Re: Fate of the MD-11, MD-90, MD-95

Date:         19 Dec 96 03:06:32 
From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
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>I think the DC-10 and MD-11 are the ugliest things ever to fly, but
>thats just one person's opinion.

I hate to admit it, since it seems to be a wildly unpopular position,
but I find the Constellation one of the least attractive airliners.
Yet Lockheed's next two airliners, the Electra (L-188) and L-1011
are at the top of my list.

>... and DC-8. (note the conspicuous LACK of Douglas designs...)

If the DC-8 isn't a Douglas design, whose is it?  (The DC-8 is another
one I've always been fond of.)

>Even the 737 has quirky flattened engine nacelles to make it
>'interesting' if not attractive.

You'll be disappointed in the third generation -- judging from the
pictures and drawings I've seen of the 737-700, most if not all of
the "stuffed hamster cheeks" are gone.

>it seems to me that rear-mounted engines have many design advantages-
...
>less wing structure

But far more fuselage structure.  Since the wings are what's holding
the plane up in the first place, hanging the engines from them doesn't
add all that much structure, whereas hanging them on the back of the
plane adds considerable structural weight.

>less plumbing in the wing

Wiring and bleed air.  Most of the fuel and hydraulics would be there
anyway.  Doesn't seem like that big of a deal.

>cleaner wing aerodynamics

That was a big reason for aft-mounted engines in the 1950s and 1960s.
With more refined understanding of aerodynamics and modern CFD, the
problems of hanging engines from the wing are soluable, if not
trivial, and other issues win out.

>less noise (at least in most of the cabin) etc.

When Boeing was trying to decide between seven- and eight-abreast
seating for the 767 (and thus the fuselage width), United CEO Richard
Ferris made the following comment:

    "Don't bug me about double-aisle or seven-abreast.  I want the
    most efficient airplane.  Just guarantee the seat-mile performance.
    As for customer preference, I couldn't care less.  Thirty-two
    percent of our cost today is in fuel."

I think that effectively sums up the value of less noise, unless most
everything else is equal.

You left out several advantages -- lower risk of foreign object damage
(FOD), and a noise shielding effect of the wing, which MD used to good
effect in reducing ground noise from the MD-90.

>What are some of the DISadvantages that made Boeing abandon the
>design, and Airbus never adopt it?

Structural weight was probably a big one.  Wing-mounted engines also
are closer to the ground and hence easier to work on.  Aft-mounted
also tend to mean the wing is close to the tail (and engines), so
there are problems with both elevators and engines being in the
"shadow" of the wings in high angle of attack situations, hence the
tendency to use a T-tail design, which further increases structural
weight.

--
Karl Swartz	|Home	kls@chicago.com
		|Work	kls@netapp.com
		|WWW	http://www.chicago.com/~kls/
Moderator of sci.aeronautics.airliners -- Unix/network work pays the bills