McDonnell Douglas YC-15

YC-15
First YC-15 prototype conducting flight testing, accompanied by an F-4 Phantom II.
Role	Tactical airlifter
Manufacturer	McDonnell Douglas
First flight	26 August 1975
Status	Retired
Number built	2
Developed into	C-17 Globemaster III

The McDonnell Douglas YC-15 was a four-engine short take-off and landing (STOL) tactical transport. It was McDonnell Douglas' entrant into the United States Air Force's Advanced Medium STOL Transport (AMST) competition to replace the Lockheed C-130 Hercules as the USAF's standard STOL tactical transport. In the end, neither the YC-15 nor the Boeing YC-14 was ordered into production, although the YC-15's basic design would be used to form the successful C-17 Globemaster III.

In 1968, the USAF started work on a series of prototype proposals, which would lead to both the AMST project and the Light Weight Fighter. The official Request for proposal (RFP) was issued in January 1972, asking for operations into a 2,000 feet (610 m) semi-prepared field with a 27,000 lb (12,000 kg) payload and a 400 nmi (740 km) mission radius. For comparison, the C-130 of that era required about 4,000 ft (1,200 m) for this load. Proposals were submitted by Bell, Boeing, Fairchild, McDonnell Douglas and the Lockheed/North American Rockwell team at this stage of the competition. On 10 November 1972, the two top bids (from Boeing and McDonnell Douglas) were selected. The companies were awarded development contracts for two prototypes each. McDonnell Douglas' prototype was designated YC-15.

McDonnell Douglas's design incorporated a supercritical wing, the result of NASA research carried out by the already famous Richard Whitcomb. This wing design dramatically lowers transonic wave drag by as much as 30% compared to more conventional profiles, while at the same time offering excellent low-speed lift. Most contemporary aircraft used swept wings to lower wave drag, but this led to poor low-speed handling, which made them unsuitable for STOL operations.

...
Wikipedia