The North American D-85: an F-93 for the Navy

In May 1948 the US Navy's Bureau of Aeronautics issued the OS-113 requirement for an interceptor fighter capable of achieving 691 miles per hour (1,110 km/h) in level flight and reaching 50,000 feet (15,240 km) in just six minutes, as well as being able to achieve controlled diving flight at supersonic speeds at both medium and high altitudes. Seven companies -- Douglas (El Segundo), Grumman, Lockheed, McDonnell, North American, Republic, and Vought -- submitted bids for the OS-113 specification, a handful equipped with auxiliary rocket propulsion.

Left: Three-view drawing of the North American D-85
Right: D-85 interior arrangement

North American's design for OS-113 was given the company designation D-85. It drew heavily upon experience gained by North American in design of the YF-93 penetration fighter, featuring a pair of scoop-style side intakes, and power was provided by one Westinghouse J40-WE-8 turbojet as well as one 1,500 lb (6.7 kN) thrust RMI A600C4 rocket motor. The D-85 was 51 feet 6 in (15.70 meters) long with a wingspan of 40 feet 6 in (12.34 meters) (23 feet 8 in [7.21 meters] when folded), a wing area of 425.92 ft2 (39.61 m2), a gross weight of 20,823 lb (9,445 kg), and a top speed of 632 miles per hour (1,017 km/h). When using the jet engine only, the D-85 could reach a top speed of 637 miles per hour (1,025 km/h) and had a gross weight of 19,993 lb (9,069 kg).

The rocket motor of the D-85 was primarily designed for the climb from 35,000 feet (10,668 meters) to 50,000 feet (15,240 meters), and when used in level flight, the D-85 could achieve 668 miles per hour (1,075 km/h) in a dive at the operational altitude. Armament for the D-85 comprised 24 unguided air-to-air rockets housed in a streamlined lower fuselage package placed roughly level with the wing root trailing edge. The pilot could select how many rockets to fire, and the complete firing cycle would take about 1.5 seconds, and like other OS-113 submissions, the D-85 could fire all its rockets within half a second.

In late 1948, the McDonnell Model 58 was selected over other proposals (including the D-85) and ordered into full-scale development as the XF3H-1.

References:

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

A Skyray for the US Air Force: the Douglas D-614

In a previous post, I mentioned that the Santa Monica division of Douglas submitted the Model 1245 design for the MX-1554 competition, which ended up being won the Convair F-102 and Republic XF-103. Recently, however, it has come to my attention thanks to research by Jared Zichek that the Douglas El Segundo division worked on its own design for the MX-1554 requirement, designated D-614 by Douglas. Therefore, I am dedicating this post to the hitherto-unknown D-614 project.

Three-view drawing of the Douglas D-614 derivative of the F4D Skyray (Frank Simons collection via RetroMechanix)

The design of the D-614 was basically similar to that of the F4D Skyray in its wing planform and in lacking any horizontal stabilizers, but it differed in having a longer nose to house the interception radar and in having a slightly taller vertical stabilizer while lacking the catapult hooks of the Skyray. It measured 50 feet 8 in (15.44 meters) in length with a wingspan of 33 feet 6 in (10.21 meters) and a height of 15 feet 2 in (4.62 meters), and it had an empty weight of 14,109 lb (6,400 kg) and gross weight of 19,740 lb (8,954 kg) along with a wing area of 557 ft² (51.7 m²). Power was supplied by one 15,000 lb (67 kN) thrust Wright J67-W-1 afterburning turbojet, and armament comprised four to six underwing rocket canisters each containing six 2.75 in (7 cm) folding-fin unguided air-to-air rockets.

Like the Model 1245, the D-614 did not make the cut in the MX-1554 competition, and the Douglas El Segundo division was free to concentrate its fighter-related business on production of the F4D as well as development of the F5D Skylancer.

Hawthorne's lost Mohawk: the Northrop N-180

In the mid-1950s the US Army and US Marine Corps published a post-Korean War assessment discussing the vulnerabilities of their existing light observation aircraft, namely the L-19/OE Bird Dog, during that conflict. With this in mind, on behalf of the US Navy the two services initiated the TS-145 requirement for a two-seat, twin-turboprop light observation aircraft to operate from small, unimproved airfields under all weather conditions. The observation aircraft specified by TS-145 had to be faster and utilize greater firepower and heavier armor than the Bird Dog in order to address the vulnerabilities that the Bird Dog had faced during the Korean War.

Three-view drawing of the Northrop N-180 from the Northrop company documents.

Northrop's proposal for the TS-145 requirement was designated N-180 by the company. It was a twin turboprop design measuring 46 feet 1 in (14.05 meters) long with a wingspan of 44 feet 6 in (13.56 meters), and it featured a large cockpit placed ahead of the propeller arcs whereby the pilot and observer sat side-by-side. Power was provided by two General Electric T58-GE-4 turboprops each generating 1,020 shp (750 kW) (the Lycoming T53 was investigated as an alternate engine option for the N-180). The engine nacelles were mounted on the lower surface of the gull wing at the break where the wings levelled out. Missions to be carried out by the N-180 included day and night observation, artillery spotting, forward-position resupply with wing-mounted 750-lb packs, and liaison duties. The N-180 would have a service ceiling of 38,200 feet (11,643 meters) and a top speed of 299 mph (481 km/h) at an altitude of 5,000 feet (1,524 meters), and 150-gallon drop tanks and up to four smoke rockets for target marking would be carried below three hardpoints under each outer wing section. 

The OV-1 Mohawk, the winner of the TS-152 competition.

In November 1956, Northrop submitted the N-180 design, but it lost the TS-145 competition to the rival Grumman G-134 design. The winning G-134 design became the AO-1/OV-1 Mohawk, and even though the Navy withdrew from the OV-1 program, the Army pressed ahead with it. The Mohawk would go on to have a long and very useful career, especially during the Vietnam War.

References:

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

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.