Convair XC-99

The Convair XC-99, AF Ser. No. 43-52436, was a prototype heavy cargo aircraft built by Convair for the United States Air Force. It was the largest piston-engined land-based transport aircraft ever built, and was developed from the B-36 bomber, sharing the wings and some other structures with it. The first flight was on 23 November 1947 in San Diego, California, and after testing it was delivered to the Air Force on 23 November 1949.

Design and development
Design capacity of the XC-99 was 100000 lb of cargo or 400 fully equipped troops on its double cargo decks. A cargo lift was installed for easier loading. The engines face rearward in a pusher configuration.

Operational history
In July 1950 the XC-99 flew its first cargo mission, "Operation Elephant." It transported 101266 lb of cargo, including engines and propellers for the B-36, from San Diego to Kelly Air Force Base in San Antonio, Texas, a record it would later break when it lifted 104000 lb from an airfield at 5000 ft elevation. In August 1953, the XC-99 would make its longest flight, 12000 mi, to Rhein-Main Air Base, Germany, by way of Bermuda and the Azores. It carried more than 60000 lb each way. It attracted much attention everywhere it flew.

The US Air Force determined that it had no need for such a large, long-range transport at that time, and no more were ordered. The sole XC-99 served until 1957, including much use during the Korean War. It made twice weekly trips from Kelly AFB to the aircraft depot at McClellan AFB, California, transporting supplies and parts for the B-36 bomber while returning by way of other bases or depots making pick-ups and deliveries along the way. During its operational life the XC-99 logged over 7,400 hours total time, and transported more than 60,000,000 lbs of cargo. The aircraft made its last flight on 19 March 1957, landing at Kelly Air Force Base, where it would remain for the next 47 years. The then-United States Air Force Museum at Wright-Patterson AFB in Dayton, Ohio, requested that the aircraft be flown there for display, but the Air Force refused due to the $7,400 cost of the flight.

Late 1950s and 1960s
The aircraft was put on display at Kelly Air Force Base near San Antonio, Texas, in 1957. During the 1960s, it was considered for restoration by the San Antonio Air Logistics Center at Kelly AFB, but the deterioration of the airframe due to the high magnesium content led to the abandonment of that plan. The aircraft was later moved to a grassy field near the base.

1990s
In 1993, the USAF moved it back to the Kelly AFB tarmac (29°22'27.19"N 98°35'14.37"W). It was planned to move the XC-99 by road to the National Museum of the United States Air Force at Wright-Patterson Air Force Base, Ohio, restore and reassemble it, and put it on display in the USAF Museum's collection of experimental aircraft. Ultimately, transporting the massive aircraft by ground proved impractical and too expensive.

Base Realignment and Closure (BRAC) action in 1995 resulted in the partial closure and realignment of Kelly AFB, with most of the former San Antonio Air Logistics Center becoming civilianized and renamed Kelly USA, while the runway and those flight line areas supporting C-5 and F-16 flight operations of the Air Force Reserve Command's 433d Airlift Wing and the Texas Air National Guard's 149th Fighter Wing reverted to adjacent Lackland AFB and renamed Lackland AFB/Kelly Field Annex.

2000s
Disassembly of the aircraft began at Kelly Field in April 2004. Portions of the airframe were then airlifted from Kelly to Wright-Patterson Air Force Base near Dayton, Ohio. Transporting the XC-99 components taxed the C-5A's cargo capacity, as the largest piece moved intact was over 75 feet by 13 ft. Upon arrival at Wright-Patterson's active base, the parts had to be further moved by truck several miles to the museum side of the base. By the summer of 2008, the XC-99 had been completely transferred to Dayton and was lying on the ramp outside the museum's restoration facility (39.77738°N, -84.09558°W ).

Upon examination, the aircraft was found to have suffered from considerable corrosion, which was not unexpected considering it had remained outside for over 50 years. The wing spar was found to be too badly corroded to restore, and a new replacement would need to be fabricated. A full restoration is being performed by the restoration crew of the Air Force Museum, although no timetable existed at the time.

2010s
As of May 2011, the corrosion control of the center wing boxes was nearing completion. Once this portion of the project is finished, the XC-99 will be reassembled and the restoration work started. Following restoration, the aircraft was expected to be displayed inside in one of the museum's new hangars. Like its relative the B-36, it is expected to become a showpiece of the museum. Once all aircraft have been moved from the Museum's current "Research and Development Hangar" or "Presidential Hangar" to a new display hangar planned to be added onto the main Museum buildings, the XC-99 restoration project will move into the vacated hangar, where visitors will be able to watch the restoration in progress. Upon completion, the XC-99 will remain on display in either the former R&D hangar, or Presidential Hangar.

Pending the restoration and display of the XC-99, in an effort to educate visitors about the aircraft the Air Force Museum has placed a model of the XC-99 on display in its Post-Cold War Gallery. The model, in approximately 1/72 scale, was constructed by Lt Col Howard T. Meek (USAF, Ret) a member of the museum's restoration staff. An explanation of the Museum's plans for the restoration and display of the XC-99 is located in the case with the model.

Recent developments
Because the XC-99 arrived in worse condition than had been expected the magnitude of the restoration was greater than the restoration staff was able to quickly accommodate. During the seven-plus years the aircraft has remained exposed to the elements at the Wright-Patterson Air Force Base it has continued to deteriorate. In an effort to protect the aircraft, in the summer of 2011, a decision was made by the restoration staff to move the disassembled XC-99 to the 309th Aerospace Maintenance and Regeneration Group (AMARG) storage facility at Davis–Monthan Air Force Base, in Tucson, Arizona. The XC-99 will remain at Davis–Monthan Air Force Base, in an area containing other aircraft belonging to the Museum, until the restoration staff has the time and resources to perform a full restoration.

Current situation
Although this article contains a number of references to information about the XC-99 at the website of the National Museum of the USAF, which were apparently valid between May and September 2011, those references are no longer valid 6 months later on 2012-03-11. The aircraft is no longer listed as a restoration project or tour destination at the Museum, as the references suggest, and the factsheet about the aircraft no longer exists. Indeed a search for the aircraft at that website using 'XC 99' produces only 3 finds, 2 of which are links to the non-existent factsheet about the aircraft. Currently few links at the website of the National Museum of the USAF confirm that the aircraft was once a restoration project at the museum.

From the previous section a decision appears to have been taken in 2011 to return the dismantled aircraft to the south-western USA (it passed 47 years at the Kelly Air Force Base in San Antonio, Texas, before being moved to the Museum in Ohio), this time to the Davis–Monthan Air Force Base, in Tucson, Arizona (the dry conditions of the Arizona desert would protect the aircraft from further corrosion until a full restoration can be carried out or until its deterioration can be otherwise prevented). It is not clear whether the dismantled aircraft has, in fact, been moved to Davis–Monthan; whether it remains at the National Museum of the USAF at Wright-Patterson; or indeed whether it has been moved elsewhere. As of 2012-03-11 this article requires fully up-to-date information about the current status of the aircraft.

On 12 April 2012, the XC-99 in very poor condition, was still at Wright Field outside of the restoration hangar. By 31 May 2012, the 337th Airlift Squadron moved the tail assembly and the propellers to Davis–Monthan Air Force Base, Arizona.

Planned civil variant
The Convair Model 37 was a large civil passenger design derived from the XC-99 but was never built. The Model 37 was to be of similar proportions to the XC-99; 182 ft length, 230 ft wingspan, and a high-capacity, double-deck fuselage. The projected passenger load was to be 204, and the effective range 4200 mi.

Fifteen aircraft were ordered by Pan American for transatlantic service. However, the fuel and oil consumption of the six 3500 hp Wasp Major radials powering the XC-99 and B-36 meant that the design was not economically viable, and the hoped-for turboprop powerplants did not materialize fast enough. The low number of orders were not sufficient to initiate production, and the project was abandoned.

Survivor

 * XC-99 s/n 43-52436 is part of the National Museum of the United States Air Force collection at Wright-Patterson AFB in Dayton, Ohio. The aircraft was disassembled at Kelly Air Force Base and its sections transported to Ohio for anti-corrosion preservation and reassembly there.