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Was There Ever A Design For A Trijet SST?  
User currently offline747400sp From United States of America, joined Aug 2003, 3758 posts, RR: 2
Posted (8 years 1 month 2 weeks 3 days 9 hours ago) and read 2959 times:

I was just wondering if any aircraft company ever look at designing a trijet SST. Every SST design I could remember had four engines.

3 replies: All unread, jump to last
 
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 1, posted (8 years 1 month 2 weeks 3 days 7 hours ago) and read 2898 times:

One of Dassult's SSBJ concept from 90's was a trijet.




The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineB2707SST From United States of America, joined Apr 2003, 1371 posts, RR: 59
Reply 2, posted (8 years 1 month 2 weeks 3 days 6 hours ago) and read 2871 times:

Full-scale SST designs are almost always quads because there have not been any turbojets or low-bypass fans with enough thrust to power a tri-jet. In its day, the GE4 was the world's most powerful engine by a significant margin (excluding the competing P&W JTF17A) and the B2707 still would have needed four.

Most SSTs on the drawing board are in the 750,000-pound class, and given the thrust-weight ratio of 0.4 found on Concorde and the B2707, you'd need engines with around 100,000 pounds of thrust for a tri-jet SST. I'm not sure that any engine core available (e.g. GE90, Trent 800) could scale to this much thrust in a low-BPR application. A quad with around 75Klbs per engine seems much more manageable.

In addition, given the greater flow instability of a tail-mounted inlet, I'd imagine that shockwave management and unstart prevention would become a serious issue, especially in an outboard engine-out situation. The added structural weight of a tail-mounted engine would also be an unwelcome feature.

--B2707SST



Keynes is dead and we are living in his long run.
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 3, posted (8 years 1 month 2 weeks 2 days 9 hours ago) and read 2747 times:

Quoting B2707SST (Reply 2):
Most SSTs on the drawing board are in the 750,000-pound class

  • Market forecasts (based on known SST-knowledge) target a certain passenger base.

  • The available engines are not favorable, designing better ones would cost more(based on known SST-knowledge).

  • The current costs(based on known SST-knowledge) of development of such a plane are large.

  • The fuel they sip to the range they travel requires a lot of fuel.
  • Making such a plane viable will require large size (per developmental costs).

  • Large size equates to minimal use at smaler airports (extending ROI).

  • Ignoring the sonic boom issue does make the project cheaper (limits where the aircraft can fly).


  • Am I missing anything?



    The meaning of life is curiosity; we were put on this planet to explore opportunities.
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