Re: MD-11F vs. 747-400F Design Philosophies

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
Date:         30 Mar 96 16:01:02 
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>Is it true that cargo is often "volume" limited rather than gross-weight
>limited?

It can go either way, depending on the cargo.  If you're flying a load
of fresh flowers for Valentine's Day, you'll probably fill the volume
of most cargo aircraft before you hit any weight limit.  On the other
hand, if you're flying cases of wine or disk drives, weight limits
will probably be hit before the volume is filled.

> is it true that the MD11F is better-designed than the Boeing 747s,
> from the "volume"-limitation perspective?

I don't think it's a matter of which is "better-designed" -- I doubt
many people would say a Concorde is better-designed than a 747 for
airmail because it's faster.  The 747 did grow out of a proposal for
what became the C5 Galaxy, and putting the cockpit above the main deck
was done with cargo in mind, but the 747 and MD-11 were both designed
mainly as passenger aircraft, with suitability for cargo a secondary
consideration.

In terms of their suitability, I think you may have it backwards --
the MD-11F is volume limited while the 747-400F is weight limited.
Here are some cargo capacities from AW&ST:

    747-400C	103,240 lbs
    747-400F	268,300 lbs
    MD-11C	144,300 lbs

Unfortunately, they don't list the MD-11F, but the above suggests that
it should be a pretty healthy fraction of the 747-400F.  They don't
list volumes, either, but clearly the 747 has a much higher volume
because of the wider fuselage and greater interior length.  (Length is
greater both because the aircraft is about ten feet longer and because
the cockpit is taking up some of that space.)

A carrier like FedEx transports a lot of documents, and paper is heavy
for its size, so their flights will most likely be weight limited.  A
747-400F costs significantly more than an MD-11F (probably around $140
million vs $100 million in very rough terms) and costs more to operate
due to the additional engine to feed and maintain, plus the higher
weight which turns into higher landing fees.  In return, FedEx gets an
aircraft that can carry much higher volumes but only somewhat more
weight.  Since they're already limited by the weights, the extra
volume is of no value to them, which is why they're dumping their 747s
(older ones; they've never owned -400s) and gobbling up MD-11s.

The 747-400F probably has a slight edge in range over the MD-11F (both
passenger and combi versions do), but this isn't an advantage either.
Unlike passengers, cargo isn't bothered by a fuel stop somewhere along
the way.  Their are fairly few routes where a 747-400F can eliminate a
fuel stop as compared to even an older 747-200F, never mind an MD-11F,
which appears to be one reason why the 747-400F hasn't been a runaway
success.

--
Karl Swartz	|Home	kls@chicago.com
		|Work	kls@slac.stanford.edu
		|WWW	http://www.chicago.com/~kls/
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