Much has been written about the Boeing B-47 Stratojet, the world's first multi-engine swept-wing jet bomber to go into production and operational service, especially with regards to its development, flight testing, and operational career. However, it should be emphasized that the B-47 was not a product of its own creation despite being the first American swept-wing jet bomber but instead was part of a years-long effort by the United States to shop for a gas turbine-powered strategic bomber to replace its fleets of B-17, B-24, and B-29 bombers through solicitations from different aircraft manufacturers, including Boeing. As a matter of fact, the aviation industry in southern California that manufactured the B-24 Liberator, B-25 Mitchell, and B-32 Dominator during World War II put out two rival designs to the B-47 Stratojet using the old-fashioned straight wing planform, the North American B-45 Tornado and the Convair XB-46. In an unusual twist of fate, the B-45 went into production, but the XB-46 remained at the prototype stage only.
 |
| Models of the North American B-45 Tornado (left) and Convair XB-46 (right) at the Lyon Air Museum, Chino (photographed by me in November 2021) |
In 1944 the US Army Air Force became aware of Nazi Germany's fielding of the world's first jet bomber, the Arado Ar 234, so in March the US War Department issued a requirement for a multi-engine strategic jet bomber with a top speed of 500 mph (804 km/h), a range of 2,500-3,000 miles (4,023-4,828 km), a service ceiling of 35,000-40,000 feet (10,668-12,192 meters), and a 16,500 lb (7,484 kg) bombload. Four companies -- Boeing, Convair, Martin, and North American -- submitted bids for the intermediate-range strategic bomber requirement, with North American's proposal bearing the company designation NA-130 and the Convair submission being designated the Model 109 (later changed to Model 1). Both the NA-130 and Model 109 were straight-winged designs powered by four Allison J35 turbojets housed in pairs in two underwing nacelles. The designation XB-45 was allocated to the NA-130, and a contract for three XB-45 prototypes (serial numbers 45-59479/59481) was signed on September 8, 1944. Five months later, on February 27, 1945, three Convair Model 109 prototypes (serial numbers 45-59582/59584) were ordered and the Model 109 was officially designated XB-46. (The other submissions, the Boeing Model 432 and Martin Model 223 [designated XB-47 and XB-48 respectively], were designed outside southern California and thus are outside the scope of this blog.) Although the end of World War II caused many wartime aircraft projects and production orders to be cancelled, the War Department did not cancel the XB-45, XB-46, XB-47, and XB-48 programs, given its recognition that jet aircraft were the wave of the future.
Left: First North American XB-45 prototype (serial number 45-59479) in flight
Right: The sole Convair XB-46 prototype (serial number 45-59582) in flight
The XB-45 Tornado was 74 feet (22.55 meters) long with a wingspan of 89 feet 6 in (27.28 meters), a height of 25 feet 2 in (7.67 meters), a wing area of 1,175 square feet (109.2 square meters), an empty weight of 41,876 lb (18,953 kg), a gross weight of 66,820 lb (30,309 kg), and a maximum speed of 516 miles per hour (830 km/h). The engine nacelle arrangement adopted for the B-45 was reminiscent of that of the Arado Ar 234C four-engine variant of the Ar 234 jet bomber, and the nose of the XB-45 had window panels at the upper surface. The XB-45 crew comprised a pilot, co-pilot, bombardier/navigator, and a tail gunner; the pilot and co-pilot sat in a bubble cockpit canopy, while the bombardier/navigator sat in the nose and the tail gunner operated a tail gun turret. The XB-45 prototype made its first flight on March 17, 1947 (which happened to be St. Patrick's Day), and the three XB-45 prototypes (each instrumented for different specialized phases of the flight test program) carried out more than 130 test flights; the first XB-45 prototype crashed on take-off from Wright-Patterson Air Force Base in Dayton, Ohio, on June 28, 1949, due to a failure of the landing gear. The XB-46, on the other hand, had a very slender fuselage oval in cross-section and very high-aspect ratio wings, with its four J35s paired in two integral nacelles, and it featured a bubble cockpit canopy to accommodate the pilot and co-pilot as well as a Plexiglas nose section for the bombardier/navigator. The XB-46 measured 105 feet 9 in (32.23 meters) long with a wingspan of 113 feet (34.44 meters), a height of 27 feet 11 in (8.51 meters), a wing area of 1,285 square feet (119.4 square meters), an empty weight of 48,018 lb (21,781 kg), a gross weight of 91,000 lb (41,277 kg), and a maximum speed of 545 mph (877 km/h); the production version was to be armed with two 0.50-caliber Browning machine guns in the tail and carry 22,000 lb (10,000 kg), with power to be provided by four General Electric J47 turbojets. During the course of developing the XB-46, Convair worked on a forward swept wing attack aircraft project, the XA-44 (redesignated XB-53 in 1946), and the end of the World War II caused severe defense budget cuts, putting Convair in a tight financial bind with regards to the XA-44/XB-53 and XB-46 programs. Facing a tight budget, Convair urged the US Army Air Force to cancel the second and third XB-46 prototypes to save money for the XB-53, and the USAAF agreed to this request in June 1946. (The XB-53 program was cancelled in December 1946 due to concerns about the ability of the forward-swept wing to endure aerodynamic loads at high speed.) The first XB-46 was eventually completed as a stripped-down airframe devoid of armament or military equipment, and it made its first flight on April 2, 1947. A total of 14 test flights at Muroc Army Air Field were conducted until September, after which the XB-46 was used for variety of tests such as noise measurements and tail vibration investigations, with additional stability and control tests being performed at West Palm Beach Air Force Base in Florida from August 1948 to August 1949. After an additional 44 flight hours, the XB-46 was taken out of service due to high maintenance costs and a lack of spare parts, and eventually flown to Eglin Air Force Base where its pneumatic system was tested in cold weather conditions from July to November 1950. The nose section of the sole XB-46 prototype was sent to the Air Force Museum at Wright-Patterson Air Force Base, but the remainder of the aircraft was scrapped in February 1952.
A B-45A Tornado (serial number 47-025) dropping bombs in flight
Even before the XB-45 had made its first flight, on August 2, 1946, the USAAF decided that the XB-45 was superior to the XB-46 because it determined that the XB-46 would be inferior in performance to the XB-45 design and that the slender fuselage of the Convair design would be unable to accommodate the required radar equipment. Therefore, a production order was placed for 96 B-45As and one static test airframe (serial numbers 47-001/097), with the company designation NA-147 used for the B-45A. The B-45A featured improved ejection seats for the pilot and co-pilot, safer emergency exits for the bombardier/navigator and the tail gunner, along with provisions for an E-4 automatic pilot, a bombing navigation radar, and an A-1 fire control system were provided. The first B-45A flew on February 24, 1948, and the first 22 B-45As (deliveries of which began in April) had four Allison J35s, while the remaining B-45As were powered by four General Electric J47 turbojets. Although designed to use a remote-controlled fire control system for the tail gun turret, the B-45As were fitted with a tail gunner's position because of the unavailability of the remote-controlled fire control system. The B-45B was to be a B-45A variant fitted with new radar and fire-control systems, but was not built. The B-45A reached operational USAF units at Barksdale Air Force Base in Louisiana in November 1948, but the B-45A fleet was plagued by maintenance problems with the J47 engines and APQ-24 bombing/navigation radar system, several structural weaknesses in the airframes, difficulties with the gyrocompass at high speed and the E-4 automatic pilot when the bomb doors opened, the lack of suitable bombsights or fire control bombing equipment, and inadequate ferry range and combat radius. Despite these problems, the B-45A found a role as a tactical bomber to deter a Soviet attack on western Europe in the wake of the outbreak the Korean War when the US Air Force in December 1950 initiated the Backbreaker program to fit several B-45As with improved bombing/navigation systems and the Norden bombsight, bomb bays to accommodate lightweight tactical nuclear bombs, and additional electronic equipment, and nuclear-capable B-45As were deployed to the UK beginning in May 1952. As the 1950s progressed, the B-45As were retired from US Air Force service and replaced by the B-47 and also the Douglas B-66 Destroyer tactical bomber, and by July 1958, all B-45As stationed in the UK were relocated to bases in mainland Europe and North Africa, many of them being retired there and broken up for scrap. Some J35-powered B-45As were used for training purposes and designated TB-45A, a few of them serving a target tugs for a Chance Vought target drone glider. On the other hand, one B-45A was modified for use as a launch platform for guided weapons and designated DB-45A, while the last production B-45A (serial number 47-096) was used as an in-flight engine testbed and designated JB-45A.
Left: A classic aerial view of the first B-45C Tornado (serial number 48-001)
Right: An RB-45C Tornado (serial number 48-037)
In September 1947, North American envisaged a variant of the Tornado that could be refueled in midair, the B-45C (company designation NA-153). Although similar to late-production B-45As in having four General Electric J47 turbojets, it differed in having a pair of 1,200-gallon wing tip fuel tanks that could be dropped in flight when necessary, a strengthened cockpit canopy with several reinforcements, a boom receptacle on the top of the fuselage for refueling, and a single-point ground refueling receptacle on the left side of the bomb bays. A total of 43 B-45Cs (serial numbers 48-001/043) were ordered, and the first aircraft flew on May 3, 1949, but by 1950 the US Air Force had decided to place huge orders for the B-47 Stratojet, so the last B-45C to be built in bomber configuration was completed on April 13, 1950. The remaining 33 B-45Cs on order (48-011/043) were completed as reconnaissance aircraft under the designation RB-45C. Unlike the B-45C, the RB-45C had the transparent nose section replaced by a duckbill-shaped nose housing a forward oblique spy camera, and it could carry at least 10 spy cameras (four in the rear fuselage, four at the split vertical section, one tri-metrogen K-17C in a pallet aft of the wing's trailing edge, and one forward oblique camera in the nose) but also 25 M-122 photoflash bombs in the bomb bay. The RB-45C first flew in April 1950, and deliveries of the RB-45C to Strategic Air Command began in June 1950, continuing until October 1951. The RB-45C conducted its first-ever reconnaissance flights over North Korea during the Korean War in the fall of 1950, and for several months the RB-45Cs of the 91st Strategic Reconnaissance Wing were able to evade MiG jet fighters, but after a couple of incidents on 1951 in which the RB-45Cs narrowly escaped interception by MiGs, all RB-45Cs were restricted from overflights of North Korea in daylight operations and converted for night reconnaissance operations in January 1952, receiving black paint to evade interception by enemy searchlights. However, night operations of the RB-45C went awry because the aircraft buffeted badly when the forward bomb bays door opened to release photoflash bombs, and the RB-45Cs were thus withdrawn from use in the Korean War. When the RB-47E reconnaissance version of the B-47 became operational, the RB-45Cs in Air Force service were transferred to the 19th Tactical Reconnaissance Squadron stationed in Europe, with which they served until their retirement in the spring of 1958. The Royal Air Force also used the RB-45C, and four aircraft were leased to RAF crews as part of Operation Ju-jitsu to form the Special Duties Flight, which was headed by Squadron Leader John Crampton and stationed at RAF Sculthorpe in Norfolk, eastern England. The most prolific reconnaissance mission to be carried out by the Special Duties Flight was on April 17, 1952, when three RB-45Cs overflew Kiev from RAF bases in West Germany to obtain intelligence about Soviet military strength; despite being intercepted by Soviet fighters, the RB-45Cs survived and returned to West Germany, and this flight was to serve as a wake-up call for the USSR to reform its air defense systems by making the PVO Strany a branch of the Soviet armed forces independent of the Soviet Army and VVS in 1954. The RB-45C would remain in service until 1959, when it was replaced by the RB-47E and other new-generation reconnaissance aircraft. In the meantime, one B-45C were modified for use as a guided weapons launch platform and designated DB-45C, while the ninth B-45C (serial number 48-009) served as a testbed for the Pratt & Whitney J57 and J75 turbojets under the designated JB-45C.
Although the B-45 Tornado wasn't as prolific as the better-known B-47 Stratojet given its limitations as a strategic bomber and ended up serving mainly as a reconnaissance platform, its significance was not lost on the fact that it was the first American multi-engine jet bomber to enter service and also the third multi-engine jet bomber to fly, after the Junkers Ju 287 forward-swept wing jet bomber and the Arado Ar 234C four-engine tactical bomber. On the other hand, the XB-46's ability to carry required military equipment was compromised by its fuselage design despite having very high-aspect ratio wings. Like the earlier Douglas XB-43 Jetmaster, the Tornado inadvertently cemented southern California's role as the birthplace of the jet bomber in the United States, but in due time the swept-wing B-47 emerged as the true jet-powered successor to the B-17 and B-29, making clear once again that swept wings were the key for new-generation US bomber aircraft to attain high subsonic speeds.
References:
Bradley, R., 2010. Convair Advanced Designs: Secret Projects from San Diego 1923-1962. North Branch, MN: Specialty Press.
Frederiksen, J.C., 2009. The B-45 Tornado: An Operational History of the First American Jet Bomber. Jefferson, NC: McFarland. ISBN 978-0-7864-4278-2.
No comments:
Post a Comment