Northrop's forgotten subsonic spyplane projects of the 1950s

On September 15, 1955, the Air Research and Development Command (ARDC) of the US Air Force in Wright Field, Ohio initiated a study contract for a high-altitude reconnaissance aircraft with slightly better performance than the Lockheed U-2, the soon-to-fly Martin RB-57D, and the in-development Bell X-16, pursuant to the WS-118P High-Altitude Reconnaissance Program (HARP) initiated by the USAF in January 1955 under Systems Requirement SR-12 for a purpose-built high-altitude spyplane. General Thomas Power, the commander of the ARDC, had felt quite upset at the USAF being left out of the loop regarding the U-2's development, which had received the blessing of the Central Intelligence Agency in spite of General Curtis LeMay (the head of the Strategic Air Command) deriding the U-2 as being too aerodynamically frail to be a practical reconnaissance aircraft. The RB-57D appears to have been considered Phase I of the HARP requirement while the X-16 was developed for HARP Phase II because the RB-57D and X-16 had been approved by the USAF for full-scale development in 1954. Thus, the study contract from the ARDC for a high-altitude spyplane with slightly greater performance than the RB-57D or X-16 became HARP Phase II-1/2, aiming for a spyplane with a service ceiling greater than 75,000 feet (22,860 meters) and an operating range of 2,762 miles (4,445 km) to become operational in 1958.

An artist's conception of the Northrop N-165 proposal for Phase II-1/2 of the WS-118P HARP program. 

In response to the parameters outlined for HARP Phase II-1/2, in late 1955 Northrop envisaged a clean-sheet design for a high-altitude reconnaissance plane, internally designated N-165 by the company. It was 68 feet (20.72 meters) long and had straight wings featuring a very large root cord and spanning 175 feet 6 in (53.49 meters) and having a wing area of 2,800 ft² (260 m²). Power was provided by six 6,075 lb (2,755 kg) thrust Westinghouse J54-WE-2 turbojets, of which four were housed in two paired underwing nacelles and the other two were arranged individually outboard of the podded nacelles. Reconnaissance systems envisaged for the N-165 included infrared and photographic spy cameras capable of gross mapping or high-resolution detailed imagery, mapping and search radars, and ferret sensors to assist in overflying enemy territory. The N-165 would have a cruising altitude of 80,950 feet (24,673 meters) along with a service ceiling of 77,500 feet (23,622 meters) when overflying enemy territory, and the top speed and operating range of this design were estimated at 475 mph (764 km/h) and 3,475 miles (5,593 km) respectively. The N-165 design was submitted by Northrop to the Air Force on May 16, 1956, but by this time successful flight tests of the U-2 had convinced the USAF that it needed to procure U-2s of its own, prompting Strategic Air Command to buy 29 U-2 aircraft (which were originally to be designated R-17 but ended up being designated U-2 anyway). This development, along with the Bell X-16 program being canceled in October 1955 just as the first aircraft was nearing completion and the start of flight tests of the Martin RB-57D, made HARP Phase II-1/2 redundant, and thus the N-165 and the rival North American D265-26 supersonic design envisaged for Phase II-1/2 were shelved.

Left: Northrop proposal for a backswept wing spyplane with boundary layer control surfaces
Right: Cutaway view of the N-204's crew compartment, engine layout, and reconnaissance equipment from the project documents 

Despite the end of the N-165 project, Northrop continued to look at advanced subsonic reconnaissance aircraft designs for the remainder of the late 1950s. In 1956, Northrop proposed a huge subsonic high-altitude spyplane utilizing boundary layer control (BLC), which had slender backswept wings spanning 195 feet (59.43 meters) with a wing area of 3,180 ft² (295 m²), airfoil-shaped braces between the wings and the lower fuselage, and two underwing turbojets. This design had an unrefueled operating range of 6,329 miles (10,186 km), and as with all BLC aircraft designs from Northrop, it had suction slots on the forward part of the upper and lower wing surfaces to reduce aerodynamic drag at high altitudes over enemy territory. In the fall of 1957 Northrop conceived a new high-altitude reconnaissance aircraft design, the N-204, which measured 105 feet 8 in (32.2 meters) in length with a wingspan of 273 feet 9 in (83.44 meters), a wing area of 5,000 ft² (464.52 m²), a gross weight of 34,000 lb (15,422 kg) and a maximum takeoff weight of 75,000 lb (34,019 kg). The N-204 married the U-2's long, slender fuselage with the high-aspect ratio wings of the RB-57D, along its wings were much bigger and it also had a butterfly-shaped tail along with dual-wheel main landing gear and a tail-dragger landing skid. Power was to be supplied by eight 6,075 lb (2,755 kg) thrust Westinghouse J54-WE-2 turbojets, with four engines buried in each outboard end of the wing center section; uprated 6,750 lb (3,062 kg) thrust J54-WE-228Fs and the far more powerful 10,000 lb (4,535 kg) thrust PD-50 derivative of the J54 were investigated for future incorporation into the N-204 design. The N-204 itself was to have a range of 3,452 miles (5,556 km) (4,488 miles [7,222 km] with in-flight refueling) and a speed of 552 mph (889 km/h) at an altitude of 85,000 feet (25,908 meters) with J54-WE-2s (increased to 90,000 feet (27,432 meters) with more powerful engines. It had a pressured compartment for a crew of two, a pilot in the front seat and either a flight engineer or reconnaissance systems officer seated behind and below the pilot, and three camera or surveillance equipment packages were situated behind the N-204's crew compartment.

Northrop estimated that if the US Air Force greenlighted full-scale development of the N-204 project in January 1958, then the N-204 could enter service by January 1960. It is interesting to note that Northrop looked at incorporating low-observable technology into the N-204 proposal to make it undetectable by Soviet air defenses because LO itself was being investigated by Convair and Lockheed for their designs for a high-speed U-2 successor under the CIA's Project Gusto beginning in 1958. Although the N-204's low-observable capabilities might have potentially made it invisible to enemy radars at high altitude, like the earlier N-165, the N-204 project would never materialize because of Northrop's growing focus on the F-5 and T-38 programs and the fact that the U-2 was doing most of the reconnaissance duties which the N-204 would have conducted.

Reference:

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