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And now the Boeing 777...

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james_s:

--- Quote from: hans on May 18, 2022, 10:35:47 pm ---I do wonder if failed engine blades of turbofan engines is going to be a more common theme. I also remember reading about another recent incident (Southwest_Airlines_Flight_1380) with a 737. Totally different engine mfgr though, but nonetheless, the trend for turbofan is to go big.. get the largest bypass ratio you can make fit and produce reliably. Intuitively those longer fan blades will put more strain at the connection points to the axle. For the Southwest flight, it were mini cracks that caused failure, which has seen increased inspection measures to prevent them..

--- End quote ---

I'd like to see turboprop make a comeback for large airliners. While not as fast, they're considerably more efficient than turbofans, the controllable blade pitch offers significant advantages. I remember reading that the fuel burn on a Q400-8 is around 25% lower than a comparable turbofan jet. I think they look cooler too.

tom66:
I doubt it would ever make economical sense.  The "life" of the aircraft is one of the significant costs you pay for when you fly.  Would you pay 2x more per flight to get to your destination more slowly?  Not to mention ETOPS certification for a twin turboprop is uncommon so it would be restricted to internal flights only - might work for USA but unlikely to work well for European carriers.

ve7xen:
I also don't think they are actually more efficient during the cruise phase. They get used for short-haul flights because their efficiency in the dense air near the ground, and therefore for takeoff and climb, is somewhat better. There is not enough time in cruise on these short haul flights for the high altitude efficiency of turbofans to make up for their poorer efficiency in the climb, and most of the flight time is not affected by the higher speed too (taxi, takeoff, climbout are a significant part of such flights, and more or less fixed-time). So for such flights, they will not take much longer but will use less fuel than with a jet. The longer the flight, the more the cruise advantage matters, and there will be a turning point somewhere where the jet wins. And it's faster too.

There are also a lot of time-based costs that would need to be factored into it too, if you're taking about the nearly 50% slower cruise speed. Fewer destinations accessible with a single crew, crew hours, time on the airframe and engines for maintenance, the need for a larger fleet to service the same routes, and so on.

I also wonder if it's even technically feasible to build a long-range widebody turboprop. You'd probably have to start getting into weird things like contra-rotating props and stuff to put enough thrust on the wing to carry the extra fuel and passengers, which seems like it's inviting mechanical issues. Turboprops are already more mechanically complex than turbofans, and this wouldn't be helping.

Bassman59:

--- Quote from: SiliconWizard on February 23, 2021, 02:06:19 am ---Sad days for Boeing really.
https://www.nbcnews.com/news/us-news/faa-orders-stepped-inspections-boeing-777s-after-engine-failure-united-n1258477

--- End quote ---

Somebody give the pilots a huge bonus and a medal of honor (or whatever they call the local equivalent).

hans:
I think the ETOPS rating is a pretty big deal for airliners, especially the larger ones. Even though the ETOPS rating is minutes, it's about being able to fly safely with 1 engine into an alternate airport with 1 engine (=range, nm). The turboprop engines may be more fuel efficient but they also tend to fly at a lower Mach number while doing so. I'm sure they can get a ETOPS rating on the airplane given the resources, you got to wonder why would you? If a turboprop flies at half the speed, then an ETOPS-370 rating of the A350XWB halves to that of a pretty mainstream jet with ETOPS-180 rating (A320, 737, etc.).

Or in other words, the plane has to divert it's routing to fly over anything but a small puddle of water.   The 777 is often used to fly routes over or close to the north pole, and newer planes will only go on more direct routes. The A350XWB has a ETOPS-370 rating and claims to be able to fly 99.7% of earth's surface in 1 trip, e.g. do flights like Sydney-London without any intermediate stops, etc. Taking those shortcuts also saves fuel.

And any of those long haul flight you might do, may now take 36hrs instead of 18hrs, probably requiring close to a dozen pilots onboard (and also some serious safety/health concerns of locking a few hundred people in a big tube for 36hrs)

So I doubt we'll ever see them on large airliners again. Economically it doesn't make sense, unfortunately.

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