Genesis of the Lockheed C-141 Starlifter: designs for the SOR-182 competition from California

The Lockheed C-141 Starlifter earned its place in military aviation history as the first US jet-powered strategic airlifter, representing a quantum leap in US transport technology in the post-World War II era in terms of combining jet power with the strategic range and payload capacity of the propeller-driven Douglas C-124 Globemaster II and C-133 Cargomaster. I finally had the chance to see the C-141 Starlifter in person when I saw one C-141 at the March Field Air Museum in Riverside, California, especially when bearing in mind that the C-141 would serve half of the USAF's strategic airlift needs from the 1960s until 2006, when it was supplanted by the C-17 Globemaster III. However, very little emphasis has been paid to unbuilt competitors to the C-141 in most publications on strategic military aviation, including designed in southern California. Thanks to a copy of the book American Secret Projects 2: US Airlifters 1941-1961 that I received last year, I am now able to discuss strategic airlifter designs by aircraft manufacturers in southern California for the Air Force's SOR-182 requirement of 1960.

The Lockheed C-141 Starlifter (serial number 65-0257 Spirit of the Inland Empire, photographed by me in the outdoor section of the March Field Air Museum in Riverside, California), winner of the SOR-182 competition.

By the end of the late 1950s, the Military Air Transport Service (MATS) of the US Air Force saw the need for a new-generation airlifter powered by jet engines to supplant its fleet of C-124 Globemaster II piston-engine airlifters. The Boeing C-135 Stratolifter transport version of the KC-135 Stratotanker provided the USAF with an interim solution to some airlift requirements outlined by MATS, with 48 aircraft built, but it wasn't enough to truly satisfy the logistical demands issued by the Air Force in its search for a dedicated jet-powered airlifter. Therefore, two companies based in southern California with experience in building commercial and military transports, Convair and Douglas, decided to tinker with designs for dedicated strategic airlifter designs in the late 1950s. The San Diego division of Convair unveiled the 'Model 105' airlifter design with two podded pairs of Pratt & Whitney JT3D turbofans, and Douglas conceived the jet-powered Model 1467-79 and Model 2204 derivatives of the Douglas DC-8 jet airliner as well as the turboprop powered Model 1467-55. None of these proposals moved beyond the design phase, but they at least gave America's leading builders of large transport planes, especially Douglas, a starting point from which to plan for the USAF's transition to a wholly jet-powered airlifter force.

Left: A display model of the Convair (San Diego) Model 63
Right: A desktop model of the Douglas (Santa Monica) Model 2085

In May 4, 1960, the US Air Force issued its formal requirement for a jet-powered strategic airlifter able to carry the load of the C-124 Globemaster II, the SOR-182 specification. This specification stipulated that the aircraft conduct airlift missions over a distance of 4,600 miles (6,440 km) with a maximum payload of 70,000 pounds (31,780 kg), and that the new airlifter accommodate troops and battlefield vehicles within 6,000 cubic feet (170 cubic meters) of usable space within a rectangular fuselage measuring 70 feet long, 10 feet wide, and 9 feet high (21.35 m x 3.03 m x 2.75 m). Convair, Douglas, and Lockheed responded with the Model 63, Model 2085, and the GL-207-45 Super Hercules designs respectively. The Convair Model 63, like the earlier 'Model 105', had jet engines mounted in podded pairs under the wings, but differed in having the main undercarriage retracting into large fairings extending beyond the trailing edges of the wings. The Douglas Model 2085, on the other hand, departed from earlier Douglas jet strategic airlifter studies in its double-lobe, double-deck fuselage, whose flight deck was positioned above the cargo compartment in a manner similar to that of the cancelled XC-132 heavy turboprop-powered airlifter. Lockheed submitted a new design for the GL-207-45 Super Hercules with four Pratt & Whitney JT3D turbofans and a T-tail configuration*, the latter feature contrasting with the placement of the horizontal stabilizers below the base of the vertical stabilizer in the Douglas and Convair proposals. Convair built a mock-up of the Model 63 for the purpose of carrying out loading tests for military payloads, including Army vehicles.

After evaluating all proposals for the SOR-182 specification, the US Air Force picked Lockheed's design to be the successor to the C-124 Globemaster II, and five development aircraft were ordered under the designation C-141A. Production orders were placed for 132 aircraft (later increased to 248 units), and the first flight of the C-141 Starlifter occurred on December 17, 1963, the 60th anniversary of the Wright brothers' historic flight at Kitty Hawk, North Carolina. Deliveries of the Starlifter commenced in October 1964, with entry into service in April 1965. Over the course its service life, the C-141 Starlifter would eventually be deployed abroad to war zones in Southeast Asia, the Middle East, and the Hindu Kush during the Vietnam War, Operation Nickel Glass, Operation Desert Shield/Desert Storm, Operation Enduring Freedom, and Operational Iraqi Freedom. In one interesting chapter of its late operation career, in September 2005 it was used by the US Air Force to evacuate thousands of people seeking refuge from Hurricane Katrina. With the deployment of the McDonnell Douglas/Boeing C-17 Globemaster III picking up the pace, the C-141 itself was phased out of Air Force service in May 2006.

*The T-tail design trait seen in the C-141 Starlifter has become the tail empennage design philosophy for all American jet-powered strategic airlifters, while the tail empennage configuration of the Douglas Model 2085 and Convair Model 63 is similar to that of the Antonov An-124 Ruslan.

[EDIT: Since I wrote this post, project documents pertaining to the Convair Model 63 and photos of the Model 63 mockup came to my attention via the Secret Projects Forum and Flickr websites. My many thanks to the San Diego Air and Space Museum for alerting me to this.]

References:

Cox, G., and Kaston, C., 2019. American Secret Projects 2: U.S. Airlifters 1941 to 1961. Manchester, UK: Crécy Publishing.