Comment by loeg
3 months ago
Essentially every new design is a twinjet, so it's clearly possible to make appropriate decisions in that design space. And both Boeing and Airbus have given up on quadjets.
3 months ago
Essentially every new design is a twinjet, so it's clearly possible to make appropriate decisions in that design space. And both Boeing and Airbus have given up on quadjets.
The MD-11 isn't a new design. It's a stretched version of a first generation widebody whose design dates back to the mid-1960s. Before the MD-11 was developed, McDonnell-Douglas toyed with the idea of a dual engine variant before settling on a three engine version of the DC-10. Trijets in general came about because the engines of the day were too unreliable and too small to work in twin engine configuration at that scale.
The plane which ended up being the final nail in the MD-11's coffin, the 777, didn't start development until the 90s. Of its three initial engine choices, two were derivatives of engines that were around when the trijets came to be. The initial version of that Rolls Royce engine was so late (and so unreliable) that it essentially killed the Lockheed trijet. The third option, the GE90, was the largest turbofan engine at its introduction until it was succeeded in 2020 by the GE9X.
Scaling these earlier engines up to fit an MD-11 sized twin was never an option.
When I replied to this thread[0], with this comment[1], both the comment I was replying to and my comment were talking about trijets in the abstract, not MD-11s in particular, and the current year, or perhaps as early as the 1990s, but definitely not as early as the 1960s.
Several comments, including yours, seem to have misconstrued that to mean I think the MD-11 in particular could be retrofitted into a twinjet. That's, uh, wildly mistaken, and not something I've ever claimed. I just think trijets in general are a design dead-end. Again, that doesn't mean it didn't make sense in 1960s when the DC-10 was being designed.
[0]: https://news.ycombinator.com/item?id=45996787
No, big twins weren't possible and didn't make sense in the 60s. The engines were simply far too unreliable.
>both Boeing and Airbus have given up on quadjets.
It is possible “to make appropriate decisions” up to a certain size. They didn’t stop making new quadjets because the design doesn’t work as well as a twin engine, but because airlines don’t need/want aircraft that large. You wouldn’t build a successor to the A380 as a twin engine.
Yes, and? If no one wants them, it's a commercial dead end.
Airlines currently don't want them (which is not even 100% accurate since airlines pulled A380s out of storage, and continue to push back plans to retire them). You started this by saying "You know you can just make the wing engines 50% more powerful, right?". You weren't talking about commercial decisions, you were talking about engineering decisions and capabilities. So, no you can't just make twin engines bigger in all situations. If airlines want large capacity aircraft again, they will be quad jets, not super powerful twin engines.
It would be way cheaper to replace the airplane with a modern twin-engine plane than to retrofit new engines onto an old plane.
No one is talking about retrofitting new engines on MD-11s.
Now it is, yes. At the time, it would have required 4 total engines, which is a different matter altogether.