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. 

MX-1554 designs from the Los Angeles Basin, part 1: the Lockheed L-205

In June 1950, the US Air Force initiated the MX-1554 requirement (aka 1954 Interceptor) for a long-range supersonic interceptor to defend the US from the Soviet Union's recently deployed Tupolev Tu-4 strategic bomber (a reverse-engineered copy of the B-29) and still-in-the works gas turbine-powered Tu-16, Tu-95, and M-4. One of the winning designs for the MX-1554 contest, the F-102 Delta Dagger built in San Diego, has been extensively covered in numerous publications, and some people, myself included, know that the unbuilt Republic XF-103 design powered by both a turbojet and a ramjet was also a winning entrant in the MX-1554 competition, although it never reached the hardware phase. However, what has been heavily overlooked is that Lockheed entered its own design into the MX-1554 competition and was awarded a development contract, only for it to be subsequently canceled before that design could be given a military designation, and equally forgotten are designs by North American and Northrop for the MX-1554 requirement. Therefore, this and the next post will cover designs by Lockheed, North American, and Northrop devised for MX-1554.

A desktop model of the Lockheed L-205 (Model 99) interceptor. The similarity of the dorsal air intake to that of the F-107 is apparent.

As early as 1949, Lockheed had been working on design studies for a lightweight jet interceptor, known by the company designation L-190, which covered proposals with straight, delta, and variable-geometry wings. None of the L-190 studies never materialized, but after the Request for Proposals (RFP) for the MX-1554 competition was released in June 1950, Lockheed immediately returned to the concept of a purpose-built interceptor when it conceived a design for an all-weather interceptor, designated L-205 by the company, by the beginning of January 1951. The overall L-205 design submission had straight wings with tapered leading and trailing edges like those on the F-104 Starfighter but nevertheless retained the tail empennage of the XF-90 prototype penetration fighter. It measured 63 feet 9 in (19.4 meters) long with a wingspan of 30 feet 4 in (9.2 meters), a wing area of 300 ft² (27.9 m²), and a gross weight of 32,125 lb (14,572 kg), and power was provided by one 15,000 lb (66.7 kN) thrust General Electric J53 turbojet fed by air flowing through a dorsal air intake behind the cockpit (similar to that seen on the North American F-107). Unlike those of the F-104, however, the L-205's wings were low-mounted and lacked anhedral. The L-205 would be armed with six Falcon air-to-air missiles housed in a mid-lower fuselage bay and twenty 2.75 in (7 cm) folding-fin unguided air-to-air rockets placed on the sides of the bay, and it would climb to 40,000 feet (12,192 meters) in 1.6 minutes, while the service ceiling was to be 63,000 feet (19,202 meters) and operating range would be 1,760 miles (2,834 km).

On July 2, 1951, the US Air Force declared the Convair Model 8 along with the Lockheed L-205 and Republic AP-57 (the latter one of the three Republic designs proposed for the MX-1554 requirement) the winners of the MX-1554 competition, and these designs were given the go-ahead to proceed to the full-scale mock-up phase under a Phase I development contract. After being awarded a Phase I contract, the L-205 received the Basic Model Number 99, hence it being also called Model 99. However, the US Air Force couldn't afford to fund all three interceptor designs, and the L-205/Model 99 also was heavier than the Convair design and thus would have had consequent reductions in performance, so the USAF canceled the L-205 project by late 1951, even as the Convair Model 8 and Republic AP-57 were given the designations YF-102 and XF-103 respectively.

Although the L-205 project ended up becoming a loser-turned-winning design for fiscal reasons in spite of having been selected for development along with the F-102 and XF-103, Lockheed would apply a few features of the L-205, namely the tapered straight wings, to design of its future F-104 Starfighter, the first American supersonic lightweight jet fighter to be built.

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. 

Lockheed's first gas turbine-powered Connie: the L-151

The Lockheed Constellation family was unquestionably one of the finest airliner dynasties to come of age after the end of the World War II, spawning evolutionary developments such as the improved L-649 and L-749 versions of the original Constellation, the L-1049 Super Constellation, the L-1649 Starliner, and the EC-121 Warning Star, but also the turboprop-powered L-1249 (R7V-2/YC-121F) and the unbuilt XB-30 heavy bomber. The L-1249 that was derived from the Super Constellation constituted the first instance of any variant of the Constellation family being built with turboprop engines, although it never advanced beyond the prototype stage. However, what has been overlooked in books on the Constellation is the fact that even as World War II was winding down, Lockheed looked at fitting the baseline Constellation with gas turbine powerplants.

Left: Three-view drawing of the Lockheed L-151-1 jet airliner
Right: Three-view drawing of the L-151-2 along with a side view of the L-151-3 (upper right)

In 1945, the development of jet engines was destined to make the Lockheed Constellation and many other large piston-powered American transport aircraft designs envisaged during the years of US involvement in World War II slowpokes compared to jet or turboprop aircraft designs being worked on by US aircraft manufacturers in the 1943-1945 timeframe. Lockheed had developed America's first jet engine design, the L-1000 (military designation XJ37), to power its L-133 jet fighter project, but when the L-133 itself was deemed too advanced for its time and the initial L-1000 design turned to be more complex than imagined by engineer Nathan Price, it ended up being redesigned as a simple jet engine comprising two sixteen-stage axial compressors connected by an intercooling stage. Capitalizing on flight testing of the P-80 (later F-80) Shooting Star jet fighter, Lockheed in early 1945 conducted design studies to equip the Constellation airliner with gas turbine engines under the company designation L-151. The first design, called L-151-1, replaced the L-049's Duplex Cyclones with six L-1000 turbojets in two underwing nacelles (three engines per nacelle), and judging from what little technical data has survived, the L-151-1 had the same length and wingspan as the commercial L-049 but would have a slightly higher gross weight of 100,000 lb (45,359 kg). Two turboprop-powered L-151 iterations were worked out, the L-151-2 with four General Electric TG-100 turboprops and the L-151-3 with four Westinghouse turboprops. These designs had same gross takeoff weight as the L-151-1 and compared to the L-049, they would have greater top speed, with the L-151-2 being designed to cruise at 335 mph (539 km/h) and the L-151-3 having a cruising speed of 370 mph (595 km/h). The L-151-2 and L-151-3 also had a higher service ceiling and rate of climb at 18,000 feet (5,486 meters) than the L-049, with L-151-2 having a climb rate of 610 ft/min (3.10 m/s) and capable of reaching a 28,000 ft (8,534 meter) altitude and the L-151-3 featuring an estimated climb rate of 1,060 ft/min (5.348 m/s) and an altitude of 31,000 feet (9,449 meters). Nevertheless, the one performance pitfall of the L-151-2 and L-151-3 designs was operating range. The L-151-2 and L-151-3 would have had operating ranges of 3,500 miles (5,633 km) and 3,100 miles (4,989 km) respectively, well below the L-049's maximum range of 4,400 miles (7,081 km). The dearth of specifications for the L-151-1 makes it unclear whether the L-151-1's range would have been equivalent to or exceeded that of the Constellation, but the marginally lower operating range of the L-151-2 and L-151-3 compared to that of the L-049 meant that Lockheed did not pitch those designs to the airlines. In the meantime, the L-1000 engine which the L-151-1 would have used ended up being cancelled by the late 1940 without leaving the development phase, and the L-151-1 also would never reach the hardware phase.

Front views of the different L-151-5 variations accompanied by side and bottom views of different auxiliary turbojet placements proposed for the L-151-5 (far-right)

This was not the end of the L-151 story, however. In 1950, Lockheed took advantage of its development of the L-1049 Super Constellation with a stretched fuselage by envisaging a spree of design studies for an L-1049C with two 4,200 lb (18.7 kN) thrust auxiliary jet engines, designated L-151-5. The proposed L-151-5 was quite akin to the B-36 Peacemaker being fitted with four auxiliary General Electric J47s in two podded pairs for extra speed beginning with the B-36D version, and a number of L-151-5 schemes were proposed as follows:

• Mounting the auxiliary turbojets below underwing pylons (as with the B-36)
• Placing the auxiliary turbojets at the rear of the outboard R-3350 Duplex Cyclone radial piston engines to provide minimum drag for jet engine out condition
• Placing the auxiliary turbojets on the wingtips to provide minimum drag when all engines were operating (with or without auxiliary fuel tanks pyloned below the outboard wing sections)

Lockheed calculated the performance of the L-151-5 design and determined that when compared with the L-1049C, the L-151-5 offered 25 percent greater block speed and a shorter takeoff distance of 3,750 feet (1,143 meters) along with a slightly lower operating cost. Still the operating range of the L-151-5 would be slightly lower than that of the L-1049C due to the drag generated by the jet engines when they were not in operating condition. Even though the L-151-5 would have been easy to create by equipping an L-1049C airframe with auxiliary turbojets because it required no substantial structural modifications compared to the L-151-2 and L-151-3, no airline expressed an interest in the L-151-5 at all.

Notwithstanding the fact that the L-151 was used by Lockheed as a catchall company designation for a variety of proposals to fit the Constellation with gas turbine engines, one good question arises: would the L-151-1 have been an outstanding and profitable airliner with respect to its impact on passenger air travel in the late 1940s and early 1950s had it been built? There's no question that US industry was developing more advanced jet engines with high power/weight ratios by the time that World War II ended, including the Allison J35 and General Electric J47, but since the L-1000 engine had offered the L-133 project far greater estimated top speed than that of the Shooting Star or Airacomet, in my own opinion, the L-151-1 would have carried out passenger flights at much shorter flight times, although it have somewhat slower the Boeing B-47, B-52, and 707 due to its straight wings.

References:

Slayton, B., 1999. "The Lockheeds That Never Were, Part II." AAHS Journal 44 (2): 102-113.

Lost Broncos from Burbank and El Segundo

Much has been written about the Light Armed Reconnaissance Aircraft (LARA) competition of the mid-1960s for an aircraft designed to carry out counter-insurgency (COIN) operations, which produced the North American OV-10 Bronco (which won the LARA competition) and the rival, prototype-only Convair Model 48 Charger. However, the Model 48 Charger, despite being manufactured in my home state, was not the only LARA design conceived in southern California. Two additional companies based in southern California put out design bids for the LARA competition, one emanating from Burbank and another coming from the design offices of the El Segundo Division of Douglas. 

Company artwork of the Douglas D-855

Following the issuance of the tri-service LARA requirement in late 1963, nine companies submitted bids for the LARA competition by March 1964, of which three (Convair San Diego, Douglas El Segundo, and Lockheed) were based in southern California. The Douglas proposal, designated D-855, took the form of a high-wing airplane with a T-tail empennage, a rear loading door, a crew of two seated in tandem, a length of 35 feet (10.67 meters) long, and a wingspan of 29 feet (8.83 meters). The D-855 would carry six fully-equipped troops or a 6,000 lb (2,721 kg) payload in the fuselage, and various weapons loads (e.g. folding fin unguided air-to-ground rockets and bombs) were carried below five hardpoints, one situated below the fuselage centerline, two below the wing roots, and two positioned just inboard of the wingtips. Top speed of the D-855 was to be 230 mph (370 km/h), and power would be provided by either two United Aircraft of Canada T74 or Garret AiResearch T76 turboprops. The El Segundo Division of Douglas informally referred to the D-855 as the "Skyraider II", a testament to its rich experience with attack aircraft design.

Full-scale mockup of the Lockheed CL-760 with external weapons carried onboard or individual displayed on the ground. 

The Lockheed submission for the LARA competition, the CL-760, shared the high-wing layout and the  tandem seating arrangement for the two crewmembers with the D-855, but it had a conventional tail empennage whose horizontal stabilizers formed a triangular planform. It measured 40 feet 3.5 in (12.28 meters) long with a wingspan of 30 feet (9.14 meters), an empty weight of 5,106 lb (2,316 kg), a gross weight of 9,270 lb (4,205 kg), and a top speed of 325 mph (523 km/h). Accommodations were provided for either eight fully equipped troops or six paratroopers in the cargo hold, and power was to come from two Garrett T76 turboprops, while the retractable main landing gear and four 7.62 mm machine guns would be housed in two fuselage blisters. The CL-760 had four racks below the wingtips (two below each wingtip) and a fifth pylon below the fuselage centerline for carrying various weapons, including folding-fin unguided air-to-ground rockets, air-to-surface missiles, and bombs. When configured for reconnaissance, the CL-760 itself would carry advanced cameras and sensors to allow it to loiter over positions and movements of enemy insurgents in various terrains such as dense forests and open fields at low altitudes. 

In August 1964, the US Navy declared North American NA-300 was declared the winner of the LARA competition (although the US Air Force and US Marine Corps had preferred the rival Convair Model 48 design, of which a prototype was under construction at the time of the announcement of the outcome of the LARA competition), receiving the designation OV-10 and the official name Bronco. Because the Douglas El Segundo Division and Lockheed lost the LARA competition to the NA-300, the Model 48  would be the only competing LARA design from southern California to be built and flown, making its first flight on November 25, 1964, eight months before the OV-10 took to the skies.

References:

Francillon, R., 1987. Lockheed Aircraft Since 1913. Annapolis, MD: Naval Institute Press. 

Ginter, S., Auten, H., Knebel, J, and Fink, J., 1997. Convair Model 48 Charger (Naval Fighters No. 39). Simi Valley, CA: Ginter Books.