|To commemorate the
Flight Test Center, which was established June 25, 1951, the AFFTC History Office recalled
of the milestones in flight that took place here during
the last half century.
By Dr. Raymond L.
Air Force Flight Center historian
On Aug. 26, 1975, a stubby new jet transport touched down
on the Air Force Flight Test Center's main runway. It proved
to be a highly unusual bird.
first glance it seemed conventional, but a closer look
revealed four jet engines projecting an unusual distance ahead
of its high wing, and a very tall horizontal tail. This was
the McDonnell Douglas YC-15, and on that day, just 26 years
ago, the aircraft had just completed its maiden flight from
Long Beach to take part in the Advanced Medium STOL Transport
(AMST) program. Over the next two years, the AFFTC and
contractor pilots would fly the YC-15 repeatedly to assess its
performance potential and to compare it with an equally
unusual rival, the Boeing YC-14.
The AMST was a concept demonstration program designed to
evaluate the applications of advanced thrust technologies and
their potential value for military tactical airlift. The
medium-capacity C-130 Hercules had first flown in 1954, and in
the early 1970s the Director of Defense Research and
Engineering announced that tactical airlift should gain the
same efficiencies that the airlines experienced when they made
the transition from propellers to turbofan engines. Hence, the
need to prove that the new technologies could produce a new
medium transport with greater load capacity and the ability to
operate in and out of very short, 2000-foot runways.
The YC-15 that arrived at Edwards that day was the first of
two prototypes that would be jointly tested here and at the
McDonnell Douglas flight test base in Yuma, Ariz.
most innovative design feature of the YC-15 was an externally
blown flap (EBF) powered lift system. The four Pratt &
Whitney JT8D-17 turbofan engines were mounted forward and very
closely under the wing, which had large double-slotted flaps
that spanned 75 percent of the wing's trailing edge. During
takeoff and landing, the flaps were extended directly into the
engine exhaust, deflecting the jet blast downward for
additional lift. Part of the blast would flow through gaps
between the flap segments and continue downward, increasing
lift on the flap upper surfaces — a phenomenon called the Coanda effect. The
flaps were made largely of titanium to resist the intense heat
of the jet exhaust, which was also mixed with ambient air to
reduce its temperature and load intensities at the flap
The first of two Boeing YC-14s arrived at Edwards on Nov.
9, 1976. The rival transport was a high wing aircraft with two
high-bypass-ratio turbofan engines mounted forward and above
the wing's leading edge. From this position, the jet exhaust
impinged directly onto the wing's upper surface.
When the large, compound flaps were lowered, the jet
exhaust would cling to the surface and be deflected downward — the Coanda effect again — in much the same way that water from a
faucet follows the curve of a spoon. The result of this
technique, called upper surface blowing (USB) was additional
lift. The YC-14 was also equipped with thrust reversers,
variable camber leading edge flaps, and an electronic flight
The AFFTC and the contractors flew the four concept
demonstrators through two years of development and evaluation
testing, and assisted in utility testing conducted by the Air
Force Test and Evaluation Center.
The Graham Ranch runway beyond the end of Runway 22 was
used for testing on unimproved runways. Takeoffs and landings
were made with heavy payloads, and loading tests were made
with Army tanks and howitzers. Both the YC-15 and the YC-14
proved themselves in the grueling tests and turned in some
remarkable performances. Pilots even claimed that the YC-14,
with its advanced flight control system, flew like a fighter.
Unfortunately for all of this inspiration and effort, the
AMST program was terminated in 1977.
were no funds for future development and the four concept
demonstrators quickly went into storage. However, many of the
design innovations that the YC-15 displayed went on to be used
in the highly successful C-17 Globemaster III. And after
languishing at Davis-Monthan Air Force Base for 18 years,
McDonnell Douglas refurbished YC-15 Number 1 and it began a
second career as test-bed aircraft for still newer