Convair XB-36 Peacemaker

Last revised February 20, 2000


The Convair B-36 was the largest bomber, in sheer physical size, that has ever gone into service with the USAF. During the late 1940s and early 1950s, the B-36 was the mainstay of the USAF's long-range strategic bombing deterrent. Serving primarily as a strategic deterrent, the B-36 never saw any combat, although some B-36 reconnaissance aircraft flew some rather hazardous missions near or perhaps even over Soviet territory during the height of the Cold War in the mid-1950s.

The origin of the B-36 can be traced back to the early days of 1941, at a time when it seemed that Britain might fall to a German invasion, depriving the USA of any European allies in case of war, and, in particular, leaving the Army Air Corps without any bases outside the Western Hemisphere. Consequently, the Air Corps felt that it would need a truly intercontinental bomber with unprecedented range, one that could bomb targets in Europe from bases inside the continental USA. In search of such an aircraft, on April 11, 1941, the USAAC, in an atmosphere of high secrecy, opened up a design competition for a bomber with a 450 mph top speed, a 275 mph cruising speed, a service ceiling of 45,000 feet, and a maximum range of 12,000 miles at 25,000 feet. It had to be able to carry a 10,000 pound bombload a distance of 5000 miles away and return, and had to be able to carry 72,000 pounds of bombs over a reduced range. It had to be able to take off and land on a 5000-foot runway. These requirements were far beyond the state of the art at the time.

Invitations for preliminary design studies were sent to the Consolidated Aircraft Corporation and to the Boeing Airplane Company. A month later, Northrop Aircraft, Inc was asked for further design studies on its "flying wing" bomber proposal. On April 19, the Douglas Aircraft Company was given a contract to determine if the Allison V-3420 W-type liquid-cooled engine could be adapted as a bomber powerplant. Much later, the Glenn L. Martin Company was also solicited, but declined the invitation due to a shortage of engineering personnel.

On May 3, 1941, a preliminary proposal was submitted by Consolidated. The company designation for the project was Model 35, although at this time it was still uncertain whether a 6-engine or a 4-engine format would be used. Twin fins and rudders were employed by the Model 35.

In order to accelerate the intercontinental bomber project, a conference of high-ranking USAAF officers met on August 19, 1941 and decided to scale down their requirements. The maximum range requirement was reduced to 10,000 miles and the effective combat radius requirement was cut to 4000 miles with a 10,000 pound bombload. The cruising speed should be somewhere between 240 and 300 mph, and the service ceiling should be 40,000 feet.

On October 3, 1941, a review of preliminary data from Boeing, Consolidated, and Douglas was held. At that time, the Materiel Division of the USAAF decided that the Consolidated study was the most promising. At this stage, the Consolidated proposal still covered several different designs, both 4- and 6-engine pusher and pusher-tractor combinations. On October 16, Major General Henry H. Arnold, Chief of the USAAF directed that the Consolidated proposal should be proceeded with. On November 15, 1941, a contract for two experimental aircraft was issued under the designation XB-36. The contract was designated W535-AC-2232. On November 22, the Engineering Division at Wright Field concluded that the 6-engine design rather than the 4-engine design should be adopted, but the twin fin-and-rudder format was retained. On December 10, Consolidated redesignated the Model 35 the Model 36 so that it would not be confused with the Northrop flying wing, which was then known as the B-35.

The two XB-36s were to be built in San Diego, with the first one to be delivered by May of 1944. At the head of the chain of command at Consolidated was I. M. Laddon, the executive vice president. Key members of the Model 36 team were Harry A. Sutton, head of the Engineering Department, Ted P. Hall, head of the preliminary design group, Ralph L. Bayless, head of the Aerodynamics Group, Ken Ward, in charge of finalizing the external shape, and Robert H. Widmer, in charge of wind tunnel testing. By this time, the wing span had grown to 230 feet with an area of 4772 square feet. The wing had a slight sweepback, and sat high on a circular-section fuselage. The aircraft was to be powered by a set of six 28-cylinder Pratt & Whitney "X" air-cooled radials. This engine was based on a pair 14-cylinder R-1830 Twin Wasp engine connected together, and in 1941 existed only on paper. These six engines were each to drive a 19-foot three-bladed Curtiss propeller in pusher configuration. The engines were to be accessible for maintenance in flight via passageways in the 7.5-foot thick wing root. Six fuel tanks with a capacity of 21,116 US gallons were incorporated into the wing. The 163-foot fuselage had four separate bomb bays with a maximum capacity of 42,000 pounds. Like in the B-29, only the forward crew compartment and the gunner's weapons sighting station compartment behind the bomb bay were to be pressurized. A 25-inch diameter, 80-foot long pressurized tube ran alongside the bomb bays to connect the forward crew compartment to the rear gunners' compartment. Crewmen could use a wheeled trolley to slide back and forth. The crew consisted of 15 (pilot, copilot, radar/bombardier, navigator, flight engineer, two radiomen, three forward gunners, and five rear gunners). Four rest bunks were provided for relief. An extremely heavy defensive armament was to be provided, consisting of five 37-mm cannon and ten 0.50-inch machine guns. These guns were to be distributed among four retractable turrets and a radar-directed tail turret. The guns were to be remotely directed by gunners situated at sighting stations distributed throughout the fuselage.

The B-36 mockup was inspected on July 20, 1942. The Mockup Committee felt that the aircraft carried too many guns and crew members to meet the 10,000 mile range requirement, and recommended that drastic reductions be made in the defensive firepower. However, some people on the committee felt that such changes would render the B-36 tactically useless, making it little more than a "flying laboratory" like the Douglas XB-19. If such reductions were actually necessary, the USAAF threatened to recommend the cancellation of the entire B-36 project and the diversion of funds to more productive bomber programs. The Mockup Committee compromised and eventually agreed to delete only the "less necessary" items of equipment from the aircraft. This reduced weight and saved the B-36 project from cancellation at that time.

In August of 1942, the San Diego plant was very heavily involved with work on the PBY and B-24, and Consolidated recommended that the XB-36 project be shifted from its San Diego, California plant to its new government-leased plant in Fort Worth, Texas. Although the USAAF approved this plan, it caused a delay of several months in the XB-36 project, since all the drawings, the mockup, the engineers, and the tooling had to be moved from California to Texas. At Fort Worth, R. C. Seybold became chief of engineering and Herbert W. Hinkley became the XB-36 project engineer. However, progress on the B-36 at Fort Worth was rather slow because of the higher priority of the B-24 Liberator and later the B-32 Dominator.

In order to speed things up, Consolidated recommended that the USAAF place a production order for the B-36 right away, arguing that two years could be saved if preliminary work on production aircraft could be started right away without waiting for completion of the experimental planes. However, the war in the Pacific was going badly at the time, and the USAAF felt that it should devote its full effort to planes which could be ready for combat in a much more timely fashion, and the request was denied.

In the summer of 1942, the USAAF agreed to the development of a cargo version of the XB-36 under the designation XC-99, provided that at least one of the two experimental bombers could be produced at least 3 months ahead of the cargo plane.

On March 17, 1943, the Consolidated Aircraft Corporation merged with Vultee Aircraft, Inc, becoming the Consolidated Vultee Aircraft Corporation. This name was often truncated to "Convair", although this name did not become official until April 29, 1954, when Consolidated Vultee Aircraft Corporation became the Convair division of the General Dynamics Corporation.

In the spring of 1943, China appeared near collapse in its war against invading Japanese forces, and the USAAF was faced with the unpleasant prospect of the loss of bases in China from which it planned to launch B-29 raids against Japan. It might turn out that the longer-ranged B-36 would be the only means of attacking the Japanese home islands if bases nearer Japan could not be secured. However, the president of Convair complained that it would be difficult to obtain subcontractors for an order for only two planes and that the company would be in a position to pursue the project with much more vigor if a large-scale production order were promised. Consequently, on June 19, 1943, General Arnold directed that orders be placed for 100 production examples. The letter of intent was signed by Convair on July 23. Under the new schedule, the XB-36 prototype should be ready for flight by September 1944. The first production B-36 was due in August of 1945, with the last one being delivered in October of 1946.

In late 1943, the twin tails were replaced by a single tail, which was almost 47 feet tall.

Unfortunately, progress on the XB-36 was still slow. The first Pratt & Whitney R-4360-5P Wasp Major test engine was to have been delivered to Fort Worth in May of 1943, but design improvements delayed it until October. Wind tunnel tests had to be postponed until the spring of 1944 because of the higher priority of other projects. The Pratt & Whitney Wasp Major engines had turned out to be somewhat heavier than expected, and some consideration was given to the use of different engines such as the Lycoming BX liquid-cooled powerplant. However, work on the Lycoming BX was discontinued on the basis that it would demand manpower, facilities, and materials that could be much better used elsewhere.

By mid-1944, the military situation in the Pacific had improved materially. The Marianas campaign was near its end, and preparation was being made for the deployment of B-29s from these bases to attack the Japanese mainland. The B-29's difficulties were now well on their way to solution, and it was felt that a super long-range bomber was not now so urgently needed and the Air Force directed that Convair should devote its main effort to the B-32 program as a backup for the B-29. Although the B-36 project would still continue, it would now do so with a lower priority. The contract for the 100 B-36s still remained in effect, but no longer carried any priority rating.

Following the surrender of Germany and the end of the war in Europe, aircraft production contracts were drastically cut back. However, the contract for the B-36 was untouched. The enormous losses suffered in seizing island bases in the Pacific convinced that USAAF that there was still a definite need for a long-range bomber. In addition, the forthcoming atomic bomb would require a long-range delivery vehicle capable of retaliating against an enemy without the need for faraway forward bases. On August 6, 1945, General Arnold accepted the Air Staff's recommendation to keep the B-36 contract for a hundred planes intact. Funds from the cancelled B-32 program were transferred to the B-36 project. On August 9, an Air Staff conference recommended that four B-36 groups be included in the postwar USAAF.

Work on the XB-36 continued even after the Japanese surrender. By 1945, Convair was still having problems with the high weight of the Pratt & Whitney R-4360-25 engines. The need to add nose guns required an extensive rearrangement of the forward crew compartment. A mockup of the new nose section had been approved in late 1944. This new nose would be too late for the first prototype, but would be fitted to the second XB-36. The radio and radar equipment in the new nose promised to add considerable weight.

Labor strikes at Convair in October 1945 and February 1946 delayed the B-36 program by several months. On March 25, 1946, General Thomas Power indicated that structural limitations of the forthcoming XB-36 might actually make it useless.

The B-36 was to have been provided with the Sperry-built K-1 bombing system, which consisted of an AN/APQ-23 radar and A-1 electromechanical bombing computer. The AN/APQ-23 was essentially an APQ-13 search radar combined with a CP-16 computer. The system supplied range, azimuth, distance, and drift information to the crew. The AN/APQ-23 was eventually succeeded by the AN/APQ-24.

The first XB-36 (42-13570) was rolled out of the Fort Worth factory on September 8, 1945. It sat on massive single 110-inch diameter main wheels, which restricted it to only three runways in the USA which had sufficiently thick concrete to support the weight of the aircraft.

The first XB-36 took off from Fort Worth on its maiden flight on August 8, 1946, remaining in the air for 37 minutes. It was piloted by Beryl A. Erickson and G. S. "Gus" Green, assisted by seven other crew members. It was the heaviest and largest landplane ever to fly up to that time. Flight tests turned up problems with the wing flap actuating system, the engine cooling was poor, and turbulent airflow off the wings caused propeller vibration which adversely affected the wing structure. The aircraft's overall performance fell below the original expectations. Engine cooling was a problem which resulted in the inability of the XB-36 to maintain altitudes over 30,000 feet for any extended period of time. The range was too short and the speed was too low. Besides the known structural limitations, the XB-36 had the single-wheel landing gear and carried only a minimum number of components, and lacked the nose armament that had been planned for the second XB-36. There were also problems with the aluminum wiring that had been fitted to save weight in place of the more reliable but heavier copper.

On December 12, 1946, General Kenny, head of the Strategic Air Command, believing the B-36 to be inferior to the B-50, suggested that the B-36 contract be reduced to only a few service test aircraft. However, neither the Air Staff nor General Nathan Twining agreed with this assessment, arguing that the B-36 should not be judged solely on the performance of the XB-36 which had just started its flight testing. General Carl Spaatz, the commander of the USAAF, agreed with General Twining, and the B-36 contract was spared.

On March 26, 1947, a hydraulic retraction cylinder failed just after takeoff, which caused engine number 4 to catch fire. After spending a few hours in the air to burn off excess fuel, pilots Erickson and Green managed to bring the crippled bomber safely in for a landing.

After being grounded for modifications, the XB-36 was flown for 160 hours by pilots of the USAAF Air Materiel Command. It was then returned to the contractor for further testing. Convair pilots made 53 test flights with the XB-36, logging a total of 117 flying hours.

In June of 1948, the single-wheel main undercarriage was replaced by a four-wheel bogie-type undercarriage, which was to be standard on production models. Each wheel had a 56 inch diameter. This reduced the runway thickness requirements. In addition, 3500 hp R-43660-41 engines were fitted. The plane was then redesignated YB-36A. It was reflown in this configuration in June of 1948. The original single-wheel landing gear tire is on display at the USAF Museum in Dayton, Ohio.

The YB-36A was then turned over to the USAF in June of 1948, one week before the scheduled delivery of the first production B-36As. It had limited operational value and was used by the Strategic Air Command primarily for training. It was soon returned to Convair-Fort Worth, where it sat idly out in the open for the rest of 1948 and much of 1949. It was tested briefly with a track-type undercarriage in 1950. The aircraft was taken back on charge by the USAF at Wright Patterson AFB in August of 1950. However, the Air Force concluded that it would be too costly to bring it up to production standards, and the airplane was returned to Fort Worth and put in storage. It was officially retired on January 30, 1952, and towed over to a field at the north end of the Fort Worth plant. Engines and equipment were removed and the plane sat out in the open for five years. It was eventually towed across the runway to Carswell AFB and used as a prop in the base's firefighting program.

The second prototype, which was designated YB-36 (42-13571), had been chosen as the production prototype on April 27, 1945. It had the new high-visibility canopy with the raised roof and redesigned forward crew compartment, which became a standard production feature. The XB-36's poor cockpit visibility had been noted by the test pilots, but engineering studies on an improved cockpit layout had begun as early as June of 1945. The new crew compartment enabled nose armament to be fitted, which was added at Air Force insistence because of experience during the war which had shown that American bombers had been especially vulnerable to frontal attacks. The new cockpit covered the pilot, co-pilot, and flight engineer. The flight engineer now faced aft, looking towards the engines whose status he was responsible for monitoring. The turbosuperchargers were more efficient. Since the YB-36 was primarily intended for flight testing, no defensive armament was fitted. The YB-36 took off on its maiden flight on December 4, 1947, with Beryl Erickson again at the controls. It easily outperformed the XB-36, and during its third flight, it reached an altitude of more than 40,000 feet. The YB-36 still had the original single-wheel undercarriage that had been initially fitted to the XB-36, but the new four-wheel main landing gear struts were retrofitted to the aircraft during testing.

The YB-36 was turned over to the USAF on May 31, 1949. It was returned to Convair in October of 1950 to be fitted for reconnaissance, and was redesignated RB-36E. In the spring of 1957, it was placed in the Air Force Museum at Wright-Patterson AFB in Ohio. However, it was scrapped in 1971 when the new museum facility was built. However much of the scrapped aircraft was saved by collector Walter Soplata and is now stored on his land in Ohio.

Serials of XB-36 and YB-36:

42-13570	Consolidated XB-36
42-13571	Consolidated YB-36

Specification of Convair XB-36:

Engines: Six 3000 hp Pratt & Whitney R-4360-25 Wasp Major air cooled radial engines. Performance: Maximum speed 346 mph at 35,000 feet. Cruising speed 216 mph. Initial climb rate 1740 feet per minute. An altitude of 25,000 feet could be attained in 42 minutes. Service ceiling 36,000 feet. Absolute ceiling 38,000 feet. Range 9500 miles with 10,000 pounds of bombs, 3850 miles with 77,784 pounds of bombs. Weights: 131,740 pounds empty, 276,506 pounds gross. 19,976 gallons of fuel. Dimensions: Wingspan 230 feet 0 inches, length 162 feet 1 inches, Height 46 feet 8 inches, wing area 4772 square feet. Armament: No defensive armament fitted. Normal bomb load up to 72,000 pounds.

Sources:


  1. United States Military Aircraft Since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian, 1989.

  2. Post-World War II Bombers, Marcelle Size Knaack, Office of Air Force History, 1988.

  3. General Dynamics Aircraft and their Predecessors, John Wegg, Naval Institute Press, 1990.

  4. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.

  5. Convair B-36: A Comprehensive History of America's "Big Stick", Meyers K. Jacobsen, Schiffer Military History, 1997.

  6. USAF Museum website, http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2595