In the early 70s of the last century, the US Air Force sought a new tactical military transport aircraft that could replace the old Lockheed C-130 in the 50s, and put forward strict design standards. Among the many competitors, Boeing's YC-14 stood out and attracted a lot of attention with its excellent performance. However, fate played a joke on this excellent design, and despite meeting all the criteria, the YC-14 ultimately failed to go into production.
In 1972, the Air Force set stringent design requirements, including the ability to fly at least 1,000 miles (1,610 kilometers) with a payload of 27,000 pounds (about 12,250 kilograms) without in-flight refueling, including a takeoff run of no more than 2,000 feet (610 meters). This standard was very challenging at the time, but the YC-14 still managed to meet these requirements.
The YC-14 is a tactical transport aircraft with an empty weight of about 53,400 kg and a maximum take-off weight of about 113,000 kg. The aircraft adopts a supercritical high monoplane and a large-size T-shaped vertical tail design, and uses the Kangda effect to meet the requirements of the military. Unlike competitor McDonnell Douglas' four-engine blowing flap design, the YC-14 is fitted with only two turbofan engines and mounted higher on the leading edge of the wing to ensure adequate airflow to the upper surface of the wing.
The YC-14 was designed to produce a peculiar "tornado" phenomenon when thrust reversers were turned on on the ground, but pilots said it never caused engine damage by inhaling solids. The aircraft was installed with 2 General Electric CF6-50D turbofan engines with a thrust of 230kN. The airflow generated by the engine through the upper surface of the wing, combined with the high-angle deflection of the trailing edge flaps, can produce strong thrust and greatly shorten the take-off and taxi distance of the aircraft.
However, during the tests, the designers found that when the YC-14 flew at low altitudes and low speeds, there were problems with the airflow, which seriously affected the diffusion of the airflow from the engine nozzles on the surface of the wing, reducing the lift of the wing. To solve this problem, the designers added a retractable vortex generator above the wing.
The YC-14 performed well, with an improved prototype capable of not only meeting the 2,000-foot take-off run, but also landing at a low speed of 99 mph (159 kmh). Its maximum flight speed is 811 kmh, its cruising speed is about 760 km/h, and its maximum range is about 5,000 km. In terms of transport capacity, the YC-14 surpassed McDonnell Douglas competitors and could transport one M60 tank directly.
Despite the YC-14's outstanding performance, in 1976 the Air Force revisited the idea of transport aircraft and strategic and tactical airlift, leading to the termination of the entire project at the end of 1979. The Lockheed C-130, which was originally planned to be replaced, not only did not decommission, but continued to serve in an upgraded version. The ill-fated YC-14, despite meeting all the design criteria, could not escape the fate of being eliminated.