Boeing YC-14 Prototype STOL Aircraft

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The Boeing YC-14 was a chunky-looking prototype aircraft developed in the 1970s. It was Boeing’s entry into the USAF Advanced Medium STOL Transport (AMST) competition. The competition was seeking to replace the Lockeed C-130 Hercules with an aircraft which required an airstrip of just 2,000 ft (610 m) when carrying a payload of 27,000 (12,000 kgs). In comparison, C-130s of the time, equally loaded, required 4,000 ft (1,200 m) of runway.

 Of the initial proposals from several aircraft manufacturers, two were green lighted for further development, and both Boeing and McDonnell Douglas received contracts for two prototypes each. The Boeing aircraft was called the YC-14, while the McDonnell Douglas aircraft was designated the YC-15.
The Boeing YC-14 featured a high-wing layout and utilized an advanced and unusual flap design intended to improve lift at low speeds – a highly desirable trait in STOL aircraft. Including both externally-blown flaps, as well as upper-surface blowing (USB), the high position of the engines allows the exhaust to be blown over the rear portion of the wings and flaps. When the flaps are lowered the Coandă effect makes the jet exhaust “stick” to the flaps and bend down towards the ground, increasing lift.

 The Boeing YC-14 first flew on 9 August 1976, almost a year after the McDonnell Douglas YC-15 had first taken to the air. By November ’76 the two aircraft began a series of head-to-head tests at Edwards Air Force Base. During flight testing, the YC-14 was flown at speeds as low as 59 knots (67 mph) and as high as 38,000 feet (11,500 m). During the initial flights it was discovered that the YC-14′s drag was 11% higher than originally predicted. However after several minor modifications this was reduced to 7%. The YC-14 also managed to carry the 109,200 lb (49,500 kg) M60 Patton main battle tank. something that was not attempted with the competing YC-15.
Unfortunately, despite both the YC-14 and YC-15 being a success, and either meeting or exceeding all aspects of the original brief, the USAF was changing its strategies, and the need for a large STOL transport aircraft was diminishing. Instead the Air Force was becoming more interested in transport aircraft with increased range and payload capacity for the strategic airlift role. Both the YC-14 and YC-15 programs were wound down in 1979. In the end it wasn’t all in vain however, as the Boeing C-17 Globemaster III was a development of the McDonnell Douglas YC-17 (McDonnell Douglas and Boeing merged in the 1990s).

 Both prototypes of the Boeing YC-14 survive. Aircraft serial number 72-1873 is on display at the Pima Air & Space Museum in Tucson, Arizona. While the other is in storage at Davis Monthan Air Force Base. [via]


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