[ramesh31]

I remember seeing renderings precisely like this in my middle school textbooks in the 90s, claiming the same thing. The truth is that commercial airliners are a solved engineering problem. We are at the absolute limits for speed, reliability, and safety that can be achieved with a flying machine in the earth’s atmosphere. Which is why the fundamental layout has not changed since the 707 was introduced over 60 years ago.

Blended wing designs fall short on many of these constraints, namely the complete lack of inherent stability. With total power loss, they become completely uncontrollable. This is an acceptable tradeoff for military aircraft (modern fighters have the same issue), but not for civil aviation.

[AlexandrB]

Yup, I've been seeing these futuristic airplane concepts for most of my life, but commercial airframes seem to be converging to be more and more similar. Unusual elements like a third engine in the tail or horizontal stabilizers mounted above the rudder have largely disappeared. Given the thin margins in air travel, I suspect this is because this design is the most successful. It might be a local minimum, but when it comes to these radically different designs: "I'll believe it when I see it".

[hotpotamus]

My understanding is that tri-engine jetliners were actually more to fulfill a regulation than for engineering reasons. There are regulatory limits to how far a plane is allowed to fly on one engine called ETOPS - I forget what it really stands for, but the colloquial expression is: Engines Turn Or Passengers Swim. It used to be limited to around 2 hours I believe, meaning you've got a bit of time to divert and make an emergency landing. But if you're crossing the ocean, it's not really possible, so for a long time if you were crossing an ocean, you needed a 3 or 4 engined plane to do it.

Jet engines are extremely reliable however, they fail on the order of several hundred times less often than piston engines, and are very well proven and have basically only improved, and so ETOPS rules have been relaxed quite a bit meaning that a lot more ocean crossing routes are available to twinjets.

[robocat]

Plus having more engines doesn’t help if failures are correlated, such as some fuel issues, or http://news.bbc.co.uk/2/hi/uk_news/magazine/8622099.stm

[jabl]

Yes, ETOPS ratings have been extended as engines have gotten more reliable.

Another factor is that we have learned to make bigger engines as well. So nowadays with two engines you can power a pretty big plane. And due to how turbine efficiency tends to scale with size, two big engines is more fuel efficient as well as saves on maintenance costs vs. having more but smaller engines.

For an extreme example, look at the B-52 with 8 engines. That was what was available back when the plane was designed, but nowadays the thrust from those 8 engines (about 600kN in total) can easily be exceeded by two modern large turbofans.

[coredog64]

Extended Twin Operations.

[jabl]

Horizontal stabilizers above the rudder went away with the engines mounted on the body in the back, the reason for the high tail was to keep the elevators away from the jet blast of the engines.

As to why create a design like that in the first place, I don't know. My understanding is that the 'engines under the wings' layout won because with the engines in the back the fuselage needs to be stronger (and thus heavier) to support the engines.

(Business jets tend to still have the engines in the back layout, because mounting the engines high allows shorter landing gear so that a stair that is part of the door is enough to board the plane, no need for an external stair. But that's not much of a consideration for a passenger plane operating out of airports with infrastructure available.)

[ramesh31]

A lot of the reasoning for business/regional jets maintaining the high tail mount engine layout is FOD avoidance. Operating out of shorter runways/smaller airports this becomes an issue.

[jabl]

Isn't much FOD ingestion due to the wheels kicking up something? If so, mounting the engines in the back seems like a bad idea, as even if they are higher up than an under wing mounting there's a risk that the wheels might kick up some debris?

See also SAS flight 751, where ice broke off from the wings and were ingested into the engines https://en.wikipedia.org/wiki/Scandinavian_Airlines_System_F...

From a FOD perspective, in my admittedly very non-expert opinion the best location would be to have either a high mounted wing with engines in the traditional under wing position, or then engines above the wings like the Honda business jet?

[lstodd]

Something like An-72.

But maintenance becomes a bitch, so they put'em back under the wings eventually.

[daveslash]

Came to the comments to make nearly the exact same remark. I, too, remember seeing these in middle school in the 90s, as well as high school. Though, they weren't in my textbooks - but were in the supplemental "educational magazines" that the science teachers would supplement their coursework with, and "Popular Science" magazines that the school had in the library.

[throw827474737]

Dito, but before doubting myself.. radical new, wow.

[dver]

Here's some info on stability, https://www.sciencedirect.com/science/article/pii/S100093612....

I think you're thinking of pure flying wings.

[upofadown]

>With total power loss, they become completely uncontrollable.

* https://en.wikipedia.org/wiki/Marske_Pioneer

Note that this entirely powerless aircraft with a fairly high aspect wing and no tailplane first flew in 1968. Something that is basically a blob would be a lot easier to make inherently stable.

[inkcapmushroom]

>speed, reliability, and safety

The article states that other designs are being looked at due to improvements in other areas, namely sustainability and suitability to alternate fuel sources. I would think that if you had a design that came close in reliability and safety, sacrificing speed for better efficiency would be a good tradeoff on many commercial flights with passengers or cargo.

[runarberg]

No. commercial airliners are only a solved problem if you ignore the climate crisis. There is no way you can run the current design on electricity during intercontinental travel. This is the problem that engineers are trying to solve with innovative and radical design changes.