FreightWaves Classics: Fairchild XC-120 was ahead of its time

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On August 11, 1950, the Fairchild XC-120 (also known as the Pack Plane) made its first flight. Without exaggeration, it was among the more unconventional airplanes built in the United States in the post-World War II era. Built by Fairchild Aircraft for the U.S. Air Force, the transport plane took off from the company’s airport in Hagerstown, Maryland, for a 45-minute test flight.

The airplane’s background 

A review of the XC-120’s predecessors will help describe the XC-120. Fairchild Aircraft’s C-119 was a utilitarian military cargo aircraft first flown in 1947. It was the successor aircraft to Fairchild’s C-82 Packet, a military transport aircraft used during World War II to carry cargo, personnel, litter patients, and mechanized equipment. It was also used to drop cargo and troops by parachute. 

Unofficially known as the “Flying Boxcar,” the C-119 had a large fuselage suspended from a twin-boom airframe. The first C-119 made its initial flight in November 1947, and by the time production ceased in 1955, nearly 1,200 C-119s had been built. They saw action in the Korean and Vietnam wars, and served with great success in a variety of roles.

The Fairchild engineers who developed the C-119 believed there was untapped potential in the design. As described above, military transport aircraft were equipped to perform a number of missions, such as transporting personnel, carrying cargo, delivering paratroopers and dropping bulky loads by parachute. Therefore, the aircraft’s fuselage had to have features to permit the performance of all those tasks; this meant it had to carry additional weight that might not contribute to a specific mission. 

That factor led the Fairchild engineers to the idea that a military cargo airplane could operate more efficiently if equipped just for the specific mission it was performing. They surmised that the best way was for an aircraft to have a specialized fuselage for each mission. Lastly, their premise was that the C-119 should be the basis from which to develop such an aircraft.

The engineers’ premise led to one of the most unusual transports to ever fly – the XC-120 Pack Plane. Fairfield engineer Armand J. Thieblot developed the idea for the XC-120 (X for “experimental”; C for “cargo”). It retained the C-119B’s twin-boom configuration, but with an entirely new, drastically reduced central fuselage. 

What made the airplane so completely different from other aircraft were the “detachable cargo pods that could be installed below its fuselage and used in place of an internal freight compartment.” The twin-engine XC-120 “was designed to serve as an airborne tractor-trailer” – with the ability to pick up and deliver cargo-filled pods much quicker than a traditional airplane could be loaded or unloaded.  

The new fuselage had a flat bottom to which a variety of specialized cargo pods could be attached, depending upon the mission. For example, cargo pods could be configured to deliver troops or heavy equipment by parachute. Other pods could “serve as portable hospitals, radar stations, command centers or perform other specialized functions.” 

Because the XC-120 was intended to be deployed to forward landing fields, it would be able to quickly detach its pod and take off again. This greatly reduced the aircraft’s ground time – time when another airplane was most vulnerable because it needed to be unloaded or loaded. With the XC-120, it could land, detach a pod, take off while forward ground personnel began to unload the pod. While the pod was being unloaded, the Pack Plane could make another trip to retrieve a new pod. After the XC-120 returned to the forward location, it would drop a new pod and return to its home base with the first container, now empty.

A key change was the replacement of the C-119’s tricycle landing gear with a very different four-wheel undercarriage, with all four components built into the twin booms. That meant that the XC-120’s ground clearance could be adjusted by raising or lowering the height of the landing gear. That allowed the aircraft to accommodate different-sized cargo pods. Each cargo pod had four small wheels, which allowed it to be easily maneuvered on the ground, also reducing the time the aircraft had to be on the ground. Once positioned underneath the fuselage, the pod was raised into position by electric winches built into the four corners of the fuselage. The pod was then locked into place with ball-and-socket joints. Finally, the seam between fuselage and pod was sealed with an inflatable gasket.

The XC-120 Pack Plane had a C-119B fuselage; at a point just below the flight deck it was cut off to create the space for the detachable cargo pod. The wings were raised between the engines and the fuselage, raising the fuselage by several feet and giving the plane a gull wing look. Smaller diameter “twinned” wheels used as nosewheels were installed forward of the main landing gear struts. Concurrently, the main struts were extended further back.

The matching “nose” and “main” landing gear units were raised and lowered in a scissor-like fashion to lower the XC-120 as well as to facilitate the removal of a variety of wheeled pods that were to be attached below the fuselage to transport cargo. Because cargo was to be preloaded into the pods, Fairchild asserted that cargo could be loaded/unloaded much faster. 

The specifications for the airplane included a length just under 83 feet and a height of just over 25 feet. The XC-120 had a 106.5-foot wingspan and a wing area of 1,447-square feet. It was powered by two Pratt & Whitney R-4360 Wasp Major radial engines, each of which developed 3,250-horsepower for takeoff; its top speed was 258 mph. The aircraft had a five-man crew (pilot, copilot, flight engineer, two loadmasters), with a capacity of either 20,000 pounds or 2,700 cubic feet of cargo.

The airplane’s first flight was observed by an Associated Press (AP) reporter, who described it this way: “the XC-120 can land, drop off its cargo-carrying ‘pod’ and leave it for ground crews to unload and reload as time conditions permit.” The AP article also stated, “From a logistical standpoint, that will save precious time, provide greater mobility and reduce potential loss under enemy attack.”

After its first flight, the XC-120 was tested extensively by the Air Proving Ground Command at Eglin Air Force Base, Florida, in 1951. It also appeared at several airshows during the early 1950s. Production aircraft were to be designated as the C-128.

However, when the Air Force made the decision not to order a production run of the airplane, the project was abandoned in 1952. Fairchild only manufactured one prototype of the XC-120; it was later scrapped.

Issues with the aircraft

During the XC-120’s test flights, it flew well when carrying a pod, but was very unstable without an attached pod. The aircraft’s handling was commented on by James Winnie, who served as flight engineer during the XC-120’s test flights at Eglin Air Force Base. “Glad they only made one,” was his terse comment.

Given time, the XC-120’s stability issues may have been solved. However, when the Korean War began, the military needed more C-119s, which were proven and dependable aircraft. In addition, testing of new concept aircraft became a much lower priority for Fairchild and its military customers because of the war. 

What if?

As noted above, because of the XC-120’s instability and the Korean War (which caused an increase in the production run of the Fairchild C-119 and significantly changed the military’s focus) the aircraft’s modular transport design never moved forward. 

However, researching the XC-120 made me think more than once about Malcom McLean, who developed the intermodal cargo container just a few years later. McLean’s container and Fairchild’s pods seemed to be very similar. While the XC-120 project was shelved, McLean’s intermodal container ultimately revolutionized the transportation of goods by ship, rail and truck.

Consider this – the Pack Plane flew for the first time on August 11, 1950. McLean was developing his ideas and design for the cargo container and container ship from 1952-1955; the first voyage of his converted tanker (which became the world’s first container ship) did not take place until April 1956.

If the two ideas had overlapped from a timing perspective, who knows what might have happened. Certainly the idea behind the XC-120 would not have seemed so radical. 

FreightWaves Classics thanks aviastar.org, history.net, militaryimages.net, transportationhistory.org and Wikipedia for information and photographs that helped make this article possible.

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Editor: Scott Mall