Pratt and Whitney's Next-Gen Geared Turbofan and the “Double-Bubble” Airliner

Pratt and Whitney's Next-Gen Geared Turbofan and the “Double-Bubble” Airliner(aviationweek.com)

34 points by aerocapture 11 years ago | 20 comments

frik 11 years ago |

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), 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.

Sanddancer 11 years ago | |

Trijets have been around for a very long time, and aside from the DC-10's various misfeatures, have been rather reliable, even when the number two engine goes out with or without detonating itself in various ways. Given that this plane will almost certainly be fly by wire, I imagine that it'll be a lot easier to design the hydraulic systems in ways to further avoid certain failure modes that did occur in those planes.

Regarding maintenance, the article discusses how the reverse design gives a benefit of having the parts of the engine most difficult to service in a position to make such service easier, so I imagine maintainability will be /different/ but not necessarily worse.

frik 11 years ago | | |

Trijet design will almost always consume more fuel than a comparable twin engine design. This results in higher operating costs and reduced range. Although trijets are more efficient than four-engine aircraft, the difficulty and complexity of mounting the center engine through the tail will somewhat negate this advantage.

quote from http://en.wikipedia.org/wiki/Trijet

rdtsc 11 years ago | | |

http://en.wikipedia.org/wiki/Tupolev_Tu-154

Is also a popular trijet. Not only that but one of the fastest passenger civilian aircraft. It is on its way out and in limited operation.

nether 11 years ago | |

Much of the downsides of burying engines in the wing versus in the fuselage (below the H-tail) are irrelevant because the engines are not in a cantilever loaded portion of the structure. A beam has zero bending moment at a free end, and we may treat the fuselage as a long beam with free ends, like a see-saw balanced on a fulcrum in the middle (the wing in this case; we are neglecting the downforce from the horizontal tail). Placing the engines at a far end of the minimizes the bending load they must withstand. Placing engines at a wing root means putting them at the location of maximum bending moment due to the lift acting on the wing.

usefulcat 11 years ago | |

The article addresses debris-related engine failure mitigation.

Shivetya 11 years ago | | |

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.

scrumper 11 years ago | | |

Only in as far as a novel 'core canting' approach to protecting one engine from an unconfined failure of the adjacent unit. It didn't discuss protecting the tail or fuselage (unless I'm forgetting something; read it a couple hours ago so maybe I did.)

frik 11 years ago | | |

Yes the second engine may be saved (not mechanically linked).

But the debris could destroy parts of the tail/wing/fuselage.

jessaustin 11 years ago |

More on the D8: https://www.nasa.gov/content/the-double-bubble-d8-0/

msandford 11 years ago | |

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.

mikeyouse 11 years ago | | |

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?

woah 11 years ago | | |

IIRC airlines are very unprofitable

pc2g4d 11 years ago |

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

maxerickson 11 years ago | |

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

http://web.mit.edu/drela/Public/papers/Hawaii_11/Drela_AIAA2...