Decomposing Behemoth; The Convair XC-99

July 5, 2024

You know, quite a few people have said to me: “Hey Ed, you should cover the Convair B-36 bomber. That’s a Forgotten Aircraft.”

And truth be told, I probably will do something on the B-36 one day, because it really was such a beast. I mean, look at in in comparison to the B-29, which was hardly a Cessna itself!

But is the B-36 a proper Forgotten Aircraft? I mean, with so many requests that I cover it, not really.

Do you know what is a Forgotten Aircraft?


The Convair XC-99; the transport version of the B-36 that makes its giant sibling look like a proper light weight! And as I am sure I don’t need to tell you, the requirements for both aircraft essentially began at the same time.

In early 1941 the United States was progressing in the development of their next generation of heavy bomber which was required to have unprecedented range; designs that ultimately resulted in the Boeing B-29 and Consolidated B-32. But it was also feared that the United Kingdom may still at that time fall to Nazi Germany, in which case should the United States find itself at war with Germany it would have limited means to prosecute any offensive (I’m sure the US Navy had their opinions on this issue, but they seem to have been overlooked).

The USAAF wanted a bomber that could strike Europe from the Continental United States. When America found itself fighting Japan in late 1941 across the vast expanse of the Pacific, this further reinforced the need for a super long-range bomber, and development of what became the B-36 progressed steadily, if perhaps never as an urgent priority.

And Consolidated (which became Convair in 1943), the company responsible for the new mega-bomber, thought that the basic design might not just prove useful as a fighting machine, but also as the basis for a truly massive, long-range transport.

Thus was created the XC-99.

Concept and design work started in 1942 shortly after the B-36, which makes sense considering that the XC-99 was to use the same wings and powerplant allied to a new fuselage. And that fuselage was extremely impressive.

The XC-99 was to have a truly huge structure which measured 182 ft 6 in (55.63 m) long while the wingspan was 230 ft (70.10 m). Capacity was massive for the day, with the original intention being that the double deck aircraft would be able to carry 400 troops, more than 300 stretchers with attendants or a payload of up to 100,000lb (45,000kg), all in a pressurized cabin and be able to do it over huge distances.

I mean, it’s not quite comparable, but Convair practically invented the 747 twenty years before Boeing.

Such a massive machine naturally took a while, especially as the company was flat out building aircraft like the ubiquitous B-24, and the sheer size of the aircraft required it to be made in sections at different locations, with the wings built in Forth Worth, Texas and then transported to San Diego in California where they were matched up to the fuselage. Indeed, the XC-99 was 20 feet (c.6.1m) longer and its tail was 10 feet higher (c.3m) than the already huge B-36 and the sheer size of the plane meant that it had to be finished outside as no building at Convair was high enough to house the giant aircraft with its main landing wheels installed, or wide enough to house it with outer wing panels in place.

The wings, as said the same as used on the first models of B-36, had six of the massive Pratt & Whitney R-4360-41 Wasp Major engines. These 28-cylinder air-cooled radials each produced 3,500hp and, mounted in the same distinctive pusher configuration as its bomber sibling, gave the XC-99 a top speed of 307 mph (494 km/h).

With existing workload and the complexities of the new aircraft it wasn’t until November 1947 that the XC-99 first took to the air. However, it was at that time the most capable transport aircraft in terms of payload and would ultimately be the biggest piston-engine aircraft the United States ever built. In comparison to the Douglas C-74 Globemaster, the United States closet comparable heavy transport aircraft at the time, the XC-99 could carry more than double the maximum payload and around four times the number of personnel in troop transport.

In addition, the huge undercarriage Convair developed for aircraft meant that it could land on the same runways as the much smaller C-54 which was the USAF’s principle transport. Initially the landing gear featured huge tires but this would be switched during the XC-99’s service life to the same four-wheel system as used on production B-36s.

It wasn’t until the end of May 1949 that the USAF took delivery of the XC-99 and followed Convair’s own extensive testing with more than a year of their own. Considering how impressive and cutting edge the XC-99 was, such an long test program isn’t really surprising, but it obviously worked out well enough because on the first official cargo mission the aircraft flew it carried freight with a total weight of 101,266 pounds (45,933 kg) – greater than the design maximum.

Indeed, the XC-99 soon exceeded this and from then on was employed in service that saw it in constant use all over the world, commonly carrying even heavier loads. One of its regular runs was between San Diego and Texas carrying components used by the B-36 fleet, but the outbreak of the Korean War saw the XC-99 employed heavily carrying freight that was destined for the combat zone, including one emergency delivery of 42 engines for C-54’s that were employed in the theatre.

According to the USAF between July 1951 to May 1952 the big aircraft flew 600 hours and airlifted seven million pounds (3,175,147kgs) of equipment and supplies. That’s more than 3,000 metric tonnes, of which around half went to supporting the forces in Korea.

To top it all off and despite its size,  the XC-99 was also apparently a nice plane to fly and even, according to aircrews, surprisingly good to handle on the ground, being capable of backing easily into parking areas with its reversible props.

The XC-99 with Boeing B-50 bombers for scale.

Outside of Korea, the XC-99 was used for heavy lift operations in support of US forces in Europe, on one famous occasion flying between the United States and Germany via Bermuda and the Azores, and then back again…carrying more than 60,000 pounds (c.27,000kg) each way.

It was also used extensively in flights to Iceland, delivering critical components and personnel to the new Distant Early Warning Line system that was being constructed in the Arctic.

The constant use of the XC-99 was only occasionally interrupted by important upgrades, which saw the aircraft receive improved engines, undercarriage and the fitting of an AN/APS-42 weather radar with its distinctive “thimble” radome on the nose in 1953.

There was no denying that this behemoth of a plane made an impression, especially when it showed up at air shows. In one famous example at Wright– Patterson AFB in Ohio, a woman asked the pilot how they moved the gargantuan. When he told her they flew it, she retorted: “Young man, what kind of a fool do you take me for?”

The XC-99 was also surprisingly cheap to operate. In 1953, the aircraft flew 200 missions at an average cost of 13 cents per ton-mile, which the USAF calculated was less than half the ton-mile cost of its contemporaries.

Indeed, so impressive did the aircraft seem that Convair began to market a civilian variant; the Convair Model 37. This would have been slightly longer than the XC-99 and been capable of carrying 204 passengers over 4,200 mi (6,800 km).

And this was close to becoming reality as Pan American actually ordered fifteen for use on their New York to London route.

There was just one proviso. For manufacture to be economically viable, Convair would need a production order for the C-99, as it would have been in service.

And that never happened because, just like the B-36, the writing was on the wall about where the future lay – jets…and arguably turboprops but they are, in comparison to the piston radials of the XC-99, essentially the same thing.

Though using many components from the B-36 might have seemed a perfectly logical choice at the time of the XC-99’s development, the short production and lifespan of that bomber, replaced by the B-52 essentially by 1955, meant that the obvious obsolescence of the XC-99 in the face of new technology was all too apparent.

In 1956 the Douglas C-133 Cargomaster flew for the first time. This turbine-powered aircraft could carry more weight than the XC-99 over similar distances at quicker speeds, all with the benefit of a continuous and fully open cargo deck, in contrast to the XC-99’s awkward twin-deck configuration.

The pending introduction of the new turboprop and then jet transports meant that in March 1957 the USAF decided they no longer needed the big aircraft, and she was removed from service.

In total the XC-99 had flown 1.5 million miles and logged more than 7,400 flying hours. It had also transported more than 27,215 metric tonnes (30,000 tons) of cargo. Not bad in a seven-year service life.

The XC-99 was also important in giving the USAF experience in what it needed from its future strategic airlifters, an element of its history that it is easy to overlook. After all, when it flew there was no other transport that really came close to it.

“So”, I hear you ask, “what happened to this great monster of an aircraft”?

Well, it is still with us…kind of.

The XC-99 was for many decades on display at Kelly AFB in Texas. In 2004 it was decided to move it to the National Museum of the United States Air Force in Ohio, a process that required the aircraft be broken down and transported in parts, an operation that was completed in 2008.

And then…problems.

Unfortunately, the XC-99 used a lot of magnesium alloy in its construction and that apparently did not age at all well. In fact, the level of restoration required is, by all accounts, prohibitive, with the aircraft needing major structural parts to be replaced.

In an effort to preserve the rapidly deteriorating airframe, the broken-down XC-99 was moved to Davis–Monthan Air Force Base, the famous “boneyard”, where it waits until enough resources can be mustered to begin the process of restoration. If this occurs it can then be shipped to whichever museum may be lucky enough to house it, put back together and bask in the adoration of enthralled onlookers, just as it did in the ‘50s.

But to be honest, it doesn’t look hopeful. The level of work and expense needed to restore this unique aircraft has not been forthcoming for years now, and though there is always talk of its preservation, it always seems to be just talk.

I can’t really blame the various authorities; there is always more things requiring money than money to go around. But it does seems a real shame, because the XC-99 really is a truly magnificent Forgotten Aircraft.



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