MX-1554 designs from the Los Angeles Basin, part 2: the North American D-103, Douglas 1245, and Northrop N-65

As I mentioned previously, the Lockheed L-205 (aka Model 99) was one of the three winners of the MX-1554 announced by the US Air Force in July 1951, but it eventually was canceled without ever entering full-scale development due to weight issues and budget constraints. However, Lockheed was not the only company based in Los Angeles County to propose a design for the MX-1554 requirement. Three more aircraft manufacturers headquartered in Los Angeles County worked out with their own interceptor designs for the MX-1554 requirement, and paradoxically, they all had prior experience with design and development of all-weather interceptor fighters, putting them in a nominal position to come out with cutting-edge interceptor designs in response to MX-1554.

Desktop models of the twin-engine (top) and single-engine (bottom) North American D-103 interceptor designs.

North American Aviation's design work for the MX-1554 competition deserves discussion first with regards to MX-1554 proposals that didn't make the cut when it came to being chosen by the USAF for full-scale development. Although a handful of publications noted that North American envisaged and submitted two designs for MX-1554 in January 1951, until the 2010s, only photos of desktop models of these proposals were known in published literature (e.g. Buttler 2007). However, technical data for the two designs unearthed from North American Aviation company documents by Buttler (2013) has shed new light on those proposals, especially dimensions and performance. Judging from North American Aviation's list of Preliminary Design Designations, the company designation D-103 was allocated to the North American designs for the MX-1554 contest. Although it is would be wasteful to replicate the detailed account of the D-103 designs provided by Buttler (2013), these two proposals had slightly clipped high-mounted delta wings and  mid-fuselage horizontal stabilizers with slight dihedral. One of these designs was powered by a single turbojet (exact type unknown) fed by a large chin intake, and the other proposal had two side-by-side turbojets (exact type again is unknown) on the sides of the fuselage with their air intakes protruding from the wing roots. The armament for both North American proposals consisted of cannons in the forward weapons bay, Falcon air-to-air missiles in the center weapons bay below the centerline, and 2.75 in forward-firing air-to-air rockets in the rear weapons bay, and the twin-engine iteration was much heavier than the single-engine design. Despite being heavier than the single-engine D-103 proposal, the twin-engine D-103 iteration had a greater climb rate, with an estimated climb to 45,000 feet (13,716 meters) in 2.98 minutes compared to the single-engine D-103 being estimated to reach the same altitude in 3.60 minutes.

Three-view drawing of the Douglas Model 1245 (courtesy of National Archives)

In the same month that North American conceived the D-103 designs, the Santa Monica division of Douglas came out with a design submission for the MX-1554 of its own, designated Model 1245 by the company. Like a handful of aircraft projects conceived by Douglas Santa Monica, the Model 1245 bore some similarity to the Douglas X-3 Stiletto supersonic research aircraft in having the tail empennage situated above the exhaust pipe for the jet engine, but it differed from the X-3 in having a Wright J67 turbojet with air fed through a pair of air intakes ahead of the wing's leading edge, wings backswept at 35 degrees, a shorter nose, and horizontal stabilizers with 25 degree dihedral just below the base of the vertical stabilizer. Unlike the D-103, however, the Model 1245 would have no internal weapons bay, instead featuring six outboard hardpoints on which the Falcon missiles would be carried, while two drop tanks would be carried below the innermost pylons. The pilot accessed the cockpit of the aircraft through a hatch in the floor, and the Model 1245 was to be 66 feet 1 in (20.14 meters) long with a wingspan of 37 feet 6 in (11.43 meters), a wing area of 400 ft² (37.20 m²), and a top speed of 1,071 mph (1,723 km/h). The design philosophy of the fuselage, air inlets, and wings of the Model 1245 is rather reminiscent of that of the left fuselage nacelle of the proposed Douglas Model 1265 supersonic parasite bomber.

Left: Northrop N-65 proposal with diamond-shaped wings and horizontal stabilizers (drawing number PD-1170-1)
Right: Design iteration of the N-65 with an underslung TJ-15 turbojet (drawing number PD-1173-3)

Now this brings me to Northrop's forgotten interceptor designs for MX-1554. Northrop had worked on designs for a supersonic interceptor under the company designation N-53 back in 1949, but when the MX-1554 requirement was issued, in late June 1950 it shelved work on the N-53 to begin undertaking new supersonic interceptor studies under the designation N-65. Some initial N-65 designs resembled the N-53, but one early concept (drawing number PD-1168-6) resembled a manned version of the Northrop XSSM-A-5 Boojum supersonic cruise missile project with two General Electric J47 turbojets at the wingtips and armed with six air-to-air missiles carried within an internal weapons bay. Later N-65 configurations utilized the Wright TJ-15 turbojet (probably a variant of the Wright XJ61-W-3 turbojet), either in single- or twin-engine layout. One TJ-15 powered N-65 iteration, which bore the drawing number PD-1170-1, was 63 feet 4 in (19.3 meters) long with a wingspan of 45 feet (13.72 meters), and it sported high-mounted diamond-shaped wings with two TJ-15 turbojets situated the wing roots on the sides of the fuselage, and diamond-shaped horizontal stabilizers halfway up the vertical stabilizer; armament comprised four Falcon missiles that would be fired from forward-facing launch tubes in the belly and 16 2.75 in folding-fin unguided rockets to be carried within the outer rims of the turbojets. Another iteration, drawing number PD-1173-3, had a single TJ-15 housed in a ventral inlet below the fuselage and resembled one of Northrop's N-53 design studies in the wing planform, and it measured 58 feet (17.9 meters) long with a wingspan of about 34 feet (10.5 meters), with armament consisting of four Falcon missiles and 16 folding-fin unguided rockets housed in pop-out shoulder weapons bays aft of the cockpit. Other N-65 concepts included a design powered by two Pratt & Whitney J57 turbojets and an unmanned aircraft (drawing number PD-1188) similar in planform to the PD-1173-3. The latter was 52 feet 3.6 in (15.94 meters) long with low-mounted wings spanning 24 feet 9.6 in (7.56 meters), and it had one Westinghouse J46 turbojet in the rear fuselage fed by air intakes on the sides of the fuselage, while a single conventional warhead would be housed in the forward fuselage. 

In end, Northrop axed design work on the N-65 by October 1950 because of its growing preoccupation with the F-89 Scorpion all-weather fighter program, so no N-65 design was submitted to the US Air Force for consideration. The North American D-103 and Douglas Model 1245 that were submitted would be passed on in favor of the F-102 and XF-103. North American by then was undertaking production of the F-86D Sabre Dog (originally F-95) interceptor version of the F-86 Sabre that entered service in 1951, and the Douglas company was pretty busy with production of the AD (A-1) Skyraider, A3D (A-3) Skywarrior, F4D (F-6) Skyray, and DC-6, so it would almost certainly have not have had the resources to develop a long-range interceptor for the USAF.

References:

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

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

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