Re: 707 and KC-135 relationship and something about the 747 (was: Subsidies)

From:         Don Stokes <>
Organization: Victoria University of Wellington
Date:         20 Apr 96 14:02:48 
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  or MIME structure writes:
>According to the then-current Jane's All the World's Aircraft, the
>KC-135 prototypes were being built when Boeing decided to offer an
>airliner version.  They, Boeing, had to get permission from the USAF
>to use the KC-135 R&D rather than develop the 707 completely from
>scratch (which would, of course, be impossible--the genie was out of
>the bottle, after all).  The USAF also had to grant permission for
>Boeing to set up the 707 production line, as it competed with the
>KC-135 line for skilled workers.  I verified this in contemporaneous
>Flight International articles.  (Fortunately, Dryden has an extensive
>collection of past issues and editions of these, making it very

The 707 *was* intended as an airliner, right from day one, but with an eye
to a military tanker as well.  Partly, there was a recognition that
airliners needed to be build *as* airliners, not cobbled together from
bits of military aircraft as Boeing had done on the past as in the
Stratoliner and Stratocruiser.

The 707 model number was actually picked for the airliner before the
Dash-80 (Model 367-80) development was approved.  The 707 number was
withdrawn for the prototype in an attempt to put the competition off the

The issue of the tooling was that the KC-135 programme price included the
tooling required to build the planes.  As such, to use the same tooling
for the 707 required Pentagon permission.  At this stage, the 707 and
KC-135 were going to have the same fuselage width, so building a separate
line for the 707 would have been ludicrous.  Eventually Boeing agreed to
pay part of the tooling cost, and the 707 could be built on the same line.

>The only significant difference between the two airframes is the
>fuselage shape; the KC-135 has a circular cross section, while the 707
>has a bi-lobar cross section, with the floor at the intersection of
>the two circular lobes.  The 707 fuselage was designed to give
>passengers shoulder room, something fuel tanks don't require, and more
>baggage space.

I understood that the KC-135 also has a bi-lobar cross-section; it's just
not as pronounced since the upper lobe is smaller than on the 707.  I
tend to believe this as a circular cross section on would have been very
much more difficult proposition to modify than one that already had the
crease beam (at floor level) taking some of the pressure.

The change of course came when United built mockups of the proposed DC-8
cabin alongside the 707 cabin and demonstrated how the DC-8 would be able
to accomodate six-abreast seating whereas the 707 would only manage five.
After that, the 707 design was modified to be an inch wider than the
DC-8, but still retaining the same basic airframe.

>Thus, the 707 is, in fact, a KC-135 derivative, rather than the
>reverse, although the reverse is very commonly believed.

I don't think that interpretation is any better -- the 367-80/707/717
airframe was designed with an eye to both the commercial airliner and the
military tanker.

>In addition, the 747 is rather vaguely based on the Boeing entry into
>the competition that resulted in the C-5 buy.  The USAF funded the
>initial design work for the various paper planes, of course.  However,
>there's not a lot of the original remaining in the 747, but they did
>do the general calculations for sizing, etc.  However, I would not
>really say that the 747 is a derivative of this paper plane, at all,
>as so little of the latter survived in the former.

The key to both the C-5 and 747 deveopments was the high-bypass engine,
which was originally developed by GE.  Boeing proposed the C5 to the Air
Force based around this engine -- and lost the subsequent competition to
build the thing to Lockheed, mainly because Lockheed would build the C5
in the more politically important Georgia.

In fact the Pratt & Whitney JT-9D used on the 747 was a more conservative
design than the GE engine, with a much lower bypass ratio and designed
for the higher cruising speed of the 747 over the C5.

Bear in mind that the 747 went through a number of iterations, most
involving much narrower double deck configurations, before the wide body
was settled on.  If anything, the 747 is a scaled-up 707 (but with the
flight deck moved out of the way of the nose so that it can accomodate a
cargo door) much more than it is a re-work of Boeing's C-5 proposal.

Of course many of the Boeing engineers who worked on C-5 proposal moved
to the 747...

Don Stokes, Network Manager, Victoria University of Wellington, New Zealand. +64 4 495-5052 Fax+64 4 471-5386