Moderators: richierich, ua900, PanAm_DC10, hOMSaR
seahawk wrote:History imho teaches us only one thing, which seems to indicate that over 5000nm effective range is a positive factor for sales, which is shown by the ER versions selling better on the 767 and the A332 and A333 balance before and after the A333 reached this range.
For the rest I am much more careful. Sure there are plenty 767s still flying, but imho it does only mean that so far retiring the 767 early and buying a new replacement was not seen as efficient, it does not mean that airlines are wanting a 767 replacement.
seahawk wrote:Interesting charts and I think nobody has ever disputed that there is a gap. The question is, if there is a market. 757 and 767 sold when the best option below was the 737-400, MD-80, 707 or 727 and above you had the DC-10, Tristar and 747. Once A321-200 and 737-900 came on, sales of the 757 dropped and once the A330 came on sales of the 767 dropped. (just like they did for A300/A310)
The I would not dispute the need for something a bit larger than the A321 and maybe something a bit less heavy than the A332/338/788 but the question imho is, if the size in between might be the three seat car. For which you could draw all the same diagrams and find the same "gap" in the car market.
Polot wrote:Amiga500 wrote:767333ER wrote:
Well it outsold and killed off its 2-4-2 and LD3 capable competitors, the A300 and A310.
The A330/A340 fuselage is "identical" to the A300/310. You not including those in your figures?
The A330/A340 are completely different beasts than the 767/A300/A310. They share the same fuselage as the A300/A310 but little else...so kind of hard to use them when talking about the feasibility of the 767 fuselage/7 abreast in the MoM. That is like saying the 737/A320 fuselage is perfect for a ~100 seat market while the C series's fuselage sucks for it because look at all those 738s/739s/A320s/A321s.
Amiga500 wrote:Regarding the earlier point about reducing the fuselage diameter - see image below.
There is some fat could be cut away - incorporating side rollers (mounted between the ribs) to guide the LD3 via their sloped lower surface would help reduce the gap required to run them along the fuselage. But I'd reckon your looking at around 10-15 cm. Beyond that it gets difficult - moving the fuselage toward a taller ovoid would help further - but your then fighting hoop stress concentrations to keep weight equivalent
flipdewaf wrote:To make this a more useful debate on the mom I have made these charts to show where I believe the middle of the market is.
They represent cabin area of current airliners, the first with the 757 and 767 variants included
This is without the 757 and 767 variants to see where the gap is without them.
I believe this shows the perceived gap that is trying to be filled by these MOM offerings/ideas without the muddying effects of seat counts and premium cabins etc.
This shows a scatter plot of cabin area Vs range (the 757 and 767 models are highlighted in red (seems I have left the 767-400 off)) This again shows the gap from a range perspective, I see this gap at around 5000nm but I think there is more to read in to this in that a widebody airliner has a lot of capacity spare for cargo and so the marketing ranges that I have used are out by a larger factor for the widebodies than they are for the narrow bodies. I think the modern push for veryhigh range is more of a marketing spin that is derived from the fact that MZFW range goes up a bit and as engines become more efficient the slopes of payload range curves drops giving the benefit of huge marketing ranges that might be useful to some airlines but really not many.
It also shows that the 757 is no special case, it sits squarely with the narrowbodies. If anything the 767 is the special case.
This last chart shows the cabin area vs How many seats abreast the cabin is, i have put the 77L and 77W as 9.5 abreast as it is on the cusp of 9 and 10. Again the 767 is the one that sticks out here.
I then took a cabin width of 175m^2 and used a 6 abreast width and 7 abreast 2 aisle widths based on 20"seats and 20" aisles with 10 inch total wall width. I then calculated the cabin length based on these dimensions. To get the total length of the fuselage I added 3.5x the fuselage width (1.5x for nose + 2x for tail taper). to give me a single aisle length of 59m and a twin aisle length of 53m. I then used this to plug in to my weight estimation tool which gave me a fuselage structure weight of 10610kg for the narrow and 14256kg for the wide body.
My thoughts on that are on a weight perspective is that its a no brainer but I think there is a significant issue with rotation angle but it would have to be seen what size a ~2025 40klb thrust engine is, my guess is not small.
Fred
keesje wrote:flipdewaf wrote:To make this a more useful debate on the mom I have made these charts to show where I believe the middle of the market is.
They represent cabin area of current airliners, the first with the 757 and 767 variants included
This is without the 757 and 767 variants to see where the gap is without them.
I believe this shows the perceived gap that is trying to be filled by these MOM offerings/ideas without the muddying effects of seat counts and premium cabins etc.
This shows a scatter plot of cabin area Vs range (the 757 and 767 models are highlighted in red (seems I have left the 767-400 off)) This again shows the gap from a range perspective, I see this gap at around 5000nm but I think there is more to read in to this in that a widebody airliner has a lot of capacity spare for cargo and so the marketing ranges that I have used are out by a larger factor for the widebodies than they are for the narrow bodies. I think the modern push for veryhigh range is more of a marketing spin that is derived from the fact that MZFW range goes up a bit and as engines become more efficient the slopes of payload range curves drops giving the benefit of huge marketing ranges that might be useful to some airlines but really not many.
It also shows that the 757 is no special case, it sits squarely with the narrowbodies. If anything the 767 is the special case.
This last chart shows the cabin area vs How many seats abreast the cabin is, i have put the 77L and 77W as 9.5 abreast as it is on the cusp of 9 and 10. Again the 767 is the one that sticks out here.
I then took a cabin width of 175m^2 and used a 6 abreast width and 7 abreast 2 aisle widths based on 20"seats and 20" aisles with 10 inch total wall width. I then calculated the cabin length based on these dimensions. To get the total length of the fuselage I added 3.5x the fuselage width (1.5x for nose + 2x for tail taper). to give me a single aisle length of 59m and a twin aisle length of 53m. I then used this to plug in to my weight estimation tool which gave me a fuselage structure weight of 10610kg for the narrow and 14256kg for the wide body.
My thoughts on that are on a weight perspective is that its a no brainer but I think there is a significant issue with rotation angle but it would have to be seen what size a ~2025 40klb thrust engine is, my guess is not small.
Fred
Nice graphs!
I think the fuselage weights differences between a widebody and narrowbody tell a lot. Even with all your assumptions, it's what we see in the 757 vs 762 weight differences.
The "significant issue with rotation angle" I don't see. Many aircraft are 60, 70 or even 80m long. Of course it would need long legs, but not exceptionally long.
DC8-73
When you make relatively narrow bodies very long (DC8-73, 757-300, MD90, A340-600) compared to their cross sections, you increasingly start to pay a price
- in terms of required weight/structure to provide strenght and stiffness to the aircraft, diluting overall economics/ structural efficiency.
- passenger / crew movement in the cabin start to be an issue during ground as well as inflight operations.
- perceived comfort of small seats/cabin starts to play at long stretches.
- so far composites prove less useful on narrowbody fusealges. E.g. impact (hail, ground) starts to overrule longitudinal load requirements in determining skin thickness.
Adding cross section (30 inch versus the 54m 757-300) keeping it a efficient narrowbody but removing/reducing some of the above constrains, opens new opportunities.
As Newbiepilot says, keeping everything else equal, fuselage weight is only a limited percentage of the aircraft.
Newbiepilot wrote:I'd say that talking about cabin area/seats and ranges is done a lot because that is where the choices are, where decisions have to be made whereas with wing area and thrusts the physics tell you what they need to be (more or less).Looking at cabin area and comparing weights and ranges is only part of the story. Why is no one talks not about wing area and thrust? A 767 has a wing that is 50% larger than the 757 and more powerful larger engines. That is where much of the OEW difference comes from.
Keesje wrote:But keeping everything else equal is not possible, you cannot preserve performance (payload/range, takeoff and landing distances, fuel burn) and increase the weight at a given technology level.As Newbiepilot says, keeping everything else equal, fuselage weight is only a limited percentage of the aircraft.
flipdewaf wrote:Newbiepilot wrote:I'd say that talking about cabin area/seats and ranges is done a lot because that is where the choices are, where decisions have to be made whereas with wing area and thrusts the physics tell you what they need to be (more or less).Looking at cabin area and comparing weights and ranges is only part of the story. Why is no one talks not about wing area and thrust? A 767 has a wing that is 50% larger than the 757 and more powerful larger engines. That is where much of the OEW difference comes from.Keesje wrote:But keeping everything else equal is not possible, you cannot preserve performance (payload/range, takeoff and landing distances, fuel burn) and increase the weight at a given technology level.As Newbiepilot says, keeping everything else equal, fuselage weight is only a limited percentage of the aircraft.
Fred
keesje wrote:I think wing, fuel engine dimensions are determined by MTOW, which are mainly determined by payload - range requirements. Keep payload, range requirememnt the same expanding the fuselage cross section by 20% versus a narrow narrowbody has effect mainly on drag. A slightly wider long narrowbody gives positive better structural efficiency. I can't really imagine a 150 inch fuselage getting longer then 55m, like the 757 or DC8. You need some height to reduce strains / material to carry these loads.
Newbiepilot wrote:I have seen you post "a slightly wider long narrowbody gives positive structural efficiency" multiple times. Please provide the definition of structural efficiency that you are using. Please also show the equations that you are using to come to the conclusion that a 10 inch wider cabin increases structural efficiency and has a positive benefit, but a 34 inch wider cabin does not. Such math is going to be quite complicated because I don't see where there is a difference between 140 inches and 150 inches where getting wider reduces structural weight and then flips to the point where 180 inches is too wide and has such an impact on drag. Using your logic, drag is not a big factor going from 140 to 150in width and structural weight decreases yet drag is a big factor and structural weight increases (?) at 180 inches. I would like to see the math you use to derive 150 inches being most structurally efficient. Such math would probably require significant analysis by some masters and PhD level mechanical engineers who know as much or more about structural efficiency than the Airbus and Boeing design teams.
I have seen you share anecdotal comments supporting your idea of a wider narrowbody, but I cannot understand how making the cabin 10 inches wider is going to reduce the weight of the airplane. I don't know what definition you are using for structural efficiency either. It doesn't have a common definition like strength, strain, stress, etc does that can be found in an engineering text book.
seahawk wrote:More importantly, when the smaller diameter needs to be increased due to needed strengthening for bending stress, you also have the option to just built it a tad shorter and trade in some seats. And this points out the big problem of the MoM. For the upper part of the market a wide body is better, for the lower part a single aisle is better.
Newbiepilot wrote:I would think that the fuse diameter would be based on trade studies rather than equations, not sure Keesje has done that (I'd be surprised) but I would be surprised if there was an equation to get such a thing because the variables are not easily measured. I'd be very surprised if was lighter than a narrower fuse maybe lighter per area but not per seat. I've put my computer away for the weekend so wont be checking till Tuesday.Fred, I agree with you. I want to know how Keesje came up with the 150 inch wide and 55 meter long airplane that is ideal. What math did he use? How does he know 150 inches is better than 140 inches or 180 inches?
Newbiepilot wrote:less of a more complicated equation and more the same equation but with more bits, it may be more complex than a simple cylinder but the factors scale in the same way so it's a good enough proxy.A fuselage is a lot more complicated than a simply supported cylinder. An engineer can break down a simple cylinder, but airplanes aren't simple cylinders. The fuselage is made of frames, stringers and stiffness. Adjusting the dimensions of them can radically alter the equations for how to deal with the bending moment.
flipdewaf wrote:Newbiepilot wrote:I have seen you post "a slightly wider long narrowbody gives positive structural efficiency" multiple times. Please provide the definition of structural efficiency that you are using. Please also show the equations that you are using to come to the conclusion that a 10 inch wider cabin increases structural efficiency and has a positive benefit, but a 34 inch wider cabin does not. Such math is going to be quite complicated because I don't see where there is a difference between 140 inches and 150 inches where getting wider reduces structural weight and then flips to the point where 180 inches is too wide and has such an impact on drag. Using your logic, drag is not a big factor going from 140 to 150in width and structural weight decreases yet drag is a big factor and structural weight increases (?) at 180 inches. I would like to see the math you use to derive 150 inches being most structurally efficient. Such math would probably require significant analysis by some masters and PhD level mechanical engineers who know as much or more about structural efficiency than the Airbus and Boeing design teams.
I have seen you share anecdotal comments supporting your idea of a wider narrowbody, but I cannot understand how making the cabin 10 inches wider is going to reduce the weight of the airplane. I don't know what definition you are using for structural efficiency either. It doesn't have a common definition like strength, strain, stress, etc does that can be found in an engineering text book.
Its based on the second moment of inertia for the bending stresses and the hoop stresses for the pressure stresses. Normally one of these is the dominating stress on the fuselage and the other doesn't really add any mass to overcome it. As the fuselage gets longer the the bending moment stresses go up and as the fuselage gets wider the hoop stresses go up. There is a magic number at which point the dominating forces cross over and the fuselage will not be overbuilt for each of the driving conditions. I believe this is what Keesje is trying to achieve here. Its my understanding that you have to get very very very long before something becomes bending dominated over pressure dominated, like ~60m for a narrow body and probably over 70 for a 7 abreast. My weight estimation spreadsheets have this built in to help understand the dominating stresses. Whilst you need thousands of engineers to design the things getting a close estimates of where those engineers will end up can be quite accurate.
Fred
Newbiepilot wrote:[photoid][/photoid]Keesje, I agree with your last post. Different capacities have different optimized cross sections and dimensions. I also agree with Fred. It sounds like you backed down from the point you made about a slightly wider narrowbody improving structural efficiency.
With that said, I think Airbus wants to continue to push A321 sales. A new airplane would hurt those sales. I also think Airbus is still committed to the A330neo even if the entry into service date and first flight keeps getting delayed.
It sounds like you backed down from the point you made about a slightly wider narrowbody improving structural efficiency.
keesje wrote:
Newbiepilot wrote:keesje wrote:
Cool image. Why are you reducing wingsweep angle from the A321? The A320 already has lower wingsweep than anything else that Airbus makes. Are you suggesting slower cruising speeds?
Wingsweep angles :
717 24.5
737 25
a320 25
757 25
a300 28
a310 28
a330 29.7
a340 29.7
767 31.5
777 31.6
727 32
707 35
747 37.5
keesje wrote:Newbiepilot wrote:keesje wrote:
Cool image. Why are you reducing wingsweep angle from the A321? The A320 already has lower wingsweep than anything else that Airbus makes. Are you suggesting slower cruising speeds?
Wingsweep angles :
717 24.5
737 25
a320 25
757 25
a300 28
a310 28
a330 29.7
a340 29.7
767 31.5
777 31.6
727 32
707 35
747 37.5
A slight reduction in sweep to improve aspect ratio and lift to drag ratio. Wingsweep is one of many variables determining optimal wing design. Cord, thickness, dihedral, materials, fuel capacity, flexibility, weight and profile all play a role. New materials and CFD analyses make possible higher aspect ratio, lower drag wings. I think we'll see less sweep / higher aspect ratio's over the next 30 years. https://www.nasa.gov/sites/default/files/styles/946xvariable_height/public/sugar_volt_semispan_2014_14-l-00010lh.jpg?itok=U_d8goya
Newbiepilot wrote:Airbus increased wing sweep angle on the A350 to 31.9 from the A330 and A340. So far we haven't seen a transition to lower sweep, which is why I asked. The A350 should have the latest materials and computational fluid dynamic models.
Newbiepilot wrote:A 60.3 meter narrowbody? That is longer than the A330-800. That thing is going to take an hour to board.
keesje wrote:Newbiepilot wrote:A 60.3 meter narrowbody? That is longer than the A330-800. That thing is going to take an hour to board.
In case you missed, this is a rather wide narrowbody concept, where people can pass each other in the 30 inch wide aisle. Aisles are usually 18-20 inch.
Newbiepilot wrote:A 60.3 meter narrowbody? That is longer than the A330-800. That thing is going to take an hour to board.
keesje wrote:Will Airbus ever launch a dedicated replacement to fill their A320 series - A330 series gap ?
Airbus A370-800 60t Medium Concept
Newbiepilot wrote:A 60.3 meter narrowbody? That is longer than the A330-800. That thing is going to take an hour to board.
keesje wrote:Newbiepilot wrote:A 60.3 meter narrowbody? That is longer than the A330-800. That thing is going to take an hour to board.
And to think something significant narrower and just 3 meters short has been in operation for almost 50 years, in-cre-di-ble https://www.airliners.net/photo/KLM-Royal-Dutch-Airlines/McDonnell-Douglas-DC-8-63/1377444
Btw toxtethogrady, that fly is just to prevent a picture starts its own life. picture gives some scale. Cross section would be around 15% wider than a A320 and the loads wouldn't change much.
flipdewaf wrote:I don't think loading times are an issue for the mom, if you want to fly 4/5 hrs then you would be flying something far more capable than required if you are doing 7/8 hrs then you don't really care all that much. I wouldn't think airlines are too bothered about turnaround times on TATL.
Fred
seahawk wrote:But a widebody with more range will be having a hard time to compete with the A321 in economics on missions that are time critical when it comes to turning the plane around. We would be talking less than 2500nm range missions.
seahawk wrote:But a widebody with more range will be having a hard time to compete with the A321 in economics on missions that are time critical when it comes to turning the plane around. We would be talking less than 2500nm range missions.
ASQ400 wrote:You realize that aircraft could be payload-restricted on some transcons, and couldn't make it across the pond, right? 2800nm for the MoM is cringeworthy.
keesje wrote:ASQ400 wrote:You realize that aircraft could be payload-restricted on some transcons, and couldn't make it across the pond, right? 2800nm for the MoM is cringeworthy.
Yes, it would give in on range and hardly qualify as medium range. But it would cover large domestic and regional markets like Europe, China and 90% of Americas. An uncomplicated cheap fully compatible 250 seater. Leisure and LCC's would probably love it.
keesje wrote:A321 a failed premise?
A321LR has 4000NM range. Add 3t to OEW + 2t payload & it should still have decent range. Probably better than A321CEO? I don't have a payload range graph..
Slug71 wrote:I'd be really surprised if Airbus went ahead with this. I'd imagine that right now they are focused on getting the A400m, A320 and A330NEO engine woes addressed. And the issues with Zodiac.
I think this market will be addressed with the A320 replacement and the A319 going away.
Perhaps going back to another four member family with a "323".
I could see something like a replacement being 2/3 meters longer than the A320 and A321. The 322 being the same length as the A321 but, a wide body in 2-4-2 configuration. Uses the same wing, horizontal tp, VTP, mlg, and windscreen as the A320/A321.
323 being a stretch of the 322 to around 50/51 meters.