747400sp
Topic Author
Posts: 3833
Joined: Sat Aug 09, 2003 7:27 pm

Was There Ever A Design For A Trijet SST?

Sat Nov 11, 2006 6:58 am

I was just wondering if any aircraft company ever look at designing a trijet SST. Every SST design I could remember had four engines.
 
lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

RE: Was There Ever A Design For A Trijet SST?

Sat Nov 11, 2006 9:13 am

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.
 
B2707SST
Posts: 1258
Joined: Wed Apr 23, 2003 5:25 am

RE: Was There Ever A Design For A Trijet SST?

Sat Nov 11, 2006 10:13 am

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.
 
lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

RE: Was There Ever A Design For A Trijet SST?

Sun Nov 12, 2006 7:23 am

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.