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DocLightning
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757 Vs A321LR

Thu Mar 12, 2015 5:20 pm

(Mods, I'm not sure if this is better suited to tech ops, so mea culpa if I guessed wrong)

Lately, I've seen a lot of debates on the 757-200 with winglets vs the A321LR and what limitations the A321LR will have with respect to the 757.

The trouble with these discussions is that people make all sorts of claims about the A321LR and yet I cannot find very much factual information about it. So, if you comment in this thread, I'd ask you to post specifics and your sources.

The only real info I've been able to find is this:
http://oi57.tinypic.com/5pof8z.jpg

This would indicate that at most missions, the A321LR is similar to the 75W in capability, if not slightly better.

So what operational limitations would affect the A321LR?
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tortugamon
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RE: 757 Vs A321LR

Thu Mar 12, 2015 5:30 pm

I have a hard time believing a chart that says the A321LR has more range than the 752 with winglets;

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bgm
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RE: 757 Vs A321LR

Thu Mar 12, 2015 6:05 pm

Quoting tortugamon (Reply 1):
I have a hard time believing a chart that says the A321LR has more range than the 752 with winglets;

Why is that?

The A321 NEO has much more efficient engines, and both planes are comparable in size, so it's not unbelievable at all. Doc, where is this graph is sourced from?
 
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RE: 757 Vs A321LR

Thu Mar 12, 2015 6:10 pm

To expand on the above, it has been my understanding that the 321NEOLR will still fall a few percent short the further "up and to the right" you get on the graph (longer range at a given payload). It gets ever closer to the 757, but still falling short at the extreme end of the range chart with a full load. If that's not the case then great, but it would be news to me if so.
 
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RE: 757 Vs A321LR

Thu Mar 12, 2015 6:11 pm

Quoting tortugamon (Reply 1):

I have a hard time believing a chart that says the A321LR has more range than the 752 with winglets;

It's not the range that gets me, it's the payload. That said the 757 is an older airframe so I suppose the more advanced wing + engines makes all he difference.
 
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RE: 757 Vs A321LR

Thu Mar 12, 2015 6:17 pm

This is one of two charts we need to make a basic evaluation of the two aircraft. The other is the field performance chart. The LR will have more thrust, more weight, and the same undersized wing... will it maintain the A321's acceptable, but not great, field performance?

There may be other factors for specific operators (such as UA's ability to get high enough out of DEN to cross the Rockies with a margin of safety for engine failure) but at a general level those are the two things we need.

This payload-range chart shows that the A321LR will probably out-range the 757 in typical low-density international configurations, but won't be able to keep up with the 757 in high-density charter configurations or with really heavy cargo.

[Edited 2015-03-12 11:18:09]
 
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RE: 757 Vs A321LR

Thu Mar 12, 2015 6:28 pm

Quoting bgm (Reply 2):
The A321 NEO has much more efficient engines, and both planes are comparable in size, so it's not unbelievable at all. Doc, where is this graph is sourced from?

This is actually an Airbus chart that was produced when the LR was launched.

Quoting LHCVG (Reply 3):
it has been my understanding that the 321NEOLR will still fall a few percent short the further "up and to the right" you get on the graph (longer range at a given payload). It gets ever closer to the 757, but still falling short at the extreme end of the range chart with a full load. If that's not the case then great, but it would be news to me if so.

The thing that made this chart interesting is that, where the Leeham articles which signposted the LR decision quoted a range of 4000Nm with 168 passengers, Airbus quoted a range of 4000Nm with 206 passengers as shown on the chart.
That is significantly more capable than had originally been envisaged in the early Leeham articles.

I'm sure I've seen a quote from ALC the only customer, somewhere that corroborates this slight advantage over the 757 but have to confess I can't find it, so take that as you will.

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RE: 757 Vs A321LR

Thu Mar 12, 2015 8:40 pm

The most obvious disadvantage of the A321LR is simply space, a bit less space in the cabin and really less space in belly due to the three belly tanks.
I do not know if there is a design freeze with clear data for the A321LR?

Regarding the graph, I think the range with full load is a bit on the low side for a 757-200WL, perhaps rather data for the 757-200 without winglets. I would add about 200 nm to that.

[Edited 2015-03-12 14:16:32]
 
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RE: 757 Vs A321LR

Fri Mar 13, 2015 3:05 am

The A321NeoLR design isn't frozen yet. However also consider Boeing's specs on the 757 without winglets
passengers 200-228
range 3900 Naut miles (7222 KM)
MTOW 255,00 lb (115,680 KG)

Well Airbus got one number correct so should we base a paper airplanes performance against skewed data and call iot a meaningful discussion?
 
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RE: 757 Vs A321LR

Fri Mar 13, 2015 5:06 am

Quoting kanban (Reply 8):

Well Airbus got one number correct so should we base a paper airplanes performance against skewed data and call iot a meaningful discussion?


APB offers this chart. Who knew payload-range charts could be so subjective?

Quoting seabosdca (Reply 5):

This is one of two charts we need to make a basic evaluation of the two aircraft. The other is the field performance chart. The LR will have more thrust, more weight, and the same undersized wing... will it maintain the A321's acceptable, but not great, field performance?

I heard it will have Thrust/MTOW ratio slightly higher than the 752. I don't know if that helps at all. I also know the A321 is the only family member to feature double-slotted flaps to help with field performance.
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RE: 757 Vs A321LR

Fri Mar 13, 2015 8:15 am

Quoting DocLightning (Reply 9):
APB offers this chart. Who knew payload-range charts could be so subjective?

If you go by the A330neo Launch Presentation a Boeing nautical mile has around 1650-1700 meters instead of the more conventional 1854 meters Airbus uses.....   

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RE: 757 Vs A321LR

Fri Mar 13, 2015 12:03 pm

And how many current 757 routes need the top right of that chart?

18% of the current 757 fleet are used on routes of over 4000km. 17% have more than 200 seats fitted.

http://www.flightglobal.com/news/art...sis-what-are-757s-used-for-409003/
 
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RE: 757 Vs A321LR

Fri Mar 13, 2015 12:28 pm

It'll probably carry similar payloads over similar distances, but I believe it'll trail the 757 badly in terms of takeoff performance, especially in hot and high scenarii.

Now, does it really need that kind of performance? Doubt it.
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RE: 757 Vs A321LR

Fri Mar 13, 2015 3:53 pm

Quoting DocLightning (Reply 9):
I heard it will have Thrust/MTOW ratio slightly higher than the 752. I don't know if that helps at all.

That definitely helps, but it still has a much smaller wing than the 757. The double-slotted flaps help it get off the ground, but they don't help climb performance in the air (which is likely the biggest of the "issues" UA was talking about because it's very important for DEN-Hawaii).

A bigger wing (with the bigger tanks it implies) would make the A321neo into a 757 beater in every respect. Unfortunately for Airbus, it would be a lot more expensive than anything else they're doing to the A320 series.

[Edited 2015-03-13 08:54:07]
 
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RE: 757 Vs A321LR

Sat Mar 14, 2015 2:43 am

Quoting seabosdca (Reply 13):
That definitely helps, but it still has a much smaller wing than the 757. The double-slotted flaps help it get off the ground, but they don't help climb performance in the air (which is likely the biggest of the "issues" UA was talking about because it's very important for DEN-Hawaii).

Are you saying that out of DEN on a hot day, the A321LR might take over 30 miles to get above the peaks that go no higher than FL 140? The foothills of the Rockies are about 30 miles west of DEN. The peaks don't get tall for ~40mi.
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RE: 757 Vs A321LR

Sat Mar 14, 2015 1:52 pm

Quoting DocLightning (Reply 9):
I also know the A321 is the only family member to feature double-slotted flaps to help with field performance.
Quoting seabosdca (Reply 13):
The double-slotted flaps help it get off the ground,

No. The double slotted flaps on the A321 are only there in order to increase the aft-body rotation clearance of the stretched fuselage, i.e decreasing the landing attitude. The Cl increment is, very basically, negligible, hence the much higher approach speed of the A321... but the max Cl is achieved at a much reduced AoA... and attitude.

It is interesting to notice that, with the data at our disposal, the 757 and the 321LR have the same thrust to weight ratio and probably very comparable Cl/Cd ratios, which suggests that their climb performance at their respective MTOW could be similar, the 321LR using in all probability a higher climb speed.
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RE: 757 Vs A321LR

Sun Mar 15, 2015 2:49 am

Quoting Pihero (Reply 15):
No. The double slotted flaps on the A321 are only there in order to increase the aft-body rotation clearance of the stretched fuselage, i.e decreasing the landing attitude. The Cl increment is, very basically, negligible, hence the much higher approach speed of the A321... but the max Cl is achieved at a much reduced AoA... and attitude.

I hoped you'd chime in, Pihero. Thanks!  

I did not know that. How does that work? Do they cause an aftward shift in the center of lift when extended?
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RE: 757 Vs A321LR

Sun Mar 15, 2015 1:29 pm

Quoting DocLightning (Thread starter):

This would indicate that at most missions, the A321LR is similar to the 75W in capability, if not slightly better.

That chart does not actually say that. Virtually no airline is operating a 75W beyond the second kink in the curve. The maximum 757 range is between the 3300nm and 3700nm kinks in the chart. The first kink is when the airplane approaches maximum take off weight. The second kink in the curve is where the airplane reaches fuel tank capacity. Using data beyond the second kink (to the right of it) is not very useful in real world operations. The second kink can always be moved to the right by adding more fuel (more aux tanks). As far as I know, no flights on the 757 are operating at fuel tank capacity limit (even TXL-EWR on UA is not necessarily at fuel tank capacity). If you go beyond the second kink, weight is being reduced with no additional fuel added so that the airplane burns less in the air. This is a terribly inefficient way to increase range since payload restrictions are severe. Airlines are operating at MTOW usually when range limited. The A321 & A320 can be fuel volume limited at MTOW, which is why there are aux tanks needed. The 757 doesn't really have this problem.

That chart shows the A321LR having more range at extremely high ranges with 3 full aux tanks. In reality, Airbus is increasing the takeoff weight by 7,000lbs, yet those three tanks require 15,000lbs of fuel. There is not an adequate payload increase for all aux tanks to be efficiently used. I have heard from load planners and pilots that with an aux tank the A321 gets very sensitive for weight and balance when any cargo (even passenger baggage) is being carried. For marketing purposes, Airbus shows all three aux tanks, but there are some problems with that because they MTOW is not high enough for them to not reduce useable payload. What that means is that there are going to be some payload restrictions and weight and balance problems at a 4000nm range. I don't think any airline will operate the plane near those limits because I don't know of any airline that currently operates a 757 at that extreme end of the performance chart.

In summary, the horizontal lines don't really represent a realistic configuration. Move back to 3300-3700nm to see the maximum realistic range. At these numbers, the 757 does have more range or payload. If an airline was trying to operate a 757 way out at those low payload, long range numbers, they would have added an aux tank and ended up exactly on top of the 2nd kink on the A321LR. For the purpose of marketing, Airbus and Boeing can always add an aux tank, adjust the payload numbers and increase range. Boeing did this with the 737-900ER potentially 738ERX and Airbus has done it with the A321. With multiple aux tanks, those airplanes become a nightmare for weight and balance in regular operation.

At realistic operating ranges, the A321LR is similar, but the 757 is a little better until at the extreme edge of the payload and range.. The very interesting thing from that chart is that between the first and second kink, you can see the 757 drops off much faster than the A321LR. That is showing how much more fuel efficient the A321LR is going to be. I know that will excite some interest since those are massive fuel burn rate differences. Even if the A321LR won't quite match range in the realistic range, it will burn far less fuel.

[Edited 2015-03-15 06:33:25]
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RE: 757 Vs A321LR

Sun Mar 15, 2015 2:42 pm

Quoting DocLightning (Reply 16):
Thanks!

And thank you !
There is on the net - if you wish I could provide the link - a NASA paper on *airliners'high lift systems* which studies and compares most of the major OEMs productions, from the 707 to the 777, the DC-10, the L-1011 and all the Airbus products. Missing are of course the latest entrants, i.e the 787 and the 380 and 350.

Quoting DocLightning (Reply 16):
How does that work? Do they cause an aftward shift in the center of lift when extended?

The main advantage of the A321 double-slotted flap system is achieving the same Cl.appr at a reduced ( circa 3 degrees ) AoA, hence attitude, but at the cost of some major complication.
See for instance the number of fairings on an A321 compared to an A320 :

The A320 :


View Large View Medium
Click here for bigger photo!

Photo © Marco Zeininger



and the A321 :


View Large View Medium
Click here for bigger photo!

Photo © Vyacheslav Firsov - Almaty Spotting Club



This is the link to NASA study 1996

See figures 2.22 and 2.23 for the schematics of the A320 /321 ;

Regards.

[Edited 2015-03-15 07:51:59]

[Edited 2015-03-15 07:52:45]
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RE: 757 Vs A321LR

Sun Mar 15, 2015 7:00 pm

Quoting Pihero (Reply 18):
The main advantage of the A321 double-slotted flap system is achieving the same Cl.appr at a reduced ( circa 3 degrees ) AoA, hence attitude, but at the cost of some major complication.
See for instance the number of fairings on an A321 compared to an A320 :

So it would increase the lift, but because the A321 cannot take off or land with the same pitch angle as her shorter sisters the overall effect is that the lift stays the same but pitch decreases. Is that accurate?
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RE: 757 Vs A321LR

Sun Mar 15, 2015 9:22 pm

Quoting DocLightning (Reply 19):
Is that accurate?

Correct
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RE: 757 Vs A321LR

Mon Mar 16, 2015 1:11 am

Quoting DocLightning (Reply 14):
Are you saying that out of DEN on a hot day, the A321LR might take over 30 miles to get above the peaks that go no higher than FL 140? The foothills of the Rockies are about 30 miles west of DEN. The peaks don't get tall for ~40mi.

And of course the ability to fly west out of Denver is of no interest to airlines that don't fly from there. Certainly UA are a big customer but they aren't the only one.
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RE: 757 Vs A321LR

Thu Mar 19, 2015 4:40 am

Quoting Jetlagged (Reply 21):
And of course the ability to fly west out of Denver is of no interest to airlines that don't fly from there. Certainly UA are a big customer but they aren't the only one.

OK, but if the aircraft can't climb 20k+ feet in 30-40 miles, is that a problem?
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RE: 757 Vs A321LR

Thu Mar 19, 2015 2:47 pm

When an engine fails an airliner cannot maintain a cruise altitude in the 30s. It will slowly drift down until it reaches an altitude it can maintain on one engine. This altitude is usually in the low 20s, but I could see a full 321 with enough fuel for Hawaii having issues maintaining terrain clearance in the Rockies, especially in icing conditions. These are likely some of the performance issues United is talking about.
 
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RE: 757 Vs A321LR

Tue Mar 24, 2015 5:57 am

Quoting N353SK (Reply 23):
When an engine fails an airliner cannot maintain a cruise altitude in the 30s. It will slowly drift down until it reaches an altitude it can maintain on one engine. This altitude is usually in the low 20s, but I could see a full 321 with enough fuel for Hawaii having issues maintaining terrain clearance in the Rockies, especially in icing conditions. These are likely some of the performance issues United is talking about.

The highest peak in the Rockies is ~14,000 feet in height. I know that in the case of an engine out, the A320 has to drift down to a maximum of 22,500 feet to be able to run the APU and pressurize the cabin. http://theflyingengineer.com/flightdeck/airbus-a320-experience/

Would 14kft peaks be an issue for a fully-loaded A321LR fifteen minutes out of DEN?
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RE: 757 Vs A321LR

Tue Mar 24, 2015 7:58 am

Quoting DocLightning (Reply 24):
Would 14kft peaks be an issue for a fully-loaded A321LR fifteen minutes out of DEN?

In an engine out situation, yes. But, then again, if the engine was lost just after V1, then the best course of action would be an immediate return.

Quoting DocLightning (Reply 24):
The highest peak in the Rockies is ~14,000 feet in height. I know that in the case of an engine out, the A320 has to drift down to a maximum of 22,500 feet to be able to run the APU and pressurize the cabin. http://theflyingengineer.com/flightd...ence/

I glanced at the reference you noted. I would be very careful as there are quite a few mistakes in that piece of journalism. One glaring error was in the FMC/GPS/IRU description, that jumped out at me with just a quick scan of the article.
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RE: 757 Vs A321LR

Tue Mar 24, 2015 10:19 am

Quoting mmo (Reply 25):
One glaring error was in the FMC/GPS/IRU description

  

Quoting DocLightning (Reply 24):
Would 14kft peaks be an issue for a fully-loaded A321LR fifteen minutes out of DEN?

We do not have the performance charts for the A321LR, but considering new - and thrustier engines / new aerodynamics, it is reasonable to assume it should be at least equal to the A321-200.
In this case, FL240 could be maintained after one engine failure . After takeoff, DEN being at 6000 ft, it shouldn't be a problem to clear your 14000 ft range.
If the failure happens during descent, a drift-down profile isn't even needed as the max alt would be around 26000 ft.
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RE: 757 Vs A321LR

Tue Mar 24, 2015 10:43 am

Quoting DocLightning (Reply 24):
The highest peak in the Rockies is ~14,000 feet in height. I know that in the case of an engine out, the A320 has to drift down to a maximum of 22,500 feet to be able to run the APU and pressurize the cabin. http://theflyingengineer.com/flightdeck/airbus-a320-experience/

Would 14kft peaks be an issue for a fully-loaded A321LR fifteen minutes out of DEN?

I have no idea what the A321's performance is like. I do know that if there are icing conditions forecast the drift down altitude is usually much lower (having to use bleed air for anti-icing robs a lot of thrust). I know that a fully loaded RJ has terrain clearance issues in the rockies if icing is forecast, and just stretched that speculation to the A321 since it has RJ-esque performance.
 
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RE: 757 Vs A321LR

Tue Mar 24, 2015 2:14 pm

Quoting N353SK (Reply 27):
I have no idea what the A321's performance is like. I do know that if there are icing conditions forecast the drift down altitude is usually much lower (having to use bleed air for anti-icing robs a lot of thrust). I know that a fully loaded RJ has terrain clearance issues in the rockies if icing is forecast, and just stretched that speculation to the A321 since it has RJ-esque performance.

It's a little silly to think that the A321 can not clear the Rockies after having departed from DEN westbound. It's another a-net myth about Airbus climb performance. The highest MORA I have seen west of DEN is about 13,000'. Lowest engine out altitude, at MTOW, for the (regular) A321 is about 20,000'. Transport Canada adds "factors" to that, bringing the EO Altitude to about 17,000' (That would be the worse case scenario you envision, like icing. I would expect newer versions to be not much different.

I have about 5000 hours on the A320 series, and yes the A321 is G limited at higher altitudes, but it's climb to 25,000 is not much different than anything else. Its takeoff performance is better than the A320, but not as good as the A319.

But with regard to the A321LR vice the B757 ... of course it performs better. The B757 is a dated old airframe with 1970s thick wings. The two are performing the same mission, but the A321 is 50,000 lbs lighter! The only issue I see with the chart above are the three ACTs ... that takes up a lot of cargo space.
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RE: 757 Vs A321LR

Tue Mar 24, 2015 3:35 pm

Quoting DocLightning (Reply 22):

OK, but if the aircraft can't climb 20k+ feet in 30-40 miles, is that a problem?

Not if terrain isn't a factor, otherwise it's just economics. You were the one assuming the A321LR couldn't do that. Perhaps it can?
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RE: 757 Vs A321LR

Wed Mar 25, 2015 2:15 am

Quoting Jetlagged (Reply 29):
You were the one assuming the A321LR couldn't do that.

I wasn't assuming anything. I was asking because I didn't know.  
Quoting longhauler (Reply 28):
The B757 is a dated old airframe with 1970s thick wings. The two are performing the same mission, but the A321 is 50,000 lbs lighter!

And maybe that makes up a bit for the A321LR's smaller wings.
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RE: 757 Vs A321LR

Wed Mar 25, 2015 2:55 pm

Quoting Jetlagged (Reply 29):
Not if terrain isn't a factor, otherwise it's just economics. You were the one assuming the A321LR couldn't do that. Perhaps it can?

Depending on the cost index, the climb profile can be very shallow. This is for economics, not because the aircraft can not perform a steeper climb. When required, a TOGA thrust / green dot climb can be very impressive ... even in an A321 or an A340-300! In some instances where terrain (unlikely) or ATC requirements (more likely) dictate, the climb is somewhere between the two.

Quoting DocLightning (Reply 30):
And maybe that makes up a bit for the A321LR's smaller wings.

The other way around. The A321s wing is smaller (by design) than the B757 because it is not hauling around all of that extra weight of old technology. As seen on other airframes, Airbus is more than capable of designing a large oversized wing where mission requires it. But, if they had done that with the A321, then it would be as inefficient as the B757.

What the original charts do not clearly point out, is that while the capabilities of the two airframes are similar, the A321 is burning far less fuel to accomplish the same thing as the B757. And ... that was the aim.
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RE: 757 Vs A321LR

Wed Mar 25, 2015 6:07 pm

Quoting longhauler (Reply 31):
The other way around. The A321s wing is smaller (by design) than the B757 because it is not hauling around all of that extra weight of old technology. As seen on other airframes, Airbus is more than capable of designing a large oversized wing where mission requires it. But, if they had done that with the A321, then it would be as inefficient as the B757.

The A321 also has smaller wings than the 757 because the wings were optimized for the A320. But yes, even the A321 is so much lighter than the 757 that it doesn't need that huge 757 wing.
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RE: 757 Vs A321LR

Wed Mar 25, 2015 10:43 pm

Quoting DocLightning (Reply 32):
The A321 also has smaller wings than the 757 because the wings were optimized for the A320. But yes, even the A321 is so much lighter than the 757 that it doesn't need that huge 757 wing.

The A321 wing is larger than the A320 wing. Not just the double slotted flaps, but also longer chord for greater wing area. (The sharklets on the CEO or NEO versions will further enhance the wing area.) This makes me think that the decision to keep the A321 wing close to A320 sized was a result of requirements, and not necessity. In other words, had a larger (B757 sized) wing been necessary, it would have been designed that way.

By closely matching the wing to requirements, and no further, it keeps the airframe efficient. The down side of that, is that while efficient, the airframe is virtually running close to its capabilities all of the time. We have seen that when people suggest whether the A321 can match some of the B757 longer missions, and no ... it can not, by design.

Conversely. By "over building" the wing of the B757, it makes the airframe very capable. But, for the 99% of the time an airline does not need that capability, it makes the aircraft inefficient with regard to fuel burn. Not a big deal when designed to 1970s fuel prices, but certainly a big deal today.
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DocLightning
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RE: 757 Vs A321LR

Sat Apr 11, 2015 6:01 am

Quoting longhauler (Reply 33):
Conversely. By "over building" the wing of the B757, it makes the airframe very capable. But, for the 99% of the time an airline does not need that capability, it makes the aircraft inefficient with regard to fuel burn. Not a big deal when designed to 1970s fuel prices, but certainly a big deal today.

The 757 was designed as a response to the 1970's fuel crisis. While prices then were laughable by today's standards, the 757 was designed to be the most efficient airframe possible at the time. The A320 family came along 10 years later.

Quoting longhauler (Reply 33):
The A321 wing is larger than the A320 wing.

My sources say that all variants have 122.6 sq. m
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longhauler
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RE: 757 Vs A321LR

Sat Apr 11, 2015 2:26 pm

Quoting DocLightning (Reply 34):

The 757 was designed as a response to the 1970's fuel crisis. While prices then were laughable by today's standards, the 757 was designed to be the most efficient airframe possible at the time.

And in the 1970s, it certainly was fuel efficient by standards of the day. It was replacing domestic B707s, etc. flying medium haul routes. Before deregulation, the B757 didn't do a lot of trans-cons, as that was the territory of wide-body "premium" aircraft.

It wasn't until after deregulation, when fare was more important that comfort, that narrow body aircraft ruled the skies.

That's why I always chuckle when I read people here asking that the B757 line be re-opened to guarantee non-stop trans-cons in all conditions. I say hell, go back a step further .... build new B707s for trans-cons, it makes as much sense. (But I am biased. I think the B707-320B is one of the sexiest aircraft built.)

Quoting DocLightning (Reply 34):
My sources say that all variants have 122.6 sq. m

The A321's wing is 128 sq. m. (1380 sq ft.) Also, it is thicker at its thickest point. At cruise speeds, the A321 wing generates about 60,000 lbs more lift than an A320 wing.

In my opinion, it is one of the feats of the A320 series. Not that Airbus was able to design such an efficient wing, but making it larger, adding more flap area ... then ... programming the FBW systems so that it flies just like an A318 that is 56,000 lbs lighter!
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Chaostheory
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RE: 757 Vs A321LR

Sat Apr 11, 2015 4:39 pm

Quoting longhauler (Reply 35):
Not that Airbus was able to design such an efficient wing,

  

Pretty remarkable for a 1980s wing.

I recall the MD Fleet Manager telling me an A320 with IAE engines would burn almost 200USG less than an MD90 with the same payload on a 800nm sector.

That is despite the A320 being at least 2000lbs heavier.
 
astuteman
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RE: 757 Vs A321LR

Sat Apr 11, 2015 5:42 pm

Quoting Roseflyer (Reply 17):
In reality, Airbus is increasing the takeoff weight by 7,000lbs, yet those three tanks require 15,000lbs of fuel. There is not an adequate payload increase for all aux tanks to be efficiently used.

Sorry, but that is not true.
One of the reasons the original A321 MTOW went up from 89t to 93.5t was to accommodate 2 x ACT's AND a decent payload.

The ACAP charts clearly show that the 93.5t plane achieves this showing a 20t payload with maximum fuel with 2 x ACT's.
This is corroborated by A321's with 2 x ACT's routinely performing real world 2 650NM missions with up to 212 seats.

Airbus have increased the MTOW of the LR by 7 000lb to accommodate 5 000lb more fuel and 500lb more tank with a bit to spare.

Quoting Roseflyer (Reply 17):
In summary, the horizontal lines don't really represent a realistic configuration. Move back to 3300-3700nm to see the maximum realistic range.

It's fairly easy to replicate the R/P chart in the OP for the A321LR from that for the A321NEO
At maximum fuel the payload should be about 19 tonnes.
And max fuel with 3 x ACT will be in excess of 4 00Nm   

As others have said, the issue with the 3 x AC's isn't the aircraft's ability to use them - that's a given.
It's the impact that 3 x ACT's have on the belly capacity.

Rgds
 
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RE: 757 Vs A321LR

Sat Apr 11, 2015 9:24 pm

Quoting longhauler (Reply 35):
The A321's wing is 128 sq. m. (1380 sq ft.) Also, it is thicker at its thickest point. At cruise speeds, the A321 wing generates about 60,000 lbs more lift than an A320 wing.
http://www.flightglobal.com/FlightPDFArchive/1993/1993%20-%200507.PDF

I was able to verify your claim in this article, but many other sources quote the A320 wing area...
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LH707330
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RE: 757 Vs A321LR

Sat Apr 11, 2015 10:39 pm

Quoting DocLightning (Reply 38):
Quoting longhauler (Reply 35):
The A321's wing is 128 sq. m. (1380 sq ft.) Also, it is thicker at its thickest point. At cruise speeds, the A321 wing generates about 60,000 lbs more lift than an A320 wing.
http://www.flightglobal.com/FlightPDFArchive/1993/1993%20-%200507.PDF

I was able to verify your claim in this article, but many other sources quote the A320 wing area...

That's probably because not many people know about the wing differences. I might be wrong, but I think there's a veeery slight kink just inside the aileron where the thicker chord section starts on the A321.
 
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RE: 757 Vs A321LR

Sat Apr 11, 2015 11:53 pm

Quoting LH707330 (Reply 39):
That's probably because not many people know about the wing differences. I might be wrong, but I think there's a veeery slight kink just inside the aileron where the thicker chord section starts on the A321.

The difference in size is pretty minimal and is mostly to accommodate the double-slotted flap.
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flyboy80
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RE: 757 Vs A321LR

Tue Apr 14, 2015 5:07 am

How much larger is a 757 wing? Is it even one-quarter larger in terms of area then the 321?

Quoting ChaosTheory (Reply 36):
I recall the MD Fleet Manager telling me an A320 with IAE engines would burn almost 200USG less than an MD90 with the same payload on a 800nm sector.

This is very surprising to me. I've always thought the MD-90 is slightly heavier then the A320, and I'm surprised the typical fuel burn of of the less bulky 90 is higher on a similar 800NM mission.
 
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RE: 757 Vs A321LR

Tue Apr 14, 2015 5:52 am

Quoting flyboy80 (Reply 41):
How much larger is a 757 wing? Is it even one-quarter larger in terms of area then the 321?

181.25 m^2 versus 128, so that's 1.41x the size.

Quoting flyboy80 (Reply 41):
Quoting ChaosTheory (Reply 36):
I recall the MD Fleet Manager telling me an A320 with IAE engines would burn almost 200USG less than an MD90 with the same payload on a 800nm sector.

This is very surprising to me. I've always thought the MD-90 is slightly heavier then the A320, and I'm surprised the typical fuel burn of of the less bulky 90 is higher on a similar 800NM mission.

I could buy that. The MD90 wing was designed in the 1960s as the DC-9-30, then it got a 5-foot root extension and constant-chord tip extension in 1980 with the MD-81, and by the time the MD-90 came around, the wing design was old. Contrast that with the clean-sheet A320 wing, which was pretty good for its time, and the MD-90 was worse off.
 
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RE: 757 Vs A321LR

Tue Apr 14, 2015 1:22 pm

Quoting astuteman (Reply 37):
Quoting Roseflyer (Reply 17):
In reality, Airbus is increasing the takeoff weight by 7,000lbs, yet those three tanks require 15,000lbs of fuel. There is not an adequate payload increase for all aux tanks to be efficiently used.

Sorry, but that is not true.
One of the reasons the original A321 MTOW went up from 89t to 93.5t was to accommodate 2 x ACT's AND a decent payload.

The ACAP charts clearly show that the 93.5t plane achieves this showing a 20t payload with maximum fuel with 2 x ACT's.
This is corroborated by A321's with 2 x ACT's routinely performing real world 2 650NM missions with up to 212 seats.

Airbus have increased the MTOW of the LR by 7 000lb to accommodate 5 000lb more fuel and 500lb more tank with a bit to spare.

You missed the word efficiently. The advertised range of the current A321 with sharklets is 3300 nm. No one has ever operated an A321 with aux tanks more than 2650 nm in regularly scheduled service. Airbus can publish 4000nm ACAP, but I'll eat my hat if any airline ever operates an A321neoLR in a 206 seat config more than 3500 nm without further payload increases. They can't fill all three aux tanks and have enough payload for 206 passengers with all the various factors included.

Weight, balance and real world performance limitations for the A321 in a normal 2 class configuration utilizing two aux tanks rarely gets close to the current ACAP or advertised range and you admitted that when you said A321s are routinely performing real world 2650 nm flights despite a 3300nm advertised range.
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astuteman
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RE: 757 Vs A321LR

Tue Apr 14, 2015 3:29 pm

Quoting Roseflyer (Reply 43):
Weight, balance and real world performance limitations for the A321 in a normal 2 class configuration utilizing two aux tanks rarely gets close to the current ACAP or advertised range and you admitted that when you said A321s are routinely performing real world 2650 nm flights despite a 3300nm advertised range

The R/P chart for a non-wingletted A321's shows a range of 2 900nm with a 20t payload (my assumption for a 212 pax payload).
(I've no idea where you pluck 3300Nm from)

The non-wingletted A321 CEO's that have been and are doing 2 650Nm sectors with 212 pax are thus performing a mission that is within 250Nm of the nominal still-air range shown on the R/P chart for that aircraft at that payload.
Which I personally find quite phenomenal given that any real world sector won't be "still-air"
And certainly not reflective of "weight and balance" issues.

There is no plane around from any manufacturer that will fly a real-world mission that actually sits on it's range/payload chart.
The wind blows and passengers will insist on eating and drinking stuff that weighs a bunch.
Show me another plane flying range/payloads meaningfully greater than 90% of what the chart shows

So "yes", the A321's today get about as close to the nominal still-air R/P chart as it's possible to get in a real-world, wind affected mission.

I understood your argument to be that the A321NEO only sports a 7 000lb MTOW increase but has to carry 15 000lb of fuel plus the weight of tanks - thus it's payload in reality would take a hit.
This is absolutely incorrect in that sense that the extra 7 000lb only has to lift 5 000lb of fuel plus 1000lb (my error upthread) of ONE tank.
The other 2 tanks have already been accommodated by the MTOW of the baseline plane.
Therefore there is actually a positive impact on the payload it can carry at max fuel of 1000lb compared to an A321NEO.

Nobody expects an A321NEO LR to actually fly a real-world 4 100Nm with 206 pax.
But no 757 flies a 4 000Nm mission with 185 pax.
I'll challenge you to find a regular 757 route longer than 3 650nm.

Quoting Roseflyer (Reply 43):
They can't fill all three aux tanks and have enough payload for 206 passengers with all the various factors included

And that's the point.
They can.
It just won't be enough to undertake a 4 100nm mission in the real when headwinds are factored in.
more like 3 750nm.
but that's not an 321NEO LR fuel load vs payload issue.
That's a still-air range-payload chart vs real-world issue.
And every aircraft has that issue   

Rgds
 
roseflyer
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RE: 757 Vs A321LR

Tue Apr 14, 2015 4:50 pm

Quoting astuteman (Reply 44):
The R/P chart for a non-wingletted A321's shows a range of 2 900nm with a 20t payload (my assumption for a 212 pax payload).
(I've no idea where you pluck 3300Nm from)

3212nm according to Airbus' website: http://www.airbus.com/aircraftfamili...ft/a320family/a321/specifications/

Quoting astuteman (Reply 44):
I understood your argument to be that the A321NEO only sports a 7 000lb MTOW increase but has to carry 15 000lb of fuel plus the weight of tanks - thus it's payload in reality would take a hit.
This is absolutely incorrect in that sense that the extra 7 000lb only has to lift 5 000lb of fuel plus 1000lb (my error upthread) of ONE tank.
The other 2 tanks have already been accommodated by the MTOW of the baseline plane.
Therefore there is actually a positive impact on the payload it can carry at max fuel of 1000lb compared to an A321NEO.

Sure the A321 already has the option of two aux tanks. The current A321 has trouble with 206 passengers and two full aux tanks. The A321neo will help this since fuel burn is going down but I don't know exactly how those numbers work. I believe that the performance gap is still to big for the 7,000lbs increase allowing full utilization out of all three aux tanks and 206 passengers. That is an I believe not I know statement because it is a bit hard for me to decipher the payload charts at that detail.
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tommy1808
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RE: 757 Vs A321LR

Tue Apr 14, 2015 5:21 pm

Quoting Roseflyer (Reply 45):
3212nm according to Airbus' website:

with 185 pax, with means about 300 miles worth of fuel they can tank on top. Hence 2900nm with 206 pax is correct.

Quoting Roseflyer (Reply 45):
I believe that the performance gap is still to big for the 7,000lbs increase allowing full utilization out of all three aux tanks and 206 passengers. That is an I believe not I know statement because it is a bit hard for me to decipher the payload charts at that detail.

50 tons OEW plus 20 ton for 200 pax leaves 27.000 kg allowance for fuel. Which is more than fits in 3 ACT plus Wings combined by about 1000kg.
And all those tanks full are good for over 10 hours aloft.

Best regards
Thomas
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astuteman
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RE: 757 Vs A321LR

Tue Apr 14, 2015 5:33 pm

Quoting Roseflyer (Reply 45):
3212nm according to Airbus' website

That's a) with 185 pax, and b) with sharklets.
A321's without sharklets have been doing 2 650Nm sectors with 212 pax for a long time now.

Quoting Roseflyer (Reply 45):
The current A321 has trouble with 206 passengers and two full aux tanks.

By definition it doesn't, as operators have flown them on the sectors I've mentioned above, which require 2 full ACT's, with 212 pax.
Sectors that have been within 250Nm of the STILL-AIR range/payload chart

Quoting Roseflyer (Reply 45):
I believe that the performance gap is still to big for the 7,000lbs increase allowing full utilization out of all three aux tanks and 206 passengers

I'm quite comfortable that they can fill all 3 tanks with 206 pax, with the one proviso that the operator is not flying a configuration that drives the DOW up too far.
I'm sure that in some cases this might happen, in which case 3 full tanks with 185-195 pax might be the limit.
But again, I see that as being little different to a top weight 757

Rgds
 
flyboy80
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RE: 757 Vs A321LR

Tue Apr 28, 2015 11:43 pm

Quoting LH707330 (Reply 42):
181.25 m^2 versus 128, so that's 1.41x the size.

Wow, almost half larger. First I did the equation wrong and came up with 29%. I guess this makes sense as to why the 757 burns so much more fuel. Also makes sense as to why it has such capability.
 
parapente
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RE: 757 Vs A321LR

Fri May 01, 2015 10:40 am

Considering the need for an extra crew member and the associated costs I imagine that 200 PAX is the magic number for a Trans Atlantic A321NEO LR

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