Re: differents in DC10-30 and -40

Date:         31 Jul 97 12:30:27 
From:         Kees de Lezenne Coulande <lezenne@compuserve.com>
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Karl Swartz, INTERNET:kls@ohare.Chicago.NOSPAM.COM wrote:
>One other difference between the DC-10-40 and the -30 is that some of
>JAL's are domestic models, and the DC-10-40(D)s lack the center main
>landing gear.  Apparently the structure is still there as I've seen
>reports of conversions in both directions.  I'm not aware of this
>being done to a DC-10-30, though perhaps there are examples.

     There might be more to this than meets the eye. Many years ago
(probably Spring 1979) I was photographing landing aircraft at Miami (MIA).
When I had developed the pictures, it turned out that I had photographed
the same National Airlines DC-10-30 on successive days with and without the
centre gear. This didn't seem right, so I checked the photographs very
carefully for airframe differences, but did not find any.
     I then started asking around and finally dug up a DC-10-30 flight
manual. It turns out that the flight engineer can isolate the centre gear
(i.e. keep it retracted). The manual shows performance graphs for this
configuration. The benefit is an increase in climb-limited landing weight
(less drag for the landing climb), at the expense of a lower structural
landing weight. This could result in a higher payload in hot and high
conditions. Now Miami was certainly hot, but it is not high. So I do not
see any specific benefit at MIA, other than saving on wear and tear when
the landing weight is low enough to allow it.
                           Kees de Lezenne Coulander
--
C.M. de Lezenne Coulander
Amsterdam-Zuidoost
The Netherlands
E-mail: Lezenne@CompuServe.com

Aircraft Development and Systems Engineering B.V.
Schiphol-Rijk, The Netherlands