YC-14 vs YC-15: How a Cancelled Program Led to the Success of the C-17
In the mid-1970s, two American planemakers built four extraordinary transport prototypes that could land almost anywhere and stop almost immediately. The Boeing YC-14 and McDonnell Douglas YC-15 were designed to meet the Air Force's Advanced Medium STOL Transport (AMST) program requirements, which included hauling heavy loads into short forward airstrips.
Both aircraft used innovative techniques to generate huge lift at low speed. The YC-14 mounted its two engines high and forward, blowing exhaust over the top of the wing, while the YC-15 used four engines under the wing to blast air through slotted externally blown flaps.
Despite exceeding the specified requirements, the AMST program was cancelled in 1979 due to shifting priorities. The Air Force no longer wanted a medium tactical transport but instead sought a larger aircraft with the range to move heavy loads strategically across oceans.
The YC-15's design, however, lived on and directly influenced the development of the C-17 Globemaster III. When the Air Force launched the follow-on C-X program, McDonnell Douglas reached back to the YC-15's layout and short-field lessons, resulting in one of the most capable and heavily used transports in the world.