Guest column: envisioning the next round of airplanes

By James N. Krebs

Leeham News recently forecast that the next all new Boeing airplane will be a 757 successor with an entry-into-service around 2025, followed by a smaller NSA (New Small Airplane), a 737 MAX/A320 neo successor, in maybe 2027. I believe it will be clear in the next few years that the technology is and can be available here to build a reasonable-risk NSA with 20% fuel savings over the MAXes/ neos (at same seats) for initial service by 2025 (which will demand perhaps 40 more than 162 seats for even better economics). Its production would ramp up over ~5 years or so.

I hope this would be mainly a “Made in the USA” Boeing NSA: American engineering, American manufacturing, American jobs and American competitive edge. If that takes some helpful brainpower and/or investments from NASA, Northrop Grumman, Lockheed Martin, etc, good.

Boeing and Airbus might love to build a combined 100/mo. MAXes and neos “forever,” but technology and market forces aren’t likely to permit this. The companies won’t want to whet any appetites soon but I hope Boeing’s advanced design people are already at work–I’d be disappointed if they aren’t.

Airbus could certainly put an A320neo successor in service 10 years after their 2015 neo. A reengined A330 and a possible A350-1100 aren’t the only new projects they are capable of in the next decade.  The market response to their A320neo family completely surprised Boeing a couple years ago. What’s next?

A few thoughts about this NSA:

For best economy, the NSA could be designed for 2,000-2,200 nm range (covering > 98% of 737 missions) and .72-.75 mach cruise. Don’t burden the fleet with the neo/max’s extra weight, fuel burned, carbon and costs for ~3,500 nm range and .8 mach cruise.  Airlines can continue to use MAX/neos for transcon ranges.

The NSA’s wings could be more efficient high aspect ratio, composite designs, with less area and sweep and the current ~118’ span to fit airport slots — plus folding 8-10’ wing tips (why not) for ~138’ in flight. There will be significant weight benefits in fuselage and tail materials and construction–better than the A320/737s and even the 787/A350s–plus modest gains from some advances in practical laminar flow, riblets, more-electric systems etc. Technology moves ahead.

New twin ~20,000 thrust class engines could be mounted on-wing. Bypass ratios would be well above the A320neo’s 11-12, not only from smaller, lighter, more efficient cores but also from lower pressure ratio fans for higher propulsion efficiency. Propulsion and airframe integration will continue to improve. Further noise reduction will come automatically. Fossil fuels, better new biofuels and mixtures will be accepted. NOX will reduce.  GE, RR and PW would eagerly serve up some beauties for 2025 service.

Until now, we have missed gains from the airplane configuration itself. If Boeing could get even 5% net fuel savings from a low risk configuration, it could provide an important edge. It isn’t cast in concrete that a NSA should be single aisle, or must await proof of some revolutionary new aircraft or engine concept. The NSA isn’t going to be a hybrid wing body (HWB) or flying wing or joined wing design and it isn’t going to be powered by two open rotor engines with two very large counter-rotating, reversing fans.

The best, practical NSA design could be twin aisle, eight abreast, 17” wide seats. Note the MIT D8 concept with its wide double-bubble (or alternatively, smooth ovoid) twin aisle cross section and Pi tail. Two recent issues of Aviation Week have reported NASA work on MIT’s later, more advanced, rear engine boundary layer ingestion (BLI) model. But note that MIT AIAA and SAE papers in 2011 reported that 10% fuel burned savings vs 737-800 could be realized from its wide body/ lifting nose/Pi tail configuration itself — with engines on-wing at 118‘span. Its aero, materials, structures, manufacturing, weight and cost details should be evaluated. It makes a good looking airplane. Also explore any other useful NSA concepts.

Regarding the 757: the NSA family and a 200+ PAX, 4,000 nm 757 successor might have high commonality — the same twin aisle fuselage, the 757 one with stretch — the same flight deck — the same engine family, the 757 type with growth and refan — many of the same subsystems –maybe the same wingbox but two different wings, the .85 mach 757 type with more area, sweep and span–and somewhat different tails. I see the 757 type as following the NSA, ideally, as a derivative. Put the major league market before the little league.

Considering that the NSA family’s global fleet might grow to 10-20,000 aircraft over several decades, I expect that this class could save way more fuel, carbon emissions, and dollars than any other class–even compared to several thousand 787/A350’s. And note: less CO2 generation will be even more important in 2025 than the public recognizes today.

James Krebs is retired from GE Aircraft Gas Turbines. He has four decades of experience in the design, development, marketing, manufacture and management of military and commercial jet engines.

27 Comments on “Guest column: envisioning the next round of airplanes

  1. Good idea to have guest articles Scott. Thank you.

    The one thing I take exception to in this article is the reference to ‘American competitive edge’ which suggests to me a belief that America is superior. I also disagree with the notion of the benefit and/or desirability of going native, irrespective of real or imagined superiority.

    Most interesting to me is Krebs’ belief that open rotor will not feature. My impression had been that timing for a 737/320 replacement is actually held back by the timeframe on this but, nevertheless, tied to this, assuming it offers the step change claimed for it.

  2. Ditto on the “Made in America”, I thought that kind of lingo had disappeared by now. We are in 2014 after all. Be proud of what you make, by all means, but using that kind of ideology feels very stuck inte 80’s (or before).

    I also find the conclusion either a little too sweeping or somewhat naive, e.g. the by Woody referenced topic on open rotors or the “Further noise reduction will come automatically”. Oh yeah? Will it? They will come, but by hard work, definitely not automatically (not with the level of design optimization we already have). Or “NOX will reduce”. Well, that will also be a hard fought battle. _NOx_ has already been much reduced in the last generation of engines, reducing NOx further pushes combustion temperatures down, but lower T3 lowers efficiency, so it is not so easy. One has to be very skilled and careful when designing the combustion chamber, for it can be done, but at great effort.

    And the J Krebs I remember was a manager at GE since the late 70’s, mostly in production, quite far from the concept design office (they at least used to have)…

    I do agree with the idea that range should be kept shorter, however. Tat would save more than a little weight on a global scale…

    • I agree with the range argument.
      Longer range probably could come with PIP improvements and/or re-engine later in the life of the program.

  3. Mach 0,75 vs 0.85 is a speed delta of 12%, mach 0,72 vs 0,85 even 15,5%.
    For any airline where utilisation factor of aircrafts is important, that slower aircraft must be roughly 12% (respectible 15,5% for mach 0,72) more economic than a comparable aircraft with mach 0,85. In fact it must be even more economic because people will vote with their feet for longer range flights if they can book another flight for the same pricepoint but four instead of five hours flight time (at least I would).

    Can a slower design speed really offset that in terms of economics ?

    The “MIT D8 concept” performance claims are interestic. If you could get a wider cabin and still the same economics as a traditional narrower design – that would definitly be game changer – no ?

    • Turn time is a good reason for twin aisle on 2-4 hour flights. Cabin comfort is a good reason for twin aisle on longer flights. The world does not need another 757-300, leave that bad idea in the dustbin of history.

    • 737s cruise at Mach .78/.79. Dropping to .75 is only about 29 mph slower or less than 5% or adding ~16 minutes on a US trans continental flight. For a cheaper ticket I am confident that the slower airplane would prevail. That is why we are flying slower now then we were in the 1980s.

  4. About the “Made in the USA” ignore. The author probably didn’t realize the names & texts on this blog are English but he’s among young Germans, Brazilians and Koreans that don’t share all the same sentiments. Leehams cozy community is global.

    Fully agree with the 4 hr range requirements. US transcon doesn’t determine minimum range anymore. 2 Billion live within a few hours in Europe, China.

    I dreamed up a similar 7 abreast standing cabin CROR (ECR-20), only problem is.

    If Boeing builds an 8 abreast 2 aisle machine, it will be heavier then a 3-3 single aisle A320 type usung the same technology (or a little more advanced 😉 ). That still carries cargo containers and can “easily” be re-winged to cross the Atlantic.

    IMO if Airbus even suggests it can do a dedicated 199/200 A320 inbetween A320 and the 50 seats larger A321, all operators will jump on it. Boeing then has no longer alternatives then just do an enhanced, carbon Boeing 320 series ASAP. Probably with a high wing to never again run into engine ground clearance.

  5. Let’s look at the (NEO+MAX) —-> (NFA+NFB) phase-out/phase-in overlap period with an objective mind … we’re talking about some 1,000 units/annum or 85 units/month, ie a major social/industrial disruptive upheaval over … (l propose) ten years : if started – say – in 2028 (the later, the more leapfrogging advances), the last NEO or MAX units will be delivered … well until 2035-38 ? Krebs’ assumption that the replaced types – millésimes 2010 thru 2035 – will co-exist with the New Feeders (of A or B) is credible and pertinent, I’d add the precision : until after 2060, just as some 1,000 757 are still flying around up there in 2014 … !

  6. Cross-section design closely inter-relates to overhead stowage capability. The elliptic “Fatty” (2+3+2) is a ‘no-go’ when examined closely : above a Y-class twin-seat (2″+18″+2.5″+18″+2″ =) 42.5″ wide, with sidewalls curving in, there just isn’t sufficient space to install a proper hatrack, except above the centre triple. Whence the relevance of the Wankel tri-elliptic patented cross-section of Airbus’ New Feeder R&D proposals. This being said, the most efficient twin-aisle small feeder could be (1+4+1), ie the staggered C919, with the obvious hic-et-nunc (sub-optimal but ‘realistic’) NEO or MAX counters : (1+3+1) ?

  7. A NSA can IMJ easily be countered by a re-winged A32X-series in addition to having new engines a generation beyond the ones that are going on the A32Xneo-series. Currently, composites doesn’t scale down well, and empty weight isn’t all that critical on single aisles as it is on long range wide-bodies. Therefore, the A32X-series may be fine for another 15-20 years. I’m not so sure about the MAX, though; the dash-9 can’t seemingly compete properly with the A321 and Boeing is barely managing to hold a 40 percent market share. I’m predicting it will keep sliding.

    However, the A32X-series should IMO be replaced with a game changing new platform. Perhaps this one will do:

    On September 12, Europe’s EADS unexpectedly assigned a schedule and a market segment to its “E-Thrust” hybrid propulsion concept, which was revealed at the Paris Air Show this year with Rolls-Royce. The “E-Airbus,” under its new moniker, is to enter into service in 2030 as a regional aircraft, probably a 70- to 100-seater. The announcement came during a conference organized by the French government in Paris about its industrial policy.

    According to EADS chief technology officer Jean Botti, who introduced the project, the E-Airbus will have six electric fans. One gas power unit (in short, a gas turbine connected to a generator) will provide the electric power for the six fans and for the recharging of the energy storage. During part of the descent phase, the fans will windmill and produce electricity.

    The serial hybrid architecture offers the possibility to improve overall efficiency by allowing the separate optimization of the thermal efficiency of the gas power unit (producing electrical power) and the propulsive efficiency of the fans (producing thrust). The hybrid concept makes it possible to downsize the gas power unit and to optimize it for cruise. The electric energy storage will provide the additional power required for takeoff.

    The bypass ratio (or its equivalent number for such a distributed propulsion system) is expected to be greater than 20. Among the hoped-for enabling technologies are lithium-air batteries as well as superconducting cables, generators and motors. A dedicated fan, driven by the gas turbine, will re-energize the wake, thus reducing drag.

    Botti referred to Europe’s Flightpath 2050 goals of a 75-percent reduction in CO2 emissions, 90 percent in NOx emissions and 65 percent in noise, compared to 2000 levels, without clarifying where the E-Airbus would position itself in 2030.

  8. Looking at the advacement of the wing to body fairing over the years, and looking at the chines and fairings on fighter aircraft, one has to wonder if there will be advancements in sculpting the fuselage of passenger aircraft to gain more lift. Since at cruise, the fuselage is angled up a few degrees. Like wingtip devices, this could be an area to harvest a few more percent in lifting efficiency by riding the high pressure cushion.

  9. IMHO the neoisation of the current NB families pulled the rug from
    any NSA ( A or B ) for yet another decade.

    A flat oval fuselage introduces compression forces into the floor. not good.

    Then I think the reincarnated 757 is a red herring.

    Pushed forward to obscure the “dirty dozen” kindergarten of Boeing problems.

    The 757 was an “american plane” tailored to a large continent strewn with smalish settlements that lack fast connecting infrastructure. Its second life use case was exactly that extending use in an environment where old hardware is available and where larger strategic investments are no longer en vogue.

  10. I agree with Uwe that a B757 re-incarnation is a red herring, not enough market left after most B757 routes have been turned over to B737-9s or A321 Neos, and Boeing knows it.

    If a slower 2000 mile aircraft is what eventuates a turboprop NSA becomes more and more likely. Airbus must be looking closely at the tech they have in the A400M to see what they can use. That might also explain Airbus´ reluctance to see ATR go ahead with their own large turboprop, it could be a stepping stone to a competitor with Airbus itself.

  11. That was an enjoyable guest column. The difference in speed between 0.8 and 0.72 mach is roughly 48 miles per hour so not that huge a difference. I wonder if a “hybrid” engine is possible, similar to the Prius concept whereby the jet turbines provide lift and thrust but throttle back as electric engines provide cruise capability. I suppose the problem would be turnaround electrical recharge capability tho. Hmmm…

  12. There is a significant market for 200-300 seat short/medium haul.

    Please don’t call it “757” replacement, because people tend to Pavlov the 757 is gone. Forgetting it’s a segment where the 757, 767, A300, A310, Tu154 operate(d) too and there no god given gap between 200 short haul and 300 seat long haul. God didn’t create earth like that.

  13. Must we continue to suffer with 17-inch seats on transcontinental flights? Why is that such a magic number? It’s a tortuous width for most North American males. (Not so much in terms of the lower body — it’s the shoulder room that is cruel.)

    • For most North American males the lower body constraints (between armrests) will sadly be even worse …

  14. Great writing! As I used to work on these subjects, a few thoughts.
    The MIT 8-abreast concept doesn’t convince me (and I am not alone). The efficiency of such a fuselage is still not proven. I know all the NASA-sponsored N1, N2 and N3 concepts. But some a rather wishful thinking.

    I thank Mr. Krebs for pointing out the speed-question. An open-rotor with high aspect ratio wings, possibly with struts, might enable the 25% fuel burn saving. Current configurations, even if all technologies are used, will only achieve a 8-15% margin towards current re-engined concepts. And the 8 is much more realistic than the 15. Trust me!
    Engines are approaching the physical limits, there will be no simple NEO^2 in 10 years.

    Or short: a B737/A320 replacement with a 20+% margin versus the re-engined models will require a radical departure from current designs. Fuel is rather cheap today, expect it to cost at least twice in 10-15 years (in this year’s USD, so inflation comes on top). Then speed is no issue then.

  15. A word regarding this hybrid concepts: very early stage, and most concepts rely on extrapolation of battery technology developments. However, any such concept would require utmost efficiency of the airframe & engine (=slower).

  16. And a word towards American workshare: aircraft being build not far from here (I live in Hamburg) have up to 40% American “value share”, depending on engine choice and specific cabin layout options. So, no need to get too worried. An Airbus delivered to Kookonistan Airlines supports American jobs, even if the particular aircraft never enters US air space.

    • 40% american parts.

      Isn’t that att he core of this “amercian exceptionality” thing?
      Others making a better product based on the same parts 😉
      Same for all the strive directed at John Leahy
      an American selling European Airbus. obviously a traitor 😉

      Then, behind the big historic post WWII achievements stood
      to a significant part foreign research and foreign educated people.

      • Uwe, you forget your History : John (as are the remaining 99 % other North-Americans) is just another dislodged European … I don’t see where he failed ?

        • This was about ( interpretation of ) feelings and not about historic correctness 😉
          Educational TV programming here recently shew a range of pre WWI retrospectives. Interesting to see the parallels in verbiage.

  17. What a refreshing innovation to have a guest commentator, truly excellent, more please…..

    I take issue with promoting the mainly made in America concept as this works against Boeing in so many ways. Historically Boeings capability in selecting quality third party suppliers is an object lesson on how not to do business & it could do better by learning from the Airbus model which while not perfect is streets ahead & extremely successful in poaching long loyal Boeing markets

    A broadening of attitudes is demanded from Boeing to address the alienation it suffers in vital & growing global markets, with so much reliance on domestic & political alliances it’s growth model is seriously flawed.

    Whilst controversial moving production overseas is essential, clearly a challenge but it must occur to encourage lost markets to return to the fold. The task will be arduous with current US foreign policy (yes it has an impact & is critical) but it is not insurmountable.

    Without this shift of emphasise I fear Boeing will further alienate itself & dig itself into an even bigger hole.

  18. Speed on feeder routes (increasingly jammed with time !) will inflexe from cruise optimisation towards ATC-regulated pre-set common feeder fleet speeds throughout. Only climb speeds and descent/approach speeds will be left available to slight variations. Therefore, ‘speed’ (not airspeed but true – geographic – speed) is becoming a Community issue, to be debated/decided/regulated between all parties involved, wherefore I’m afraid aeronautical engineers will probably not have the last word ?

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