Date: 16 Sep 99 16:42:55 From: firstname.lastname@example.org (Stephen H. Westin) Organization: Cornell University Program of Computer Graphics References: 1 2
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kls@ohare.Chicago.COM (Karl Swartz) writes: > Comparing the 747-400 and 777-200 seems reasonable. The 747-400 uses > engines of about 56k lbs of thrust, versus an average of around 84k for > the 777-200. That's a 50% increase in thrust. (The smallest engine > I've noticed on a 777-200 is a PW4084 derated to 77k, the largest is > around 92k on an ER.) Engine weights, in pounds: > > mfr 747-400 777-200 inc 747-400 engine 777-200 engine > --- ------- ------- --- -------------- -------------- > GE 9,499 16,644 75% CF6-80C2B1F GE90-85B > RR 9,470 13,100 38% RB.211-524H-T Trent 884 > PW 9,400 14,995 60% PW4056 PW4084 > > >From this small sample, it appears that weight is roughly propotional to > thrust, so for a comparable total thrust, the engines of a four-engined > aircraft wouldn't weight more than those of a twin. This ignores the > nacelles, pylons, and other factors which might not scale so easily. I believe there's also a fundamental economy of scale. I remember spending time many years ago with Aviation Week's listing of all available engines; at that time, there was about a 4:1 difference in specific fuel consumption between the smallest contemporary turbofans (Williams research engines for cruise missiles etc.) and the biggest (GE CF6, as I recall). Is that still true? I suspect it is, or Boeing would have built a 4-engine (or 3-engine) 777 to get the same fuel economy with less engineering investment and risk. -- -Stephen H. Westin Any information or opinions in this message are mine: they do not represent the position of Cornell University or any of its sponsors.