Nuclear-powered airborne giants from southern California, part 3: Santa Monica's atomic airlifters

In my blogpost on the Lockheed CL-1201 flying aircraft carrier project of the late 1960s, I mentioned that Lockheed worked out a heavy-lift transport variant of the CL-1201 that could carry a massive military payload far bigger than that of the C-141 and C-5, and slightly exceeding the cargo capacity of a number of hybrid airship designs envisaged in the 1990s and early 2000s. However, the California division of Lockheed was not the only manufacturer in southern California to propose a strategic airlifter utilizing a nuclear powerplant. More than a decade earlier, even while the US Air Force was formulating requirements for a nuclear-powered strategic bomber, the Douglas company responsible for the C-74, C-124, and C-133 designs in additional to its prolific dynasty of airliner designs toyed with the idea of a giant nuclear-powered transport aircraft. 

Three view drawing of a twin-fuselage Douglas Model 1875 design study (dated April 20, 1955). An additional side view of the single-fuselage Model 1875 iteration is shown on the lower right corner of the drawing. 

In December 1954, Douglas began tinkering with fitting a nuclear reactor to a strategic bomber when it conceived a nuclear-powered version of the C-132, officially labeled "A.P. Transport" ("A.P." stood for "Atomic Power"). Starting in early February 1955 Douglas investigated design studies for a nuclear-powered heavy-lift aircraft for the Aircraft Nuclear Propulsion (ANP) program under the company designation Model 1875, and after a down-selection of numerous concepts with a diverse array of design configurations, it worked out eight Model 1875 designs in March-April 1955 the first four being exploratory concepts embodying twin-pod, twin-fuselage, twin-boom, and single fuselage layouts. one with twin cargo pods and four turboprops connected to a nuclear reactor in the center fuselage, a twin-boom design with four turboprops connected to a nuclear reactor in the center fuselage, a single-fuselage transport with four turboprops fueled by two nuclear reactors in the inboard engine nacelles, and a six-turboprop design with the two nuclear reactors in the outboard engine nacelles. The twin-pod, twin-fuselage, and single-fuselage Model 1875 designs envisaged in April 1955 measured 181 feet 6.3 inches (55.33 meters) long, and whereas the twin-pod and twin-fuselage proposals had a wingspan of 264 feet 8 inches (80.67 meters) and four turboprops housed in coupled pairs in two nacelles in the wing center section, being fueled by a nuclear reactor in the center fuselage, the conventional single-fuselage design spanned 200 feet (60.96 meters) and had four turboprops, of which the inboard engines were fueled by two nuclear reactors in the wings. Parametric evaluations by Douglas indicated that the conventional single-fuselage proposal was superior to other layouts in weight and aerodynamic drag, and engineers deduced that cruise flight could achieve 60 percent of nuclear reactor power necessary for take-off if the reactor were scaled down to meet the cruise power requirement to allow jet fuel to give supplemental thrust, effectively balancing increased payload with reduced gross weight.

After completing analysis and trade-offs for different Model 1875 layouts, in January 1956, Douglas launched a Detailed Study effort examining a common tube-and-wing layout scaled to different wing aspect ratios, fuselage cross-sections, and overall sizes. Two Model 1875 studies dated February 8, 1956, dubbed Studies No. 4 and No. 5 would have been 200 feet (60.96 meters) long with a wingspan of 323 feet 4 inches (98.55 meters); Study No. 4 had six turboprop engines, of which the two outboard engines were fueled by two nuclear reactors in the wings, while Study No. 5A had four turboprops, with the outboard engines being fueled by two nuclear reactors. In July 1956, Douglas worked out a slightly smaller Model 1875 with a 295 foot (89.92 meter) wingspan and powered by six Pratt & Whitney T57 turboprops connected to two nuclear reactors. The large-fuselage Model 1875 proposals from 1956 with an oversized fuselage would have had a capacity for 572 troops seated on two decks when configured for troop transport, and power for the turboprops of these designs would have been supplied by two AC-300-1 reactors.

A cutaway view of the Douglas Model 1444, a proposal for a C-133 Cargomaster to serve as a testbed for the General Electric X211 (J87) nuclear-powered turbojet.

Given the sheer size of the General Electric X211 nuclear-powered turbojet (military designation J87) being considered for the Model 1875, in February 1958, Douglas worked out the Model 1444 scheme for a C-133 Cargomaster to serve as a testbed for the X211 turbojet. The X211 would be housed in the aft section of the cargo compartment, its jet engines being fed by a nuclear reactor behind the cockpit (whose crew compartment had rudimentary lead and rubber shielding from nuclear radiation). Studies done by Douglas for a nuclear-powered transport under the ANP program ended in August 1958, but although the Model 1875 might have carried troops and military equipment for indefinite periods of flight time without having to stop at air bases to refuel, neither it nor the Model 1444 ever materialized, for March 1961, the ANP program was canceled by President John F. Kennedy. 

References:

Cox, G., and Kaston, C., 2020. American Secret Projects 3: U.S. Airlifters Since 1962. Manchester, UK: Crécy Publishing.

Pan Am Clippers from southern California

The Boeing 314, Martin M-130, and Sikorsky S-40 and S-42 flying boats, nicknamed "Clippers" by Pan American World Airways after the clipper merchant ships of the mid-1800s, epitomized the romance of US air travel in the 1930s by providing passengers with a unprecedented level of luxury during long-distance transoceanic flights. However, as noted in a handful of publications, near the end of the 1930s, Pan Am articulated plans to field even larger passenger aircraft in the 1940s that could utilize a new generation of piston engines far more powerful than those used on the Boeing 314, Martin M-130, and Sikorsky S-40 and S-42, namely the Wright R-3350 Duplex Cyclone and Allison V-3420. No aircraft manufacturer from southern California was ever given the chance to build a large passenger aircraft for Pan Am in the late 1930s, so I'm dedicating this post to "Clipper" airliner designs conceived in southern California during this timeframe.

An artist's rendering (left) and cutaway interior view (right) of the Consolidated Trans-Oceanic Flying Boat from the project documents.

Months before the first flight of its new PB2Y Coronado patrol flying boat, Consolidated Aircraft in July-August 1937 conceived a passenger flying boat design that was similar in size and seating capacity to the Boeing 314 despite the fact that Pan Am had selected the Boeing 314 among design submissions for the 1936 flying boat requirement for full-scale development. Officially dubbed the Trans-Oceanic Flying Boat by Consolidated, this design had a rounded nose section faired into the fuselage hull lines, a single vertical stabilizer, seating capacity for 54 passengers in stateroom-type accommodations on two decks, a wingspan of 185 feet (56.39 meters), a wing area of 2,911 ft² (270.44 m²), and a gross weight of 110,000 lb (49,895 kg). Power was provided by four radial piston engines (probably Wright R-3350 Duplex Cyclones or Pratt & Whitney R-2800 Double Wasps), and the top speed of the Trans-Oceanic Flying Boat was estimated at 226 mph (363 km/h). Given that the Trans-Oceanic Flying Boat had a single vertical stabilizer as in the initial Model 30 ("XPB3Y-1") design conceived in early 1937 and a similar wingspan, it is plausible that this project was an evolutionary derivative of the initial Model 30 flying boat design.

Artist's concepts of Consolidated's pusher engine 100 passenger floatplane (left) and 100 passenger flying boat (right) designed in early 1938 for the December 1937 requirement by Pan Am for a new long-range passenger aircraft. The latter design was chosen by Consolidated for eventual submission to the Pan Am requirement.

On December 9, 1937, Pan Am announced a requirement for a long-range airliner with seating capacity for 100 passengers, a range of 5,000 miles (8,046 km), a 25,000 lb (11,340 kg) payload, and a cruising speed of 200 mph (321 km/h), and invitations were sent out to eight companies. Consolidated worked out two proposals in January 1938, one being a gigantic floatplane and the other a conventional flying boat. The floatplane iteration was powered by four 2,600 hp (1,938 KW) liquid-cooled piston engines buried in the wing in pusher arrangement, and it had twin vertical stabilizers, a wingspan of 220 feet (67 meters), a wing area of 4,850 ft² (450.58 m²), an elliptical widebody fuselage, and a gross weight of 200,000 lb (90,718 kg). The flying boat design also had twin vertical stabilizers but arranged the liquid-cooled piston engines in tractor position, and it was 120 feet 9 in (36.80 meters) long with a wingspan of 200 feet (61 meters), a wing area of 4,000 ft² (371.6 m²), a gross weight of 170,000 lb (77,112 kg), and a top speed of 261 mph (420 km/h). Consolidated judged the floatplane design to be slower and heavier than the conventional 100-passenger flying boat design, so it selected the flying boat proposal for eventual submission to Pan Am. The 100-passenger flying boat proposal was subsequently tweaked to have a shorter hull truncated at the water line and a more upswept aft fuselage that supported the tail empennage (similar to that seen in the P4Y Corregidor), a more streamlined and shorter nose, and a broader fuselage to better accommodate the interior arrangement. With these refinements, Consolidated submitted the flying boat iteration to Pan Am by the March 1938 deadline for design submissions.

A front view of and seating maps for the 1938 Douglas land-based airliner submission for the December 1937 Pan Am requirement for a new-generation transoceanic airliner (from a 1954 issue of Interavia)

While Consolidated tinkered with passenger flying boat proposals roughly rivaling the Model 30/PB3Y  designs in length and wingspan, the Santa Monica division of the Douglas Aircraft Company apparently responded to the December 1937 specification by Pan Am by submitting a design for a slightly scaled-up version of the DC-4E airliner powered by six radial piston engines and with greater seating capacity sometime in the first half of 1938. The exact company designation for this proposal is unknown and any other technical data for this project are uncertain, but the the tail empennage design and slight dihedral of the wings could indicate a potential relationship of the design to the Douglas XB-19 prototype heavy bomber.

Although the Consolidated and Douglas design submissions for the Pan American's December 1937 requirement for a new-generation long-range airliner would, like other proposals for this competition, have provided a greater level of luxury than the Boeing 314, Martin M-130, and Sikorsky S-42, the outbreak of war in Europe in 1939 caused Pan Am to shelve its grandiose plans for a new generation of long-range flying boats, and neither the Consolidated 100 passenger flying boat nor the Douglas design were ever built.

References:

Bradley, R., 2010. Convair Advanced Designs: Secret Projects from San Diego 1923-1962. North Branch, MN: Specialty Press.

Nuclear-powered airborne giants from southern California, part 2: Lockheed CL-1201 flying aircraft carrier

In today's world, the US Navy's fleet of aircraft carriers relies on nuclear propulsion to allow those ships to traverse and stay afloat on the high seas without fear of running out of fuel, as does the French aircraft carrier Charles de Gaulle (all other carriers in service around the world are conventionally powered). The first American nuclear-powered surface vessels, the aircraft carrier USS Enterprise and guided missile cruiser USS Long Beach, were commissioned in 1961, giving the US Navy's surface ships the ability to stay afloat on the high seas indefinitely. However, almost lost in talk about military nuclear-powered vehicles is the fact that even as the US Navy gradually commissioned more nuclear-powered surface vessels, Lockheed in the 1960s came out with an rather unorthodox proposal for a giant flying aircraft carrier running on nuclear power! This may sound surprising to most aviation historians and gurus, but even though the US Air Force gave up on nuclear-powered combat aircraft development in 1961, there was still a sliver of interest in giant nuclear-powered aircraft from the aerospace industry in southern California.

Artist's conception of the CL-1201-1-1 flying aircraft carrier, late 1960s

In 1969, the California division of Lockheed began studies to determine the uses and capabilities of the largest aircraft feasible with existing technology. Using the earlier CL-1170-6-2 long-range maritime reconnaissance aircraft project as a baseline, Lockheed envisaged a clean-sheet design for a colossal nuclear-powered aircraft, designated CL-1201 by the company. The CL-1201 design had a wingspan of 1,120 feet (341 meters), a length of 560 feet (170 meters), a height of 153 feet (46 meters), a wing area of 125,000 square feet (11,612 square meters), a gross weight of 5,265 tons (5,350 metric tons) and a cruise speed of Mach 0.8 at an altitude of 30,000 feet (9,144 meters). Four gigantic turbofans were mounted atop the rear center section of the CL-1201, providing a total cruise thrust of 500,000 lb (2,224 kN), and these were fueled by a 30 foot (9.1 meter) wide nuclear reactor onboard the aircraft generating 1,830 megawatts. At altitudes up to 16,000 feet (4,876 meters), the turbofans would run on normal JP-5 fuel, but while operating at higher altitudes, they would powered by nuclear energy from the reactor. Substantial shielding would be needed to protect the crew and the reactor would be designed to have failsafe crash performance even in a high-speed head-on impact. The CL-1201 would have provisions for facilities to accommodate a maximum of 845 crewmembers, and the undercarriage comprised four separate landing gear struts, each with six wheels positioned towards the rear of the fuselage, as well as two further six-wheel units outboard of the wing roots, four-wheel stabilizing gear positioned about half way along each wing, and a substantial four-wheel nose gear unit.

Top: Lockheed CL-1201-1-1 three-view (from Lockheed project documents)
Bottom: Schematic view of the Lockheed CL-1201-1-3

Two versions of the CL-1201 were proposed. The CL-1201-1-1 Attack Aircraft Carrier (AAC) was a flying aircraft carrier intended to carry a total of 24 tactical aircraft, 22 below the wings on pylons (these would be recovered in-flight after completing a mission), and two more in the fuselage hangar. There would be direct access to the aircraft via pylons for flight crews and maintenance staff with the aircraft being rearmed and refueled while attached. The notion of a flying aircraft carrier was not new; in World War II Daimler-Benz investigated designs for giant flying aircraft carriers able to carry smaller combat aircraft, and in the late 1940s and early 1950s Douglas initiated design studies for versions of  the 1211 and 1240 bomber projects able to carry an array of small combat jets. None of these schemes reached the hardware phase, but the CL-1201-1-1 was destined to be the largest flying aircraft carrier design of all time, bearing uncanny resemblance to similar machines usually seen in science fiction movies like the Star Wars series, Sky Captain and the World of Tomorrow, and The Avengers series. The AAC was also considered for use as an airborne command and control center. (A CL-1201-1-2 variant may also have been considered, but no details are available.) The CL-1201-1-3 Logistics Support Aircraft (LSA) was intended to carry 400 combat troops and 1,150 tons of military equipment, and it could also dock five Boeing 707-sized transport aircraft (each with a capacity for 150 troops or 32 tons of military equipment) using nose receptors positioned at the CL-1201-1-3's trailing edge and tail. For vertical takeoff, the AAC would have featured 182 turbofan lift engines delivering 15 million pounds (66,723kN) of thrust, located along each wing behind the rear spar and in extendable units at the front of the fuselage, each containing 24 units. The LSA would have utilized 54 turbofan lift engines with a total yield of 82,500 lb (367 kN) thrust for VTOL, and accommodations for 462 crewmembers. In a serious combat situation, a single AAC would be dispatched and escorted by seven LSAs in order to deliver and keep supplied a US Army brigade comprising 3,896 troops and 6,207 tons (5,630 metric tons) of military equipment (e.g. artillery, mortars, light aircraft, and attack aircraft) for 30 days.

Despite being impressive on paper, the CL-1201 concept was all for naught. Due to the sheer size of the CL-1201, operational problems with this design would have been evident, and thus CL-1201 never proceeded beyond the drawing board. No large aircraft project was to approach the 1,120 foot span of this behemoth, namely the Bel Geddes No.4 flying ocean liner, Conroy Virtus space shuttle carrier aircraft, Boeing RC-1, Junkers J1000 flying wing airliner, Adlershof Riesenflugzeugen bomber projects, Rumpler twin-hull flying boat, and the Boeing, Lockheed, and McDonnell Douglas proposals for flying wing cargo aircraft. The Scaled Composites Model 351 Stratolaunch (which first flew in April 2019) has displaced the Hughes H-4 Hercules in terms of being the largest aircraft by wingspan (385 feet), but its span is nowhere near the monstrous wingspan of the CL-1201.

References:

Lowther, S., 2007. "Blended Wing Bodies". Aerospace Projects Review 1(3): 30-64. Link available at 

http://www.aerospaceprojectsreview.com/ev1n3.htm.

Rose, B., 2010. 

Secret Projects: Flying Wings & Tailless Aircraft. Hinckley, UK: Midland Publishing.

Nuclear-powered airborne giants from southern California, part 1: the Northrop N-34 and Lockheed nuclear-powered bomber proposals

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.

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. 

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. 

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.

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. 

Aerial refueling to orbit: the Northrop Grumman Military Space Plane

Northrop Grumman and its predecessor company Northrop historically are best known for development of tailless aircraft, jet fighters, and night fighters plus the YA-9 prototype attack aircraft, cruise missiles, the Tacit Blue stealth technology demonstrator, and the N-23 Pioneer and YC-125 STOL transports. However, as documented by Chong (2016), Northrop also made rare forays into spacecraft design during the Cold War with the N-206, N-256, and HYLEAP military spaceplanes s the N-212 Broom suborbital capsule, and the N-227 design for the late 1950s Mercury capsule competition won by McDonnell (whose spacecraft design carried Alan Shepard to the edge of space in May 1961 and became the first manned spacecraft to orbit the Earth in 1962), even though these schemes remained unbuilt. Northrop Grumman did not get heavily involved in the space industry until after acquiring Orbital ATK in June 2018, and it is no wonder that during my latest visit to the Western Museum of Flight last September, I happened to see a Northrop Grumman desktop model of a spaceplane that looked unfamiliar, eventually finding out on the Internet that the spaceplane design from Northrop Grumman had been conceived in the 1990s for military purposes. For this reason, the scope of this post centers upon the company's proposal for a military spaceplane designed to be refueled on its way to orbit.

A desktop model of the Northrop Grumman Military Space Plane at the Western Museum of Flight, photographed by me on December 16, 2023.

In the mid-1990s, Northrop Grumman began design studies for a single-stage-to-orbit (SSTO) military spaceplane designed to go to low Earth orbit by means of in-flight refueling under the descriptive label Transatmospheric Vehicle (TAV). This project was influenced by the Black Horse concept for an SSTO spaceplane capable of refueling from tanker aircraft en route to orbit that was conceived in 1993 by US Air Force Captain Mitchell Burnside Clapp, who knew very well the USAF's use of aerial refueling to extend the performance of combat aircraft. As with the Black Horse concept the Northrop Grumman spaceplane was intended to take off from a runway with rocket power but with nearly empty liquid oxygen tanks and refuel from another spaceplane, after which it would utilize a suborbital boost and then launch an upper stage from the inner bay in order to reach orbit. To signal to the US Air Force its desire for greater involvement in military space programs, Northrop Grumman rebranded the TAV by the moniker Military Space Plane in the late 1990s. Three different designs of the Northrop Grumman Military Space Plane were done for various propellant combinations, including one utilizing a jet fuel/hydrogen peroxide fuel combination and a bulbous vehicle fueled by liquid hydrogen and liquid oxygen. The design of the Military Space Plane featured a blunt nose section, voluminous space in the center section for the fuel tanks and two outwardly canted vertical fins at the edges of the wings. 

 In 2000, NASA and the Defense Department jointly established the Space Launch Initiative (SLI) to determine the requirements to meet all of the hypersonics, space launch and space technology needs on part of the US in the civil and military fields, awarding reusable launch vehicle study contracts to the various aerospace companies involved in RLV design. The Northrop Grumman Military Space Plane ended up languishing at the design phase due to a lack of customer interest from the USAF, Northrop incorporated aspects of the design, including the outwardly canted vertical fins and blunt nose, into a manned spaceplane proposal which it jointly conceived with Orbital Sciences in 2002 for the Orbital Space Plane (OSP) program, which was now one of of the two components of the Second Generation Reusable Launch Vehicle program that evolved from the SLI (the other being the Next Generation Launch Technology (NGLT) program) after the X-33 and X-34 programs were cancelled in March 2001. It didn't matter in the end, however, because the OSP program was axed in 2004 after President George W. Bush announced the Vision for Space Exploration.

References:

Chong, T., 2016. Flying Wings & Radical Things: Northrop's Secret Aerospace Projects & Concepts 1939-1994. Forest Lake, MN: Specialty Press.

The CL-278: Lockheed's first high-altitude spyplane design

The Lockheed U-2 spyplane that made headlines when one was shot down over the USSR in May 1960 and also ignited the October 1962 missile crisis by photographing Soviet ballistic missile sites in Cuba is easy recognizable by sailplane-like wings married to a slender, cigar-shaped fuselage (as a matter of fact, the initial CL-282 design that gave rise to the final U-2 design was a cross between the F-104 Starfighter and a sailplane). However, the U-2 was not first subsonic spyplane design that Lockheed conceived during the Cold War. Even before Clarence "Kelly" Johnson envisaged the initial CL-282 design, his company was already tinkering with the idea of a subsonic sailplane-like reconnaissance aircraft, envisaging not one, but two designs for such an aircraft with an airframe different from that of the CL-282.

A three-view drawing of the CL-278-1-1 (aka L-278-1-1) and a close-up of the aircraft's nose section for the spy cameras from project documents.   

In early 1954, after being informed about the Air Material Command's MX-2147 program (codename Bald Eagle) for a high-altitude reconnaissance plane for the US Air Force (which was won by the Bell X-16 and Martin RB-57D), Kelly Johnson decided to initiate design studies for a subsonic high-altitude spyplane under the company label L-278 (later CL-278) without input from the Air Force. In particular, he railed against government bureaucracy for obstructing any progress faced by his company's cutting-edge aircraft projects in reaching full-scale development, so he felt it convenient to go it alone working out the design of the CL-278 with the slightest hope that the US Air Force would approve this project for eventual prototyping. The first CL-278 design, the CL-278-1-1 (aka L-278-1-1), was very much a jet-powered sailplane like the U-2 but was far bigger than the first-generation U-2s, with a length of 76 feet (23.16 meters) and a wingspan of 98 feet 8 inches (30.07 meters) compared to the 50 foot length and 80 foot wingspan of first-generation U-2 variants, and its wing area of 650 square feet (60.38 square meters) and wing aspect ratio were bigger than that of the U-2A and U-2C. The wings would be braced with external struts on the underside to keep them structurally stable, and the pilot sat in a huge bubble-shaped cockpit canopy to aid him in navigating the CL-278-1-1 through hostile airspace. Power was provided by one General Electric J79 turbojet situated below the fuselage and extending to the base of the tail empennage, and air was fed into the J79 through two intakes on the sides of the fuselage. The CL-278-1-1 utilized a tricycle landing fear for takeoff and landing like the designs submitted for the MX-2147 competition. Four spy cameras were housed in the nose section to allow ground personnel to disconnect the nose in order to remove the cameras and install newer ones in the nose.

A three-view drawing of the CL-278-1-2 (aka L-278-1-2) tailless spyplane from the project documents

The second CL-278 concept worked out by Lockheed, the CL-278-1-2 (aka L-278-1-2), had a rather different layout than than the CL-278-1-1, taking the form of a tailless aircraft with the J79 situated inside the fuselage nacelle aft of the pilot's seat and backswept wings with rounded wingtips. As with the CL-278-1-1, the CL-278-1-2 carried its spy cameras inside the nose, which was rounded like that of the P-80/F-80 Shooting Star, and two triangular vertical stabilizers were located near the wingtips with control surfaces situated along the wing's trailing edge (similar to that proposed for the Junkers EF 128 jet fighter project of early 1945). The lack of a tail empennage as well as the slender backswept wings gave the CL-278-1-2 a length of 42 feet (12.8 meters) and wingspan of 100 feet (30.48 meters), the latter slightly shorter than that of second-generation U-2s, although the CL-278-1-2's wing area was the same at that of the CL-278-1-1. Although data for the performance and weight of the CL-278 designs is lacking in project documents for the CL-278, it is reasonable to assume that either CL-278 proposal would have flown at same altitude of the U-2, X-16, or RB-57D with a top speed comparable to or approaching that of the U-2 and RB-57D, high enough to escape interception by Soviet jet fighters and interceptors.

Although the CL-278-1-1 would have exhibited outstanding flight characteristics like the U-2 and the CL-278-1-2's tailless layout might have afforded it greatly reduced aerodynamic drag compared to the CL-278-1-1, Johnson eventually discarded the CL-278 project and instead saw the CL-282 as the most promising design for full-scale development by virtue of using the fuselage of an existing aircraft and dispensing with landing wheels to save weight when reaching its design altitude. The initial CL-282 proposal may have been frowned upon by LeMay as well as John Seaberg and William Lamar of the AMC's New Developments Office as too aerodynamically frail when submitted for consideration, but an undaunted Johnson chose to revise the CL-282 design to include the CL-278's rounded nose and incorporate low-mounted horizontal stabilizers, and with these changes, he managed to win the backing of the CIA for the CL-282, which eventually became the U-2.

References:

Rose, B., 2010. Secret Projects: Flying Wings & Tailless Aircraft. Hinckley, UK: Midland Publishing.