Bjorn’s Corner: New aircraft technologies. Part 5. Optimal fuselage

By Bjorn Fehrm

March 24, 2023, ©. Leeham News: This is a summary of the article New aircraft technologies. Part 5P. Optimal fuselage. The article discusses different cross-sections and how these drive drag and weight. The cross-section chosen depends on the container type employed for the area below the floor.

Figure 1. Cross sections using different size cargo containers. Source: Leeham Co.

Single aisle or dual aisle fuselage

In last week’s article, we realized we might end up designing the next volume model airliner as a dual aisle aircraft instead of a single aisle.

What cross section gets chosen depends much on the cargo container that shall go with the concept. Figure 1 shows that for anything other than an LD3-45 container, a full dual aisle cross section is the result, either a 767 cross-section if the LD2 is used or the eight abreast A330 cross-section if the LD3 is used (Figure 2).

The original Airbus A300 was designed for 300 passengers intra-Europe flights. Eventually, it was scaled down to 250 passengers, then called A300B. The fuselage was designed around the ubiquitous LD3 container, creating the successful A330/300 eight-abreast cross-section, Figure 2.

Figure 2. The A300B cross-section at eight abreast and two LD3s. Source; Wikipedia.

But an eight-abreast fuselage builds more circumference length per seat abreast than a single aisle cross-section or a dual aisle elliptical fuselage. In fact, the only dual aisle cross-section that can compete with an A320 single aisle is the elliptical dual aisle, Figure 1. But such shapes have not been produced as they introduce fatigue-inducing bending moments in the structure.

The result of such forces results in fatigue failures, as in Figure 3.

Figure 3. The fatigue rupture of the Aloha Airlines 737 roof. Source; Wikipedia.

The only way to handle such bending forces is to change from an aluminum to a carbon fiber fuselage, which is largely agnostic to fatigue stresses.

Then the caveat becomes how to produce 60 to 80 carbon fiber fuselages per month when we struggle to produce 10 to 15. This is the subject of the next Corner.

97 Comments on “Bjorn’s Corner: New aircraft technologies. Part 5. Optimal fuselage

  1. For the same seating specs and capacity, a seven abreast fuselage would be >20% wider for the one seatper row (& a 40% bigger cross section..) but only 14% shorter.

    I haven’t seen the magic for realizing that in a light, efficient way. Only moving goalposts to make it work (changing the capacity, seat specs, changing material properties for only one configuration).

    It seems the airlines have been waiting for a decade for Boeing to see A got it right with the A320 (&A300) cross section and better enhance on that. Presenting moonshots to delay investment / create free cash flow, has taken its toll.

    • Keejse you posted the same eliptical pic on Anet a couple of years ago.

  2. There is a risk they design a single aisle 4+4 seating to cram out max revenue per lb fuselage of min allowed diameter. It effects size of aisle, emergency exists number and type. Still it is an option Wizzair and Ryanair bean counters would like.

    • Not going to happen:

      14 CFR 25.817 Amdt 25-15

      Maximum number of seats abreast.

      On airplanes having only one passenger aisle, no more than 3 seats abreast may be placed on each side of the aisle in any one row.

        • Hello Claes,

          Re: “Ok, been on widebody with 5 abreast in middle section.”

          Did that widebody have more than one aisle? If so, you were not on an airplane with “only one passenger aisle” and 14 CFR 25.817 Amdt 25-15 would therefore not be applicable. I think the idea is that passengers cannot be more than 3 seats from an aisle. If there are two aisles then you could have up to 6 seats between aisles.

          • All widebodies have more than one aisle in the main cabin.

    • One thing is what low-cost carriers would love to do, and another thing is what they can do

      Safety Regulations are there, after decades of research
      In commercial aviation, the aisle can not be further than 3 abreast

  3. Hello Keesje,

    Re: ”For the same seating specs and capacity, a seven abreast fuselage would be >20% wider for the one seatper row (& a 40% bigger cross section..) but only 14% shorter.

    I haven’t seen the magic …”

    If you were using the most important parameter for comparing the efficiency of streamlined subsonic airliner fuselage cross sections, i.e.: perimeter per seat, not cross section area, then it would not be hard to understand why Bjorn’s proposed 7 seat elliptical fuselage cross section is potentially about equally efficient as the A320 fuselage cross section for passenger capacities where both would be near optimal length for streamlining and fuselage stiffness. Apparently, like most who post here, and unlike Bjorn, you are neither an aerospace engineer nor have you taken an introductory course in aerospace engineering?

    This has nothing to do with magic, it follows pretty trivially from correct scientific and engineering analysis.

    See below for the perimeter per passenger for each of the three fuselage designs in the diagram in the present installment of Bjorn’s series.

    Listed from lowest perimeter per passenger (highest efficiency) to highest perimeter per passenger (worst efficiency). Efficiency will also be subject to the fuselage not becoming too stubby or too slender for near optimal streamlining, structural stiffness, and control surface effectiveness.

    7 abreast ellipse: 194 wide x 176 inch high ellipse, 7 abreast.
    Perimeter = 581.5 inches.
    Perimeter per Passenger = 581.5 inches/7 abreast = 83.1 inches/passenger

    A321: 155.5 inche wide x 163 inch high near circular, 6 abreast.
    Perimeter = 500.3 inches.
    Perimeter per Passenger = 500. 3 inches/6 abreast = 83.4 inches/passenger

    Boeing 767: 198 inch wide x 213 inch high near-circle, 7 abreast.
    Perimeter = 645.6 inches.
    Perimeter per Passenger = 645.6 inches/7 abreast =92.2 inches/passenger

    Significant points:

    I) The perimeter per passenger of the 7 abreast ellipse and A321 are within 0.4%.

    II) The perimeter per passenger of the 767 is 11.1 % greater than that of the 7 abreast ellipse and A321.

    I calculated the perimeter of circles according to Pi x diameter, the perimeter of near circles according to Pi x (Average Diameter), and for the 7 abreast ellipse I assumed that the cross section was close enough to a true ellipse for the ellipse perimeter calculation tool at the link below to give an acceptable answer.

    • So the elliptical bending issues can be solved by using carbon fiber? Interesting.

    • The analysis above does not take into account that the in plane tensile forces on the wider elliptical fuselage section are greater because of pressurisation loads (assuming the same differential pressure). Thus a per unit perimeter comparison is flattering to the wider fuselage if this is not taken into account.
      A wider section has to be stronger, so it has to be heavier.

      • Yes a pressurized body want to go circular/spherical. When reaching this shape the “stress stiffening” helps reduce deformations.

    • Mate, are you sure there`s no cognitive problem on your argument?
      Because no matter what you studied, hard to beat physics and logic.

      Still, the question would be, why 2-3-2 cross section.
      If you can manufacture a elleptical fuselage without running into too much load peaks if under pressure (and thus being to heavey and to expensive) –
      why would you choose a 2-3-2 layout?

      Wouldn`t you go for a A330 replacement and do a 2-4-2 or even better, go for the more ideal 3-3-3 layout.
      You will get way better numbers if you simply add another seat to a scaled up fuselage design.

  4. In view of the increasing number of LCC flights in today’s aviation world, and the fact that many/most LCCs do not utilize the belly for cargo, it’s curious that fuselage cross-section layouts are still “stuck” in the same configuration that has been used for decades. I can think of a few airline CEOs who would jump at the opportunity to carry passengers in the belly. Sure, floor/ceiling positions have to be adjusted, as do seat orientations, and the wingbox will cause a division of available space — but it’s not impossible.
    Qantas was recently talking about putting (containerized) sleeping berths in the belly on longhaul flights. Lufthansa has toilets/galleys in the belly on its A340s. And the L-1011 had a lower lounge.

    • The Hold toilets, and galleys that you mention, are certified for cruising altitude only, not for take off and landing. No passengers are allowed in these areas during take off, or landing

      Most Low Cost Carriers holds, are fill up with the passengers luggage
      In some flights, they have to leave some luggage behind, due to weight limitations

      • The certification limitation is due to the lack of emergency exits in *current* hold designs.

        The hold isn’t “filled up” with baggage: baggage is stored in a relatively small compartment at the rear of the hold.

          • In the Leeham discussion on A321LR the calculations are 206 passengers require 9 baggage containers- of 10 spots in a A321 fuselage. Thats almost all the space. You can get more in by not using containers but takes longer to load.

            A320 is only 7 positions ( 3F and 4 R) for less passengers

            Short haul is less baggage normally but LCC usually have higher density which means more bags
            Which ever way you look at it , the majority of hold in single aisle is baggage

          • In Europe, at least, relatively few shorthaul LCC passengers have a check-in bag: the carry-on baggage allowance seems to be enough to cover the type of trip that most of them are going on.
            Watch the baggage handlers at an LCC airport and note how few bags are loaded for a plane with a full passenger load. Use is made of only one cargo hold door (usually the rear one) — at nowhere near full capacity. If you search the web, you’ll see lots of photos of small piles of neatly stacked cases right at the back of the aircraft.

          • Huh?? ULCC like Frontier charges a fee on *carry-on* (one “personal item” included with fare). Time to wake up.

        • The Holds in narrow-body aircrafts, have very low clearance
          The fwd hold is frequently empty, because of the aircraft’s weight balance
          Is normally used to stow light stuff, like strollers, live animals, or coffins

          B-737 Holds:
          An adult man, can hardly remain seated, inside a B-737 hold
          Hold door dimensions 34″x 45″ (71 x 114 cm)
          Hold clearance, from floor to ceiling 44″ (112 cm)
          Fwd hold volume 423 ft3 (12 m3)
          Aft hold volume 642 ft3 (18,2 m3)

          • …which is why my original comment above referred to adjustment of floor/ceiling positioning in a modified cross-section…

    • The future of many LCC is uncertain, due to high inflation, the consequences of the pandemic, and the volatility of energy costs

      This situation will probably shape the World’s economy for years
      Very often, many of the passengers that fly LCC, have a low income
      Many of them, will stop flying due to the economic crisis

        • LCC

          Very recently, a well positioned LCC, Norwegian had to stop all B-787 operations. The Airline could not overcome the economic challenges, and cancelled all long haul flights

          Here are some of the Worlds LCC that recently stopped their activity:

          Air Pegasus
          Air Asia Japan
          Indonesia Air Asia
          Jet Star Hong Kong
          Thomas Cock Airlines
          Wow Air
          Primera Air
          Monarch Airlines
          Air Berlin
          FlyBMI (British Midland)

          • Are you also going to provide us with a list of all the recent aircraft orders placed by other, expanding LCCs?

        • I was totally wrong…
          The LCC market share is bigger than I thought, sorry…

          According to Eurocontrol, LCC in Europe, made up 32,5% of flights in 2022. In in 1998, the LCC market segment in Europe was close to zero.

          According to Statista, the World’s LCC market share, has been growing during the last decade, and reach 35% in 2020

          According to ICAO, LCC carried 984 million passengers in 2015, 28% of the World’s total passengers

          • No apologies necessary: it’s just courteous discussion here, and nobody is ever 100% correct.

            By the way, I suspect that LCC now dominates shorthaul (i.e. more than 50%) in Europe and Asia.
            I don’t think that this is a matter of pricing: I think it’s more a matter of convenience in terms of routing (lots more routes to secondary cities) and frequency (multiple flights per day).
            In addition, my personal experience is that LCCs in Europe and Asia tend to have excellent punctuality performance — much better than legacy carriers.

            Not sure what the situation is in Africa, South America and Australia.

            LCCs in the US seem to have a harder time taking market share from the big carriers. And they seem adverse to serving secondary cities.

            Returning to your original list above:
            – Norwegian is making a comeback.
            – WOW has re-appeared as PLAY.
            – The two small Air Asia units were merely consolidated into the much larger Air Asia operations in Malaysia and Thailand. The same for Jetstar (consolidated into the Singapore branch).
            – Technically, Thomas Cook was a charter company rather than an LCC.

            Remember that LCCs received no government aid during the pandemic, whereas legacy carriers did — that explains many entries in your list.

          • The WSJ has recently reported that average airfares are now significantly lower in Europe than here in the US. Seems that the frenzy of mergers of US carriers may have gone a bit too far.
            Before we had overcapacity and occasional bankruptcies. While rcently we have full flights, record profits, and higher fares.
            …a win for the shareholders, a loss for consumers.

          • @ John
            This chimes with my own experience.
            Air fares are also much lower in SE Asia than in the US, thanks to LCCs (particularly Air Asia).
            The biggest airline in Europe (by passenger numbers) is an LCC – Ryanair. Although it has become customary in the media to deride that airline, it’s actually very satisfactory. Same applies to Easyjet and Wizz. Between the three of them, they wipe the floor with Europe’s legacy carriers.
            Wizz is now starting to venture into longhaul to Abu Dhabi and Asia…it will be interesting to see how that goes.

          • Of course european LCC received state aid during pandemic.
            this was very early on, May 2020 and it was already at $730 mill for Ryanair
            They have made a lot of fuss and some court cases against some forms aid given to other airlines.
            A typical O’Leary stunt as some european countries werent so generous to Ryanair as Britain.

          • @ DoU
            Got any links to back up this assertion that European LCCs received state aid?
            The fact that Ryanair filed unfair competition suits on this subject doesn’t mean that it received any aid — in fact, it shows the complete opposite.


            Only O’Leary would take other airlines to court over their *more favourable* aid terms than he got , such as from Finland and Sweden.

            Smokescreen for the aid Ryanair got, after all it literally couldnt have survived without money coming in when lockdowns and border closures and restrictions meant traffic fell 80% in 2020

            it even says so in Ryanair accounts
            ‘Since Mar. 2020, the Group has lowered cash burn by cutting costs, participating in EU Govt. payroll support schemes, cancelling share buybacks and deferring non-essential capex.’

          • @ DoU
            Ryanair is incorporated in Ireland: any link to financial support from the Irish government?
            And what about other EU LCCs, like Wizz and Vueling?

          • The realities of business cash flow and the generous payments available meant all the european LCC got government subsidies when flying was impossible due to government restrictions.
            Its clear that Ryanair got money and they said so in their financial report. A corner cafe couldnt operate without a government subsidy in that time so its silly to suggest otherwise for a LCC burning cash with 80% of their passengers gone.
            It seems that some ‘flag carrier’ airlines got additional aid and capital injections that Ryanair didnt get

  5. A lot of comments, but it may would help to have a look into this subject not just from an per-pax view point. For example, the eliptical cross section in Figure 1 already does show a major problem: The scenario of such an cross section together with an AKH container leaves a lot of unusable space in the tunnel areas left and right of it. It is adviseable to look at the whole issue from a combined main deck and lower deck perspective as well as pax and cargo, and range and available fuel QTY as has its important input. There are patents on this subject out in the industry which at the end came to the conclusion that pro bably either a 196 inch (7-abrest / 2-isle) or a 188 inch round diameter (6-abrest / 2-isle) in combination with different lower deck ULD approaches and potential lower deck seating-option can have quite interesting overall aspects for in both cases up to 260 -275 ECO-Pax at 31 inch spacing.

    • I took a very basic view of ‘which cross section has the least ‘yellow’ – wasted space – single aisle.
      The more recent history of airframe development is atrocious so I’d stick with an AlLi or CRFP skin/winged a320/1/2neo and reliable engines for this half century. There’s just something missing in the OEM/supplier sphere to jump forward… Let’s just shuffle like ab old lady with a walker.

  6. From the previous installment (Part 4) of Bjorn’s present series.

    “At cruise, when we fly at high speed, the friction drag is the dominant drag. The air friction decreases with thinner air at altitude. Even though induced drag increases with thinner air, it’s beneficial for an airliner to fly high, to reduce the dominant friction drag.

    It’s why airplanes that can climb high, like jet airliners, fly between 30,000ft and 40,000ft, where the air density is one-third of the density at sea level.

    Friction drag depends on the skin area that rubs with the air, the so-called Wetted area. If we develop the parameters that drive wetted areas of different fuselage types, we find the drivers for the dominant drag. But we also find the driver for fuselage mass and weight (mass is mass, weight is a force).

    It comes from airliners being stressed skin designs. The skin of the aircraft creates the dominant drag and, as it’s the premier carrier of the loads, also the mass of the plane.

    So if we can find which fuselage construction has the least wetted area per carried passenger, we understand which fuselage type is best for our next-generation heart-of-the-market aircraft.”

    For the tube shaped portion of a fuselage, whether we have a circular or elliptical tube, wetted area = perimeter x length. Repeat: perimeter x length, not cross section x length.

    Here is a concrete example of how similar perimeter per passenger results in similar wetted areas and thus similar skin friction drag.

    According to my post above, perimeters for Bjorn’s proposed 7 abreast elliptical fuselage, an A321, and a 767 are as follows.

    7 abreast ellipse: 581.5 inches
    6 abreast A321: 500.3 inches
    7 abreast 767: 645.6 inches

    Suppose we have 33 inches per seat row, then seats per inch of length are as follows.

    6 abreast: 6 seats per row / 33 inches per row = 0.1818 seats per inch of length.

    7 abreast: 7 seats per row / 33 inches per row = 0.2121 seats per inch of length,

    Suppose we want 250 seats.

    For 6 abreast: Length = 250 seats / 0.1818 seats / inch = 1,375 inches.
    For 7 abreast: Length = 250 seats / 0.2121 seats per inch = 1,179 inches.

    Wetted areas for the tube shaped portion of the fuselage for a 250 seat 7 breast ellipse cross section, a 250 seat A321 cross section, and a 250 seat 767 cross section would then be approximately as follows.

    Wetted surface area = perimeter x length.

    7 abreast ellipse: Wetted Area = 581.5 inches x 1,179 inches = 685,888 square inches.

    A321: Wetted Area = 500.3 inches x 1,375 inches = 687,912 square inches.

    767: Wetted Area: = 645.6 inches x 1,179 inches = 761,162 square inches.

    The wetted areas for the 7 abreast ellipse and the A321 cross sections are within 0.3%, essentially identical, the wetted area for the 767 cross section is about 10% greater than those for the 7 abreast ellipse or A321 cross sections.

    • So the Elliptical cabin is not so far fetch. Just have to find a way to scale up carbon fiber production as Bjorn states.

  7. @Bjorn, so, I guess you are only going to consider single tube and wing designs in your evaluation.

    this is very disappointing.

    BWBs, true flying wings and side by side double bubble concepts offer significant aerodynamic advantages and if you are already going down the composite fuselage path, then the majority of objections become moot.

    • Have you not read the aim is to reduce wetted area and fuselage structure weight per passenger.
      Those shapes do nothing for that, which is why they arent even considered.

      • then explain how they show 20-30% reductions in fuel burn vs traditional tube and wing. because they do.

        could it be because induced drag (which still matters) goes waaay down and interference drag goes waaay down, and the structural penalties are nowhere near as severe in a composite aircraft as they would be in a metal one?

        so talk about it, don’t ignore it.

        • Its a fantasy figure 20-30%
          If there was reality in that it WOULD be under development now.

          I dont know what special knowledge you have to enables you to know this but its beyond those in the ultra competitive airframers industry, or those in up and coming countries ?

          • NASA and DARPA’s public statements regarding the results of their studies.

            not special knowledge, public knowledge.

          • Any links for that ?

            But this isnt about ‘volume fuselages’ being more efficient but just flight controls
            Even the newest clean sheet electrics ( where savings are highest priority) are still in modified ‘tube’ universe.
            Other Darpa projects are submersible planes… fantasy stuff. Other stuff from NASA is mainly wings or composite manufacturing

  8. I’m not an aerospace professional, so I’ve always wondered why the A300 wasn’t a bigger success than it was, and why neither of the OEMs is attempting to produce aircraft that are optimised for the vast majority of missions rather than cater for the increasingly niche extreme upper ends of range requirements. As the world’s skies become increasingly crowded short range and efficient, and relatively small narrowbodies must make more and more sense, and freight is less of an issue on this sort of operation where road and rail can compete effectively.

    • Good point about the A300. I think it came down to trusting Airbus which was an upstart at the time. Remember back then domestic widebodies were three engine aircraft namely the DC10 and L1011. A300 did become a popular later in life with the update as a freighter and Trans Atlantic aircraft. Eventually the A330.

    • The A300 fuselage and its CF6-50 engines could not take the cycling. The inital operators using it for 1-2hr jumps were pouring out money especially as engine spare parts prices started their long march north. Airbus was unexperienced and lots of structural modifications were required. Today one could argue that it could be designed for durability with 2-4 RISE engines as its huge bypass ratio would help T-O performance and cruise speed is not that important for short range flights. Maybe the Chinese would give it a try with a domestic RISE instead of the C929?

      • Airbus wasnt ‘inexperienced’. It was a consortium of France and UKs existing airliner manufacturers who had plenty of experience.
        The flight profiles they designed for were very short by todays standards, even below the later A330R which was up to 5 hrs.
        There were two loose groupings of ‘airbus’ type medium haul airlines being talked about . The Sud-Dassault Galion ( which might include BAC) and Nord- Breguet-Hawker Siddeley HBN100. Both very similar in the 240-260 seater, the Sud version being 9 abreast.
        The HBN100 concept at 8 abreast eventually became the A300 and included Sud and german participants.
        These descriptions from Flying Review International Aug 66

        • They were unexperienced in designing a large pax aircraft for 1-2 hr jumps. They tried lots of new technology and some did not work. But they learned and eventually made a “home run” with the A330.

          • The only new tech on the A300B was fibreglass ‘composites’ for leading edges .
            Thats petty stuff even then as fibreglass was used in military aircraft

            They quickly developed carbon fibre for certain structures, pressure bulkheads and so on. It wasnt even FBW back then.

            They right sized the plane for existing large fan engines and launch model was the CF650 from GE – who worked with Snecma- now Safran. Then and now a very productive collaboration and no more troubles than other widebody engines.
            Not using Rolls meant UK government dropped out ( but H-S stayed in) but in hindsight a good choice for Airbus ( P&W and RR were later engine options) as that left opening for German government support ( and amalgamation of German airframers- MBB)
            Aerospatiale in France resulted from the merger of Nord and Sud for this project

          • There were other problems with structural adhesives… I agree that the CF6-50 was the best high thrust engine back then, still it was not suited for cycling like a P&W JT8D (on Super Caravalle, DC-9, 727 ) hence only when the 37k RB211-535 arrived you got a somewhat high thrust engine that could take the cycling. The PW2000 had to be improved over the years (94′ package) until it was competitive. Still today you have no widebody engine (>50k) designed for 1hr jumps, there are operators using widebodies with de-rated engines for short haul but they pay a high overhaul shop price for it.

  9. That poses the question does a domestic WB need to the ability to carry to LD3s? And if not then the Elliptical seems like the way to go for a people hauler.

    • In theory could a twin narrowbody fuselage under fairings be optimal as you want as small of a diameter round fuselage as possible for min mass/pax. Hence you get an oval fuselage but with round cylindrical pressure vessels inside and just 2 pilots for a “double A320neo” fuselage with folding wingtips on new carbon wings and new 50k engines. I’ll go for new main landing gears as well to raise the fuselage for the new 50k RISE engines. I know the problem of having evacuation on one side only.

  10. The cause of the Aloha Airlines 737 fuselage failure was corrosion of the fuselage structure. The airplane was operated in the hot, humid, rainy, tropical climate of Hawaii and proper precautions to drain moisture from the structure were not taken. Pressurization loads then led to failure.

  11. Bjorn:

    The fuselage blow out on the Aloaha flgiht was not a result of cross section but a consequnce of failure to maintian the hull correcly.

    Boeing had delineated exacatly what Alaha had to do with the high cycle hull.

    Alaha failed to inspect or various inpsector lied about what they had not done.

    The FAA also had the same in hand and failed to monitor Aloha Airlines was doing it (their single inspector was saturated with monitoring airlines all across the Pacific region)

    Boeing had the inspection process in place and repeatedly warned Aloha what needed to be done.

    The Pattern of blow off on failure to maintain may be due to the fuselage shape but the only times it has let go has been when maint was not done (or in once case quality control drilling issues at Boeing itself).

    • Yes, but the primary cause was still the fatigue from the age of the plane and the extremely high cycle number.
      The maintenance schedule was probably too ambitious for most airlines not just steamy tropical Aloha, why most let them go to scrap instead.

      In the reverse, Ryanair for some time had a revenue stream from letting go its planes around 6 or seven years – when no longer under guarantee- before the big bills started in come in and they could take a cash on-sale to monetise the volume discounts price they paid initially. Means they then buy even more from Boeing!

      • 1. Those were early days?!

        2. Back in 2004, Ryanair sold 20 732 including spare engines and parts to Autodirect Aviation. Those were built between 1980 and 1983 and Ryanair had flown them roughly ten to twelve years when they were retired. Some were scrapped but I believe a majority of them continued in service for another decade or so. It’s said that “[t]he aircraft, spare parts and engines will be fully depreciated at their date of disposal and accordingly, there is *no gain or loss arising on their disposal*.”

        3. Ryanair’s current fleet of 738 has an average age of *14 year*, with *over a dozen approaching nineteen year of age.

      • Duke:

        Its worth it to read the Aloha NTSB report. They in fact recognized the issue, well in time inspections were mandated on exactly those areas that let go.

        Aloha failed to carry those inspections out (very likely pencil whipped).

        They were told what was needed inspection wise and where and in a more than timely manner.

        The FAA allowed rolling inspections and Aloha was hell bent on maintaining the schedule (said inspections were done over night and if a plane failed to fly they had no backup)

        The FAA failed as it over tasked its oversight inspector.

  12. Although composite fuselage is a great engineering accomplishment, it is difficult to scale up, and very challenging to build

    After a only few years of use, airlines are starting to experience some unusual problems with the composite fuselage

    • I attended a few years ago a technical session during the Singapore Airshow (I think it was the 2014 one) and there was a discussion on Al versus Composites during that session. At that time, a rep from Hexcel was arguing that composites were not viable for narrowbody aircraft. While the cost of composites was something like 4 to 10 times the cost of Al, the showstopper was the inability to meet the required production rates due to the time taken by the curing process.

      Has anything changed drastically? I am not aware of any breakthroughs which would make composites viable for narrow body high volume aircraft.

      • A widebody flying very long range has better use of a lighter but expensive carbon fuselage, carrying less mass during 10-19hrs flight makes a difference. A short range A320/737 is not as mass sensitive. However carbon makes better use in the wings to give high stiffness and slender long wings. Can carbon come down in price and speed of producing fuselages everybody will switch as it also has better corrosion properties if assembled right (Al-C in contact gives you a battery)..

        • However, we have yet to see how carbon behaves long-term as regards exposure to UV and/or cosmic rays, in constant temperature and humidity cycles…

          • Carbon fibre composite has been used as major part of airframe since the A310 had complete tail fin of the material and went into service in 1983 ( later adapted for the A300 as well)
            There are still flying around 120 A300F, so we have 40 years since and maybe some planes that have over 25 years service flying

    • A somewhat cryptic comment, I feel. Is this a reference to the A350/787 paint adhesion problems, or are you referring to something else?

  13. Lot of work on the field recently, but the most important part has been on wing production for narrowbodies.
    Airbus “wing of the future” is coordinating the effort of suppliers & research centers to get the 100/month production required, with lower costs and better performances.

  14. Bryce…..
    Boeing was at the forefront of Belly Passengers long before Airbus was even a glimmer in the eyes of Europeans. Air transport startef with single engine airplanes flying the mail. One of the most efficient of these was the Boeing Model 40. It was an open cockpit biplane with a large mail “hold” between the engine and the pilot loaded through a hatch on the top of the fuselage. As this airplane flew the mail routes thru major population centers, people started asking to be carried on these routes instead of train travel…… Boeing responded by installing seats inside the belly of the airplane with access through a triangular door. It was triangular due to the placement of the existing steel truss tubing. The Model 40B carried 4 passengers in reasonable comfort. I was lucky enough to fly in the last 40B and it was a wonderfull experience. I am a “belly passenger” and it wss great

    • The Stratocruiser also had a lounge in the belly.
      There’s no fundamental reason why passengers can’t be carried in the belly: replace cargo door(s) by emergency exits, add a few windows, and away you go.

      The forward cargo hold door is rarely (if ever) opened on many (European) LCC aircraft…total waste of space.

      • Check the cross sections ( single aisle) at the top of the article provided by Bjorn.

        That might provide a good idea of the actual space available. Head room seems to be the first of many problems. The curved fuselage in the upper lobe is in the right place for head room, not so below.

        One airline has talked about stacked bunks for economy passengers, maybe best suited for the bottom section, but thats long haul

        • We’re talking about modified cross-sections in future designs — not present designs.

          • The shape will be similar . There is no breakthrough shape other than a double bubble like is used in all single aisles.

            Even the 767 is a double bubble rather than the more elliptic of the larger WB. Same headroom and space issues as present, unless you are thinking of sideways seating along a central aisle, but we can rule that one out.

          • A fuselage can be ovalized in the vertical direction — just like the A380 is.
            It may incur a drag penalty, but that’s compensated by extra revenue from lower-deck passengers.

          • A380 is effectively a 3 decker . Can you see why thats different to the size of large single aisle or a small twin aisle….. even without considering one of the major issues why it failed to reach its potential.
            Weight, being between 10-15% heavier per passenger even than 747-8

            I cant see a heavier per passenger *excessively ovalised* shape being a choice for a better plane in this class

          • @ DoU
            We’re talking about shape here — not size 😏

  15. Would an inverted “ovalised triangle” be possible for shorthaul planes, to give a wider passenger deck and smaller hold, where large amounts of baggage or cargo are not an issue?

        • Well that is reality for you, its a square space in a round world.

        • Hello Bryce,

          Re:”Still a lit of “wasted” space below the floor…”

          On the airlines that I fly most frequently, Delta, United and American, the area under the floor would not be wasted space, but rather just about the right amount of space for the baggage and freight load on a typical flight. Unless on an overnight trip, I almost always check a bag, and I would estimate that on 50% to 75% of the passengers on a Delta, United and American flight show up at the baggage carousel to pick up one or more bags. Most of the people at the baggage carousel will probably not have paid a checked baggage fee. Contrary to the prevailing opinion in the Leeham comments section, it is pretty easy to avoid checked baggage fees on the US Big 3. For all of the big 3, you get one free checked bag if you have the airlines credit card, another free checked bag if you have reached the lowest status in their frequent flyer program, and another free checked bag if you are flying First Class. Only non-frequent flyers who are buying cheap tickets, priced to compete with ULCC’s and LCC’s, pay baggage fees. I get the feeling that when they fly, most of the people who comment here are buying cheap tickets on fee for everything ULCC’s or LCC’s or cheap major airline tickets.

          My guestimate of the number of people who typically show up at the baggage carousel is roughly consistent with the data reported by Statista at the link below, according to which, in year 2017, 15% of personal domestic passengers checked zero bags, 60% checked one bag, 19% checked 2 bags, 4% checked 3 bags, and 2% checked 4 bags.

          In the video at the link below, I counted 61 bags being removed from the baggage/cargo compartment of an E190, the video caption says that the stars of the video removed 73 bags. This is one of 2 baggage compartments on an E190 (fore and aft). For weight and balance reasons, the baggage and cargo load would have been split between the fore and aft compartments, i.e., there would have been more bags in another compartment.

          Delta, United, and American don’t fly E190’s; however, they have many E175’s, with the same fuselage cross section as an E190, in their regional operations. On their E175 flights, there almost always isn’t enough overhead bin space for all the carry-on bags that people want to carry on, and the gate agents usually end up first offering, then pleading, for people to offer up their carry-on bags to be placed (at no charge) in the baggage hold before boarding starts. Overhead bins are usually filled up by the time the last few passengers board, and for those passengers if they want to take their bag, it needs to go in the underfloor baggage compartment. CRJ’s are even shorter on overhead bin space than E175’s.

          In addition to being used for baggage, Delta, American, and United also use the underfloor baggage/cargo compartments for their cargo services. On Delta, you can ship EQ containers of up to 150 pounds, EH containers of up to 250 pounds, or E containers of up to 300 pounds on an E175.

          Another use of the underfloor area is for routing of electrical lines, hydraulic lines, ventilation and pressurization ducting, and control cables (E 175 and E190 use control cables for ailerons). Every control in the cockpit needs to have a connection to what it controls, and those connections (two redundant paths on an airliner), need to go somewhere.

          • Yes. Even the underfloor holds dont comprise all the fuselage as theres everything from undercarriage to computer systems and cabin air conditioning, toilet tanks and myriads of other things we are probably not even aware of. Cabin crew sleeping arrangements in WB have migrated to the spare space above the passengers , but thats a ‘busy’ area too.

          • Hello AP,
            You could have saved yourself some time and effort if you had noted that my original comment above related to (European/Asian) LCCs — who are not interested in carrying cargo, and who often/mostly fly with an empty forward hold and only partially (baggage-)filled rear hold.

            LCCs have a much larger market share in Europe/Asia than legacy carriers — a very different situation to the US. I live in a city of just 400.000 people — and, yet, the local airport serves more than 50 non-stop destinations, all done using LCCs.

          • As I noted above, the space under the floor used for baggage/cargo compartments is not wasted on the airlines that I fly on; rather it is used for baggage and cargo.

            What about the space under the floor that is not used for baggage/cargo compartments? Is it wasted space? Anyone who has ever walked a ramp or maintenance hangar and looked into these spaces will know that they are not empty wasted space, but rather space filled with electronics racks, electrical cables, hydraulic lines, and ventilation and pressurization units and ducting. Do those suggesting otherwise imagine that all the instruments and displays on the control panel are run off of an iPhone or iPad glued to the back of the control panel, and connected to all of the equipment controlled from the cockpit by a single USB cable? Do they imagine that large air conditioning and processing units are not required to mix hot engine bleed air with outside air at (-60 C to -75 C at cruise altitudes) and send it at the right temperature and pressure to the cabin and to the wing for anti-icing, or that this is done without having to have processed air ducts run under the floor and out to the wings? Do they imagine that the equipment that converts electrical signals to commands to the hydraulics that move control surfaces, and the hydraulics powerful enough to move the control surfaces, do not take up substantial space? Do they imagine that the APU in the tail does not require a fuel line under the floor from the wing fuel tanks, or that there is not a need for electrical distribution panels where electrical power from the APU can be fed into the main electrical bus? Do they imagine that hundreds or thousands of sensors in the engines and control surfaces and their actuators do not need to have their data fed back to the flight deck through hundreds and thousands of cables through racks of analog to digital converters, digital to analog converters, signal amplifiers, signal conditioners, and network controllers? Do they imagine that all of this equipment, which must in most cases be redundant with duplicate line runs, processors, and computers, does not take up a significant amount of space or that it is not necessary to space the equipment out so that maintenance personnel can move (or at least crawl) around it when maintenance is needed?

            All airliners that I am familiar with have a forward avionics/equipment bay under the cockpit and ahead of the forward baggage/cargo compartment, lots of equipment and interfaces in the wing box area to communicate with and control the engines and wing control surfaces, and an aft equipment bay behind the aft baggage/cargo area for controlling and communicating with the tail control surfaces and APU. The redundant air conditioning and pressurization packs are also usually near the wing box area. To get an idea of the size of the air conditioning packs, take a look sometime at the air conditioning units on the roof of a commercial building.

            I have included below some links to videos of airliner underfloor equipment and avionics bays for the benefit of anyone who has never had a chance to look in these compartments, and is-having trouble imagining the size of the necessary equipment in the non-wasted space of these compartments.

            787 Forward and Aft Avionics and Equipment Bays.


            A350 forward avionics and equipment bay. Note that when the pilot enters the baggage/compartment from the equipment bay, there is not, even in this large wide body aircraft, enough room for an adult to stand up. The designers of this aircraft wisely and efficiently provided only enough height in the baggage/cargo compartment for the 64 inch (5 foot 4 inch) tall LD3 containers that this aircraft is designed to use. I would hope that no one is going to silly enough to suggest that baggage/cargo compartments on wide body long haul aircraft are wasted space.


            A320 forward avionics/equipment bay under the cockpit floor.


            A320 aft avionics/equipment bay.


            E190 forward avionics/equipment bay under the cockpit floor.

          • Re in my post above:” … outside air at (-60 C to -75 C at cruise altitudes) …”

            Correction – this should have been degrees F instead of C, i.e.: ” … outside air at (-60 F to -75 F at cruise altitudes).

        • Its not wasted . Its there for structural and aerodynamic reasons. We could all live in tiny homes with zero wasted space too but dont

          Your rectangular flat sided fuselage plane the Shorts 360 isnt pressurised . Braced wing too ! Cant think what the other downsides of this plane of the future are…..hehehe

          #35 answer on this page shows comparable 3 and 4 across fuselage X section.

          The CN235 is the most flattened ellipse fuselage , but that had antecedents as a cargo plane

          • Hello Bryce,

            Re: “If it’s empty, then it’s wasted.”

            Once again, the space under an airliner floor is not empty.

            See the link below for video tour of the forward and aft avionics/equipment bays of a 787. As in most airliners, the forward bay is under the cockpit and extends back to the forward baggage/cargo bay, and the aft avionics/equipment bay is behind the aft baggage/cargo bay. The space between the cargo bays is filled by the wingbox in and around which there are air conditioning packs and lots of cables, interface racks and processors for communication to and from wing control surfaces and engines.


            See the link below for a video tour of the forward avionics/cargo bay of an A350.


          • Yes. APB. Unless its a cargo conversion , half of the passenger cabin is ‘wasted’ if thats the novel approach to take where it has to ‘filled up’. Have a look at suburban train in rush hour , thats no wasted space when you can have standing passengers

          • Re in my post above:” As in most airliners, the forward bay is under the cockpit and extends back to the forward baggage/cargo bay, and the aft avionics/equipment bay is behind the aft baggage/cargo bay.”

            Correction: In the 787 the main underfloor aft electronics and equipment bay is actually behind the wing box and extends back to the aft cargo bay, which can be entered from the aft E & E bay. There are smaller equipment compartments further aft where the APU is mounted, for the equipment and processors for communicating to and from the tail control surfaces and APU, fuel supply to the APU, and for the hydraulics that move the tail control surfaces.

  16. The point is, if you can handle the load peaks without adding tons of weight due to reinforced structure, and reach an optimum that`s better than the round versions, why would you build an 2-3-2 abreast oval?
    You would be much better off with going for a new 3-3-3 fuselage, or at least a 2-4-2, as this would attack the oldes WB fuselage left in the market.

    In the end, this is an old discussion. Because in fact, that`s why the blended wing doesn`t exist yet. It`s difficult to build a cabin in there.
    Once you can, and integrate fuselage and wing, we`ll have a major step foreward.
    So far, we still all fly in convetional civil airplanes.

  17. AP_Robert:

    “Apparently, like most who post here, and unlike Bjorn, you are neither an aerospace engineer nor have you taken an introductory course in aerospace engineering?”

    Hi Robert, what a low, incorrect and insulting comment. I hope it’s just an incidental burb and it doesn’t happen to you too often.

    A 3-3 fuselage will in general be lighter than a 16% shorter 2-3-2, using the same materials, technology up to a certain capacity. The proof is in the pudding.

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