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A350 Economic Cruise Speed Will Be M0.84  
User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Posted (8 years 7 months 3 weeks 1 day 19 hours ago) and read 3916 times:

I could not find any threads regarding this article so here it goes:

Flight International - Aerodynamic ‘tweaks’ boost Airbus A350 cruise speed

Airbus has, after assessing the areodynamics of the wings and nose, remodelled the aircraft before the due design freeze. The mid-section of the upper wing surface has been changed, as well as the fairings. They have also changed the shape of the nose in order create more room for the crew rest area, and improve aerodynamics. This modified design includes a [simplified] version of the flight deck windows.

The economic crusing Mach No. of the A350 is now M0.84  Smile


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20 replies: All unread, jump to last
 
User currently offlineKaneporta1 From Greece, joined May 2005, 739 posts, RR: 12
Reply 1, posted (8 years 7 months 3 weeks 1 day 18 hours ago) and read 3860 times:

The winglets are also 30% than the A330/340


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User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Reply 2, posted (8 years 7 months 3 weeks 1 day 18 hours ago) and read 3813 times:

Quoting Kaneporta1 (Reply 1):
The winglets are also 30% than the A330/340

Sorry I don't understand. What do you mean? 30% the size of the winglets on the A330/A340?



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User currently offlineA360 From Portugal, joined Jun 2005, 434 posts, RR: 8
Reply 3, posted (8 years 7 months 3 weeks 1 day 18 hours ago) and read 3785 times:

Quote:
Hunter says the changes “delay the onset of drag rise and push long-range cruise speed up from Mach 0.82 to 0.83, and economic cruise speed to Mach 0.84”.

In the article it says the long range cruise speed will be of mach 0.83 and the economical cruising speed will be 0.84 mach.
What's the diference between long range cruise speed and economical cruising speed??

Regards:
A360


User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Reply 4, posted (8 years 7 months 3 weeks 1 day 18 hours ago) and read 3745 times:

Quoting A360 (Reply 3):
What's the diference between long range cruise speed and economical cruising speed??

M0.84 will be the most economic cruising speed, but M0.83 will be the cruising speed to fly the longest range.



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User currently offlineSabenapilot From Belgium, joined Feb 2000, 2714 posts, RR: 47
Reply 5, posted (8 years 7 months 3 weeks 1 day 18 hours ago) and read 3714 times:

in fact this has been reported already somehow on the forum:

http://www.airliners.net/discussions...ion/read.main/2472795/6/#ID2472795

Quoting A360 (Reply 3):
What's the diference between long range cruise speed and economical cruising speed??

-) long range cruise speed is -at the word already says- the speed you need to fly to get a considerable better range out of your fuel than normally, (not the absolute longest range possible, because that would be called 'longest range cruise speed' which is much lower than 'long range cruise speed'). You are however, trading in on speed, and thus loosing some time.

-) economical cruising speed is the speed you need to fly to get the trip costs as low as possible, taking into account both fuel used as well as time spent over the stretch. You could do it faster, but then you are burning more fuel, or you could burn less than at economical cruising speed, but than it will take you longer (which will cost you more over time because of maintenance, less flights a year with one plane etc)

[Edited 2005-12-13 13:45:59]

User currently offlineMidnightMike From United States of America, joined Mar 2003, 2892 posts, RR: 14
Reply 6, posted (8 years 7 months 3 weeks 1 day 18 hours ago) and read 3698 times:

Quoting Kaneporta1 (Reply 1):
The winglets are also 30% than the A330/340

Can you explain that one a little better? 30% of the size or weight?



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User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Reply 7, posted (8 years 7 months 3 weeks 1 day 18 hours ago) and read 3681 times:

Quoting Sabenapilot (Reply 5):
in fact this has been reported already somehow on the forum:

http://www.airliners.net/discussions...72795

Nope, that was an article from last week and discussed something different. This article just came out from the oven today and includes new developments  Smile

Also, the title of that thread is not correct anymore since the speed has been increased again.



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User currently offlinePyrex From Portugal, joined Aug 2005, 3948 posts, RR: 28
Reply 8, posted (8 years 7 months 3 weeks 1 day 18 hours ago) and read 3641 times:

Just for some comparison, what are the equivalent values for the 787?


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User currently offlineA360 From Portugal, joined Jun 2005, 434 posts, RR: 8
Reply 9, posted (8 years 7 months 3 weeks 1 day 18 hours ago) and read 3620 times:

I see... what would be the values for the eco cruise speed and long range cruise speed for a 777, or 744 for example?
I know that the cruise speeds are 0.84 for the 777 and 0.855 for the 744... but are those economical cruise speeds or long range cruise speeds?

Regards:
A360


User currently offlineKappel From Suriname, joined Jul 2005, 3533 posts, RR: 17
Reply 10, posted (8 years 7 months 3 weeks 1 day 18 hours ago) and read 3583 times:

Quoting A360 (Reply 9):
I see... what would be the values for the eco cruise speed and long range cruise speed for a 777, or 744 for example?
I know that the cruise speeds are 0.84 for the 777 and 0.855 for the 744... but are those economical cruise speeds or long range cruise speeds?

I believe those are the economical cruise speeds. For the 787 it would be 0.85



L1011,733,734,73G,738,743,744,752,763,772,77W,DC855,DC863,DC930,DC950,MD11,MD88,306,319,320,321,343,346,ARJ85,CR7,E195
User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Reply 11, posted (8 years 7 months 3 weeks 1 day 18 hours ago) and read 3560 times:

According to the website, the economic cruise speed for the B744 is M0.85, the B773 is M0.84, and the B787 is M0.85.

If you want to compare, that's M0.86 for the A388, M0.83 for the A332, and M0.84 for the A358.

But please lets just aknowledge that all of the above are great works of engineering, and lets not make this another AvB thread!!! Thanks  Smile



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User currently offlineKappel From Suriname, joined Jul 2005, 3533 posts, RR: 17
Reply 12, posted (8 years 7 months 3 weeks 1 day 17 hours ago) and read 3517 times:

Quoting FlyAUA (Reply 11):
that's M0.86 for the A388, M0.83 for the A332

I thought it was 0.85 for athe a380 and 0.82 for the a332. The a345 and 346 have an econ cruise speed of 0.83. I could of course be wrong.



L1011,733,734,73G,738,743,744,752,763,772,77W,DC855,DC863,DC930,DC950,MD11,MD88,306,319,320,321,343,346,ARJ85,CR7,E195
User currently offlineKaneporta1 From Greece, joined May 2005, 739 posts, RR: 12
Reply 13, posted (8 years 7 months 3 weeks 1 day 17 hours ago) and read 3517 times:

Actually, I'm sorry everyone, I meant to type that the winglets will be 30% BIGGER but I was in a big hurry. Sorry again.


I'd rather die peacefully in my sleep, like my grandfather, not terrified and screaming, like his passengers
User currently offlineGrbld From Netherlands, joined Dec 2005, 353 posts, RR: 3
Reply 14, posted (8 years 7 months 3 weeks 1 day 17 hours ago) and read 3474 times:

There just simply is NO "fixed" economic airspeed. For any given trip, distance, payload, it's different. And this figure is set in the FMC by way of the Cost Index (CI), which is your ratio between fuel costs and time costs. A CI of 0 (zero) means that fuel costs are most important and you don't care about time. It is roughly equivalent to Long Range Cruise speed. A CI of 900 means that time is more important than fuel costs, and the speed is also higher. Both are "the most economical speed" to fly that leg on that day on that route.

Time costs are related to ATC slots, airport closures, crew duties, airframe usage and also related to routing and weather conditions. If you have to fly a slightly longer route than average for to avoid headwind jet streams, you may risk arriving late and it is possible that it's better to increase your CI to offset this, even though your fuel burn goes up.

So "the most economic speed", I don't know what it is. The range between zero and a high CI may be as much as .06 Mach (which is a lot!)

Grbld


User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Reply 15, posted (8 years 7 months 3 weeks 1 day 17 hours ago) and read 3457 times:

Quoting Kappel (Reply 12):
I thought it was 0.85 for athe a380 and 0.82 for the a332

Sorry I am not sure about the A388, so if I was mistaken, I stand corrected. But I am about the A332... I think most captains will tell you it's (to be precise) M0.825, however I noticed it as M0.83 almost always, not M0.82.

It's tricky to compare because both manufacturers use different ways of representing their aircraft specifications. One uses Maximum Operating while the other uses Economic Operating. You will find that, in real life, it will vary from one operation to another anyways. It depends on the weight of the aircraft that day, the fuel on board, the cost index which the captain has opted to fly at, and many other things. Mach numbers are not concrete but rather an indication of an aircraft's ability. The real cruising number will be mostly calculated by the FMS. It can of course vary when the flight crew decide that they need to catch up on lost time, or if ATC imposes a speed restriction to ensure separation.

Because of all of the above, this is why I prefer to know about Max. Operating Mach Numbers instead of Economic. Economic is a very vague term that changes from one operation to another. I wish Boeing would also use it in their aircraft specs, or at least I wish that both manufacturers displayed both, so that it is left to the industry to decide how they want to compare.

Having said all that, don't forget when you are talking about the difference between M0.82 or M0.83 this - using the rule of thumb - represents only 6 knots of groundspeed, roughly.

Edit: Grbld you beat me to it! LOL Big grin

[Edited 2005-12-13 14:29:43]


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User currently offlineZeke From Hong Kong, joined Dec 2006, 8883 posts, RR: 75
Reply 16, posted (8 years 7 months 3 weeks 1 day 17 hours ago) and read 3411 times:

Quoting Sabenapilot (Reply 5):
-) long range cruise speed is -at the word already says- the speed you need to fly to get a considerable better range out of your fuel than normally, (not the absolute longest range possible, because that would be called 'longest range cruise speed' which is much lower than 'long range cruise speed'). You are however, trading in on speed, and thus loosing some time.

Only nil wind, or for maximum ground naultical miles, with a headwind you maybe better off with a higher speed, and tailwind, closer to a cost index 0 speed for the real long range distance.

The long range cruise speed is generally a fuction of angle of attack, and will vary with mass.



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User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3477 posts, RR: 67
Reply 17, posted (8 years 7 months 3 weeks 1 day 16 hours ago) and read 3320 times:

In Airplane Performance terms, Long Range Cruise (LRC) speed has a fixed definition, ie a speed faster than Maximum Range Cruise (MRC) speed with 1% lower fuel mileage.

If an airplane flies at MRC, the resultant range will be the best it can achieve for a given payload and fuel quantity.

LRC is picked on the high side of MRC to make sure the airplane has speed stability. At MRC, drag varies only slightly for speeds to either side of MRC and the airplane "hunts" for a stable speed if flown hands off. This was more of a problem with early autopilots and autothrottles than it is for today's airplanes.

Zeke is correct that MRC and LRC are not constant but vary with weight and altitude. However, if an airplane is operated in a weight/altitude band consistent with normal operation, it is possible to determine a typical LRC as follows:

757/767: .80
A330: .82
A345/6: .83
777: .84
747: .85
787: .85

If Airbus says the A350 LRC is .83M, that is fairly well defined. By saying economic cruise speed is .84, they are saying the resultant fuel burn increase is offset by other cost factors such as crew pay, increased flights per day etc.

[Edited 2005-12-13 15:33:25]


Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineA360 From Portugal, joined Jun 2005, 434 posts, RR: 8
Reply 18, posted (8 years 7 months 3 weeks 1 day 16 hours ago) and read 3231 times:

Hum.... will it be the same speed as the 345/346 (0.825) or really 0.830?

Regards:
A360


User currently offlineOHLBU From Finland, joined Jan 2005, 226 posts, RR: 0
Reply 19, posted (8 years 7 months 3 weeks 1 day 13 hours ago) and read 2997 times:

When Finnair recently ordered the A359 they said that they demanded Airbus to increase the speed closer to MD-11's. I don't know if this the result or whether Airbus is studying a further increase?

User currently offlineMikkel777 From Norway, joined Oct 2002, 370 posts, RR: 1
Reply 20, posted (8 years 7 months 3 weeks 1 day 11 hours ago) and read 2805 times:

IIRC, a heavy 744 at the beginning of a long trip at FL290 will have a machnumber that is more than 0.01 lower than the machnumber at the end of the trip, 10 000ft higher. TAS on the other hand, will be a lot more constant. I don't remember if the TAS is constant, or only close. Tis is, of course, with the same CI.

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