Re: 737-200 Stage 3

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
Date:         13 May 94 02:01:17 
References:   1
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>Is it possible to mount JT8D-219 engines to the older 737-222 and -291

Sounds like you work for (or are interested in) United -- don't forget
the pair of -2A1 models as well (N974UA and N976UA).

In any case, I doubt it would be feasible.  Compare the 737-500 to the
-200.  Same fuselage length (give or take an inch or two) and the same
wingspan.  But on the -500 the wings are positioned further forward on
the fuselage, in order to get the CG right.

The problem is those new engines.  For one thing, they're bigger, so
they can't fit under the wing.  Obviously the solution was to hang
them in front of the wing, which moves their weight forward.  Worse,
they're heavier (around 4,300 lbs for the CFM-56 vs. 3,400ish for the
JT8D used on the 737-200 series), which moves the CG even further
forward.  The solution was to move the wings (and hence the engines)
forward on the fuselage, or really to move the fuselage back, putting
more fuselage in back to counterbalance that forward engine weight.

The JT8D-219 you asked about is even worse.  It's about seven inches
smaller in diameter than the CFM-56, but at fourteen inches bigger
than the older JT8D models it would still need to hang in front of the
wing.  It's also over *sixty* (60) inches longer than the CFM-56, so
presumably the weight is even further forward.  Speaking of weight, at
about 4,500 lbs, it's even worse than the CFM-56.  The JT8D-219 sounds
to me like it would be *really* poorly suited to the 737.

(For completeness, I also looked up the V2500 version used on the
A319.  Compared to the CFM-56, it's only 4 1/2 inches greater in
diameter, but 35 inches longer, and at 5,139 lbs is a whopping 800
lbs heavier.  Except for the weight, this isn't a problem for the A320
and derivatives because they sit higher, and thus can accomodate the
larger engine under the wing.  I suspect the 3rd generation 737 will
also have extended landing gear, since it's necessary for a stretch
beyond the 737-400, so probably the engine dimensions are less con-
straining, like the A320.  The V2500 was a contender for the 737-X
family, but isn't offered because of non-technical reasons.)

I suppose one could include a fuselage plug aft of the wing, maybe
creating an aircraft comparable to the 737-300 in size while getting
the balance right.  That's not unprecedented (the C-141 was stretched
with fuselage plugs after being in service for some years) but seems
to be getting rather expensive for a pretty old aircraft, especially
when one considers that many of the -222s you're asking about are
amongst the first 737s built.

Karl Swartz	|INet
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