|The B-36D used both piston and jet engines.|
|National origin||United States|
|First flight||8 August 1946|
|Retired||12 February 1959|
|Primary user||United States Air Force|
|Unit cost||US$4.1 million (B-36D)|
|Developed into||Convair YB-60|
The Convair B-36 "Peacemaker" was a strategic bomber built by Convair and operated solely by the United States Air Force (USAF) from 1949 to 1959. The B-36 was the largest mass-produced piston-engined aircraft ever built. It had the longest wingspan of any combat aircraft ever built, at 230 ft (70.1 m). The B-36 was the first bomber capable of delivering any of the nuclear weapons in the U.S. arsenal from inside its four bomb bays without aircraft modifications. With a range of 10,000 mi (16,000 km) and a maximum payload of 87,200 lb (39,600 kg), the B-36 was capable of intercontinental flight without refuelling.
Entering service in 1948, the B-36 was the primary nuclear weapons delivery vehicle of the Strategic Air Command (SAC) until it was replaced by the jet-powered Boeing B-52 Stratofortress from 1955. All but five examples were scrapped.
The B-36 set the standard for range and payload for subsequent U.S. intercontinental bombers.
The genesis of the B-36 can be traced to early 1941, prior to the entry of the United States into World War II. At the time it appeared there was a very real chance that Britain might fall to the Nazi "Blitz", making a strategic bombing effort by the United States Army Air Corps (USAAC) against Germany impossible with the aircraft of the time. The United States would need a new class of bomber which would reach Europe and return to bases in North America, necessitating a combat range of at least 5,700 miles (9,200 km), the length of a Gander, Newfoundland–Berlin round trip. The USAAC therefore sought a bomber of truly intercontinental range, similar to the German RLM's ultra-long-range Amerika Bomber program, which itself as a 33-page proposal was submitted to Reichsmarschall Hermann Goering on May 12, 1942 at the RLM.
The USAAC sent out the initial request on 11 April 1941, asking for a 450 mph (720 km/h) top speed, a 275 mph (443 km/h) cruising speed, a service ceiling of 45,000 ft (14,000 m), beyond the range of ground-based anti-aircraft fire, and a maximum range of 12,000 miles (19,000 km) at 25,000 ft (7,600 m). These proved too demanding — far exceeding the technology of the day — for any short-term design, so on 19 August 1941 they were reduced to a maximum range of 10,000 mi (16,000 km), an effective combat radius of 4,000 mi (6,400 km) with a 10,000 lb (4,500 kg) bombload, a cruising speed between 240 and 300 mph (390 and 480 km/h), and a service ceiling of 40,000 ft (12,000 m), above the maximum effective altitude of all of Nazi Germany's anti-aircraft Flak guns, save for the rarely deployed 12.8 cm FlaK 40 heavy Flak cannon.
World War II and after
As the Pacific war progressed, the air force increasingly needed a bomber capable of reaching Japan from its bases in Hawaii, and the development of the B-36 resumed in earnest. Secretary of War Henry L. Stimson, in discussions with high-ranking officers of the USAAF, decided to waive normal army procurement procedures, and on 23 July 1943 — just over two months after the Germans' Amerika Bomber proposal's submission — the USAAF ordered 100 B-36s before the completion and testing of the two prototypes. The first delivery was due in August 1945, and the last in October 1946, but Consolidated (by this time renamed Convair) delayed delivery. The aircraft was unveiled on 20 August 1945, and flew for the first time on 8 August 1946.
After the establishment of an independent United States Air Force in 1947, the beginning in earnest 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 was arguably obsolete from the outset, being piston-powered, coupled with the widespread introduction of first generation jet fighters in potential enemy air forces. But its jet rival, the Boeing B-47 Stratojet, which did not become fully operational until 1953, lacked the range to attack the Soviet homeland from North America without aerial refueling and could not carry the huge first-generation Mark 16 hydrogen bomb. The other American piston bombers of the day, the B-29 and B-50, were also too limited in range and nuclear arsenal. Intercontinental ballistic missiles (ICBMs) did not become sufficiently reliable until the early 1960s. Until the Boeing B-52 Stratofortress became operational in 1955, the B-36, as the only truly intercontinental bomber, continued to be 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. While General Curtis LeMay headed SAC (1949–57), he turned the B-36 arm, through intense training and development, into an effective nuclear delivery force, forming the heart of the Strategic Air Command. Its maximum payload was more than four times that of the B-29, and exceeding that of the B-52. The B-36 was slow and could not refuel in midair, but could fly missions to targets 3,400 mi (5,500 km) 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 28-cylinder engines, putting it out of range of most of the interceptors of the day, as well as ground-based anti aircraft 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 another six 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 would encounter delays. When the United States entered World War II, Consolidated was ordered to slow B-36 development and greatly increase Consolidated B-24 Liberator production. The first mockup was inspected on 20 July 1942, following 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 3,850 pounds (1,750 kg), but this change delayed delivery by 120 days.
The tricycle landing gear system's initial main gear design, with huge single wheels found to cause significant ground pressure problems, limited the B-36 to operating from just three air bases in the United States: Carswell Field (former Carswell AFB, now NAS JRB Fort Worth/Carswell Field), adjacent to the Consolidated factory in Fort Worth, Texas; Eglin Field (now Eglin AFB), Florida; and Fairfield-Suisun Field (now Travis AFB) in California). As a result, the Air Force mandated that Consolidated design a four-wheeled bogie-type wheel system for each main gear unit instead, which distributed the pressure more evenly and reduced weight by 1,500 pounds (680 kg). Changes in the United States Army Air Forces (USAAF) requirements would add back any weight saved in redesigns, and cost more time. A new antenna system needed to be designed to accommodate an ordered radio and radar system. The Pratt & Whitney engines were redesigned, adding another 1,000 pounds (450 kg).
The B-36 took shape as an aircraft of immense proportions. It was two-thirds longer than the previous "superbomber", the B-29. The wingspan and tail height of the B-36 exceeded those of the 1960s Soviet Union's Antonov An-22 Antheus military transport, the largest ever propeller-driven aircraft ever put into production. Only with the advent of the Boeing 747 and the Lockheed C-5 Galaxy, both designed two decades later, did American aircraft capable of lifting a heavier payload become commonplace.
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 7.5 feet (2.3 m) thick, containing a crawlspace that allowed access to the engines. The wing area permitted cruising altitudes well above the operating ceiling of any 1940s-era operational piston and jet-turbine fighters. Most versions of the B-36 could cruise at over 40,000 feet (12,000 m). B-36 mission logs commonly recorded mock attacks against U.S. cities while flying at 49,000 feet (15,000 m). In 1954, the turrets and other nonessential equipment were removed (not entirely unlike the earlier Silverplate program for the atomic bomb-carrying "specialist" B-29s) that resulted in a "featherweight" configuration believed to have resulted in a top speed of 423 miles per hour (681 km/h), and cruise at 50,000 feet (15,000 m) and dash at over 55,000 feet (17,000 m), perhaps even higher.
The large wing area and the option of starting 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 the USAF jet interceptors of the day, which either could not fly above 40,000 ft (12,000 m), or if they did, were likely to stall out when trying to maneuver or fire their guns.
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 four-engine, tractor propeller layout of other heavy bombers. The prototype R-4360s delivered a total of 18,000 hp (13,000 kW).
While early B-36s required long takeoff runs, this situation was improved with later versions, delivering a significantly increased power output of 22,800 hp (17,000 kW) total. Each engine drove a three-bladed propeller, 19 feet (5.8 m) in diameter, mounted in the pusher configuration, thought to be the second-largest diameter propeller design ever used to power a piston-engined aircraft. This unusual configuration prevented propeller turbulence from interfering with airflow over the wing, but could also lead to engine overheating due to insufficient airflow around the engines, resulting in inflight engine fires. See Operating and financial problems.
The large, slow-turning propellers interacted with the high pressure air flow 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; these were also retrofitted to all extant 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 and to prevent ingestion of sand and dirt. The jet-engine louvers were opened and closed by the flight crew in the cockpit, whether the B-36 was on the ground or in the air. The two pods with four turbojets and the six piston engines combined gave the B-36 a total of 40,000 hp (30,000 kW) for short periods of time.
The B-36 had a crew of 15. As in the B-29 and B-50, the pressurized flight deck and crew compartment were linked to the rear compartment by a pressurized tunnel through the bomb bay. In the B-36, movement through the tunnel was on a wheeled trolley, pulling on a rope. The rear compartment featured six bunks and a dining galley, and led to the tail turret.
The XB-36 featured a single-wheel main landing gear whose tires were the largest ever manufactured up to that time, 9 feet 2 inches (2.79 m) tall, 3 feet (91 cm) wide, and weighing 1,320 pounds (600 kg), with enough rubber for 60 automobile tires. These tires placed so much pressure on runways, the XB-36 was restricted to the Fort Worth airfield adjacent to the plant of manufacture, and to a mere two USAF bases beyond that. At the suggestion of General Henry H. Arnold, the single-wheel gear was soon replaced by a four-wheel bogie. At one point, a tank-like tracked landing gear was also tried on the XB-36, but proved heavy and noisy and was quickly abandoned.
The four bomb bays could carry up to 86,000 pounds (39,000 kg) of bombs, more than 10 times the load carried by the World War II workhorse, the Boeing B-17 Flying Fortress, and substantially more than the entire B-17's gross weight. The B-36 was not designed with nuclear weaponry in mind, because the mere existence of such weapons was top secret during the period when the B-36 was conceived and designed (1941–46). Nevertheless, the B-36 stepped into its nuclear delivery role immediately upon becoming operational. In all respects except speed, the B-36 could match what was arguably its approximate Soviet counterpart, the turboprop-powered Tu-95, which began production in January 1956 and was still in active service as of June 2016[update]. Until the B-52 became operational, the B-36 was the only means of delivering the first generation Mark-17 hydrogen bomb, 25 ft (7.6 m) long, 5 ft (1.5 m) in diameter, and weighing 42,000 lb (19,000 kg), the heaviest and bulkiest American aerial nuclear bomb ever. Carrying this massive weapon required merging two adjacent bomb bays.
The defensive armament consisted of six remote-controlled retractable gun turrets, and fixed tail and nose turrets. Each turret was fitted with two 20 mm cannons, for a total of 16. Recoil vibration from gunnery practice often caused the aircraft's electrical wiring to jar loose or the vacuum tube electronics to malfunction, leading to failure of the aircraft controls and navigation equipment; this contributed to the crash of B-36B 44-92035 on 22 November 1950.
The Convair B-36 was the only aircraft designed to carry the T-12 Cloudmaker, a gravity bomb weighing 43,600 lb (19,800 kg) and designed to produce an earthquake bomb effect. Part of the testing process involved dropping two of the bombs on a single flight mission, one from 30,000 feet and the second from 40,000 feet, for a total bomb load of 87,200 pounds.
The first prototype XB-36 flew on 8 August 1946. The speed and range of the prototype failed to meet the standards set out by the Army Air Corps in 1941. This was expected, as the Pratt & Whitney R-4360 engines required were not yet available, and there was a lack of the qualified workers and materials needed to install them.
A second aircraft, the YB-36, flew on 4 December 1947. It had a redesigned high-visibility, yet still "greenhouse-like" bubble canopy, heavily framed due to its substantial size, which was later adopted for production, and the engines used on the YB-36 were a good deal more powerful and more efficient. Altogether, the YB-36 was much closer to the production aircraft.
The first of 21 B-36As were delivered in 1948. They were interim airframes, intended for crew training and later conversion. No defensive armament was fitted, since none was ready. Once later models were available, all B-36As were converted to RB-36E reconnaissance models. The first B-36 variant meant for normal operation was the B-36B, delivered beginning in November 1948. This aircraft met all the 1941 requirements, but had serious problems with engine reliability and maintenance (changing the 336 spark plugs was a task dreaded by ground crews) and with the availability of armaments and spare parts. Later models featured more powerful variants of the R-4360 engine, improved radar, and redesigned crew compartments.
The four jet engines increased fuel consumption and reduced range. The advent of air-to-air missiles then rendered conventional gun turrets obsolete. In February 1954 the USAF awarded Convair a contract for a new "Featherweight" design program which significantly reduced weight and crew size. There were three configurations:
- Featherweight I removed defensive hardware, including the six gun turrets.
- Featherweight II removed the rear compartment crew comfort features, and all hardware accommodating the McDonnell XF-85 Goblin parasite fighter.
- Featherweight III incorporated both configurations I and II.
The six turrets eliminated by Featherweight I reduced the aircraft's crew from 15 to 9. Featherweight III had a longer range and an operating ceiling of at least 47,000 feet (14,000 m), especially valuable for reconnaissance missions. The B-36J-III configuration (the last 14 made) had a single radar-aimed tail turret, extra fuel tanks in the outer wings, and landing gear allowing the maximum gross weight to rise to 410,000 pounds (190,000 kg).
Production of the B-36 ceased in 1954.
The B-36, including its GRB-36, RB-36, and XC-99 variants, was in USAF service as part of the Strategic Air Command from 1948 to 1959. The RB-36 variants of the B-36 were used for reconnaissance during the Cold War with the Soviet Union and the B-36 bomber variants conducted training and test operations and stood ground and airborne alert, but the latter variants were never used offensively as bombers against hostile forces; it never fired a shot in combat.
With the end of fighting in Korea, President Eisenhower, who had taken office in January 1953, called for a "new look" at national defense. His administration chose to invest in the Air Force, especially Strategic Air Command. The Air Force retired nearly all of its B-29/B-50s to be replaced by the new Boeing B-47 Stratojet. By 1955, the swept wing Boeing B-52 Stratofortress was entering the inventory in substantial numbers, replacing B-36s.
The two main factors contributing to the obsolescence of the B-36 and leading to its phaseout were:
- The Peacemaker was not designed for aerial refueling, and required intermediate refueling bases to reach its planned targets deep in the Soviet Union.
- Its slow speed made it vulnerable to Soviet jet interceptor aircraft, making long-range bombardment flights over Soviet territory extremely hazardous, seriously compromising its ability to reach its planned target and return.
The scrapping of B-36s began in February 1956. Once replaced by B-52s, they were flown directly from operational squadrons to Davis-Monthan AFB, Arizona, where the Mar-Pak Corporation handled their reclamation and destruction. Defense cutbacks in FY 1958 compelled the B-52 procurement process to be stretched out and the B-36 service life to be extended. The B-36s remaining in service were supported with components scavenged from aircraft sent to Davis-Monthan. Further update work was undertaken by Convair at San Diego (Specialized Aircraft Maintenance, SAM-SAC) until 1957 to extend the life and capabilities of the B-36s. By December 1958 only 22 B-36Js were still operational.
On 12 February 1959, the last B-36J built, AF Ser. No. 52-2827, left Biggs AFB, Texas, where it had been on duty with the 95th Heavy Bombardment Wing, and was flown to Amon Carter Field in Fort Worth, where it was put on display. Within two years, all B-36s, except five used for museum display, had been scrapped at Davis-Monthan AFB.
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