The Convair B-36 "Peacemaker" was a piston-engined, strategic bomber built by Convair and operated by the United States Air Force's Strategic Air Command from 1948 to 1959. With 384 units built, the B-36 remains the largest mass-produced, piston-engined aircraft and has the longest wingspan of any combat aircraft. The B-36 was capable of intercontinental flight without refueling.

The B-36 was powered by six Pratt & Whitney R-4360 Wasp Major radial piston engines. The B-36D through J variants were further fitted with four General Electric J47 turbojet engines, totaling 10, the most engines of any mass-produced aircraft. The B-36 was the primary nuclear weapons delivery vehicle of the United States. It was the only bomber assigned the largest of the cumbersome first generation of US thermonuclear gravity bombs, the Mark 14 (5 to 7 megatons), Mark 17, and Mark 24 (15 to 20 megatons). It was also assigned the fission-based Mark 6 and Mark 18 and the conventional T-12 Cloudmaker earthquake bomb.

The B-36 was never flown in combat. The bomber was conceived for transatlantic raids against German-occupied Europe in the contingency that United States Army Air Forces lost access to British airbases, but the war ended before its first flight in 1946. B-36s were used to signal nuclear deterrence in the early Cold War, flying to Britain and French Morocco. The RB-36 variants were used for aerial reconnaissance and were the highest- and furthest-flying US aircraft until the Lockheed U-2. RB-36s imaged the Soviet Arctic operating from RAF Sculthorpe in England, and during the Korean War, the Soviet Far East and Manchuria in China flying from Yokota Air Base, Japan.

The NB-36H tested the world's first operation of an onboard nuclear reactor under the Aircraft Nuclear Propulsion program, ahead of the unrealized X-6. B-36s trialed RF-84F Thunderstreak and XF-85 Goblin parasite fighters, XGAM-71 Buck Duck decoy missiles, and JB-2 cruise missiles. The airframe was enlarged into the prototype XC-99 cargo plane. Convair unsuccessfully proposed a fully jet-powered successor, the Convair YB-60, but the bomber was replaced by Boeing's jet-powered B-52 Stratofortress beginning in 1955. All but four B-36s have been scrapped.

Development

The design of the B-36 can be traced to early 1941, before the entry of the United States into World War II. At the time, Britain had won the Battle of Britain but was still subject to the Nazi "Blitz" attacks.

The United States would need a new bomber to reach Europe and return to bases in North America, necessitating a combat range of at least , the length of a Gander, Newfoundland–Berlin round trip. The USAAC therefore sought a bomber of truly intercontinental range. The German Reichsluftfahrtministerium would request the similar ultralong-range Amerikabomber program on 12 May 1942.

The USAAC sent out an initial request on 11 April 1941, asking for a top speed, a cruising speed, a service ceiling of , and a maximum range of at . These requirements were too demanding and far exceeded the technology of the day, so on 19 August 1941, they were reduced to a maximum range of , an effective combat radius of with a bomb load, a cruising speed between , and a service ceiling of The ceiling in both cases was chosen to exceed the maximum effective altitude of most of Nazi Germany's antiaircraft guns.

World War II and after

In the Pacific, the USAAF needed a bomber capable of reaching Japan from bases in Hawaii, so the development of the B-36 became a priority. Secretary of War Henry L. Stimson, in discussions with high-ranking officers of the USAAF, decided to waive normal army procurement procedures. On 23 July 1943, 15 months after the Germans' Amerikabomber proposals, and the same day that the German firm Heinkel began design on a six-engined bomber of its own, the USAAF submitted a "letter of intent" to Convair for an initial production run of 100, even before testing of the two prototypes was complete. The first delivery was due in August 1945, and the last in October 1946, but Consolidated (by now renamed Convair after merging with Vultee Aircraft) delayed delivery. Three months after V-E Day, the aircraft was unveiled on 20 August 1945, and flew for the first time on 8 August 1946, five years after its design."Video: Biggest Bomber, 1946/08/15." Universal Newsreel, 1946. Retrieved: 20 February 2012.

After the start of the Cold War with the 1948 Berlin Airlift, and the 1949 atmospheric test of the first Soviet atomic bomb, American military planners sought bombers capable of delivering the very large and heavy, first-generation atomic bombs.

The B-36 was the only American aircraft with the range and payload to carry such bombs from airfields on American soil to targets in the USSR. The modification to allow the use of larger atomic weapons on the B-36 was called the "Grand Slam Installation".

The B-36 from the outset faced the widespread introduction of opposing jet fighters, and was relegated to an "interim" role pending delivery of jet alternatives. The Boeing B-47 Stratojet, its jet-engined counterpart, did not become fully operational until 1953, and lacked the range to attack the Soviet Union from North America without aerial refueling and could not carry the huge Mark 16 hydrogen bomb.

The other American piston bombers of the day, the Boeing B-29 Superfortress and Boeing B-50 Superfortress, were also too limited in range. Intercontinental ballistic missiles did not become sufficiently reliable until the early 1960s. Until the Boeing B-52 Stratofortress became operational in 1955, the B-36 was the primary nuclear weapons-delivery vehicle of the Strategic Air Command (SAC).

Convair touted the B-36 as the "aluminum overcast", a so-called "long rifle", giving SAC truly global reach. During General Curtis LeMay's tenure as head of SAC (1949–57), the B-36 formed the heart of SAC. Its maximum payload was more than four times that of the B-29 and exceeded that of the later B-52.

The B-36 was slow and could not refuel in midair, but could fly missions to targets away and stay aloft as long as 40 hours. Moreover, the B-36 was believed to have "an ace up its sleeve", a phenomenal cruising altitude for a piston-driven aircraft, made possible by its huge wing area and six engines, putting it out of range of most interceptors, as well as ground-based antiaircraft guns.

Experimentals and prototypes

Consolidated Vultee Aircraft Corporation (later Convair) and Boeing Aircraft Company took part in the competition, with Consolidated winning a tender on 16 October 1941. Consolidated asked for a $15 million contract with $800,000 for research and development, mockup, and tooling. Two experimental bombers were proposed, the first to be delivered in 30 months, and the second within 36 months. Originally designated Model B-35, the name was changed to B-36 to avoid confusion with the Northrop YB-35 piston-engined, flying-wing bomber, against which the B-36 was meant to compete for a production contract.

Throughout its development, the B-36 program encountered delays. When the United States entered World War II, Consolidated was ordered to slow B-36 development to greatly increase Consolidated B-24 Liberator production. The first mockup was inspected on 20 July 1942, after six months of refinements. A month after the inspection, the project was moved from San Diego, California, to Fort Worth, Texas, which set back development several months. Consolidated changed the tail from a twin to a single, thereby saving , but this change delayed delivery by a further 120 days.

Changes in the USAAF requirements added back the weight saved in redesigns, and cost more time. A new antenna system needed to be designed to accommodate a new radio and radar system, and the Pratt and Whitney engines were redesigned, adding another .

Design

The B-36 was two-thirds longer than the previous "superbomber", the B-29, and its wingspan and height exceeded those of the Soviet Union's 1960s Antonov An-22, the largest turboprop aircraft ever produced. Only with the advent of the Boeing 747 and the Lockheed C-5 Galaxy, both designed two decades later, did aircraft capable of lifting a heavier payload enter service.

The wings of the B-36 were large even when compared with present-day aircraft, exceeding, for example, those of the C-5 Galaxy, and enabled the B-36 to carry enough fuel to fly the intended long missions without refueling. The maximum thickness of the wing, measured perpendicular to the chord, was , containing a crawlspace that allowed access to the engines.Griswold, Wesley P. "Remember the B-36." Popular Science, September 1961. The wing area permitted cruising altitudes well above the operating ceiling of any 1940s-era fighters, over . In 1954, the turrets and other nonessential equipment were stripped out (not unlike the earlier Silverplate program for the atomic bomb-carrying "specialist" B-29s), resulting in a "featherweight" configuration that increased top speed to , and cruise at and dash at over , perhaps even higher.

The large wing area, with the four jet engines supplementing the piston engines in later versions, gave the B-36 a wide margin between stall speed (VS) and maximum speed (Vmax) at these altitudes. This made the B-36 more maneuverable at high altitude than most jet interceptors of the day, which could not maneuver effectively above . However, the U.S. Navy McDonnell F2H Banshee fighter could intercept the B-36, due to its ability to operate at more than .AU/ACSC/166/1998-04 "Standard Aircraft Characteristics: F2H-2 Banshee." history.naval.mil. Retrieved: 28 August 2010. Later, the new secretary of Defense, Louis A. Johnson, who considered the U.S. Navy and naval aviation essentially obsolete in favor of the USAF and SAC, forbade putting the Navy's claim to the test."The Revolt of the Admirals." Air Command and Staff College Air University. Retrieved: 15 May 2010.

The propulsion system of the B-36 was unique, with six 28-cylinder Pratt & Whitney R-4360 Wasp Major radial engines mounted in an unusual pusher configuration, rather than the conventional tractor propeller layout of other heavy bombers. The prototype's six R-4360s delivered , which resulted in early B-36s needing long takeoff runs, which was ameliorated when power was boosted to . Each engine drove a three-bladed propeller, in diameter, mounted in a pusher configuration. This unusual configuration prevented propeller turbulence from interfering with airflow over the wing, but led to engine overheating due to insufficient airflow around the engines, resulting in inflight engine fires. The large, slow-turning propellers interacted with the high-pressure airflow behind the wings to produce an easily recognizable very-low-frequency pulse at ground level that betrayed approaching flights.

Addition of jet propulsion Beginning with the B-36D, Convair added a pair of General Electric J47-19 jet engines suspended near the end of each wing, which were also retrofitted to surviving B-36Bs. Consequently, the B-36 was configured to have 10 engines, six radial propeller engines and four jet engines, leading to the B-36 slogan of "six turnin' and four burnin. The B-36 had more engines than any other mass-produced aircraft. The jet pods greatly improved takeoff performance and dash speed over the target. In normal cruising flight, the jet engines were shut down to conserve fuel. When the jet engines were shut down, louvers closed off the front of the pods to reduce drag."Doors Shield Jets From Blowing Dirt" Popular Mechanics, October 1950, p. 117. The two pods with four turbojets and the six piston engines combined gave the B-36 a total of for short periods of time."B-36 Adds Four Jet Engines." Popular Mechanics, July 1949, p. 124.

Crew