Date: 23 Apr 97 02:58:15 From: "Darren Rhodes" <D.P.Rhodes@lboro.ac.uk> Organization: Loughborough University References: 1
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matt weber <firstname.lastname@example.org> wrote in article <airliners.1997.939@ohare.Chicago.COM>... > 6), Will such an aircraft be built? My own suspicion is yes, but in order to > make it attractive, it is not going to be anytime soon, and it will not look > anything at all like the current generation of aircraft. The current > regulatory environment places severe requirements on the stability of > commercial aircraft. We make the aircraft stable by putting drag in the right > places. It makes the aircraft stable, it also does nasty things to the overall > aerodynamic efficiency of the airframe. It > should come as no surprise that it is likely that the most aerodynamically > efficient aircraft are likely to be aircraft that are inherently unstable. > That kind of tradeoff is acceptable at the moment in military aircraft such as > the F117 and B2. It is not acceptable in a commercial passenger liner > today. A brief review of the B2 versus the B1 is quite enlightening, and > suggest that a super jumbo in the form of a blended wing, or flying wing might > be very attractive. The B1 and B2 have similar payload capacities as best I > can tell, however the B2 probably flies further, and weighs about 140,000 > pounds less. By civilian standards, the B2 engines are very inefficient. > (Specfic fuel consumption is quoted as .66, a CFM56 engine used on an A319 is > quoted as .31.This at least suggests to me that such an aircraft design with > high efficiency engines might be capable of substantially improved operating > costs over any current civilian design. Sorry, just a small point but I think the two engine SFC's you quote are for different flight regimes. The best engine around today (GE90) has a cruise SFC of around 0.52lb/hr/lb. The Pratt 4084 and RR Trent 800 are nearer 0.55lb/hr/lb. Second generation bypass engines JT9D, RB211 had values around 0.59-0.62, whilst the JT3D (B707) and JT8D have values over 0.7. The point made is correct, that engine technology is maturing and hence fuel consumption will not be significantly better for a super-jumbo. As part of my research I compared the economics of two 300 seat aircraft vs one 600 seat aircraft, both at 777 technology levels. The seat mile costs were only 10 percent lower for the 600 seat aircraft relative to the 300 seat aircraft. The research paper considered flying two smaller aircraft vs one large aircraft. Ironically, doubling the production run for the 300 seat aircraft reduced delivery cost for two 300 seat aircraft below that of one 600 aircraft. I accept this does not help with congestion, but it makes the point that civil aircraft design is virtually mature. A full copy of the research paper is available at: http://www-staff.lboro.ac.uk/~ttdpr/aff/flight.html The study was made in the context of flying the two smaller aircraft in formation, but that is separate to the economic issue considered here.