The Convair B-36 (officially named the "Peacemaker", but the name is rarely used) was an American strategic bomber aircraft, and the largest bomber ever flown by the United States. The design process began in 1941, the first prototype flew in 1945, and the first production aircraft was delivered in 1947. As the only truly long-range bomber in service, the B-36 provided the United States and the newly formed United States Air Force's Strategic Air Command with the mainstay of its nuclear deterrent until the mid 1950s when the B-52 Stratofortress became operational. The last B-36 was withdrawn from service in 1959.
The B-36 concept began with Consolidated Aircraft's successful proposal to meet a 1941 USAAC intercontinental bomber requirement. If Britain fell, bombers would have to reach Europe directly in the event of the USA joining a European war. Though that never happened, the B-36 was still considered necessary to take the war to Japan, and development continued.
The B-36 took shape as a six-engined aircraft of immense proportions; a 230 ft (70 m) wingspan, and 163 ft (50 m) in length. The engines, six Pratt & Whitney Wasp Major 28-cylinder radials, were mounted embedded in the thick wings driving (at half engine speed, to keep the tips subsonic) immense 19 ft diameter three-bladed propellers in pusher configuration, to avoid propeller turbulence interfering with wing lift and aerodynamics. The 7.5 ft (2.3 m) thick wing roots allowed the flight engineer to maintain the engines during flight.
As in the Boeing B-29 Superfortress, a pressurised flight deck and crew compartment was linked to the rear gunners' compartment by a pressurised tunnel equipped with a wheeled trolley to ride upon. A crew of fifteen was needed; pilot and co-pilot, radar/bombardier, navigator, flight engineer, two radiomen, and eight gunners (3 forward, 5 rear). Four bunks were provided for rest and relief, as well as a galley in the rear compartment.
Defensive armament was six remote-controlled retractable gun turrets, a tail turret and a nose mounting, each fitted with two 20 mm cannon; this was the most powerful defensive armament ever carried by a bomber. The maximum bomb load was 72,000 pounds (33 t) in four giant bomb bays.
The first prototype featured giant 110 inch (2.8 m) diameter single-wheel main undercarriage, but this restricted it to only three airfields in the entire United States that were strong enough to take the load; production aircraft had four-wheel undercarriages.
The first prototype XB-36 flew on August 8, 1946. Its speed and range failed to meet requirements, and there were large numbers of problems, to be expected for a groundbreaking design. Many of those problems were related to the early "placeholder" engines.
The United States Navy attacked Congressional funding for the bomber in 1947 with allegations that the aircraft failed to meet its requirements, and that the contract with Consolidated Vultee was corrupt. The United States Air Force successfully defended the project and the aircraft carrier USS United States (CVA-58) was cancelled instead, provoking the "Revolt of the Admirals."
A second prototype, the YB-36, flew on December 4, 1947; it featured a redesigned high-visibility 'bubble' canopy, adopted for production, and was much closer to the production aircraft. The YB-36 received engines that were much more powerful and efficient.
The first of 21 B-36A planes were delivered in 1948. No defensive armament was fitted (the system wasn't ready), and they were explicitly interim planes for crew training and conversion. Once newer B-36B aircraft were introduced, the B-36As were converted to RB-36E reconnaissance planes.
73 full production B-36B aircraft were delivered starting in November of 1948. The B-36B met or exceeded all the 1941 requirements but was still plagued by problems, especially with the defensive armament and engine reliability; parts supply problems left availability poor.
Even at this stage, many considered the B-36 effectively obsolete; as a piston-engined aircraft in an age of jet fighters, there were many doubts as to its effectiveness and survivability. However, the available jet bombers were still hugely limited in range, and the B-36 was the only truly intercontinental bomber available. Increasing concern about the Soviet threat kept the B-36 program alive and the aircraft in service. Some believe that the USAF may have deliberately understated the performance of the B-36 to help ensure their survival if war came.
The B-36 suffered from long, lumbering takeoff runs and a low top speed. Convair addressed this in the new B-36D model by providing auxiliary jet engines for short-term boosts in power. Pods mounted under each outer wing contained pairs of General Electric J47-GE-19 turbojets modified to run on gasoline fuel. 26 B-36D aircraft were built new, and 64 B-36B aircraft were converted to B-36D specification. B-36s crews thus referred to having 'six engines turning and four engines burning'.
The B-36F (34 built) improved on this by having 3,800 hp (2,800 kW) engines, up from 3,500 hp (2,600 kW), and improved radar. The B-36H (83 built, and 73 RB-36H) followed, with improved tail turret gunlaying radar and a redesigned crew compartment. The jets had traded range for performance, and the final B-36J version added 2770 gallons (10,500 L) of fuel in the outer wing panels.
Heavy defensive armament was falling out of favor by this time. Air-to-air missiles' range made hand-aimed guns obsolete; in addition, the B-36's remote power turrets were heavy, complex and unreliable. The final fourteen aircraft were therefore delivered as featherweights - all guns except for the radar-aimed tail turret were removed, the observation blisters were replaced by flat windows, and the crew was reduced to 13. This enabled the aircraft to climb to 50,000 feet (15,000 m) or more, and fly longer and farther. Some other B-36 aircraft were modified to featherweight configuration, including many reconnaissance versions, where range and endurance were especially valuable.
The B-36 was especially suited for reconnaissance missions; its giant size enabled it to carry large amounts of equipment, including huge, high resolution cameras; its high cruising altitude made it hard to intercept; and its long range and great endurance enabled very long distance missions. The first recon version was the RB-36D, of which 17 were built and 7 converted from B-36Bs. The aft bomb bay was converted into extra fuel tanks to give a maximum 50-hour endurance. All of the B-36A aircraft were converted into the very similar RB-36E.
More than a third of all B-36 models were reconnaissance models, and before the advent of the Lockheed U-2 in the late 1950s, the RB-36 was the mainstay of US photo-reconnaissance over hostile territory. They definitely flew over China, where Russian-supplied MiGs could not reach them; it is believed that missions approaching or even overflying the Soviet Union were also undertaken. The later RB-36 models, it is said, could reach almost 60,000 feet of altitude, and stay aloft for 50 hours.
Withdrawal from service
As the B-52 Stratofortress entered service, the B-36 fleet was scaled back. However, defense cutbacks of the late 1950s slowed the delivery of B-52s, keeping some B-36 aircraft in service through 1958, the aircraft retained being the latest B-36J models. The last aircraft in service, the final B-36J built, was withdrawn from service and donated to the city of Fort Worth, Texas on February 12, 1959.
Some B-36s were used for a variety of experiments. The most bizarre was the NB-36H flying nuclear reactor testbed. An operational nuclear reactor was fitted in the aft bomb-bay of the aircraft; a 4 ton lead shield was fitted in front of the bomb bay, and the crew was encased in a lead and rubber capsule with a tiny, 1 foot (300 mm) thick leaded glass windshield. The nuclear reactor, though operational, performed no useful work; in preparation for planned nuclear powered aircraft, experiments were to be performed to see if the radiation would damage aircraft systems. The aircraft first flew in this configuration in 1955; following the abandonment of the nuclear aircraft program, it was scrapped in 1957, the radioactive parts being buried.
Other experiments included the carriage of jet fighters by the B-36 for defensive purposes. One plan was a tiny 'parasite' jet fighter, the McDonnell XF-85 Goblin, which could be carried in a B-36 bomb bay. The concept was tested successfully, but docking with the 'mothership' proved difficult for even experienced test pilots, budgets were short, and the XF-85 was feared no match for Soviet fighters in any case; the project was cancelled.
Another project, FICON, involved modifying F-84 Thunderjet fighters so that they could be carried by specially modified B-36 aircraft. This was more successful, with ten B-36D bombers being modified into GRB-36D hosts to carry the 25 modified RF-84K reconnaissance Thunderjets ordered. These saw active service until 1959 when they were quietly withdrawn as newer reconnaissance planes were introduced.
The B-36 was certainly not a sprightly aircraft; it was one of the largest aircraft ever built when introduced, and, like the majority of large piston-engined planes, rather underpowered. Like sitting on your front porch and flying your house around. [Lt.Gen. J. Edmunson]. Its low wing loading did make it more maneuverable than USAF interceptors above 40,000 ft (12,000 m), where it usually operated, but there was concern that Soviet interceptors might have lower wing loadings than their USAF counterparts.
Despite being so huge on the outside, the pressurised crew areas were relatively tiny when occupied by a crew of fifteen, or even more when relief crews were carried. Those long missions, aloft for days at a time, were especially taxing.
Even an aircraft with the long range of the B-36 needed to be stationed as close to the enemy as possible, and this meant far north; B-36 bases were scattered throughout the northern US, with regular deployments to bases in Alaska. The B-36 was much too large to fit in any hangars, so maintenance had to be carried out outside, and the B-36 required a lot of maintenance. Special shelters were built so that the maintenance crews could have a modicum of protection while working on the engines. In extreme cold, the engines had to be kept running continuously so as not to freeze up.
Large piston-engined aircraft were notoriously fire-prone, but the B-36 was worse than most, especially in extreme cold. In most aircraft, the carburetors were behind the engine and kept warm by air flowing back from them. With the B-36's pusher design, the carburetors would ice up when the intake air was very cold and humid, causing the air/fuel mixture to get richer and richer until the unburned fuel being expelled in the exhaust caught fire.
Engine fires tended to just mean having to shut down that engine for the remainder of the flight. More serious fires could be disastrous; the B-36 airframe had a high magnesium content and burned readily.
The engines also had a prodigious appetite for lubricating oil. There was a 100 gallon (380 L) tank of oil per engine, but if that ran out, the engine had to be shut down. A B-36 could continue flying with one engine, two, or even three shut down, but sometimes the extra stress on the other engines caused additional failures.
The B-36, although giant, lumbering and somewhat outdated, was the linchpin of the United States' nuclear deterrent until faster jet bombers with sufficient range could be introduced. The B-36 was never tested in combat and it is impossible to say how well they would have fared. The SAC argument was that few fighters could reach the B-36 at its maximum altitude, and those that could were so lacking in maneuverability at that height that the B-36 could easily evade them. Others challenge this statement.
While its role in the strategic deterrent gained all the publicity, it is possible that its unsung role in reconnaissance was just as valuable. It is believed that RB-36 aircraft were involved in numerous penetrations of Soviet and Chinese airspace, and the giant cameras carried could produce photographs of incredible clarity (pictures of a golf course taken at 40,000 feet (12,000 m) on test showed recognisable golf balls).
Four B-36 aircraft survive, one a B-36H and the other 3 being B-36J models. B-36H serial 51-13730 is on display at the Castle AFB museum. Of the three B-36J models, serial number 52-2217 is on display at the SAC Museum between Omaha and Lincoln, Nebraska, US (formerly at Offutt AFB, 52-2220 is on display at the WPAFB Museum, and serial number 52-2827, the last B-36 built, is on display at its home town of Fort Worth, Texas. It is unlikely any will ever fly again; the B-36 was a challenge to keep running even when new.
The B-36 was replaced in service by the Boeing B-52 Stratofortress; Convair's challenger, a jet-powered, swept-wing development of the B-36, was awarded a contract for two prototype Convair YB-60 airplanes, one of which flew. It was an inferior aircraft to the B-52 and the second prototype was not completed.
A transport version of the B-36, the Convair XC-99, was developed and one prototype flew, but the aircraft never went into production.