A LOOK BACK: Convair XC-99, America’s first supersized plane

Dr. Marshall Michel

86th Airlift Wing Historian

When one thinks of large airlifters, the C-5, the C-17, the Boeing 747, and the Antonov An-124 leap to mind. But the ancestor of these aircrafts still holds the title of the largest land-based, piston-engine airlifter, the Convair XC-99. Dubbed the “Pachyderm Piston,” the giant XC-99 was one of the Air Force’s biggest might-have-beens.

The XC-99 was first conceived in May 1942 as a spin-off of the XB-36, the bomber intended to replace the B-29. The XC-99’s cross section was almost 470 square feet, the equivalent of ten railroad freight cars, and a huge increase over the B-36’s cross section of 226 square feet. It could carry 100,000 pounds of cargo or 400 fully equipped troops 1720 miles at a cruising speed of 290 mph. To put this in perspective, the largest American transport plane in World War II carried 24,000 pounds of cargo or 50 fully equipped soldiers at 220 mph.

***image1***The XC-99 made its first flight Nov. 24, 1947, in front of a large crowd in San Diego. Except for the Air Force requirement for a “steep dive” for all of its aircraft – which the XC-99 test pilot said “was like tipping over a skyscraper” – the testing went well and the XC-99 exceeded all the Air Force’s required performance specifications.

Convair delivered the single XC-99 to the Air Force’s Material Command but in the end the Air Force decided not to order production. It seems the XC-99’s size and load carrying capability actually worked against it. It could carry huge amounts of cargo, but the interior dimensions were wrong for military bulk cargo of the day, and it simply sat too high off the ground for convenient loading, the result of its long propeller blades. It also lacked items like front “clam shell” doors and rear loading ramps that were used on newer cargo aircraft.