I was a young teen when the McDonnell Douglas YC-15 and the Boeing YC-14 were built and tested to fulfill the proposed Advanced Medium STOL Transport (AMST) role. I was really interested in this kind of stuff back then (and still now), so it was fun to see some of the thinking that went into these unique airplanes. You may have seen my CoolPix post of the YC-14 a while back where I make it clear that the Boeing aircraft caught my eye more than the MD one, but that doesn't mean I didn't find the YC-15 to be a very cool airplane.
This video from the mid 70's shows fascinating footage of the YC-15 during some of the STOL testing of the prototype. The best parts are at the beginning where the airplane is seen landing, and at the end where it performs a STOL takeoff. It's awesome to see how high the airplane is on the approach when the dirt from the runway below first begins to stir up. It really shows how massive the amount of air is that the rather small wing is pushing down. You may already know that neither the YC-14 or the YC-15 were put into production, but the YC-15 did became the foundation for what we now know as the C-17 Globemaster III. The YC-15 and the C-17 both mount their engines below the wing and aim high velocity engine thrust at large, highly deflected flaps to significantly increase overall lift at slow speeds.
As we look into the future and the U.S. Military's need to eventually replace the C-130, it's going be very interesting to see what unique solutions arise to once again address the desire to be able to carry large cargo and get off the ground quickly. I think there are a few ideas yet to be uncovered that will combine extremely short takeoff roll with significantly improved simplicity of manufacture and maintenance. I sure hope there are anyway as I believe we are creating too many ultra-complex aircraft that are simply too expensive to design, build, and operate.