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

Date:         23 Dec 96 22:48:02 
From:         don@rata.vuw.ac.nz (Don Stokes)
Organization: Victoria University of Wellington
References:   1 2 3 4
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In article <airliners.1996.2940@ohare.chicago.com>,
Karl Swartz <kls@ohare.Chicago.COM> wrote:
>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.

The Connie looks like a flying banana.  The L-188 is a very tidy
aircraft, kinda like a turbo-prop DC-6, also a very handsome aircraft.

(Here we still see the basic L188 Electra airframe -- except with a
sensing boom out the back, otherwise known as the Orion which the RNZAF
has ostensibly for anti-submarine operations but gets used mainly for
search and rescue and general transport operations.  There was a note in
the paper that since the old 727-100 that the RNZAF keeps around for VIP
transport had had a bad run of failures recently, the Air Force was
keeping an Orion handy to get the PM to the recent APEC conference -- the
comment was also made that the Orion would do the trip just as quickly as
the 727, because it could do it non-stop whereas the 727 would have to
land twice to refuel.)

>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.

The first time I saw a 737-300, it was one looking decidedly disused,
parked in a remote corner of an airport somewhere (I forget where, might
have been HNL) and I couln't help wondering if it was supposed to be like
that or if it had suffered a gear failure....

>>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.

I'm not sure that's the whole story.  As I understand it, Boeing
developed podded engines for the B-47 because:

- the USAAF didn't want engines next to the bomb load and crew where
  battle-damage could result in jet gasses cremating the crew and payload

- Boeing, after many B-17s lost due to engine fires burning through the
  main spar, didn't want the engines buried in the wing

- The podded engines provided much-needed damping of oscillations in the
  aeroelastic wing (the B-47's No. 1 & 6 engines are right out near the
  wingtips for this reason -- by the time the B-52 came about the
  aerodynamicists and structures folk had a better handle on controlling
  the wing's vices)

As they did this, they found that the podded engines didn't in fact upset
the airflow around the wing significantly.  Someone who knows more about
aerodynamics than I do might like to correct me if I'm wrong.

To go out on a limb further, I'd suggest that the 727's rear-mounted
engines had as much to do with the flap system as anything -- to get the
727 into small strips that couldn't take contemporary jets, Boeing
developed the triple-slotted flap that's so unnerving to watch when on
approach from a rear seat in a 727; it seems to me that being in the path
of the core flow from a podded low-bypass engine would not be conducive
to the flap's health, and the alternative would be to heavily compromise
the flap design.

Of course you can get away with blasting the flaps with high bypass
engines because much of the core energy is dissipated into the turbine to
drive the fan (which is in turn pushing only cool air).  The BAe146 does
this to achieve its STOL characteristics, as do some military transport
aircraft.

Boeing did, with the B-47, B-52 and 707, have a lot more experience with
podded engines.  On the other hand, Douglas, Convair & friends also used
that layout for their 707-lookalikes.  So I don't know why Douglas put
the engines out back on the DC-9 -- maybe it was just to keep the beast
from scraping thrust reverse buckets on the runway, and perhaps since
there are only two of them, the weight penalty of the extra wing-root
and fuselage structure wasn't enough to worry about.

--
Don Stokes, Network Manager, Victoria University of Wellington, New Zealand.
don@vuw.ac.nz(work) don@zl2tnm.gen.nz(home) +64 4 495-5052 Fax+64 4 471-5386