Back to the B-36, this time for some “roads not traveled” ideas.
The YB-36C was to be powered by 6 Pratt & Whitney R-4360-51 variable discharge turbine (VDT, aka turbocompound) engines. In addition to increasing the power of the piston engine to 4300hp, it was also expected that the VDT nozzle would also provide some jet thrust, also increasing available power. The configuration of the engines would have required swapping the B-36C from pusher props to tractors. The turbocompound engines proved to be unworkable, however, and the YB-36C was canceled, and theB-36C production types were completed as B-36Bs.
Another, slightly more successful modification came with Project FICON and the GRB-36D. Ten RB-36Ds were modified to accept a similarly modified RF-84K Thunderflash fighter into the bomb-bay, with a retractable trapeze allowing the smaller jet to be brought into a semi-recessed position, the idea being that the larger plane could bring the jet along as a escort or for the F-84 to use its higher speed to drop a tactical nuke on a target, then return to the B-36.
The idea proved more sound than the previous XF-85 Goblin parasite, but improvements in technology, and the difficulty of reattaching to the trapeze, saw the end of FICON missions after only one year.
Being carried out at the same time as FICON, project Tom-Tom explored a different method of mating an RF-84 with a B-36, this time with hinge mechanisms on the wingtips of the planes, which would theoretically allow an easier hook-up. Tom-Tom followed Tip-Tow, which attempted the same system with an ETB-29 standing in for the B-36. Tip-Tow showed some promise, but ended when one of the EF-84Ds flipped onto the wing of the ETB-29, destroying both airplanes and killing all 6 crew. Tom-Tom did little better, with several successful hook-ups, but continuing problems with the wingtip vortices from the B-36 plagued the program, and developments with in-flight refueling rendering it moot.
In order to allow the B-36 to operate from soft fields and other unprepared surfaces, Convair and the USAF attempted in 1949 to fit the plane with tracked landing gear. The massive tracks, each 16 inches wide and 275 in long, reduced the ground pressure of the B-36 from 156psi with the four-wheel bogies to 57psi. Still, the gear assemblies weighed almost three tons more than the conventional gear.
The one and only flight test of the XB-36 with tracked gear occurred on 26 March 1950. The takeoff roll was described as rough and noisy, and the landing left pieces of the track up and down the runway. The idea was quickly abandoned after that.
In order to move the XB-58 fuselage to Wright-Patterson AFB for testing, Convair modified one of the remaining B-36s to carry the plane the two inboard engines of the B-36 had their props removed to give clearance for the Hustler’s wings, and the landing gear could not be retracted, forcing the Peacemaker to fly low and slow from Ft. Worth to Dayton. The B-36s jet engines were powered up for the entire flight to maintain speed.
First flown in 1947, the XC-99 was developed from the B-36 and was the largest piston-engined transport ever built. The gigantic plane was designed to carry 100,000lbs of cargo or 400 fully-equipped soldiers, and featured an internal lift for ease of maneuvering cargo. The USAF saw no need for a superlarge transport, and canceled the program after the one prototype. The XC-99 saw heavy use however, flying over sixty millions pounds of cargo in 7,400 flight hours between 1950 and 1957. In its first mission, Operation Elephant, the XC-99 flew 101,266lbs of equipment, including propellers and engines for the B-36, from San Diego to Kelly AFB in San Antonio. In 1953, the plane flew from Kelly to Rhein-Main AB in Germany, a distance of 12,000mi, carrying 60,000lbs each way. After retirement, the plane was on display outside Kelly, until 1995 when the base was closed. The plane was disassembled and moved to the USAF Museum in 2004 for restoration, but damage due to almost 50 years of weather proved to be more than the museum could handle, and it was moved again to AMARG in Tuscon.
On 25 August 1950, Convair submitted a proposal to the USAF for an all-jet, swept wing version of the B-36, tentatively called the B-36G, as competition for the B-52.
The plane, redesignated YB-60, would have 72% parts commonality with the B-36, with the fuselage and wings being mostly identical, save for a wedge-shaped insert to give the wings their sweep. A new, pointed nose was fabricated, as well as swept tail fins. The YB-60 was powered by eight of the same J57s that the B-52 used, and would have carried a heavier bomb load than its competitor. The first prototype flew on 18 April 1952, and was quickly found to be a subpar aircraft compared to Boeing’s offering. The YB-60 was a full 100mph slower, and had handling issues owing to its modified nature. Flight tests were canceled in January of 1953, with only 66 flying hour accumulated. The second prototype was unfinished, lacking engines and other equipment. Both were eventually scrapped.
In 1946, the USAAF began the Nuclear Energy for the Propulsion of Aircraft project, or NEPA, to adapt nuclear reactors to power aircraft. The result, it was hoped, would produce airplanes with nearly unlimited fuel. By 1951 the project, now under the USAF, had advanced to the point that a reactor would need to be flown on an aircraft for testing. Convair was tapped to retrofit a B-36, the largest airplane of the day, to carry the 35,000lb Air Shield Test Reactor. B-36H s/n 51-5712, damaged by a tornado that struck Carsewell AFB in 1952, was rebuilt as the NB-36H, which featured an 11-ton, lead- and rubber-lined crew compartment to shield the crew. The plane would not be powered by the reactor, these tests merely confirmed that the shielding would be sufficient. A follow-on program was planned, with a new plane, designated the X-6, would be designed to test the expected GE J-53 nuclear turbojets.
As part of the X-6/NEPA programs, the USAF contracted with General Electric’s Nuclear Materials and Propulsion Operation to build a system to service the nuclear reactor, as well as clean up in case of an accident. The result was nicknamed “The Beetle”, and was gigantic. A set of remotely operated arm, themselves mounted on an telescoping platform containing the cockpit, was grafted to the chassis of an M42 Duster SPAAG. The Beetle weighed 77 tons loaded, and was capable of moving at just 8mph. The operator was ensconced in a cramped, cube-like cabin, protected by steel and lead armor one foot thick. The pilot was provided with windows made of two-foot thick leaded glass, as well as a closed-circuit TV system. An air conditioning/filtration system, weighing three tons and rated for nuclear-biological-chemical (NBC) warfare kept the pilot cool and removed contaminants (except for what he brought with him, as the seat featured an ash tray and lighter...). A marvel of late 1950's engineering, the Beetle still had multiple issues, with the hydraulics and electrical systems being particularly troublesome. With the NEPA and X-6 canceled in 1961, no further funds were available to correct the Beetle’s flaws, and the project was abandoned.