This Over-Wing Engine Setup Helped Boeing’s YC-14 Master Short Runways
BY JACKSON LAMBROS SEPT. 16, 2025 7:25 PM EST
Wikimedia
The C-130 Hercules is one of the most beloved aircraft in military service today. Since the plane was introduced in 1956 as America’s next airlifter, military and civilian organizations have found plenty of use for its roomy cargo bay. In the past seven(!) decades, the Herc has had more utility than a Swiss Army knife, serving in airborne refueling, maritime patrol, search and rescue, aerial firefighting, and plenty of other jobs in the 70 nations it’s served.
It’s not Lockheed’s only plane to be kicking hard at age 70, but it almost wasn’t that way. Just 15 years into the Herc’s life, the U.S. Air Force was looking for something new to replace it — a jet-powered airlifter designed to carry cargo deep behind enemy lines, and work out of airfields half the size of what the C-130 was used to. The Air Force chose two finalists in this Short TakeOff and Landing (STOL) competition, McDonnell Douglas with the YC-15, and what we’re looking at today: the Boeing YC-14.
At first glance, the jet looks like one of those chibi cars squished in Photoshop to look like a cartoon, and those massive jet engines atop the wings result in a look unlike any other. But its bizarre design is all function over form, because when speeds were low and lift was lower, the YC-14 could use its massive over-wing engines to do what no other jet could: generate its own lift.
Advantages of an over-wing design
Christian Volpati/Wikimedia
Made for the Air Force’s Advanced Medium STOL (AMST) Transport Project, the YC-14 had to be able to take off and land from a 2,000-foot runway — half of what the era’s C-130 was designed for — and have a 400-nautical-mile radius, all while carrying 27,000 pounds. The Air Force was also hoping for more room on the inside … enough to carry the Army’s M109 and M110 self-propelled howitzers.
So why did Boeing pick an over-wing design? First and most obvious is clearance. For an aircraft meant to work out of unpaved or damaged runways, having the engines higher up let the wings shield them from ingesting debris. And these runways weren’t just short, but could be nestled into mountainous terrain and be surrounded by buildings, trees, and other obstacles. Boeing’s solution? Build a plane that can make its own lift.
The plane’s two General Electric CF6-50D turbofans were massive, producing over 50,000 pounds of force each. They also produced plenty of exhaust gas that, when blown over the top of the wing, could increase lift. This is known as upper-surface blowing, when airflow is directed to the top of the wing and over the flaps. With the flaps lowered, the Coandă effect keeps the engine’s exhaust glued to the wing’s surface and redirects it toward the ground, giving the aircraft a forward and upward momentum. The concept had never made it beyond NASA testing, but for a big, heavy cargo plane operating at low speeds, it was the perfect choice. Boeing rolled the dice.
If it ain’t broke …
It worked. The surface blowing made the plane a rocket taking off, only needing 800 feet to get airborne. Once aloft, the YC-14 could ascend at 6,000 feet per minute — three times the C-130’s capabilities. It was impressive on approach, too, with landing speeds as slow as 68 mph, a rough headwind letting the plane stop in just 387 feet. And with takeoff and landing possible with just 800 feet of runway, the YC-14 smashed expectations for the contest. The plane could carry 27,000 pounds or 150 paratroopers for STOL operations, and up to 69,000 on conventional runways.
After years of testing the two finalists, the Air Force declared the C130 the winner. Following the Vietnam War’s conclusion, the Air Force quickly learned two things. First, the C-130 was still a perfect airframe for its job, and a handful of upgrades could keep it in service for decades. Secondly, the Air Force also needed a bigger jet, closer to the carrying abilities of the C-5 Galaxy, with the C-130’s STOL capabilities. As a result, the AMST Project concluded in 1979, and the C-130 still holds its role. In its place came the Cargo Transport Aircraft-Experimental (C-X) project, in which the now-iconic YC-15-based C-17 Globemaster became the lifter the Air Force was searching for, able to carry 170,900 pounds of cargo to runways as short as 3,500 feet.
So technically, did McDonnell Douglas win? Or did Boeing win because it absorbed McDonnell-Douglas in 1997, including the C-130? Cool planes were made and lots was learned. Therefore, nobody lost.
Read More: https://www.jalopnik.com/1964717/boeing-yc-14-over-wing-engine-design/
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