YC-15's Legacy Takes Flight in C-17

The US Air Force launched the Advanced Medium STOL Transport (AMST) program in the mid-1970s to replace its aging C-130 fleet with a tactical transport that could land on short, rough forward airstrips. Boeing and McDonnell Douglas each built two prototypes: the YC-14 and YC-15 respectively.

The YC-14 used upper-surface blowing, where exhaust was blown over the top of the wing to generate huge lift at low speeds. The YC-15, on the other hand, employed four engines under the wing to blast air through slotted externally blown flaps. Both designs exceeded requirements but ultimately lost out.

The AMST program was cancelled in 1979 due to shifting priorities and budget constraints. However, the legacy of the YC-15 lived on as it directly influenced the design of the C-17 Globemaster III, which went on to become one of the most capable and heavily used transports in the world.