In 2006, I watched an episode of the History Channel documentary series Secret Superpower Aircraft about bomber projects of the Cold War when I heard something mind-blowing about the nature of strategic bomber design during the dark days of the Cold War: a strategic bomber exclusively running on nuclear power! Although the US Navy's large carriers run solely on nuclear power and all its ballistic missile submarines are nuclear-powered, I had previously never heard someone contemplating an aircraft design with nuclear-fueled engines. Yet the decision by a number of US aircraft manufacturers to tinker with the idea of a nuclear-powered aircraft during the Cold War was one reminder of the fact that obsession with the potential benefits afforded by nuclear energy became an American forte that other countries, including the USSR, were lagging behind. The nuclear-powered aircraft design featured in the Secret Superpower Aircraft was proposed by the Fort Worth division of Convair, so I have thus dedicated this post to discussing nuclear-powered bomber designs conceived in the Los Angeles area in the 1950s.
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| An artist's concept of the Northrop N-34 from the Northrop company documents |
On May 28, 1946, the US Army Air Force initiated the Nuclear Energy for the Propulsion of Aircraft (NEPA) program to investigate the idea of combat aircraft with air-breathing engines fueled by a nuclear reactor. Douglas and North American were instructed the USAAF, along with a coalition of American engine companies led by the Fairchild Engine & Aircraft Corporation to pursue a series of design studies for nuclear-powered aircraft. The logic behind a nuclear-powered aircraft was that it could stay airborne for indefinite periods of time without having to rely on overseas bases, especially at a time when in-flight refueling technology was in the experimental stage. Almost two years into the NEPA program, in April 1948, the Northrop company in Hawthorne, California, initiated a private venture for a nuclear-powered flying wing bomber, designated N-34. Although tailless like the earlier B-35 and B-49 flying wing bombers, the N-34 differed in having a separate fuselage and a vertical fin. It had a wingspan of 70 feet 8 in (21.54 meters), a length of 89 feet 8 in (27.33 meters), and a height of 28 feet (8.53 meters), with provisions for a crew of ten. The wings would have back swept 40 degrees on the leading edge and 35 degrees at quarter chord, and six turbojets (type unspecified) would be buried in the wing roots. There is no available information on the type of nuclear power plant intended for the N-34 or bomb load, but available drawings indicate that the N-34 itself would have featured a pair of 0.6 in (15.24 mm) gun turrets on the nose and tail. Chong (2016) notes that Northrop initiated another internal project related to the initial phase of the NEPA, the N-29, for which no further details are known. A paper presented to a meeting of the Society of Automotive Engineers by Northrop engineer Lee A. Ohlinger on April 9-12, 1956 contains artist's conceptions of nuclear-powered aircraft, from a straightforward conversion of the YB-49 to more exotic all-wing configurations, along with more conventional designs and some rather esoteric solutions for crew shielding and fighter escort towing, but there is no evidence that these conceptual schemes were serious internal projects by Northrop (Chong 2016, p. 52).
The N-34 was not the only nuclear-powered bomber design conceived for the NEPA program. In 1949, the Lockheed Skunk Works undertook design studies for giant nuclear-powered bomber designs under the company designation L-195, all of them with gross weights of up to 500,000 lb (226,800 kg) and having lengths varying from 187 feet (57 meters) to 267 feet (81.4 meters). The earliest L-195 design, the L-195-A-13, was 225 feet (68.6 meters) long with thin, straight wings reminiscent of the F-104 Starfighter and an unspecified number of turbojets in an annular cluster ahead around the fuselage ahead of the straight wings, fueled by an indirect cycle nuclear reactor in the aft fuselage. The crew compartment was located near the nose to protect the crew from radiation, and the bomb bay was situated between the engines and nuclear reactor. The L-195-A-15 was similar to the L-195-A-13 in having the nuclear reactor placed in the aft fuselage but was longer, measuring 247 feet (75.3 meters) in length, and it had two underwing nacelles each housing three turbojets as well as two smaller nacelles (each housing two turbojets) on the wingtips, while the wings were backswept. The last known L-195 design study, the L-195-A-26, featured thin, straight wings similar to those of the North American X-15, and it had a length of 205 feet (62.5 meters), a wingspan of 117 feet 6 in (35.8 meters), a height of 52 feet 6 in (16 meters), and a gross weight of 440,000 lb (199,580 kg). The powerplant installation of the L-195-A-26 design was quite unusual it that it featured ten nuclear turbojets stacked in staggering pairs along the sides of the rear fuselage, converging towards the aircraft centerline and fed by air through a pair of bifurcated intakes ahead of the wing roots and a large flush inlet on top of the fuselage.
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| Top: Lockheed L-225 proposal Bottom: Lockheed L-248-3 nuclear-powered flying wing |
In May 1951 the NEPA program was replaced by the Aircraft Nuclear Propulsion (ANP) program. A couple months earlier, in March, the US Air Force had instructed Boeing and Lockheed to undertake design studies for a nuclear-powered bomber, and Pratt & Whitney and General Electric to examine nuclear powerplants. Beginning in 1951 Lockheed began investigating designs for smaller nuclear-powered bomber aircraft capable of launching cruise missiles from low altitudes on enemy targets under the company designation L-212, pursuant to Wright Field project MX-1627. In response to a US Air Force competition for a low-altitude cruise missile-armed strategic bomber launched in late 1952, Lockheed conceived the L-225, L-232, L-233, and L-234 proposals for low-altitude nuclear-powered bomber aircraft. These designs were similar to each other in having short stubby wings and four jet engines fueled by a small nuclear reactor in the center section of the fuselage, aft of the weapons bay for carrying bombs or cruise missiles. The L-248-3 was a gigantic flying wing bomber design powered by eight Allison turboprop engines on the leading edge of the wing fueled by a nuclear reactor in the tail section and driving counter-rotating propellers, with a wingspan of 380 feet (116 meters), and a length of 89 feet (27 meters). The tricycle landing gear comprised two main landing gear struts with four wheels each and a nose strut with two wheels, and two vertical stabilizers were located along the trailing edge of the wing. For combat missions, the L-248-3 would deliver free-fall nuclear weapons and probably an early thermonuclear weapon.
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| CL-293-64 design, early 1956 |
In late 1954, the US Air Force initiated the WS-125 weapon system (covered by General Operational Requirement GOR-81 in March 1955) for a nuclear-powered supersonic dash strategic bomber with a range of 12,939 miles (20,823 km), of which 1,151 miles (1,853 km) was to be flown at an altitude of 60,000 feet (18,288 meters) and Mach 2. Lockheed responded in 1955 with two nuclear-powered strategic bomber designs under the company designation CL-293, both of which had a crew of five men, and in addition General Electric and Pratt & Whitney joined forces with Lockheed to undertake development of the XMA-1 direct-cycle nuclear engine and the NJ-2 indirect-cycle nuclear engine. One of the two main CL-293 proposals used a General Electric AC-107 propulsion system, which comprised four nuclear and four chemical turbojets, and it had a take-off weight of 527,000 lb (239,050 kg), a cruising speed of Mach 0.9 at 30,000 feet (9,144 meters), and a speed of Mach 2.5 at about 63,000 feet (19,202 meters) in supersonic dash mode. The CL-293 design with the Pratt & Whitney powerplant (dubbed 'Fireball') had the same cruise speed and altitude as the General Electric-powered design but weighed 622,800 lb (282,500 kg) and would had attained a speed of Mach 2.5 at 61,000 feet (18,593 meters) in supersonic dash mode. Both designs would carry a 10,000 lb (4,536 kg) weapons load, and the supersonic dash radius of the General Electric-powered design was 254 miles (406 km), whereas the Pratt & Whitney-powered CL-293 proposal had a dash radius of 359 miles (578 km). By early 1956, a revised design for the NJ-2 powered version was submitted, the CL-293-64, which had tapered wings, a T-tail configuration, and six nuclear-fueled turbojets arranged side-by-side across the center airframe and below the wing roots. Specifications included a length of 212 feet 9 in (64.85 meters), a wingspan of 135 feet 8 in (41.35 meters), a wing area of 4,600 square feet (427.80 square meters), a gross take-off weight of 603,900 lb (273,930 kg), a top speed of Mach 0.9 at 28,000 feet (8,534 meters), and a dash speed of Mach 2.25 at 55,000 (16,764 meters) over a combat radius of 576 miles (927 km). The initial CL-293 designs, despite meeting most of the WS-125 requirements, did not exactly meet the combat radius specified in the WS-125 specification.
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| CL-319-35-1 (top) and CL-326-40 (bottom) designs (as of July 1956) |
In July 1956, Lockheed decided to envisage a proposal for a 'tug-tow' weapon system, codenamed Blackjack, in order to fulfill the combat radius requirement of which the CL-293 designs had fallen short. The Blackjack system comprised two aircraft, the CL-326 nuclear-powered subsonic bomber and the conventionally fueled CL-319 supersonic bomber. Over 40 CL-326 designs were investigated, and one design, the CL-326-40, featured an aircraft with a long slim fuselage, a T-tail configuration, an NJ-2 indirect-cycle propulsion system in which six side-by-side turbojets were located in two large nacelles on the sides of the fuselage, and a gross weight of 337,770 lb (153,212 kg). The CL-326-40 'tug' was 149 feet 4 in (45.52 meters) long, with a wingspan of 122 feet 6 in (37.34 meters), and a wing area of 2,500 square feet (232.50 square meters). The CL-319-35-1 proposal featured a sleek aircraft similar to the CL-293 but with two Pratt & Whitney JT9A turbojets situated the center sections of the wings, and it was 161 feet 3.5 in (49.16 meters) long, with a wingspan of 81 feet 9 in (24.92 meters), a wing area of 1,800 square feet (115.940 meters), and a weight of 255,600 lb (115,940 kg). The CL-319 has a crew of four, and the Blackjack system itself was to accommodate five crewmembers (pilot, flight engineer, co-pilot, offense operator, and defense operator). For combat missions, the CL-326-40 was to fly at Mach 0.9 at an altitude of 20,000 feet (6,096 meters), and once it approached an enemy target, the CL-319 would be released by the towing aircraft and reach a top speed of Mach 2.5 at 55,000 feet (16,764 meters) over a dash radius of 956 miles (1,538 km). The CL-326 was submitted to the WS-125 project office, but officials did not consider the Blackjack scheme attractive, so at the end of July all work on the CL-326 was shelved. In November, Lockheed submitted a new design for a nuclear-powered low-altitude bomber that could use either a direct-cycle or 'Fireball' powerplant. The design had four turbojets fueled by two nuclear reactors, with a weight of 400,000 lb (181,440 kg) and a cruise speed of Mach 0.9 (or Mach 0.85 with 'Fireball') at an altitude of 35,000 feet (10,668 meters). The aircraft would use chemical fuel during take-off, landing, and emergency situation, allowing it to attain a supersonic dash radius of (1,853 km). The proposed dash radius of this design met the combat dash radius parameter laid out in the WS-125 requirement, and the WS-125 project office believed that the latest WS-125 submission by Lockheed could be developed as an operational aircraft. However, in December, the Air Force cancelled the WS-125 program because it judged the operational requirements laid out in the specification to be too ambitious and unrealistic to be achieved.
This was not the end of Lockheed's studies into nuclear-powered bomber aircraft, however. In 1958, Strategic Air Command announced the Continuous Airborne Alert Missile Launching and Low Level Penetration Aircraft (CAMAL) program (covered by operational requirement GOR-172) for a purely subsonic nuclear-powered bomber. In October, Lockheed devised a proposal to meet the requirements laid out in the CAMAL specification; no further information is available on what Lockheed's CAMAL submission looked like. In March 1959, the rival Convair Model 54 won the CAMAL competition, but in July the CAMAL program was cancelled, and by September Lockheed's design efforts were shelved.
References:
Buttler, T., 2010. American Secret Projects: Bombers, Attack, and Anti-Submarine Aircraft 1945 to 1974. Hinckley, UK: Midland Publishing.
Buttler, T., 2021. American Secret Projects 4: Bombers, Attack, and Anti-Submarine Aircraft 1945 to 1974. Manchester, UK: Crécy Publishing.
Chong, T., 2016. Flying Wings & Radical Things: Northrop's Secret Aerospace Projects & Concepts 1939-1994. Forest Lake, MN: Specialty Press.
Rose, B., 2010. Secret Projects: Flying Wings & Tailless Aircraft. Hinckley, UK: Midland Publishing.
Zichek, J.A., 2010. Mother Ships, Parasites, & More: Selected USAF Strategic Bomber, XC Heavy Transport and FICON Studies, 1945-1954 (American Aerospace Archive Number 5). La Jolla, CA: American Aerospace Archive.
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