Wsp
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A350 Increased Speed?

Mon Jul 09, 2007 6:59 am

Airbus did some housekeeping on their A350 pages recently. They now include some specs:

http://www.airbus.com/en/aircraftfam.../a350/a350-800/specifications.html

Their old flash intro (still online) claims Mach number 0.85 the spec pages now claim 0.89.

How much would the economic advantage of such an speed improvement be in real operations ?
 
ikramerica
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RE: A350 Increased Speed?

Mon Jul 09, 2007 7:16 am

that's .85 optimal cruise, 0.89 max cruise.

as a contrast, the A340 has an optimal cruise of 0.825

it makes a difference, up to an hour on longer flights.
Of all the things to worry about... the Wookie has no pants.
 
Wsp
Topic Author
Posts: 356
Joined: Sun May 06, 2007 7:43 am

RE: A350 Increased Speed?

Mon Jul 09, 2007 7:26 am

Quoting Ikramerica (Reply 1):
that's .85 optimal cruise, 0.89 max cruise.

That makes sense. Maybe they should put both values in the specs for clarity. But then given the huge gaps in there this would probably be asking too much...
 
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zeke
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RE: A350 Increased Speed?

Mon Jul 09, 2007 10:15 am

Quoting Ikramerica (Reply 1):
it makes a difference, up to an hour on longer flights.

What do you call a longer flight ?

Our schedules don't show that sort of difference where the 744 and 340 are operated on the same route, e.g. HKG-LHR the difference is 20-30 min for a 13 hr sector.
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speedbird128
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RE: A350 Increased Speed?

Tue Jul 10, 2007 3:39 am

If I remember right - every Mach 0.01 roughly equates to 6 knots TAS. So the difference from M0.825 (A330/340) to M0.855 (for the 744) is approx 18knots. That equates to around 18nm more covered in 1 hour, so on a 10 hour flight would then be 180nm ahead, which, lets say on a GS of 490, equates to around roughly 22 minutes faster at M0.855.
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ikramerica
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RE: A350 Increased Speed?

Tue Jul 10, 2007 3:49 am

Quoting Zeke (Reply 3):
Our schedules don't show that sort of difference where the 744 and 340 are operated on the same route, e.g. HKG-LHR the difference is 20-30 min for a 13 hr sector.

Give me a break.

30 minutes is longer, and it can be up to an hour, because when a plane is late getting off the gate, the 744 can make up for it much, much easier.

If it didn't matter much, as you imply, why is Airbus so adamant about the new speed of the A350? Why did customers demand it be faster than the 330/340? It matters to everyone but you, I guess...
Of all the things to worry about... the Wookie has no pants.
 
Maersk737
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RE: A350 Increased Speed?

Tue Jul 10, 2007 3:55 am

Quoting Ikramerica (Reply 5):
Give me a break.

30 minutes is longer, and it can be up to an hour, because when a plane is late getting off the gate, the 744 can make up for it much, much easier.

If it didn't matter much, as you imply, why is Airbus so adamant about the new speed of the A350? Why did customers demand it be faster than the 330/340? It matters to everyone but you, I guess...

Why don't you just admit you were a little wrong ?  Wink

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zeke
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RE: A350 Increased Speed?

Tue Jul 10, 2007 10:03 am

Quoting Speedbird128 (Reply 4):
If I remember right - every Mach 0.01 roughly equates to 6 knots TAS. So the difference from M0.825 (A330/340) to M0.855 (for the 744) is approx 18knots. That equates to around 18nm more covered in 1 hour, so on a 10 hour flight would then be 180nm ahead, which, lets say on a GS of 490, equates to around roughly 22 minutes faster at M0.855.

Sounds about right for some operators, our 744s are flown at cost index derived econ speeds, not fixed mach number (AFAIK for example SQ does fixed mach number of 0.85), so they generally start slower than .84 and build up to .85, not getting to .855.

Quoting Ikramerica (Reply 5):

30 minutes is longer, and it can be up to an hour, because when a plane is late getting off the gate, the 744 can make up for it much, much easier.

Spoken by a person who has never operated the route, they have 10 minute spacing on the route, it is not like you can just run over an aircraft infront.

Quoting Maersk737 (Reply 6):
Why don't you just admit you were a little wrong ?

Yes that seems to very hard for some....what he does not know is the 340 actually tends to make more time up HKG-LHR because of the route flown (744s and 340 take different routes), and the 340 speed was selected with customer input.
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iboam
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RE: A350 Increased Speed?

Tue Jul 10, 2007 11:41 am

Just curious, but why do A340's take different routes than B744's? Well, at least on HKG-LHR?
 
XT6Wagon
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RE: A350 Increased Speed?

Tue Jul 10, 2007 11:47 am

Zeke, so why did Airbus "wave a magic wand" with the A380 and A350 to set thier speeds to M.855 cruise, both cases without engineering changes from when they were rated lower. Only recently did the A350XWB recieve extra wing sweep over the "designed in powerpoint" phase specs.
 
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zeke
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RE: A350 Increased Speed?

Tue Jul 10, 2007 1:43 pm

Quoting Iboam (Reply 8):
Just curious, but why do A340's take different routes than B744's? Well, at least on HKG-LHR?

There are a limited number of ways to get to Europe from HKG, the older ways are not used any more as they are somewhat longer for northern Europe, but are still used for southern routes like Rome and the middle east that take you over India (sometimes also used when airspace is closed for say rocket launching). The northern routes have limited slots and you are allocated a slot for a particular flight by the Russian and Chinese authorities onto which routes you may fly most of them join up around Novosibirsk and all the traffic then basically follows the same path to St. Petersburg (another route takes you over Moscow but is longer) after that they start splitting up again depending on the destination in Europe. Sometimes you are not allowed to push back at HKG or LHR due to enroute slots times, this is also very common out of SIN where they have similar restrictions over the bay of bengal and the middle east..

I think historically the shorter routes were first to be used, and once saturated the others were populated based on slot restrictions. We tend to used the 340s to open up new long haul destinations or frequencies and then once established place larger capacity aircraft on it, so eventually I would think the other LHR flights that are being done by 340s will be upgraded to 744s and the 340s deployed onto new routes or frequencies, so give it time I think the 744 will be on the other routes as well.

Quoting XT6Wagon (Reply 9):
Only recently did the A350XWB recieve extra wing sweep over the "designed in powerpoint" phase specs.

Incorrect, the A350XWB always had a higher sweep angle than the A330 or the A350OG and the same cruise speed as the A380.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
speedbird128
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RE: A350 Increased Speed?

Wed Jul 11, 2007 1:32 am

Quoting Ikramerica (Reply 5):
30 minutes is longer, and it can be up to an hour

A one hour lead over an aircraft flying M0.825 over a 13hour leg, would require to be 490nm ahead, which would require roughly an extra TAS of 46knots extra per hour... (an extra M0.075).

Quoting Zeke (Reply 7):
Sounds about right for some operators, our 744s are flown at cost index derived econ speeds, not fixed mach number (AFAIK for example SQ does fixed mach number of 0.85), so they generally start slower than .84 and build up to .85, not getting to .855.

For sure - I was just using that based on the ECON CRZ of the 744 which I thought to be around M0.855.

The equation was just there for those wondering how much (or little) a higher mach number can make...
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Pihero
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RE: A350 Increased Speed?

Wed Jul 11, 2007 2:42 am

Quoting Ikramerica (Reply 5):
because when a plane is late getting off the gate, the 744 can make up for it much, much easier.

A piece of reasoning that I find wanting :
The schedule of a flight is based on its commercial speed. If it's late off the gate, there is a possibility of cruising at an "accelerated" mach, generally within 2 to 3 points. As the effect of the same increment is greater on the slower airplane, it has an easier job of getting to destination on schedule. (That applies to rich airlines... the cost of the extra fuel needs to be taken into account ). QED
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