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How my toddler helped explain the shape of Boeing’s NMA

Entering her room first thing in the morning slightly bleary eyed, I lamented the new hamster nest-like pile of debris on her floor. But that's when it hit me.


Jon Ostrower
How my toddler helped explain the shape of...

My toddler, standing a mere three feet and change in height, is an energetic sort of whirling dervish of curiosity and destruction. Watching her explore her new world has been a great joy for me and her mother, of course. But there are also times when that two-and-a-half year old impulse to learn how something is put together leads to its untimely demise.

We genuinely believed a book of shapes would be safe in her bedroom overnight. It wasn’t flimsy paper, it was built with toddlers in mind. But those thick heavy pages were no match for this little girl.

Though sometimes – as engineers know – breaking something can teach you something, too. Entering her room first thing in the morning slightly bleary eyed, I lamented the new hamster nest-like pile of debris on her floor. But that’s when it hit me.

I’ve been trying to find a way to properly describe the shape of the fuselage of Boeing’s NMA, the shorthand for its new middle-market airplane concept. A widebody airplane? Yes. A narrowbody airplane? Also yes. We’ve called it “ovoid,” we’ve called it “hybrid,” but how do you really illustrate what that is – short of an egregious breach of proprietary geometry?

Related: This is Boeing’s NMA

Two pages from the newly-deceased book of shapes lay on her floor. One a half moon, the other an almond. I put the two on top of each other and there it was: A high-ceiling twin-aisle above the floor and a single-aisle height cargo hold below.


That shape is nothing like we’ve seen in modern aircraft design, and Boeing believes it is the key to unlocking the efficiency and economics of this new airliner.

The benefit is a lower-profile, lower-drag design. For airlines who don’t want the belly cargo space for anything but passenger bags, it means they don’t have to carry the extra structure of an equally-deep circular cargo hold for the type of LD3-45 containers that fit inside an Airbus A320.

For generations the so-called double-bubble design has been the dominant shape. The Boeing 377 (shown below) was the most exaggerated example of this, but the configuration has been applied more subtly to virtually every popular jet airliner flying today. (Notably the A330 and 777 are both fully-round designs)

The Boeing 377 Stratocruiser was an extreme double-bubble design.

But on the double-bubble design, the floor intersects at the joining of two circular lobes. A skilled commercial aircraft engineer described the advantage to me this way: “Each lobe has to be circular to avoid out of plane loads.”

A double-bubble solves many problems, generally by ensuring the internal pressure is always pushing perpendicular to the surface of the fuselage skin.

But why is Boeing’s chosen ovoid/toddler-illustrated design design so challenging?

“As soon as you go out of a round shape the pressure won’t be uniform across the lobe,” he said. An NMA-like shape adds significant weight. As a result, it needs more structure to account for the uneven (out of plane) loads to reinforce how quickly the structure fatigues in certain areas.

Boeing 797 / NMA-6X Annotated - jonostrower.com

It’s a hard manufacturing question, too. Creating elliptic frames that don’t negate the aerodynamic benefit with added weight is a big part of getting this right.

But while Boeing has yet to even show publicly what it has come up with for the NMA, we’ll wait for an official illustration. Until then, I should go clean up.

Show Comments (6)

Comments

  • Andrew Kyle

    So, the “efficiency” of the perfect circle, and the near-zero fatigue on the sidewalls from it, are worth going away from and back to the old oval of the old days?! Odd, how history repeats itself.

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  • Roland Delhomme

    Biomimicry and natural forms will incresingly impact design as the respective merits of one morphology vs. another are better understood, compared, tested and validated, hybridized and tweaked for their intended application. Unexpected combinations and things that just don’t go together can, will, yield compelling results.

    Sharks, birds and other creatures have lots to teach us; as computing power increases, we’ll better arrive at breakthrough innovations sooner, and some of them will be counterintuitive; others will have us looking at familiar shapes and wondering why we didn’t make the creative leap sooner.

    Surprises lie ahead…

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  • Roland Delhomme

    -but, that being said, typos from shutting off spellcheck on a smartphone will still help make a case for AI over the carbon units. (Incresingly vs increasingly, my bad) Love the new site, Jon, from NASA and commercial, military space, to powered parachutes, drone and more, come check out Sun ‘n Fun or Oshkosh and the accompanying museums at each, for some real eye-opening examples of innovation from the past, and then peruse the cutting edge thinking showing up on the flight lines at these events; you’ll be hooked for life.

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  • Peter

    Take the E-Jet, a double-bubble design, and stretch it horizontally to fit 7 abreast and vertically to fit two side by side LD3-45 containers at 156 × 153 × 114.3 cm (61.5 × 60.4 × 45 in). This is your NMA and I guess it will be developed in partnership with Embraer.

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  • TCook

    I like the simplicity and success of the circular fuselage on the A330 and 777. A circular fuselage on a 2-2-2 aircraft would yield an easy to fit LD3-45 container and a spacious cabin for bins. Of course at 14.3′ diameter, it would be larger than the A320 at 13.3′ average outside dimension, or the 737 at 12.8′ average. However, I think the benefits outweigh the extra surface drag. Twin aisle improved passenger circulation and ergonomics, psychological sense of spaciousness, and number one, abundance of premium aisle seats.

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  • Andrew Boydston

    “Conestoga” Is the answer as land yachts took to the Praire in 1850’s and beyond. The Boeing “Conestoga” is an awesome design proposal

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