SFC improvement, hence less fuel (again).......etc.
A sort of virtuous circle (and how the 787 gets to be 20%+ better than its predecessors.

There's no doubt a 295t A350 should be quite capable of matching the mission capability of a 350t 773ER

Regards
 
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 5:14 am

Quoting Astuteman (Reply 20):
The improvement in engine performance, if factored in at the beginning of the design process, can have a quite dramatic effect on overall efficiency.
As you say, the necessity to lift less fuel due to better SFC, of itself confers a further aerodynamic advantage, as lift drag is proportional to weight. Hence drag redcues on top of the SFC improvement, hence less fuel (again).......etc.
A sort of virtuous circle (and how the 787 gets to be 20%+ better than its predecessors

Interesting question: If the GE90 family were to increase it's SFC to match GENX, Trent (8%), what would that do to the performance equation? MTOW would go down for the same range, etc. etc.
 
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ADent
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 5:51 am

If you can build a 777 killer on 2/3 the thrust, sounds like a 747 killer (aka Boeing Y3) isn't too hard to do either as a twin.
 
caminito
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 6:03 am

Quoting Laxintl (Thread starter):
The thrust level for the first-to-be-fielded A350-900 is now set at 83,000 lb., having previously been 87,000 lb said Gordon McConnell, chief program engineer. The thrust level has now been frozen and Rolls-Royce -- still the sole engine provider -- will work to that level.
Thrust levels for the -800, which will be introduced in mid-2014 a year after the initial version, is now 74,000 lb., rather than 75,000 lb. listed earlier. For the largest model, the -1000 set to enter service in late 2015, the rating is 92,000 lb.



Quoting Kaneporta1 (Reply 17):
A 1.5 - 4.5% reduction in thrust isn't such important news in my opinion...

The reduction of 4.6% for the -900 is indeed most important, as the plus-points for the A350 appear mainly at this sub-model, where Boeing (for the moment) has not an equivalent competitor and furthermore this one is expected to compete with the B777
The reduction for the -1000 (former 95,000 lb.) of 3.2% is equally important by similar reasons.

By the way: If wonder if the reason for the reduction is to accomodate a GE alternative!
To achieve such, the could offer the customers the RR with higher and GE with reduced thrust, the customer could than decide!
Could it be that RR is not willing to offer timely the originally foreseen thrusts?

Quoting WingedMigrator (Reply 16):
Quoting Ikramerica (Reply 7):
Now I really have doubts that they can produce a 77W killer with 44k pounds less thrust
Quoting Slovacek747 (Reply 9)
There is no way they can have 44K less pounds of thrust and still accomplish what the 77W can.
Simple physical relationships suggest that your doubts are unfounded... not only should the capability be similar, but the field performance should be better thanks to the much lower wing loading.

I think that to "kill" the B777 it would not suffice that the capability be similar or the field performance somewhat better, assuming this being the case. The reasons:
- As Boeing repeatedly stated, the B777-300ER will be upgraded
- The commonality factor
- The much earlier availability. Assuming very optimistically that that the EIS will be 2015, a meaningful production for the -1000 would not be achieved before 2017, meaning at least 6 years difference to a not upgraded B777-300ER.

Consequence: To "kill" the B777 the A350 must be substantially, not only somewhat superior!
 
texl1649
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 6:23 am

This makes weight targets and implementation all that much more difficult for the fairly broken-promises-prone A350 program. It's always nice to have that little bit of extra power available for weight increases.
 
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CaptSkibi
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RE: Airbus Decides On Lower Thrust Requirement On

Sun Sep 23, 2007 6:26 am

Then again, this could be the latest thing in the next round of jokes....

Before:
ATCT: "Airline 340, state type of aircraft. Are you an A340 or an A330?"
Airline 340: "We're an A340."
ATCT: "Then would you mind switching on the two other engines and give me a 1000 feet per minute, please?"

After:
ATCT: "Airline 350, state type of aircraft. Are you an A330 or an A350?"
Airline 350: "We're an A350 x-ray whiskey bravo."
ATCT: "Then would you mind switching on the other engine and give me a 1000 feet per minute, please?"



Edit for typo.

[Edited 2007-09-22 23:34:24]
Private Pilot, Airplane Single Engine Land / former frequent flyer with 9 straight years being elite on NW/DL
 
EDDB
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 6:36 am

Quoting ADent (Reply 21):
If you can build a 777 killer on 2/3 the thrust, sounds like a 747 killer (aka Boeing Y3) isn't too hard to do either as a twin.

Doing a little maths it's more like 4/5 the thrust, isn't it? And the problem with twins bigger than the 77W or 351 will be that the fan diameter will be really huge, concerning that one engine will have to get you off the ground with an engine failure at go... Generally speaking I would say that you'll have to build a 744-like twin with an empty weight maybe a little more than the 77W! At the moment I'd say that's a rather tough target than "not too hard to do"...
 
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RE: Airbus Decides On Lower Thrust Requirement On

Sun Sep 23, 2007 7:02 am

Quoting ADent (Reply 21):
sounds like a 747 killer (aka Boeing Y3) isn't too hard to do either as a twin.

less than 130 klbs would do the trick. While it's "not too hard" to do technically, the bigger obstacle is to develop such an engine profitably. The bigger the plane, the smaller the market. And with only two engines per frame sold... good luck.

Quoting Caminito (Reply 22):
it would not suffice that the capability be similar or the field performance somewhat better, assuming this being the case

You're entirely correct that it would not suffice. That's why the A350-1000 has been designed to burn ~15% less fuel per seat-mile than the 777-300ER, something which customers might possibly notice.

(have we met before? ... perhaps in the German district of Caracas? Or was it the Venezuelan section of Berlin?)

[edit: typo]

[Edited 2007-09-23 00:23:58]
 
gbfra
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 7:25 am

Quoting WingedMigrator (Reply 26):
less than 130 klbs would do the trick. While it's "not too hard" to do technically, the bigger obstacle is to develop such an engine profitably. The bigger the plane, the smaller the market. And with only two engines per frame sold... good luck.

Fair enough. Maybe four-haulers are less old-fashioned than some people her seem to think

Quoting WingedMigrator (Reply 26):
(have we met before? ... perhaps in the German district of Caracas? Or was it the Venezuelan section of Berlin?)

("The fourth incarnation" would probably be a reasonable pseudo, or am I wrong?)
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ikramerica
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 7:29 am

Quoting WingedMigrator (Reply 15):
Simple physical relationships suggest that your doubts are unfounded... not only should the capability be similar, but the field performance should be better thanks to the much lower wing loading.

My doubts are that they will be able to get the plane that light without losing payload. They are not unfounded, as right now it's a paper plane. But I have trouble believing they will reduce structural weight that much and still be able to fly the same missions as the 77W.

And looking at the 787 range vs. 777-200ER, others have shown that the 777-200ER is a bit more capable as even though both have about the same range with full pax only load, the 777-200ER has a significant advantage at full payload. A 777-200ER can go 5800nm with full payload, the 787 can't go nearly as far before they start sacrificing payload for fuel. But the fuel savings of the 787-9 or 787-10 would outweigh the lost revenue potential on longer routes, so the 772ER fades away.

I believe ultimately the A350 will the same type of tradeoff. On 5500nm routes, will the A350-1000 really be just as capable as the 77W? Or will the fuel savings outweigh the lost revenue potential...

Quoting Kaneporta1 (Reply 16):
The 90t is simply a structural payload, more than that would require extra strengthening of the floor, i.e. more empty weight. It's an engineering choice and should not be used to make assumptions about the performance of a whole family of airplanes.

Then please explain why the A350F doesn't have more range. If the structural payload is limited, but the fuel tanks aren't, so that they are the same tanks that can fly the A350R 9500nm with the same payload as the 772LR, why doesn't the A350F have more range than the 777F if it's carrying 20t less structural payload?

Again, maybe the numbers are not completely square with what Airbus is internally targeting.
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glideslope
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 7:36 am

Quoting CaptSkibi (Reply 24):
Before:
ATCT: "Airline 340, state type of aircraft. Are you an A340 or an A330?"
Airline 340: "We're an A340."
ATCT: "Then would you mind switching on the two other engines and give me a 1000 feet per minute, please?"

After:
ATCT: "Airline 350, state type of aircraft. Are you an A330 or an A350?"
Airline 350: "We're an A350 x-ray whiskey bravo."
ATCT: "Then would you mind switching on the other engine and give me a 1000 feet per minute, please?"

Ouch!!!  checkmark 
To know your Enemy, you must become your Enemy.” Sun Tzu
 
caminito
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 7:46 am

Quoting WingedMigrator (Reply 26):


[quote=Gbfra,reply=27]or am I wrong?)

I cannot tell, what do these cryptical remarks mean? Do you refer to my German "accent"?

[Edited 2007-09-23 00:51:59]

[Edited 2007-09-23 00:54:45]

[Edited 2007-09-23 01:02:56]
 
WingedMigrator
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 7:53 am

Quoting Ikramerica (Reply 28):
My doubts are that they will be able to get the plane that light without losing payload.

Airbus has not published any empty weight figures, so one is left to "back out" the weight from the performance numbers. Assuming the performance is as Airbus says, I would expect the A350-1000 to weigh in at ~143 tonnes empty (versus the 77W's 167) or about 10% less per seat. To flip the statement around, if the weights end up much above that, I would start having doubts that they could hit their performance targets.

They are being ambitious, because the 777 is already stunningly efficient from a structural standpoint.

Quoting Ikramerica (Reply 28):
why doesn't the A350F have more range than the 777F if it's carrying 20t less structural payload?

Dunno. The payload / OEW ratio is about the same for both. Range won't matter as much as fuel burn, which should be roughly 12% better per ton-mile for the A359F-- on that basis, the first twin to match the 748F.
 
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 10:06 am

Quoting NAV20 (Reply 3):
But one can still infer that the A350 remains largely a 'me too' response to the 787, rather than any sort of revolutionary design in its own right.

As I've said before, Airbus would have done well not to proceed with the A350 and instead jump to the 747/777 replacement that Boeing now calls Y3. Just as the 787 is a real leap forward, so too whatever Airbus designed in the Y3 category could have been a leap forward too, and been available sooner than Boeing's Y3.
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 11:21 am

Quoting Stitch (Reply 2):
On the dark side, it could mean that the engines can't scale as high as RR said they will

That seems improbable. They've been given years to design the engine and a clear run (so far) at the market and they seem very eager to make this airframe/engine combination a success. I would doubt that RR are unable to deliver.
 
tdscanuck
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 11:35 am

Quoting Ikramerica (Reply 28):
A 777-200ER can go 5800nm with full payload, the 787 can't go nearly as far before they start sacrificing payload for fuel.

I wanted to check this and discovered something interesting...Boeing has pulled all of the 787 payload-range charts off their website. Not sure if that's good or bad, but it must mean they're changing.

Tom.
 
747fan
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 1:11 pm

Quoting WingedMigrator (Reply 15):
Simple physical relationships suggest that your doubts are unfounded... not only should the capability be similar, but the field performance should be better thanks to the much lower wing loading.
Furthermore, if you compare the A350-1000 to the 773ER, there is clearly room for an A350-1100 that would still be lighter and have a more lightly loaded wing than the 773ER... The A350 family appears to have ample growth potential left before running into limitations of pavement loading, field performance or engine thrust.

 checkmark  When I spotted at JFK this summer, I made an interesting observation. While 77W's can often have quite impressive TO performance (rocket-like climbout, 5-6K ft. TO run) on flights such as JFK-CDG on AF, watching the Emirates 77W taking off to DXB can make you wonder if it will get off the ground... 77W's can seemingly eat up about 10K ft. of runway when near MTOW.

Quoting CaptSkibi (Reply 24):
Before:
ATCT: "Airline 340, state type of aircraft. Are you an A340 or an A330?"
Airline 340: "We're an A340."
ATCT: "Then would you mind switching on the two other engines and give me a 1000 feet per minute, please?"
After:
ATCT: "Airline 350, state type of aircraft. Are you an A330 or an A350?"
Airline 350: "We're an A350 x-ray whiskey bravo."
ATCT: "Then would you mind switching on the other engine and give me a 1000 feet per minute, please?"

Yikes! That was a good one, gave me a good laugh.  laughing  The A340 takeoff/climbout jokes live on... notice I didn't just say A343/A342 as the A340NG's also don't exactly wanna get off the ground, even on "short" flights such as JFK-LHR (although when I spotted at JFK, VS A346's seemed to be at a lower TO thrust setting). The 741 is even worse, even on flights such as SDF-ANC. However, I don't think a 4K lb. thrust reduction (or 1K w/ the -800) will make that much of a difference. So no, the A340 won't live on in twin-engined form.
 
caminito
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 1:23 pm

Quoting WingedMigrator (Reply 26):

Thank you for clarify the issue
 
WingedMigrator
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 1:45 pm

Quoting EBJ1248650 (Reply 33):
Just as the 787 is a real leap forward, so too whatever Airbus designed in the Y3 category could have been a leap forward too, and been available sooner than Boeing's Y3.

If Y3 is a twin-engine tube with wings, don't expect it to do much better than the A350 or the 787 in terms of fuel burn or CASM. You might consider the A350 essentially a leap forward in the Y2.5 category.

Quoting Tdscanuck (Reply 35):
Boeing has pulled all of the 787 payload-range charts off their website. Not sure if that's good or bad, but it must mean they're changing.

Lucky you! I have never even seen a payload range chart for the 787's on Boeing's website, unless I've been looking in all the wrong places. The documents are perpetually 'under revision'... if you've got something, I'd be very interested.
 
caminito
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 2:07 pm

Quoting WingedMigrator (Reply 38):
Lucky you! I have never even seen a payload range chart for the 787's on Boeing's website, unless I've been looking in all the wrong places. The documents are perpetually 'under revision'... if you've got something, I'd be very interested.

I assume you have the very detailed independent document for the B787-8

http://www.lissys.demon.co.uk/samp1/payrb.png June 2006[/url]

where a payload-range chart is included
 
sstsomeday
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 2:14 pm

Quoting Stitch (Reply 2):
On the dark side, it could mean that the engines can't scale as high as RR said they will and Airbus is being forced to lower MTOW to accommodate this, which could mean performance is being impacted.

Could it mean, because they have moved to composite panel technology, that the A/C is not as heavy as they had originally planned?
I come in peace
 
astuteman
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 4:29 pm

Quoting WingedMigrator (Reply 31):
I would expect the A350-1000 to weigh in at ~143 tonnes empty (versus the 77W's 167) or about 10% less per seat



Quoting WingedMigrator (Reply 31):
They are being ambitious, because the 777 is already stunningly efficient from a structural standpoint.

But are they?
If your starting point is a given engine SFC, then in order to make a given payload/range, the aircraft has to support X payload, plus Y fuel. This determines the necessary structural strength, wing strength, landing gear strength, tailplane and stabiliser sizes etc.

If you reduce SFC by "only" 8% say, in the design, then the "Y" fuel weight reduces.
Hence MTOW reduces
Hence structure weight, wing strength, LG strength, tail size etc also reduce
Hence MTOW reduces again
Hence fuel burn reduces, and "Y" fuel reduces again
And so on.......

An 8% reduction in SFC can easily lead to a design that is 20% lighter, especially if you add a CFRP wing's ability to be built greater span for a given weight.

But the 777, by definition, already has ALL of its components DESIGNED, sized and strengthened, for 350 odd tonnes MTOW.
Bang 8% better SFC engines on it and what you get is 8% (or so) more range.

In order to get anywhere near the A3510's efficiency, the 777 would need virtually the whole plane to be re-designed to accommodate a much lower MTOW, PLUS a new CFRP wing.
As others have said (repeatedly), growing the 787 has to be a) far easier, and b) far more likely to succeed.

Quoting PM (Reply 34):
That seems improbable. They've been given years to design the engine and a clear run (so far) at the market and they seem very eager to make this airframe/engine combination a success. I would doubt that RR are unable to deliver.

I suspect you can scratch that as a reason for the thrust reduction.  checkmark 

Guessing, I'd suspect wind-tunnel work has revealed better lift than anticipated, (maybe even better L/D  crossfingers  ),
thus allowing a lower T/O thrust rating.
Either way, it sounds like good news.

I wonder if they'll keep the 95k lb capability for growth?  Smile

Regards
 
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 4:40 pm

Quoting Astuteman (Reply 41):
I wonder if they'll keep the 95k lb capability for growth?

Always nice to have something up your sleeve.  Wink And what would an A350-11 need in terms of thrust?

RR could have a real winner on their hands here. All they need now is a sensible name for it.  banghead 
 
justloveplanes
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 10:32 pm

Quoting Astuteman (Reply 40):
But the 777, by definition, already has ALL of its components DESIGNED, sized and strengthened, for 350 odd tonnes MTOW.
Bang 8% better SFC engines on it and what you get is 8% (or so) more range.

If 8% less fuel is carried instead of extending range, is this closing the gap a bit from th 15% fuel burn advantage to say, 5%?

Maybe a CFRP wing box and slats and what nots can get the weight down enough for another 1% for maybe a gap of 4%. Af
 
sstsomeday
Posts: 821
Joined: Thu Oct 26, 2006 2:32 pm

RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 10:52 pm

Quoting Astuteman (Reply 40):
But are they?
If your starting point is a given engine SFC, then in order to make a given payload/range, the aircraft has to support X payload, plus Y fuel. This determines the necessary structural strength, wing strength, landing gear strength, tailplane and stabiliser sizes etc.

If you reduce SFC by "only" 8% say, in the design, then the "Y" fuel weight reduces.
Hence MTOW reduces
Hence structure weight, wing strength, LG strength, tail size etc also reduce
Hence MTOW reduces again
Hence fuel burn reduces, and "Y" fuel reduces again
And so on.......

Is not a factor determining optimum thrust the ability to depart smaller runways and/or runways with obstacles, etc? Plus if you get up to altitude faster, does that not save on fuel, especially with long haul flights?
I come in peace
 
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 11:27 pm

Quoting SSTsomeday (Reply 43):
Plus if you get up to altitude faster, does that not save on fuel, especially with long haul flights?

Every plane has an optimum cruise profile. Some are steeper than others. Getting to altitude quicker can make it easier to secure a higher cruise altitude from ATC, and jets are more efficient at higher altitudes.
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The heart has its beaches, its homeland and thoughts of its own
Wake now, discover that you are the song that the morning brings
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astuteman
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 11:35 pm

Quoting SSTsomeday (Reply 43):
Is not a factor determining optimum thrust the ability to depart smaller runways and/or runways with obstacles, etc?

 checkmark 

Quoting Astuteman (Reply 40):
Guessing, I'd suspect wind-tunnel work has revealed better lift than anticipated, (maybe even better L/D ), thus allowing a lower T/O thrust rating.

 Smile
 
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Stitch
Posts: 27311
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RE: Airbus Decides On Lower Thrust Requirement On A350

Sun Sep 23, 2007 11:35 pm

Quoting SSTsomeday (Reply 39):
Could it mean, because they have moved to composite panel technology, that the A/C is not as heavy as they had originally planned?

Yes. This is the more likely reason.
 
caminito
Posts: 115
Joined: Wed Sep 19, 2007 11:04 am

RE: Airbus Decides On Lower Thrust Requirement On A350

Mon Sep 24, 2007 12:00 am

Quoting Laxintl (Thread starter):
Full strory; (subscription required)



Quoting SSTsomeday (Reply 39):
Could it mean, because they have moved to composite panel technology, that the A/C is not as heavy as they had originally planned?

If so, probably McConnell should have told so.
LAXINTL or anybody: as until now we were not able to read the article, could you tell us if he mentioned the reasons of the thrust reduction?
 
Rheinbote
Posts: 1103
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RE: Airbus Decides On Lower Thrust Requirement On A350

Mon Sep 24, 2007 12:23 am

Quoting Stitch (Reply 46):
Quoting SSTsomeday (Reply 39):
Could it mean, because they have moved to composite panel technology, that the A/C is not as heavy as they had originally planned?

Yes. This is the more likely reason.

Quote from the article
"Designers learned the aircraft's low-speed performance was better than expected, allowing the move to lower thrust, said Gordon McConnell, chief program engineer."

More lift than expeted, less drag than expected, or both.
 
caminito
Posts: 115
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RE: Airbus Decides On Lower Thrust Requirement On A350

Mon Sep 24, 2007 1:32 am

Quoting Rheinbote (Reply 48):
Quote from the article
"Designers learned the aircraft's low-speed performance was better than expected, allowing the move to lower thrust, said Gordon McConnell, chief program engineer."

Please excuse my ignorance.

If the low-speed performance is better, this does imply that at the normally used speed (Cruise Speed A350 = 0.85 Mach) it is better too??
Will this nominal Cruise speed figure remain with the lower thrust engines?

Even this is probably a flawed comparison, the thrust of the A350-800 equivalent B787-9 engines is only 70,000 lb., still quite below the 74,000 lb. now indicated by Airbus. I assume this is related to that the same engine is foreseen for the larger A350s?

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