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The Convair B-36 "Peacemaker"

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The Convair (Consolidated Vultee) B-36 was a strategic bomber operated by the United States Air Force, the first to have truly intercontinental range. Unofficially nicknamed the "Peacemaker", the B-36 was the first device to carry a thermonuclear weapon, the largest piston aircraft ever mass-produced, and the largest warplane of any kind. All larger military aircraft have been transports.

 

History

After Cold War began in earnest with the 1948 Berlin airlift and the 1949 atmospheric test of the first Soviet atomic bomb, U.S. planners sought bombers capable of delivering the very large and heavy first-generation nuclear 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, as storing nuclear weapons in foreign countries was (and remains) diplomatically delicate. The nuclear deterrent the B-36 afforded may have kept the Soviet Army from fighting alongside the North Korean and Chinese armies during the Korean War.

B-36D

Type Strategic bomber
Manufacturer Convair
Maiden flight 1946-08-08
Introduced 1949
Retired 1959-02-12
Primary user United States Air Force
Number built 384
Unit cost US$4.1 million (B-36D)[1]

The B-36 was arguably obsolete from the outset, because it was piston-powered in a world of jet interceptors. But its jet rival, the B-47, which did not become fully operational until 1953, lacked sufficient range to attack the Soviet heartland from North American airbases and could not carry the huge first-generation hydrogen bomb. (Neither could the other American piston bombers of the day, the B-29 and B-50.) Intercontinental ballistic missiles (ICBMs) did not become operational until the 1960s. Until the B-52 Stratofortress became operational in the late 1950s, the B-36, as the only truly intercontinental bomber, was the mainstay of the Strategic Air Command (SAC).

Convair touted the B-36 as a "aluminum overcast," a "long rifle" to give SAC a global reach. When General Curtis LeMay headed SAC (1949-57) and turned it into an effective nuclear delivery force, the B-36 formed the heart of his command. Its maximum payload was more than four times that of the B-29, even exceeding that of the B-52. The B-36 was slow and could not refuel in the air, but could fly missions to targets 3,400 miles (5,500 km) away and stay aloft as long as 50 hours. Moreover, the B-36 was believed to have an ace up its sleeve: a high cruising altitude, made possible by its huge wing area, that put it out of reach of all piston fighters and early jet interceptors.

Nevertheless, the B-36 was difficult to operate, prone in its early service years to catastrophic engine fires and other costly malfunctions. To its critics, these problems made it a "billion-dollar blunder". In particular, the United States Navy saw it as a costly bungle that diverted funding and interest from their pet project, aircraft carrier–based nuclear bombers. In 1947, the Navy attacked Congressional funding for the B-36, alleging that the aircraft failed to meet Pentagon requirements. The Navy believed that the dominance of the aircraft carrier in the Pacific during World War II proved that carrier-based airstrikes would be decisive in future wars. To this end, the Navy designed the USS United States (CVA-58), a "supercarrier" capable of launching huge fleets of aircraft — or nuclear bombers. It then pushed to have funding transferred from the B-36 to the United States. The Air Force successfully defended the B-36 project, and the United States was officially cancelled by Secretary of Defense Louis A. Johnson. Several high-level Navy officials questioned the government's decision, alleging a conflict of interest because Johnson had once served on Convair's Board of Directors. The uproar following the cancellation of the United States was nicknamed the Revolt of the Admirals.

 

Design

In 1941, the fall of Britain to a German invasion seemed imminent, which would leave United States Army Air Corps (AAC) with no bases in Europe from which to bomb Germany. If this were the case, American bombers would need to reach Europe from bases in North America. Doing so would require a combat range of at least 9200 km, the length of a Gander Newfoundland–Berlin round trip. Hence the AAC sought a bomber of truly intercontinental range.

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A B-36 airframe undergoing structural stability tests.

On April 11 1941, the AAC announced a design competition for an aircraft with a 275 mph (445 km/h) cruising speed, a service ceiling of 45,000 ft (14,000 m), capable of delivering 10,000 lb (4,500 kg) of bombs to targets 10,000 miles (16,000 km) away. These requirements far exceeded the technology of the day. The B-36 concept began with a proposal by Consolidated Vultee Aircraft Corporation (later CONVAIR) to meet this requirement; the same design request led to the Northrop YB-35. Though the need to bomb Germany from North American bases never arose, the project was not cancelled because the B-36 was seen as playing a possible eventual role in the Pacific war.

The B-36 took shape as an aircraft of immense proportions (see [1] for a table comparing the large aircraft designed in the 1940s). It was two-thirds longer than the previous superbomber, the B-29 Superfortress. Its wingspan and tail height exceeded those of the Antonov An-22, the largest ever mass-produced propeller-driven aircraft. The wingspan of the B-36 exceeded even that of the C-5 Galaxy. Only with the advent of the Boeing 747 and the C-5, both designed two decades later, did aircraft larger than the B-36 and capable of lifting a heavier payload, become routine.

The B-36's enormous wing size made possible fuel tanks large enough to fly very long missions without refueling. The wing area made possible cruising altitudes above the operating ceiling of 1940s-era fighters, jet as well as piston. All versions of the B-36 could cruise at over 40,000 feet (12,000 m). Some claim that the low wing loading resulting from the large wing area made the B-36 more maneuverable at high altitude than the jet interceptors of the day, which either could not fly above 40,000 feet, or if they did, were likely to stall out. Retired fighter pilots of that era do not necessarily agree. Later reconnaissance versions, called "featherweights", had nonessential guns and bombing equipment removed. These are believed to have cruised at 50,000 feet (15,000 m), perhaps even higher.

The propulsion system of the B-36 made it a very unusual beast. All B-36s featured six Pratt & Whitney R-4360 radial piston engines, each displacing 4,360 in³ (71.4 L) and the most powerful and perhaps most sophisticated piston aircraft engine ever built. Each engine drove an immense three-bladed propeller, 19 ft (5.8 m) in diameter, mounted on the trailing edge of the wing. This was the rarely employed pusher configuration, favored by aerodynamic theory because the unavoidable propeller turbulence does not interfere with wing lift.

Even though these piston engines delivered 18,000 hp (13.4 MW), early B-36s were slow and required long takeoff runs. This was addressed in two ways. First, later versions of the R-4360 delivered 3,800 hp (2.8 MW) apiece. Second, beginning with the B-36D, Convair suspended from each outer wing a pair of General Electric J47-19 jet engines, modified to run on aviation gasoline. J47s were then added to most extant B-36Bs. The greater power improved performance while taking off and landing, climbing to altitude, cruising at over 35,000 feet, and (hopefully) during combat.

Thus the B-36 came to have 10 engines, more than any other mass-produced aircraft, and yet another unusual feature enabled by its enormous wings. If all engines functioned normally at full power during the pre-takeoff warmup, the lead flight engineer would say to the captain "six [engines] turning and four [engines] burning". Erratic reliability led to the wisecrack "two turning, two burning, two joking, and two smoking", with two engines not accounted for.

The B-36 required a crew of 15. As in the B-29, 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, one rode through the tunnel on a wheeled trolley, by pulling oneself on a rope. The rear compartment led to the rear gun turret, and featured six bunks and a galley for rest and relief on long missions.

The XB-36 featured single-wheel landing gear requiring the largest tires ever manufactured up to that time, 9 ft, 2in. (2.7 m) tall, 3 ft (1 m) thick, and weighing 1,320 lb (600 kg), with enough rubber for 60 automobile tires [2]. These tires placed so much weight per unit area on runways that the XB-36 was restricted to the Fort Worth airfield where it was manufactured, and to a mere two USAF bases. At the suggestion of General Henry H. Arnold the single-wheel landing gear was soon replaced by a more conventional [3] four-wheel bogie. At one point a tanklike tracked landing gear was also tried on the XB-36, but proved heavy and noisy and was quickly abandoned.

 

Weaponry

The four bomb bays could carry up to 86,000 pounds of bombs, more than five times the load carried by the WWII workhorse, the B-17 Flying Fortress. The B-36 was not designed with nuclear weaponry in mind, because such weapons were top secret during most of the period when the B-36 was engineered (1941-46), and their mode of delivery had yet to be determined. Nevertheless, the B-36 stepped into a nuclear delivery role immediately upon becoming operational. In all respects but speed, the B-36 could match what was arguably its Soviet counterpart, the Tu-95 (still in service). Until the B-52 came on line, the B-36 was the only means of delivering the first generation Mark-17 hydrogen bomb [4], 25 feet (7.5 m) long, 5 ft (1.5 m) in diameter, and weighing 42,000 lbs (19,000 kg), in size the largest American nuclear weapon 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 cannon, for a total of 16 cannons, the greatest defensive firepower ever carried by a bomber. Recoil from gunnery practice could cause the on-board electronics to malfunction, solid state then being unknown. This contributed to the crash of B-36B 44-92035 on November 22, 1950.

 

Production

Variant Built
XB-36 1
YB-36 1
B-36A 21
B-36B 62
B-36D 26
RB-36D 24
B-36F 36
RB-36F 24
B-36H 83
RB-36H 73
B-36J 33
Total 384

The first prototype XB-36 flew on August 8 1946. The speed and range of the prototype failed to meet the standards set out by the Army Air Corps in 1941. As is often the case with aircraft pushing the size envelope, the XB-36 experienced a number of problems. (For instance, the B-29 Superfortress was plagued by engine problems, and available engines were too weak to afford the Boeing XB-15 a useful top speed.) Many problems with the XB-36 stemmed from its "placeholder" engines, weaker engines used until the intended powerplant became available.

A second aircraft, the YB-36, flew on December 4, 1947. It featured a redesigned high-visibility "bubble" canopy, which was later adopted for production. Altogether, the YB-36 was much closer to the production aircraft. Additionally, the engines used on the YB-36 were a good deal more powerful and more efficient. The YB-36 was actually beaten to the air by the first production model: a single B-36A was built with enough equipment to fly to Wright Field, where its airframe was subjected to a battery of physical tests.

The first of 21 B-36As were delivered in 1948. They were admitted interim airframes, intended for crew training and later conversion. No defensive armament was fitted as 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 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. See [5] for more detail on the features and performance of each of 16 variants of the B-36.

The four jet engines raised fuel consumption, thus reducing range. Meanwhile, new air-to-air missiles made hand-aimed guns mounted in heavy turrets obsolete; they were also unreliable. In February of 1954, the USAF awarded Convair a contract to reduce the weight of the entire B-36 fleet by implementing a new "Featherweight" design in three configurations:

The six turrets eliminated by I reduced the crew from 15 to nine. III enabled a longer range and an operating ceiling of at least 47,000 feet (14,000 m), features especially valuable for reconnaissance missions. The B-36J-III configuration (the last 14 made) featured 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.

 

Reconnaissance Capability

More than a third of all B-36 models were reconnaissance models, designated RB-36. Before the development of the Lockheed U-2, the RB-36 was the mainstay of American photo reconnaissance over hostile territory. It was the only American aircraft having range enough to fly into Asia from bases in the USA, and size enough to carry the bulky high-resolution cameras of the day. The RB-36 performed a number of rarely acknowledged reconnaissance missions, and is suspected of having carried out numerous penetrations of Chinese (and possibly Soviet) airspace.

Click on Picture to enlarge

The RB-36 was well-suited for such reconnaissance missions. Its high cruising altitude made it difficult to intercept, and its fuel capacity enabled missions up to 50 hours long. The RB-36 featured a pressurized camera compartment staffed by a crew of seven, in place of a forward bomb bay. The aft bomb bay contained tanks for extra fuel. The RB-36 cameras could produce very high resolution photographs: pictures of a golf course taken from 40,000 ft (12,000 m) show recognizable golf balls. RB-36s were distinguished by the bright aluminum of the camera compartment (contrasting with the dull magnesium of the rest of the fuselage), and by a series of radar domes under the aft fuselage, varying in number and placement.

 

Operational History

Unlike the B-52, which has seen action in the Vietnam War and the two Gulf Wars, no B-36 ever dropped a bomb or fired a shot at an enemy. The closest the B-36 came to seeing action was during the 1956 Hungarian Revolution and the Suez Crisis, when nuclear-armed B-36s were dispatched to Turkey and Morocco.

Though the B-36 had a better than average overall safety record, ten crashed between 1949 and 1954 (three 36Bs, three 36Ds, and four 36H's). Goleta Air and Space Museum maintains a web site [6], with photographs and lengthy excerpts from the official crash reports.

A B-36 was also involved in two "Broken Arrow" incidents. B-36B 44-92075 describes the first loss of an American nuclear weapon. On May 22 1957, a B-36 accidentally dropped a Mark-17 hydrogen bomb on a deserted area while coming in for a landing at Kirtland AFB in Albuquerque NM. Only the conventional trigger detonated, the bomb being unarmed. These incidents were classified for decades. See list of military nuclear accidents [7] [8].

 

Maintence

The B-36 needed a great deal of maintenance between flights; although in an emergency an aircraft could be "turned" in a few hours for a ferry flight, it took much longer to get the airplane ready for an operational mission. In January 1951 a B-36 amassed 200 hours of flight time (8.3 standard 24-hour missions), an apparent record.

The B-36 was too large to fit in most hangars. Moreover, even an aircraft with the range of the B-36 needed to be stationed as close to the enemy as possible, and this meant the northern USA, Alaska, and the Arctic. As a result, most "normal" maintenance, such as changing the 56 spark plugs on each of its six engines (always at risk of fouling by the leaded fuel of the day), or replacing the dozens of bomb bay light bulbs shattered after a gunnery mission, was performed out of doors, in 100-degree summers and 60-below winters. Special shelters were built so that the maintenance crews could enjoy a modicum of protection while working on the engines. Often, ground crews risked slipping and falling from ice-covered wings, or being blown off by a propeller running in reverse pitch. Some procedures even required a mechanic to sit astride a running engine, a 19-foot diameter propeller at his feet, his hand near the 34-inch diameter cooling fan.

The wings roots were thick enough, 7 ft (2.1 m), to enable a flight engineer to access the engines and landing gear by crawling through the wings. This was possible only at altitudes not requiring pressurization.

The piston engines also had a prodigious appetite for lubricating oil, each engine requiring a 100 gallon (380 L) tank. A former ground crewman has written: "[I don't recall] an oil change interval as I think the oil consumption factor handled that." It was not unusual for a mission to end because one or more engines ran out of oil. Though the B-36 could continue flying with as many as three engines inoperative, the extra stress on the remaining engines put them at risk of failing.

 

Engine Fires

Like all large aircraft powered by piston engines, the B-36 was prone to engine fires, a problem exacerbated by the pusher configuration. When a crash occurred for any reason, the magnesium-rich airframe burned readily.

When thinking about engine fires, keep in mind that:

The design of the R-4360 engine tacitly assumed that it would be mounted in the following conventional tractor configuration:

carburetor -- 28 cylinders -- air intake -- propeller

with air flowing from right to left. The carburetor is bathed in air warmed by engine cooling, and so is unlikely to ice up. The B-36 employed the following pusher configuration:

propeller -- 28 cylinders -- carburetor -- air intake

Because the carburetor is now in front of the engine, it cannot benefit from engine heat. Hence when the intake air was cold and humid, ice gradually obstructed the carburetor air intake, increasing the richness of the air/fuel mixture, until the unburned fuel in the exhaust caught fire. Engine fires of this nature led to the first loss of an American nuclear weapon, described above. Adding electric heating to the carburetor intakes eliminated the problem.

 

Crew Experience

Training missions were typically in two parts, first a 40 hour flight, followed by some time on the ground for refueling and a bit of maintenance, then a 24 hour second flight. When thinking about missions of such great duration, two facts should be kept in mind:

Hence a 40 hour mission, with the jets used only for takeoff and climbing, flew 9200 miles (15000 km). Many missions were flown "around the flag pole"; they began and ended at the same base.

The B-36 was not a sprightly aircraft: Lieutenant General James Edmundson likened it to "...sitting on your front porch and flying your house around."[9] Despite its immense exterior size, the pressurized crew compartments were relatively cramped, especially when occupied for 24 hours by a crew of fifteen in full flight kit. Although the rear compartment included six bunks, and the radio compartment behind the flight deck included a couple of bunks, crewmen usually chose to sleep in their seats.

War missions would have been essentially one-way: taking off from forward bases in Alaska or Greenland, overflying the USSR, and landing in Europe or the Middle East. The recollections of crew veterans reveal that while crews were confident of their ability to complete a mission if called upon to do so, they were less confident of surviving the weapon delivery itself. These concerns were borne out by the 1954 Operation Castle tests, in which B-36s flew near atmospheric detonations in the 15 megaton range, at distances believed typical of wartime delivery, and experienced serious heat and blast damage.

 

Experiments

The B-36 was employed in a variety of aeronautical experiments throughout its service life. Its immense size, range and payload capacity lent itself to use in research and development programs. These included nuclear propulsion studies, and "parasite" programs in which the B-36 carried smaller interceptors or reconnaissance aircraft.

In May 1946, the Air Force began the Nuclear Energy for the Propulsion of Aircraft (NEPA) project which was followed in May 1951 by the Aircraft Nuclear Propulsion (ANP) program. The ANP program required that Convair modify two B-36s under the MX-1589 project. One of the modified B-36s studied shielding requirements for an airborne reactor to determine whether a nuclear aircraft was feasible. The Nuclear Test Aircraft (NTA) was a B-36H-20-CF (Serial Number 51-5712) that had been damaged in a tornado at Carswell AFB on September 1, 1952. This plane, designated the NB-36H, was modified to carry a 1 MW, air-cooled nuclear reactor in the aft bomb bay, with a 4 ton lead shield between the reactor and the cockpit. The cockpit was encased in lead and rubber, with a 6-inch (15 cm)–thick Plexiglas windshield. The reactor was operational but did not power the plane; its sole purpose was to investigate the effect of radiation on aircraft systems. The NB-36H completed 47 test flights and 215 hours of flight time between 1955 and 1957, of which 89 hours were with the reactor critical. The NB-36H was scrapped at Fort Worth in 1958 when the nuclear aircraft program was abandoned.

Other experiments involved providing the B-36 with its own fighter defense in the form of parasite aircraft carried partially or wholly in a bomb bay. One parasite aircraft was the tiny McDonald XF-85 Goblin, which docked using a trapeze system. The concept was tested successfully using a B-29 carrier, but docking proved difficult even for experienced test pilots. Moreover the XF-85 was seen as no match for Soviet aircraft in any case, and so the project was cancelled.

More successful was the FICON project, involving a modified B-36, a GRB-36D "mothership", carrying a F-84 Thunderjet fighter modified for reconnaissance, the RF-84K, in a bomb bay. The B-36 would ferry the RF-84K to the vicinity of the objective, whereupon the RF-84K would disconnect and begin its mission. Ten GRB-36Ds and 25 RF-84Ks were built and saw active service until 1959, when they were quietly withdrawn as newer reconnaissance aircraft were introduced.

Projects TIP TOW and Tom-Tom had F-84s docking to the wingtips of B-29s and B-36s. The hope was that the increased aspect ratio of the combined aircraft would result in a greater range. Project TIP TOW was cancelled when the combination of two EF-84Ds and a specially modified test EB-29A crashed, killing everyone on all three aircraft. The cause was attributed to one of the EF-84Ds flipping over onto the wing of the EB-29A. Project Tom-Tom, involving RF-84Fs and a GRB-36D from the FICON project (redesignated JRB-36F), continued for a few months after this crash, but was also canceled due to the violent flight characteristics induced by the wingtip vortices of the B-36.

 

Obsolescense

The operational life of the B-36 ended because:

The B-36 was gradually decommissioned as the B-52 entered service.

 

Survivors

Only four (and a half) aircraft survive from the 384 produced.

 

Related Models

In 1951, the USAF asked Convair to build a prototype all-jet variant of the B-36. Convair complied by adding swept wings and eight Pratt & Whitney XJ57-P-3 jet engines to a B-36F. The result was the B-36G, later renamed the Convair YB-60. Although the YB-60 could carry a heavier bomb load than the YB-52, it did not go forward because it was also over 100 mph (160 km/h) slower and suffered from handling problems. [10].

The B-36 was the basis for the Convair XC-99, a double-decked military cargo aircraft, the longest practical aircraft (185 ft, 56 m) of its era. Only one example was ever built; it was extensively employed for nearly a decade, especially for cross-country cargo flights during the Korean War. In 2005 the XC-99 was dismantled and moved from the former Kelly Air Force Base in San Antonio, Texas, where it has been retired since 1957. It is currently being transported in pieces to the National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio aboard C-5 Galaxy transports as space and schedule permits.

A commercial airliner derived from the XC-99, the Convair Model 37 never left the drawing board. It would have been the first "jumbo" airliner.

 

B-36 Media

The B-36 plays a feature role in only one motion picture, "Strategic Air Command" (1955) starring Jimmy Stewart and June Allyson. The film opens with Jimmy Stewart as the pilot of a B-36 forced to crash in the Arctic, and features many good aerial shots of B-36s as well as B-47s.

 

Specifications

General characteristics  (B-36J-III)

Performance

Armament

 

References

Knaack, Marcelle Size (1988). Post-World War II bombers, 1945-1973. Office of Air Force History. ISBN 0160022606.

Chilcoat, Robert T. (1998) [11] By the son of a B-36 commander.

Ford, Daniel, "B-36: Bomber at the Crossroads." Air and Space/Smithsonian. April 1996.

Jacobsen, Meyers K. (1997). Convair B-36: A Comprehensive History of America's "Big Stick". Atglen: Schiffer Military History. ISBN 0764309749

Jacobsen, Meyers K. (1999). Convair B-36: A Photo Chronicle. Atglen: Schiffer Military History. ISBN 0764309749

Jenkins, Dennis R. (1999). Convair B-36 Peacemaker. Specialty Press Publishers and Wholsalers. ISBN 1580070191

Jenkins, Dennis R. (2001). Magnesium Overcast. Minnesota: Voyageur Press. ISBN 1580070426

Jenkins, Dennis R. (2003). B-36 Photo Scrapbook. Minnesota: Specialty Press Publishers and Wholesalers. ISBN 1580070752

Morris, Col. (ret.) Ted Allan (2000) "Flying the Aluminum and Magnesium Overcast." Author was a B-36 flight engineer.

Wagner, Ray (1982). American Combat Planes. New York: Doubleday. ISBN 0930083172

 

 

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