Convair B-36 Peacemaker
The Convair B-36 "Peacemaker" is a strategic bomber built by Convair that was operated by the United States Air Force from 1948 to 1959. The B-36 is the largest mass-produced piston-engined aircraft ever built, although it was exceeded in span and weight by the one-off Hughes H-4 Hercules. It 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 fitted further with four General Electric J47 turbojet engines, totalling ten, the most engines of any mass-produced aircraft.
The B-36 was the primary nuclear weapons delivery vehicle of Strategic Air Command, and by extension the United States. The B-36 was the only bomber assigned the largest of the cumbersome first generation of US thermonuclear gravity bombs, the Mark 14, and the Mark 17 and Mark 24. 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 its access to British airbases. 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 trialled 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 design of the XC-99 cargo plane.
Convair unsuccessfully proposed to succeed the B-36 with a fully-jet powered version, 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 was at risk of falling to the Nazi "Blitz" attacks, making strategic bombing attacks by the United States Army Air Corps against Germany impossible with the aircraft available.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 anti-aircraft guns.
World War II and after
In the Pacific, the USAAF needed a bomber capable of reaching Japan from bases in Hawaii, and 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 their 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 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.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. 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 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, the B-36 formed the heart of the Strategic Air Command. 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 anti-aircraft guns.
Experimentals and prototypes
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-tail 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. The wing area permitted cruising altitudes well above the operating ceiling of any 1940s-era fighters, at over. In 1954, the turrets and other nonessential equipment were stripped out, 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 and maximum speed 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, thanks to its ability to operate at more than. 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 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.