Boeing YC-14 - Operational History

Operational History

The first Boeing YC-14 (serial number 72-1873) flew on 9 August 1976. Two aircraft were built, the second being s/n 72-1874. The competing YC-15 had started flights almost a year earlier. Head-to-head flight testing at Edwards Air Force Base started in early November 1976. During flight testing, the YC-14 was flown at speeds as low as 59 knots and as high as M=.78 at 38,000 feet. However, it was found that the YC-14's drag was 11% higher than originally predicted. Modifications developed in wind tunnel testing, comprising the addition of vortex generators to the upper aft portion of the nacelles, deletion of the nozzle door actuator fairing, alterations to the aft end of the landing gear pods and the addition of aft fuselage strakes, reduced this drag decrement to 7%. The YC-14 also demonstrated the capability to carry the 109,200 lb M60 Patton main battle tank, something that was not demonstrated with the YC-15.

At the completion of testing in the late summer of 1977, the YC-14 prototypes were returned to Boeing. The prototypes were not scrapped, and one is stored at AMARC, located at Davis-Monthan Air Force Base and the other is on display at the nearby Pima Air & Space Museum.

By this point the seeds of the AMST program's demise had already been sown. In March 1976 the Air Force Chief of Staff Gen. David C. Jones asked the Air Force Systems Command to see if it would be possible to use a single model of the AMST for both strategic and tactical airlift roles, or alternatively, if it would be possible to develop non-STOL derivatives of the AMST for the strategic airlift role. This led to a series of studies which basically stated that such a modification was not easy, and would require major changes to either design to produce a much larger aircraft.

Both the YC-14 and YC-15 met or exceeded the AMST specifications under most conditions. However, the increasing importance of the strategic vs. tactical mission eventually led an end of AMST program in December 1979. Then in November 1979, the C-X Task Force formed to develop the required strategic aircraft with tactical capability. The C-X program selected a proposal for an enlarged and upgraded YC-15 that was later developed into C-17 Globemaster III.

USB remains a fairly rare concept in use, and has been seen only on a few other aircraft, such as the Antonov An-72.