The Consolidated XC-99 was a transport aircraft based on the massive B-36 bomber, but only a single example was ever completed.
Work on the transport version of the aircraft began six months after work on the bomber, but it had a low priority and things moved slowly. A recommendation to built the prototype was made on 1 August 1942, but the order wasn't placed until 31 December 1942 and work didn't really get underway until 1945.
The prototype was constructing by matching a set of wings and a tail from Forth Worth's B-36 production line with a new pressurised fuselage built at San Diego. This was an impressive double deck fuselage, with the upper fuselage carried above the wings. In total it had a capacity of 30,000 cubic feet - in comparison the massive Antonov An-225 has 46,000 cubic feet and the deliberately bulky Boeing Dreamliner 65,000 cubic ft and the C-5 Galaxy about 35,000 cubic ft. The wartime C-47 Dakota had just over 1,200cubic ft
The lower level was split into two 40ft long cargo bays, each with four overhead electric hoists, stairs up to the upper level and electrically operating loading hatches that could be used in flight. The upper level, which was intended for passengers, was 158ft long. The aircraft could carry 400 soldiers and their kit, 300 stretchers or 101,000lb of cargo.
When the XC-99 finally made its maiden flight on 23 November 1947 it was the largest landplane in the world. After the seventh flight it was given six R-4360-41 pusher aircraft, giving a total of 21,000hp, and four wheel bogie undercarriage, which greatly increased the number of airfields the aircraft could use. The aircraft lifted a cargo of 100,000lb for the first time on 15 April 1949.
Over the next year it was strengthened to allow it to operate at a gross weight of 320,000lb (it was based on the piston engine powered only version of the B-36, and thus had a lower operating weight than the piston and jet operated versions). It was returned to the Air Force in September 1950.
The XC-99 had a limited service career. During the Korean War it operated a weekly cargo service on the US West Coast. In 1953 it spent several weeks at Wiesbaden in Germany. It also visited Keflavik and Ramey in Puerto Rico.
On 12 July 1955 the XC-99 set a landplane passenger record when it carried 212 Air Force cadets to Fort Worth.
Several attempts were made to develop the XC-99 further. In 1949 Convair offered a modified version that could carry 183 troops and 80,000lb of cargo, but it lost out to the Douglas C-124 Globemaster II.
In 1945 Pan American announced a plan to order fifteen civil versions. These would have carried 204 passengers in some luxury, with nine state rooms, a 12 bed sleeping section and two lounges, and were intended for the New York to London route. Although its operating costs would have been impressively low when fully loaded, there wasn’t enough demand and the plan was abandoned.
The XC-99 was withdrawn from service in March 1957 after clocking up 7,400 flying hours. The aircraft still survives, although is currently awaiting restoration.
Engine: Six Pratt & Whitney R-4360-41 twenty-eight cylinder air cooled radial engine
Power: 3,500hp each
Crew: 10 (two full 5 man crews)
Empty Weight: 136,000lb
Gross Weight: 310,000lb
Cruising Speed: 300mph
Range: 8,000 miles
Payload: 100,000lb cargo or 400 passengers