On 20 Mar 1997, matt weber wrote:

                         ----snip----
> In the past, new generations of aircraft offered dramatically Avaialable Seat
> Mile cost reductions over the preceding generation (707 to 747). This no
> longer appears to be the case.
>
                         ----snip----
>
> My own belief is the underlying problem is money. I've done some thumbnail
> calculations that have been 'interesting'. The first observation is that
> capital cost is a surprisingly large portion of Available Seat Mile cost. I
> don't claim to be an expert, but unless I have really fouled up, on a 747-400
> it is about 1.5 US cents per Available Seat Mile. this is about 20% of typical
> ASM costs. Based upon the preliminary cost estimates, the capital cost per ASM
> on the next generation of aircraft is going to be higher, not lower. Based
> upon the 747-500/600 estimated pricing reported in the press, using the same
> assumption  used for the 747-400 ASM costs, produces a capital component in
> the ASM cost of about 1.8US cents. The anticipated direct operating cost
> improvement suggested to date are on the order of 20%, which is not very
> impressive.
>
> Given that manufacturers estimates of direct operating costs of aircraft not
> yet even launched tend to be rather optimistic, the problem becomes clear. It
> isn't obvious that the super-jumbo is going to offer much of a cost advantage,
> and if Boeing continues to ruthlessly attack manufacturing costs on the
> 747-400, the operating cost advantage may in fact end up in favor of the
> 747-400.

   If a super-jumbo using a conventional design will not offer enough
savings to pay for its development, how do alternatives look? What
savings are claimed by advocates of blended-body designs. The articles
I've seen imply that a blended-body airliner would use about two-thirds
or three-fourths of the thrust of a conventional airliner with the same
payload. This would come partly from reduced empty weight and partly from
increased lift to drag ratio. How well founded are such claims, and if
true, would they be enough to pay development costs?
   Most airliners are eventually stretched or shortened  to fine tune
the size at a relatively small cost. It seems to me that this would
not be so easy to do with a blended-body aircraft. Since the
whole plane is one integrated aerodynamic shape, lengthening the
passenger section would change the lift and weight distribution
and make it less optimum. The way to enlarge it without changing the
aerodynamics adversely would be to widen the passenger cabin at the
center line in increments of one or two seats. Does computational
fluid dynamics make this easier that it seems? Also, if the enlarged
versions are wider, it might not fit in the same gates. It would be
very impressive to see a wing that size fold.

                        Peter Wezeman, anti-social Darwinist

                             "Carpe Cyprinidae"