Re: Why a new super-jumbo isn't going to be built anytime soon.

Date:         10 Jul 97 17:46:14 
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[Moderator's note: Poster's name withheld at the request of the poster.]

jfmezei  <"jfmezei"[no.spam]> wrote:
>There have been questions about a super jumbo having difficulty
>operating at airports because of its wingspan. (gates space etc).

Absolutely true.  Not just because of gates, but because of clearances
between aircraft on adjacent taxiways and clearances between the tail of
the aircraft and the service roads that typically runs just behind the
parked aircraft and clearance between an aircraft on the taxiway parallel
to the runway and an aircraft landing.  Oh, and not just the wings, but
the vertical tail also plays a role.

>Is it conceivable that instead of having 2 huge wings, an aircraft would
>have 4 medium wings ?

The short answer is no.

>Either 2 fore, 2 aft, or like on the old planes, wings below fuselage
>and wings directly above, above fuselage ?

I've even seen a very nice study on a three surface Large Airplane.
(For those who don't know, a three surface airplane, a la Piaggio P180,
has a canard forward, a main wing, and a horizontal stabilizer aft.)

>In the 2 fore and 2 aft scenario, perhaps the back wings could be above
>fuselage, and fore wings below with each wing equipped with one engine.
>Is this absurd, or is this something the airframe manufacturers would
>have looked at ? If dismissed, why ?

I wouldn't quite categorize it as absurd; that is a little harsh.  More
like "not really what we want."

The arguments go something like this:
  Biplane designs with one wing above the other are simply not very
efficient and at transonic cruise speeds the weak shock on the upper
surface of the lower wing would interfere with the flow on the lower
surface of the upper wing.  Pretty ugly, really.
  Tandem wing designs are more difficult to service on the ground than
a conventional design.  Further, they are not as efficient as a
conventional design, aerodynamically.  Finally, we airplane designers have
some pretty serious reservations about failure modes.  We don't understand
all of them and those we do understand look very ugly.

  The preferred solution, to coin a phrase, is the same as it was for the
747.  Dig up the old taxiways and runways and pour new ones.  One time
infrastructure revision charges are cheaper in the long run than a
suboptimal airplane design, believe it or not.