Northrop N-55: the tailless patroller from Hawthorne

In late 1948, the US Air Force concluded that its ability to defend the continental US from airstrikes was inadequate. Thus, it promulgated an across-the-board scheme to improve American air defense systems, which partly led to the WS-201 (aka 1954 Interceptor) requirement that resulted in development of the delta-winged Convair F-102 Delta Dagger and F-106 Delta Dart as well as the trisonic Republic XF-103 Thunderwarrior. After becoming aware of this situation, the Northrop company proposed an all-wing patrol plane under the designation N-55. The wingspan of the N-55 would be same as that the B-35 and B-49, but the fuselage design would mirror that of the N-31 flying wing bomber project in utilizing fore and aft crew nacelle extensions, giving the plane a length of 61.8 feet (18.8 meters). The N-55 concept was basically not just intended for long-range patrol missions but also would serve to function as an airborne radar picket ship that could fire air-to-air missiles against enemy planes that intruded into North American airspace. Search radars operating in the X-band or S-band ranges would be internally accommodated in the nose and tail of the N-55. 

Northrop N-55 sans suffixe (left) and N-55A (right) design studies for a long-range patrol flying wing

Two N-55 variants were studied. The baseline N-55 design was powered by two Northrop XT37-NA-3 turboprops each delivering 10,000 hp, and it was armed with 44 AAM-N-2 (later GAR-1/2/3/4/5/6/9 and finally AIM-4) Falcon air-to-air missiles (of which a dozen would be fired from leading edge tubes with eyelid covers, the rest being housed in two weapons bays). The N-55A had the same wingspan but was powered by six Westinghouse J40 turbojets. The turboprop-powered N-55 looked like a cross between the baseline N-31 and later N-31A versions because it had two T37 turboprop engines and a pair of vertical stabilizers, while the engine arrangement of the N-55A resembled that of the YB-49, with the jet engines buried between two pairs of vertical stabilizers on the wing's trailing edge.

References:

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

The new and improved B-49: the Northrop N-40

In 1948 Northrop began to undertake design work on an improved version of the YB-49 prototype flying wing jet bomber, bearing the mind the fact that the YB-49 had some serious deficiencies in operating range and payload capability. For example, the YB-49's operating range was more or less on par with that of the B-47 Stratojet, and its bomb bay was not big enough to carry free-fall nuclear bombs. On August 23, 1948, the US Air Force, seeing that it needed a second flying example of the B-49 bomber, modified the recently signed contract for 30 RB-49s with an amendment to convert one of the RB-49s into a B-49.

Three-view drawing of the Northrop N-40 with six Westinghouse J40 turbojets from the Northrop company documents. 

Northrop's proposal for improvising the YB-49 design was given the company designation N-40. It would have the same airframe as the YB-49 but feature a new center bomb bay in the crew nacelle that measured 170 inches in length, 80 inches wide, and 80 inches deep, big enough to carry America's large-diameter nuclear weapons. To improve bombing accuracy, the N-40 utilized an AN/APQ-24 bombing/navigation system on the lower aft portion of the crew nacelle, and a Minneapolis-Honeywell E-7 autopilot system was incorporated into the design to ameliorate the phugoid oscillations noticed during flight tests of the YB-49. Twin and quad 0.50 caliber machine gun turrets were considered for installation, and one design iteration had one remotely controlled turret below the starboard nose area outboard of the bombardier's glass and one remotely controlled turret in the aft upper fuselage, both with four 0.50 caliber machine guns. The baseline N-40 design had eight 4.850 lb (21.57 kN) thrust General Electric J47-GE-3 turbojets, six buried in the wing and two in pods below the wings. Northrop also looked an N-40 design with six wing-embedded 7,500 lb (33,36 kN) thrust Westinghouse J40 turbojets, and an option to fit the N-40 with six 6,250 lb (27.8 kN) thrust Pratt & Whitney J48s (license-built version of the Rolls-Royce Tay turbojet) was also considered. Another alternate engine provision explored for the N-40 involved the use of two Turbodyne T37 turboprops in conjunction with two or four J40s, similar to the powerplant arrangement planned for the Northrop N-37B (RB-49C).

Although Northrop hoped that the N-40 would entice the US Air Force to order more examples of the B-49, the N-40's life was destined to be short-lived. The cancellation of the RB-49 contract in January 1949 put any thought of clearing the N-40 for full-scale development to rest, and the N-40 was not proceeded with. Given that the N-40 would have had potentially greater range than the YB-49 and the ability to carry free-fall nuclear bombs, it might have been a serious competitor to the B-52 had it been built. 

References:

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

Northrop's stealthy special ops transports: SMOCA and SOFTA

In the 1980s and early 1990s the Northrop Corporation was busy developing and testing three aircraft with stealth features, Tacit Blue, B-2 Spirit, and YF-23, stealing some of the spotlight from Lockheed when it came to stealth aircraft development. However, the long-term aftermath of the failure of Operation Eagle Claw in April 1980 prompted the creation in 1987 of the US Special Operations Command (SOCOM) to handle the operation of aircraft specifically tailored for special operations, so Northrop felt keen to look at applying low observables to a notional special operations aircraft. 

Northrop made its first foray into special operations aircraft design to in April 1990 when it envisaged a design study for a special operations transport in response to an announcement by DARPA in January of that year soliciting "Research in Technologies Supporting Special Operations/Low Intensity Conflict" (SO/LIC). The design, known internally as the SO/LIC Mission Oriented Combat Aircraft (SMOCA), had a planform inspired by the Tacit Blue, namely in having highly tapered straight wings and a V-tail. The air vehicle itself was called the Special Operations Tactical Air Carrier (SOTAC) while the crew capsule was known as the SMOCA Air Vehicle Enclosure (SAVE). The initial SMOCA concept was powered by two turbofans and measured 65 feet 3 in (19.89 meters) long with a wingspan of 75 feet (22.86 meters), a height of 19 feet (5.79 meters), a mission radius of 1,726 miles (2,778 km), and a payload of 15,000 lb (6,804 kg). Super STOL (SSTOL) performance would be achieved with the use transverse-thrust lift augmentation (span-wise blowing of engine bleed air across the flaps and control surfaces to re-energize the detached airflow). An alternative SMOCA design drew upon the more rigorous edge alignment design seen on the B-2, and engine exhaust was discharged through thin, rectangular ducts ahead of the inboard flaps. It measured 87 feet 4.4 in (26.63 meters) long with a wingspan of 90 feet (27.43 meters) and a height of 25 feet 3.96 in (7.72 meters).

By November 1990, the SMOCA had evolved into an aircraft with a full perimeter chine, low-mounted intakes, and two fixed horizontal stabilizers with elevators controlled pitch. The final SMOCA design, which resembled the B-2 from the side, was powered by two 17,000 lb (78.62 kN) thrust General Electric F404 turbofans buried in the fuselage on the sides of the cargo bay, and it measured 51 feet 8 in (15.75 meters) long with a wingspan of 64 feet 6 in (19.66 meters) and a height of 11 feet 1 in (3.38 meters). Gross weight was 50,400 lb (22,961 kg) with a radius of 1,150 miles (1,852 km), and the wingspan allowed for the SMOCA to be stowed aboard a carrier without the need for wing folding. The SMOCA was envisioned by Northrop for use as a basic airlifter, gunship, covert infiltration/exfiltration aircraft, or special ops transport.

Even before it conceived its final SMOCA design, Northrop unveiled a number of Special Operations Forces Transport (SOFTA) designs for a special operations transport drawing heavily on B-2 design strategies such as edge alignment for low observability. The "baseline" and "preferred" SOFTA designs took the form of an edge aligned trapezoidal flying wing with a wingspan of 100 feet (30.48 meters), a length of 75 feet (22.86 meters), and a height of 16 feet 3 in (4.96 meters), and both were powered by four tip-driven lift fans (covered by doors during horizontal cruise) for vertical takeoff and landing and four cruise turbofans. Cruise speed was 345 mph (556 km/h), and payload was 4,500 lb (2,041 kg), with upper and lower rear cargo doors enabling access to the cargo bay and allowing for in-flight cargo and special forces to be rapidly deployed when the aircraft was hovering. The "preferred" SOFTA design differed from the "baseline" design in having the fixed engine inlets above the chines, and the "baseline" and "preferred" SOFTA designs had a low-altitude mission radius of 1,150 miles (1,852 km) and a range of 2,762 miles (4,440 km). An alternative SOFTA design, measuring 53 feet (16.15 meters) in length with a wingspan of 71 feet (21.64 meters) and 12 feet 2 in (3.71 meters) in height, retained the four tip-driven lift fans but had four F404 cruise turbofans and two turbine-driven aft fans, and it had a smaller payload bay measuring 6 ft x 6.5 ft x 15 ft (1.83 m x 1.98 m x 4.78 m). In all three designs, the wingtips were capable of being folded upwards for carrier storage.

Despite being interesting designs, none of Northrop's stealthy special operations transports would reach the hardware stage. Given that these proposals were conceived amidst the end of the Cold War and the unraveling of the Soviet Union, it is likely that US defense budget cuts in the post-Cold War context precluded the US Air Force from contemplating a contract award for the SOFTA program that would have enabled one or more aircraft manufacturers to proceed with building SOFTA prototypes.

References: 

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

Lost Crusader from El Segundo: the Douglas D-652

In 1952, the US Navy's Bureau of Aeronautics issued a requirement for a jet fighter capable of transonic speeds at 35,000 feet (15,850 meters) and Mach 1.2 in afterburner mode, with armament comprising both guns and/or collision course rockets. The El Segundo division of the Douglas company leveraged its experience with design of the F4D Skyray and the D-591 project to undertake work on a supersonic jet fighter derived from the Skyray in response to the OS-130 requirement, designated D-652 by the company.

Three view drawings of the Douglas D-652 sans suffixe (left) and D-652-1 (right)

Four D-652 designs were worked out by Douglas in early 1953. The baseline design, the D-652 sans suffixe, retained the Skyray's powerplant but differed from the Skyray in having a longer fuselage and thin wings to reduce transonic drag, and it was armed with two 20 mm cannons in the lower lip of each air intake and either two 37-shot fold-fin rocket packages below the outer underwing pylons or one 19-shot rocket package and a Sparrow-air-to-air missile below all the underwing pylons. The D-652A was a scaled-down version powered by one 13,800 lb (61.3 kN) thrust Rolls-Royce Avon RA.14 turbojet and measuring 46 feet 4 in (14.12 meters) long with a wingspan of 27 feet 6 in (8.38 meters) and a gross weight of 18,500 lb (8,392 kg). The D-652-1 design utilized the Skyray wing outboard of the fillet and existing associated features such as the main landing gear, and the cockpit was moved forward to allow more space for fuel in the fuselage, The D-652-2 had the existing airframe of the F4D but differed in electronics and provisions for 300 gallon (1,136 lit) external fuel tanks to achieve the required combat radius. Both the D-652-1 and D-652-2 proposals would have used either the J57 or Avon, and they also had a shorter nose than the baseline D-652 design, but were heavier than the D-652A.  

In May 1953, the Vought V-383 was declared the winner of the OS-130 competition and became the F8U Crusader, making its first flight on March 25, 1955. In the meantime, Douglas would apply some expertise in the design of the D-652 project to development of the F5D Skylancer.

References:

Buttler, T., 2013. Early US Jet Fighters: Proposals, Projects, and Prototypes. Manchester, UK: Hikoki Publications. 

Missile-armed hunter from El Segundo: Douglas F6D Missileer

The El Segundo division of Douglas made its only genuine forays into developing and building carrier-based jet fighters for operations in the daytime in the 1950s with the F4D Skyray and F5D Skylancer, both of which were quite revolutionary among US Navy jet fighters in their wing planform. However, the end of the F5D program and the completion of production of the F4D did not entirely spell the end of the flirtation by Douglas' El Segundo division with air-to-air combat aircraft designs, despite the company’s preoccupation with production of airliners, attack aircraft, and military transports. Towards the end of the 1950s, Douglas toyed with the idea of a long-range  interceptor designed to defend the US Navy’s aircraft carriers from Mach 2 capable aircraft, taking the world of long-range aerial interception into the realm of naval aviation. However, the concept of a subsonic fleet defense fighter by Douglas would end up being killed by a combination of both politics and the changing threat environment emanating from the Soviet Union.

An artist's concept of the Douglas F6D Missileer (D-766) in flight

In 1957, the US Navy published detailed assessments indicating that the new F4H Phantom II supersonic jet fighter might not be capable of protecting aircraft carriers from enemy aircraft capable of Mach 2 and that a purpose-built subsonic interceptor would be needed to prevent attacks on large carriers by Mach 2 aircraft. To begin addressing this demand, a new long-range air-to-air missile, the XAAM-N-10 Eagle, was envisaged with mid-course and terminal homing guidance systems and the capability to shoot down enemy aircraft 130 miles (209 km) away, and Bendix and Douglas submitted proposals for the airframe of the Eagle missile, the latter submission designated D-742 by Douglas. In December 1958, Bendix was selected by the Navy to build the Eagle, which relied on a solid-fuel rocket booster with folding fins to reach Mach 3.5, and Grumman became the sub-contractor for development of the XAAM-N-10. By late November 1959, the US Navy announced the TS-151 requirement for a long-range fleet defense jet fighter armed with the Eagle missile and equipped with a Westinghouse AN/APG-81 pulse-doppler radar while flying at a loiter time of six hours over a distance of 150 miles (241 km). In response, Boeing, Douglas, Grumman, North American, McDonnell, and Vought submitted bids for the TS-151 competition, with the Douglas proposals being designated D-765, D-766, and D-767 by the company and the North American design featuring straight shoulder-mounted wings and two jet engines slung under the wings. Douglas had previously worked on a subsonic long-range interceptor project in May 1958 under the internal designation D-746, the weapon system based on the carriage of the losing Douglas bid for the XAAM-N-10 airframe contract having been designated D-745. The D-766 design had straight shoulder-mounted wings and horizontal stabilizers and two Pratt & Whitney TF30 turbofans in the wing roots, and it was 53 feet (16.15 meters) long with a wingspan of 70 feet (21.3 meters), a height of 10 feet 1 in (3.07 meters), a wing area of 630 square feet (59 m²), a gross weight of 50,000 lb (22,680 kg), a maximum takeoff weight of 60,000 lb (27,216 kg), and a top speed of 546 mph (879 km/h). The wings of the D-766 would have underwing pylons for six Eagle air-to-air missiles, three per wing, and the tricycle landing gear had twin wheels on each leg, all folding into the fuselage.

On July 21, 1960, the US Navy declared the Douglas D-766 the winner of the TS-151 competition, with the Vought V-434 submission achieving second place, and the D-766 was officially designated XF6D-1 and christened Missileer, with two prototypes ordered. The biggest complexity of the F6D Missileer was the fact that its pulse-doppler radar and air-to-air weaponry had to work in concert with the newly deployed Grumman W2F Hawkeye airborne early warning aircraft (redesignated E-2 in 1962), given that the AEW system of the Hawkeye was capable of detecting threats at ranges beyond 230 miles (370 km) to assist the F6D in intercepting enemy aircraft and the pulse-doppler radar could cover areas over distances of 137 miles (220 km). Therefore, although development of the F6D was seen as likely to be low-cost and successful, the system as a whole was very risky and expensive. Additionally, some Navy officials had doubts about the need for a subsonic fleet defense interceptor, arguing that once the F6D Missileer fired its missiles, it would be completely unable to defend itself and would have to return to an aircraft carrier as quickly as possible to re-arm. By December 1960 outgoing Secretary of Defense Thomas Gates removed funding for the F6D from the FY 1962 defense budget, and even though Douglas in February 1961 made a last-minute plea to keep the Missileer project alive, newly sworn-in Defense Secretary Robert McNamara formally canceled the F6D program in favor having the Navy and US Air Force forge a joint requirement for a new fighter-bomber that became the TFX program, which led to the F-111 Aardvark. The Eagle AAM that would have armed the F6D also was cancelled without ever having reached the hardware phase, but some of its technologies would later find their way into the AIM-54 Phoenix air-to-air missile carried by the F-14 Tomcat. In any case, the fact that the USSR did not put much serious effort into developing supersonic aircraft that could attack the carriers from which the F6D would have operated further poured cold water on the idea of a long-range fleet defense interceptor.

References:

Buttler, T., 2007. American Secret Projects: Fighters and Interceptors 1945 to 1978. Hinckley, UK: Midland Publishing.

Thomason, T.H., 2008. U.S. Naval Air Superiority: Development of Shipborne Jet Fighters, 1943–1962. North Branch, MN: Specialty Press.

Wagner, R., 2004. American Combat Planes of the 20th Century: A Comprehensive Reference. Reno, Nevada: Jack Bacon & Co. ISBN 0-930083-17-2.

A2J encore: The North American D-190

The North American A2J "Super Savage" is one of the lesser-known US Navy combat aircraft types built in the early Cold War, having constituted an endeavor by North American to adapt the AJ Savage design to use gas turbine engines but whose turboprop engines were beset by teething troubles. Even before the A2J flew, however, North American Aviation conjured up the idea of adapting the A2J design for a wide array of both attack and non-combat missions, including close air support. 

In October 1950, the US Navy's Bureau of Aeronautics issued a specification for a general-purpose attack bomber capable of operating from modernized Essex-class aircraft carriers and small airfields, dubbed XVA(GP) by BuAer. This notional aircraft was also to be used by the US Marine Corps for close air support, and minimum requirements called for a payload of four 20 mm guns, three bombs, and twenty unguided rockets, an endurance of at least four hours on close air support missions (of which at least two hours would be on station at altitudes of 5,000 to 25,000 feet [1,524 to 7,620 meters]), and cruising speed, altitude, and service ceiling compatible with those of escorting general-purpose fighters. In addition to attack, the notional XVA(GP) aircraft would also be optimized for ECM, target towing, reconnaissance, airborne early warning, and photographic reconnaissance.

A manufacturer's model of the North American D-190 general-purpose attack aircraft.

In the fall of 1951 North American Aviation envisaged a proposal for a derivative of the XA2J to fulfill the parameters specified in the XVA(GP) requirement. Internally designated D-190, it was powered by two Allison T40-A-8 turboprops driving two contra-rotating propellers each measuring 14 feet (4.27 meters in diameter) and differed from the XA2J in having longer engine nacelles, a more blended upper fuselage, horizontal stabilizers with increased wingspan and surface area, and a wing thickness/chord ratio of 12 percent. It was 54 feet 11 in (16.74 meters) long and had a wingspan of 65 feet 9 in (20.04 meters) with tip tanks (61 feet 10 in [18.85 meters] without tip tanks), a height of 21 feet 1.92 in (6.45 meters), and a wing area of 766.87 ft2 (71.32 m2); the wings of the D-190 spanned 37 feet 2 in (11.33 meters) when folded. Gross weight without the tip tanks was to be 58,280 lb (26,436 kg), and maximum carrier takeoff would be 61,300 lb (27,806 kg), while top speed was 576 mph (927 km/h) at 24,000 feet (7,315 meters). A number of sources quote A2J-2 for the D-190, but this is not borne out by official documents, which indicate that XA2J-2 was applied to a proposed XA2J-1 with slightly increased gross weight.

The D-190 had four 20 mm cannons or alternately twelve 0.5 in (12.7 mm) machine guns in the lower nose, and offensive armament consisted of 6,000 lb (2,721 kg) or 12,000 lb (5,443 kg) of bombs along with mines, unguided air-to-ground rockets, and napalm tanks. When configured for nuclear strike missions, the D-190 was to carry a single Mk. 5 nuclear bomb and operate from modified Essex-class carriers as well as the Midway- and Oriskany-class carriers. As a land-based close support machine, it would have a gross weight of 67,899 lb (30,798 lb) and loiter over an enemy target for three hours at a range of about 345 miles (556 km), and North American also envisioned the D-190 as a photographic reconnaissance aircraft.

As it turned out, most of the design estimates for the D-190 did not meet the performance parameters outlined in the BuAer's XVA(GP) requirement, including range. Therefore, the D-190 project went no further than the drawing board. 

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.

Friedmann, N., 2022. U.S. Navy Attack Aircraft 1920-2020. Annapolis, MD: Naval Institute Press.

Ginter, S., 1992. North American AJ-1 Savage (Naval Fighters No. 2). Simi Valley, CA: Ginter Books.

The CL-1170: Lockheed's tailless patrol aircraft concepts

In 1968 the US Navy's Naval Air Systems Command (NAVAIR) began considering potential future requirements for a maritime patrol aircraft to replace the versatile Lockheed P-3 Orion and enter service in the 1975-1985 timeframe. Under contract from the Navy, Lockheed undertook a six-month study of concepts for a P-3 successor, and the company designation CL-1170 was applied to those studies. A total of six configurations ranging from conventional designs to tailless concepts were worked out.

The initial design studies under the CL-1170 designation took the form of conventional two- and four-engine designs configured to meet two different gross weight requirements of 150,000 lb (68,038 kg) and 500,000 lb (226,796 kg). The smaller aircraft would have a fuselage similar to that of the P-3 Orion, making it close in size to the Boeing 737, while the larger aircraft would be similar in size to the Boeing 747. A parallel series of CL-1170 studies looked at two different sizes of tailless aircraft designed for the same gross weight requirements, and those concepts utilized laminar flow control and future advances in high-bypass turbofan engines that would enable long, fuel-efficient loitering. To save weight, composite materials and aluminum alloys would be utilized for the CL-1170. All CL-1170 concepts investigated by Lockheed were to use multiple wheel, tricycle landing gear, and they would be capable of in-flight refueling.

Three-view drawing of the four-engine Lockheed CL-1170-6-2 concept

Two tailless CL-1170 concepts were worked out by Lockheed. The CL-1170-4-1 had two high-bypass turbofans situated below the trailing edge of the wing (two advanced turboprops were also considered), and it spanned 131 feet (40 meters) with a length of 97 feet (29.5 meters), a height of 27 feet (8 meters), a wing area of 1,890 ft2 (175 m2), a weight of 150,000 lb (68,038 kg), and a crew of ten. Armament for the CL-1170-4-1 comprised Mk 46 or Mk 50 torpedoes, mines, depth chargers, free-fall bombs, AGM-84 Harpoon anti-ship missiles, and AGM-65F Maverick air-to-surface missiles. The CL-1170-4-1 had a single vertical stabilizer and also utilized outrigger landing gear to ensure stability. The bigger design, the CL-1170-6-2, had a wingspan of 224 feet (68 meters), a wing area of 5,000 ft2 (464.5 m2), a length of 95 feet 6 in (29 meters), a height of 36 feet 9 in (11 meters), and a gross weight of 500,000 lb (226,796 kg). It was powered by four advanced high-bypass turbofans, two situated below the wing's trailing edge and two mounted above the aft fuselage (a combination of two turbofans and two turboprops was investigated as an alternate powerplant for the CL-1170-6-2), and it would have an endurance of 90 hours over a combat radius of 3,452 miles (5,556 km). Details of armament are lacking, but the CL-1170-6-2's weapons load was probably similar to that of the CL-1170-4-1.

In the end, NAVAIR made no preference for a select CL-1170 design, and the CL-1170 project was not proceeded with.

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.