
Pratt and Whitney's Next-Gen Geared Turbofan and the “Double-Bubble” Airliner - aerocapture
http://aviationweek.com/technology/reversed-tilted-future-pratt-s-geared-turbofan
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frik
The clustered beneath the pi-tail of the NASA/MIT D8 design is bad for
maintainability, isn't it?

All we learnt from early commercial jetliner like the _De Havilland Comet_
([http://en.wikipedia.org/wiki/De_Havilland_Comet](http://en.wikipedia.org/wiki/De_Havilland_Comet)),
where two pairs of turbojet engines were buried into the wings, is that such
configuration increased the structural weight and complexity of the wings.
Armour had to be placed around the engine cells to contain debris from any
serious engine failures; also, placing the engines inside the wing required a
more complicated wing structure.

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usefulcat
The article addresses debris-related engine failure mitigation.

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Shivetya
I would still think that intake at the top of the fuselage should be less
likely to ingest debris, the military would be an ideal means to test it in
transport configurations.

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Sanddancer
There's been a decent amount of research that the upper portions of the
fuselage are more durable locations for engines. The A-10 for example, has its
engines located up and to the rear for that reason, and the experimental YC-14
[1] also had the engines placed up high, albeit for different reasons, but
avoidance of ingestion was definitely a nice side effect.

[1]
[http://en.wikipedia.org/wiki/Boeing_YC-14](http://en.wikipedia.org/wiki/Boeing_YC-14)

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jessaustin
More on the D8: [https://www.nasa.gov/content/the-double-
bubble-d8-0/](https://www.nasa.gov/content/the-double-bubble-d8-0/)

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msandford
From the article:

"carrying 180 passengers 3,000 nautical miles in a coach cabin roomier than
that of a Boeing 737-800"

I would LOVE it if a bigger cabin meant that people got more space. But
considering how we've all accepted being crammed into ever smaller coach
seats, I suspect that any breakthrough here will simply to go make airlines
more profitable while ticket prices drop a miniscule amount.

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mikeyouse
Right? What are the chances that if the DoubleBubble is 20% more spacious than
a 180-seat 737, that they'd give customers 20% more space rather than just
flying a 216-passenger plane?

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olefoo
Depends on the load factor ( # of kilos/m2 ) that applies to the plane. You
could increase the cabin size by 20% but only increase max load by 5% and then
you'd have 15% more space into which to put passengers and luggage.

I myself would be happy with larger, lighter, slower and more fuel-efficient
planes. But then I am also perennially hoping that dirigible passenger liners
will make a comeback.

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msandford
> Depends on the load factor ( # of kilos/m2 ) that applies to the plane. You
> could increase the cabin size by 20% but only increase max load by 5% and
> then you'd have 15% more space into which to put passengers and luggage.

Actually what you'd need to do is increase 20% past the point at which the
load factor starts to become about weight rather than volume. What I mean is
that right now planes might be able to carry more weight, but don't because
there's not enough room. I'm not an aerospace guy so I can't tell you where
stuff lies on the spectrum right now. But it seems possible to me, which is
why the airlines keep cramming more seats into planes; they've got the lift
capacity for the increased weight.

> I myself would be happy with larger, lighter, slower and more fuel-efficient
> planes. But then I am also perennially hoping that dirigible passenger
> liners will make a comeback.

I wouldn't mind that much either. I'm headed to Scotland from Texas for a
wedding in about 6 weeks and I'd much prefer 36 hours each way on a sofa to
12-14 hours each way crammed into a chair barely big enough for me. At 4500
miles the airship would only need to manage 125mph which is fast, but not
crazy fast.

I'd also be a fan of big, ocean going ground effect airplanes. But when I say
big, I mean big. It's going to be able to have ground effect at 20-30 feet up
so that you can cut across most of the chop. I suspect that the wings would
need to be an awful shape to get that high, but that's what it would take for
comfort.

[http://en.wikipedia.org/wiki/File:Pelican-01.jpg](http://en.wikipedia.org/wiki/File:Pelican-01.jpg)

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olefoo
WIG vehicles are pretty damn cool. Unfortunately they are rather vulnerable to
weather. I am disappointed that Russia hasn't made regular Ekranoplan service
a thing, both across the polar areas and on the black sea.

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pc2g4d
For those of us who aren't aeronautical engineers, why is it called "double-
bubble"?

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maxerickson
It's just a reference to the shape of it. Page 4:

[http://web.mit.edu/drela/Public/papers/Hawaii_11/Drela_AIAA2...](http://web.mit.edu/drela/Public/papers/Hawaii_11/Drela_AIAA2011_3970.pdf)

