YC-14 vs YC-15: How a Cancelled Competition Led to the C-17

In the mid-1970s, two American planemakers, Boeing and McDonnell Douglas, built four extraordinary transport prototypes that could land almost anywhere and stop almost immediately. Both designs worked brilliantly, but neither would ever enter production.

The Advanced Medium STOL Transport (AMST) program set a hard challenge: build a tactical transport that could haul heavy loads into short, rough forward airstrips far better than the C-130. Boeing's YC-14 and McDonnell Douglas's YC-15 each chose a different trick to bend the airflow and generate huge lift at low speed.

The YC-14 mounted its two engines high and forward, blowing exhaust directly over the top of the wing, while the YC-15 used four engines under the wing to blast air through large, slotted externally blown flaps. Both let the aircraft fly startlingly slowly and land in remarkably little space.

Though both entrants exceeded the specified requirements, the AMST competition was cancelled before a winner was selected. The Air Force's priorities shifted, and it no longer wanted a medium tactical transport to replace the C-130; it wanted a bigger aircraft with the range to move heavy loads strategically, across oceans.