Lockheed's VTOL flat-rising jet fighter designs of the late '50s and early '60s

In the late 1950s, the US Air Force and Navy abandoned the tail-sitter concept as unfeasible and instead looked to the concept of lift jets and lift fans being pioneered in the United Kingdom by Rolls-Royce in the 1950s as the most suitable method of VTOL for a combat jet. With the lift jets (or lift fans) situated in the center fuselage, the pilot would easily land his plane on an airfield or any unpaved surfaces. In addition to lift jets/lift fans, the US aircraft industry looked at equipping VTOL jet fighters with jet engines housed in nacelles that could swivel upwards in VTOL mode but tilt longitudinally in forward flight. The Bell Aircraft Corporation of Buffalo, New York, was the chief leader in developing flat-rising VTOL jet aircraft in the US during the late 1950s, as exemplified by the Model 65 experimental tilt-jet and the X-14 vectored thrust technology demonstrator, before turning to the design of the D-139, D-188, and D-188A VTOL combat jets, the latter whose design philosophy influenced West Germany's EWR VJ 101C prototype VTOL jet fighter. Bell, however wasn't the only US company to undertake design studies for flat-rising VTOL combat jets. Lockheed decided to work out flat-rising VTOL jet fighter designs of its own after becoming aware of the impracticality of the tail-sitter idea, and the resulting panoply of proposals for flat-risers from Lockheed in the late 1950s would range from designs with lift jets/lift fans to aircraft with swiveling jet engines.

Top: Lockheed CL-346-1 (left) and CL-346-31 (right) designs
Bottom: Artist's conception of the CL-407 heavy fighter/light bomber

Around the time that design studies for the CL-295 and CL-349 tail-sitter projects concluded, Lockheed proposed a tilt-jet VTOL interceptor/tactical strike aircraft under the designation CL-346-1. This design retained the airframe of the F-104 Starfighter but differed in eliminating the fuselage engine and instead having two General Electric J79 turbojets in wingtip nacelles, and the horizontal stabilizer was situated on a ventral fin below the tail empennage. The J79s would tilt upwards for vertical take-off and when the CL-346-1 transitioned to forward flight, the engines would tilt horizontally so the aircraft could cruise to Mach 2 at 60,000 feet (18,288 meters). The CL-346-1 would have carried four Sidewinder air-to-air missiles below the wings in its role as an interceptor or a single nuclear bomb below the fuselage in tactical strike role. Another CL-346 design study, the CL-346-31, was an F-104 airframe with the entire propulsion housed in the inner wing section, with swiveling units and four additional lift jets in the fuselage, and the tail empennage had a tailwheel and long front undercarriage struts to provide good exhaust clearance during vertical take-off. A series of VTOL heavy fighter/light bomber designs were worked out by Lockheed under the designation CL-407, including the canard delta wing CL-407-37/40 with two jet engines in the rear fuselage that could swivel for VTOL and three lift jets situated behind the cockpit, and the canard delta wing CL-407-47-2 with two jet engines that could swivel backwards for VTOL and wingtips that could fold downwards. The CL-407 would have had a top speed of Mach 3 and an altitude of 70,000 feet (21,336 meters).

Three-view drawing of the CL-704

Beginning in 1958, Lockheed envisaged a VTOL derivative of the F-104G, the CL-521-1. which was similar to the F-104G but differed in having two large wingtip pods, each containing four Rolls-Royce RB.108 turbojets. The fuel in the wingtip pods was optionally transferred to the fuselage for use in the General Electric J79 and the engine pods could easily be removed, returning the aircraft to non-VTOL form and allowing the carriage of wingtip fuel tanks or missiles. The CL-521-1 would have a combat radius of 287 miles (460 km) and a top speed of Mach 1.4 when carrying the engine pods, although its range/payload could be increased if VTOL wasn't required, and armament comprised the 20 mm M61 Vulcan cannon and 4,000 lb (1,814 kg) of Sidewinder missiles, air-to-ground rocket, free-fall bombs, and tactical nuclear weapons. The CL-704 was a reconnaissance version of the CL-521-1 designed to conduct reconnaissance missions from NATO bases in Europe, with a secondary strike capability, and it was similar to the RF-104G in housing three KS-67A spy cameras. A total of 34 design variations of the CL-704 were probably worked out, even though documentation is lacking. 

CL-802-12 VTOL jet fighter design

From January 1962 to May 1963, Lockheed undertook design studies for a single-seat carrier-based multi-role VTOL combat jet, the CL-706, of which one proposal, the CL-706-13, was powered by two General Electric X-84 turbofans and ten 4,000 lb (17.79 kN) thrust Continental Model 365 lift jets, of which six were housed in the wingtip pods and four were situated in the forward fuselage section. Armament for the CL-706-13 consisted of a rotary 30 mm cannon, free-fall bombs, rockets, and air-to-surface missiles. A series of additional flat-rising VTOL supersonic jet fighter designs was devised under the company designation CL-802. The CL-802-12 was an F-104 Starfighter with the General Electric J79 turbojet moved further back and twelve 4,000 lb (17.79 kN) thrust Continental Model 365 lift jets, of which eight were housed in the wingtip pods and four were situated behind the cockpit, and it could be used for close air support, cargo transport, and light observation. The performance of the CL-802-12 would have been only Mach 1 or less, slower than other VTOL Starfighter design studies. The CL-802-7 was a two-seat Mach 2 fighter design with a single tail fin, two afterburning turbofans, and eight lift fans in the center fuselage section, and it would have carried four underwing munitions plus a variety of weapons in an internal weapons bay. On the other hand, the CL-802-14-3 proposal featured a two-seat Mach 2 VTOL jet fighter with two General Electric J79 turbojets in nacelles on the rear fuselage and ten Continental Model 365 lift jets (four behind the cockpit, four behind the wing's trailing edge, and two towards the tail). Armament for the CL-802-14-3 would have comprised a rotary cannon, underwing air-to-air or air-to-surface missiles, and a tactical nuclear weapon in the internal weapons bay.

Lockheed CL-757 VTOL test rig

To test the flight behavior of its VTOL jet fighter designs, Lockheed built an experimental VTOL test rig, the CL-757, which had an open cockpit for the pilot and observer and measured 23 feet (7 meters) long and 32 feet (9.75 meters) wide, with a gross weight of 7,920 lb (3,592 kg). Power came from six upright General Electric turbojets on each side of the craft, and those engines were supplied and fitted by US Air Force technicians. A total of 19 test flights of the CL-757 were carried out at Edwards Air Force Base in mid-1963, of which the initial ones were tethered. Although the Lockheed flat-rising VTOL jet fighter designs envisaged in the late 1950s and early 1960s looked good on paper and offered operational advantages over the earlier Lockheed tail-sitter designs in terms of landing characteristics, not a single one of Lockheed's flat-rising VTOL jet fighter projects progressed beyond the drawing board, largely because the US Air Force had lost interest in VTOL jet fighter technology and Lockheed itself was over-committed to other projects, including the A-12/SR-71 Blackbird and L-2000 supersonic airliner. Nonetheless, the VTOL propulsion systems utilized by Lockheed for its design studies for flat-rising VTOL combat jets would find their way into the EWR VJ 101C, Hawker Siddeley (later British Aerospace) Harrier, and Hawker Siddeley P.1154 combat aircraft.

References:

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

Rose, B., 2013. Vertical Take-off Fighter Aircraft. Hersham, UK: Ian Allan Publishing. 

Last VTOL tailsitter day fighter designs from southern California

In early 1954 the Ryan Aeronautical Company was asked by the US Air Force to study the notion of a tail-sitting supersonic VTOL jet fighter. Drawing upon experience in designing the Model 38 and X-13 Vertijet, it proposed the Model 84 hook-suspended jet fighter, of which 14 different single- and twin-engine configurations were worked out. I was initially proposed to power the Model 84 with one Pratt & Whitney J75 turbojet, but Ryan later felt that two side-by-side General Electric J79 turbojets were essential to give the Model 84 a better combat radius. One Model 84 iteration, the Model 84F-7, had two 20,000 lb (89 kN) thrust General Electric X-301 afterburning turbofans, a top speed of Mach 2.5, and armament comprising 20 mm cannons and air-to-air missiles or one free-fall nuclear weapon. The Model 84 design resembled the Convair F-102 Delta Dagger and Dassault Mirage IIIA in having engine inlets on the sides of the forward fuselage, a delta wing, and a single vertical stabilizer. A hook would be fitted below the forward fuselage, and the pressurized cockpit was fitted with a swiveling ejector.

 

3-view drawing of the Ryan Model 115C tail-sitting supersonic VTOL jet fighter

In 1955 Ryan submitted the Model 84 design to the Wright Air Development Center, and after this proposal was well-received, it began work in 1955 on an improved supersonic VTOL tail-sitting fighter design, the Model 112, which had two General Electric J79s. The Model 112 design study continued into 1956, and Ryan offered two versions of the Model 112 to the US Navy, the Model 113 and Model 114. Meanwhile, the Air Force decided to continue funding Ryan's supersonic VTOL tail-sitter studies, and thus Ryan proposed the Model 115, which was similar to the Model 112 but had a longer fuselage to accommodate a larger bay housing a single tactical nuclear weapon or four air-to-air missiles. The final version, the Model 115C, envisaged in 1957, had a slightly stretched fuselage, greater operating range, circular inlets for the J79s, and greater range, and the airframe would be made from stainless steel. Alternative methods of boosting take-off performance were considered, including water injection and use of exotic fuels, and the Model 115C also was to used a tricycle landing gear. Despite promising lower operating costs, none of the Ryan designs for supersonic VTOL tail-sitter designs progressed to the hardware phase.

Top: Convair Configuration IVa
Bottom: North American design study for a supersonic tailsitter day fighter

Even before testing of the Convair XFY, Convair investigated design studies for supersonic VTOL tail-sitting jet fighters, which like the turboprop-powered XFV hewed to the delta wing design philosophies for the F-102 Delta Dagger. Under a six-month USAF contract to study a lightweight supersonic tail-sitter issued in December 1953, Convair devised several proposals for supersonic VTOL tail-sitters, all of which shared a delta wing. One of the first supersonic VTOL tail-sitter design studies to emerge had a fuselage containing a jet engine fed by air flowing through a nose intake and unguided rockets carried in retracted forward-located packs. The aircraft stood on four dampened struts in wing nacelles and two vertical stabilizers, and the cockpit was housed in a large pod on the vertical stabilizer, with the pilot lying in a prone position. A revised design had the cockpit at the front of the aircraft, surrounded by the engine inlet. The Convair Configuration IVa had a fairly typical cockpit canopy design, an air inlet for the turbofan below the cockpit, and a ventral pod housing one M61 Vulcan 20 mm cannon and the landing strut. Wind tunnel tests of this design at NACA Langley in 1954 showed this proposal to be aerodynamically sound, but concerns about directional stability prompted Convair to devise a new Configuration IV design with delta-shaped canards on the nose and the ventral fin eliminated. North American is also known to have worked on a design for tail-sitting VTOL supersonic fighter, which stood upright on three vertical stabilizers and had three jet engines in the rear fuselage for vertical takeoff and four more in pairs in wingtip-mounted nacelles for forward flight, but this proposal is known only from drawings and no technical data is available at the moment. 

Selected Lockheed CL-295 design studies, clockwise from top to bottom: CL-295-1, CL-295-3, CL-295-4, and CL-295-2. The CL-295-2 was also offered to the Navy as the CL-349-17.

In the meantime, Lockheed in 1954 investigated several designs for tail-sitting VTOL supersonic jet fighter under the company designation CL-295. The first two proposals, the CL-295-1 and CL-295-3, were based on the F-104 Starfighter and featured a retractable hook below the nose similar to that of the Ryan supersonic VTOL tail-sitters, as well as an exhaust flow control system, reaction jets, and a secondary stabilizing horizontal stabilizer for VTOL. The CL-295-1 was powered by one Wright TJC32C4 turbojet whereas the CL-295-3 used one General Electric X-84 turbofan and had a slightly shorter fuselage and wingspan in addition to being lighter, and both proposals would be armed with one 20 mm M61 Vulcan cannon and reach a speed of Mach 2. The next CL-295 design, the CL-295-4, was powered by two General Electric X-84 turbofans and stood on two vertical stabilizers and two wingtip nacelles when standing upright for VTOL, while featuring a canards on the nose. Successful test runs of the General Electric J79 turbojet prompted Lockheed to propose a J79-powered derivative of the CL-295-4 with twin dorsal vertical stabilizers, the CL-295-2. A version of the CL-295-2 was also offered to the US Navy as the CL-349-17 in response to the Navy's TS-140 specification for a VTOL jet fighter. The CL-295-68 was similar to the F-104 in having fuel tanks at the wingtips but had rear-mounted backswept wings, a cruciform tail empennage similar of that of the earlier XFV, and one Wright J67 turbojet with low-speed vane control in the exhaust flow, fed by air flowing through a ventral engine intake. The final design for the CL-295, the CL-295-77, had nose canards as in the CL-295-2/4 and CL-349-17 but had rear-mounted backswept wings with two General Electric X-84 turbofans at the wingtips. Armament for the CL-295-77 comprised Sidewinder air-to-air missiles, and the CL-295-77 used vanes in the exhaust flow and compressed air nozzles in the wingtips for low-speed vertical control, with normal control surfaces for horizontal flight.

By the late 1950s, the US Air Force and US Navy had come to the conclusion that the tail-sitter idea was conceptually a dead end when it came to operational practicality, and after hearing the new of flight tests of the Rolls-Royce Thrust-Measuring Rig (nicknamed the Flying Bedstead) realized that the best way for jet fighter to achieve vertical take-off and landing was to use swiveling jet engines, lift jets, and lift fans. In other word, by allowing a jet fighter to rise vertically above the ground through means of downward air, lift fans, swiveling jet engines, and separate jets could give the pilot visibility during the process of landing his/her plane vertically. Thanks to the British, the US armed forces and the aircraft industry in southern California could now look in this new approach to vertical take-off and landing for jet fighters.

References:

Bradley, R., 2013. Convair Advanced Designs II: Secret Fighters, Attack Aircraft, and Unique Concepts 1929-1973. Manchester, UK: Crécy Publishing.  

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

Rose, B., 2013. Vertical Take-off Fighter Aircraft. Hersham, UK: Ian Allan Publishing.

Convair's CX-4 concepts

In 1962-1963, pursuant to the CX-4 requirement issued by the US Air Force in 1962 for for a heavy-lift transport to replace the C-133, the Convair San Diego division of General Dynamics worked out a series of advanced concepts for a heavy-lift strategic airlifter. Convair's San Diego division had some previous experience with jet airlifter design, having proposed the Model 63 design for the SOR-182 competition won by the Lockheed C-141 Starlifter, and it therefore decided that participation in the CX-4 program was worth a try.

Top: Six-engine concept by Convair San Diego for CX-4
Bottom: Convair's preferred concept for CX-4 with four STF-200-D2s

Convair San Diego's resulting design studies for the CX-4 requirement investigated three turboprop and six turbofan options. One set of designs focused on a heavy-lift transport with six Pratt & Whitney T57 turboprops fitted with variable camber propellers, and the turboprop-powered iteration measured 195 feet 6 in (59.6 meters) long with a wingspan of 210 feet (64 meters), a gross weight of 560,000 lb (254,200 kg), a payload capacity of 165,000 lb (74,842 kg). However, the propellers extended over the whole span and offered very little ground clearance. The initial baseline jet-powered design for CX-4 was powered by six Pratt & Whitney TF33 turbofans and had a low-mounted horizontal stabilizer, and alternate engine options for this iteration included six Pratt & Whitney STF-200-D2s or eight turbofans housed in four paired nacelles. The preferred CX-4 design from Convair San Diego was powered by four STF-200-D2s and measured 204 feet 6 in (62.3 meters) long with a wingspan of 230 feet (71.3 meters), a gross weight of 546,000 lb (248,200 kg), and a T-tail configuration. The high- and low-mounted CX-4 designs featured a side-hinged nose positioned ahead of the cockpit and a tail ramp to allow both drive-through loading and air-dropping, and the four-engine iteration had the flight deck raised in a bulge over the cargo area.    

In addition to land-based studies, Convair looked at an amphibious CX-4 transport proposal to address the possibility that a destination airbase might not be available and not at every brushfire war location. It was powered by four STF-200-D2 turbofans and measured 204 feet 6 in (62.3 meters) long with a wingspan of 234 feet (71.3 meters) and a payload capacity of 165,000 lb (74,842 kg). The amphibious CX-4 iteration featured a pair of clamshell doors, which were designed to load cargo at a land base and deliver it to a seadrome, and the aft fuselage had a side-loading door.

In November 1963 the CX-4 program was renamed CX-HLC (Heavy Logistics Carrier), which changed its name to CX-HLS (Heavy Logistics System) in January 1964. None of Convair's designs would ever see the light of day, and Convair itself neglected to take part in the CX-HLS competition.

References:

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

San Diego's forgotten lightweight naval jet fighter

In the early 1970s, the US Navy took heed of the fact that the unit cost of each F-14 was high and that a lightweight jet fighter comparable to the F-16 and YF-17 to complement the F-14 could be cheaper to buy in quantity. With the requirements for what became the Lightweight Fighter (LWF) program preparing to be formulated, the Convair San Diego Division of General Dynamics along with Vought decided to take a serious look at a carrier-based jet fighter in the same weight class as the F-16 and YF-17.

Drawing of a 1/15th scale wind tunnel model of a Configuration 23 design with canard deltas

The carrier-based lightweight jet fighter design studies conceived by Convair San Diego from 1970 to 1973 were internally known as Configuration 23 (sometimes incorrectly dubbed "Model 23"). Technical data for the Configuration 23 is wanting, but the Configuration 23 itself resembled the F-16 in having a chin air intake, a single vertical stabilizer, and two fairings for automatic guns below the wing roots, and it had a gross weight of 26,000 lb (11,974 kg). One Configuration 23 iteration envisaged by Convair San Diego sometime in 1973 had delta canards situated just ahead of the delta wing, and it underwent wind tunnel testing as of November 1973. Based on dimensions of the wind tunnel model, the canard delta Configuration 23 design was probably 46 feet 2 in (14.1 meters) long with a wingspan of 27 feet 8 in (8.4 meters). Armament for the Configuration 23 designs probably comprised two Sparrow or Sidewinder air-to-air missiles, perhaps mounted below underwing pylons. 

In the end, the Convair San Diego Configuration 23 design studies never saw the light of day, but General Dynamics would utilize some features of the Configuration 23, including the single jet engine, delta wing, and chin air intake, when jointly designing the losing Model 1600 submission for the Navy Air Combat Fighter (NACF) competition with Vought in the mid-1970s.   

References:

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

Long Beach's Flying Dutchman: The McDonnell Douglas MDF-100

In the late 1970s, McDonnell Douglas recognized that thousands of DC-9s and Boeing 727s along with first-generation 737s would become obsolete by the 1980s, given that the DC-9s in service were more than 10 years old. Therefore, McDonnell Douglas in 1980 conceived the DC-XX project for a twin-engine, twin-aisle narrow-body airliner derived from one of the company's Advanced Technology Medium Range (ATMR) design studies for a successor to the Boeing 727. In an unexpected stroke of luck, however, the Dutch aircraft manufacturer Fokker in June 1981 joined forces with McDonnell Douglas to create a new narrow-body airliner design combining features of the DC-XX but also Fokker's own F.29 narrow-body medium range airliner project, the latter which was too costly for Fokker to build with available financial capital and failed to win orders from the airlines.

Company artwork of the MDF-100 (D-3246-6) on take-off from Queen Reina Beatrix Airport in Aruba

The short/medium-range airliner design jointly designed by McDonnell Douglas and Fokker in early 1981 was given the commercial designation MDF-100 and the internal company designation D-3246. The initial MDF-100 layout conceived in June 1981 resembled the DC-XX and Boeing 737, but later that year, it gave way to a new MDF-100 iteration, the D-3246-6. Like the DC-XX, the MDF-100 with the D-3246-6 designation had underslung engines and twin-aisle configuration but differed in having the T-tail configuration of the F.29 project and a wider fuselage. The MDF-100 itself measured 134 feet 1 in (40.87 meters) long with a wingspan of 110 feet 9 in (33.76 meters), a height of 38 feet 2 in (11.63 meters), an empty weight of 88,896 lb (40,323 kg), and a gross weight of 151,300 lb (68,629 kg). It would carry 153 passengers in mixed-class configuration or 174 passengers in one-class configuration, and power was to come from two fuel-efficient turbofans (either the CFM International CFM56 or IAE V2500). Composite materials were to be used in manufacture of the elevators, rudder, wing moving surfaces, engine nacelles, and fuselage skins for the MDF-100.

The MDF-100 project, however, was all for naught. The expected rise in fuel prices for jet airliners which would presaged interest in new airliners with fuel-efficient turbofans did not materialize, and the airlines gradually lost interest in the MDF-100, while engine companies were hesitant to discuss development of new engines for jet airliners and a 1982 strike by air traffic controllers exacerbating the financial problems of US airlines. On February 5, 1982, McDonnell Douglas and Fokker shelved the MDF-100 project, by which time flight testing of the Boeing 757 was about to begin and McDonnell Douglas' factory in Long Beach was saturated with production of the MD-80 family. Nevertheless Fokker, meanwhile capitalized on its experience with design of the MDF-100 to undertake design work in 1983 of the smaller 100-seat Fokker 100 regional airliner, which first flew in 1986.

References:

Callaghan, J. G., and Obert, E., 2011. McDonnell Douglas-Fokker MDF-100. American Aviation Historical Society 53 (2): 186-191.

Green, W., and Swanborough, G., 1982. An Illustrated Guide to the World's Airliners. London, UK: Salamander Books. 

Lockheed's forgotten commercial gyroplanes

In the 1960s, Lockheed was busy with a variety of civil and military aircraft programs, namely the SR-71 Blackbird, A-12, C-141 Starlifter, C-5 Galaxy, F-104 Starfighter, C-130 Hercules, AH-56 Cheyenne and P-3 Orion. However, what has been seldom noticed is the company's flirtation with commercial gyroplane designs capable of intercity travel in that decade, and prior to the start of flight tests of the Cheyenne, it had investigated compound helicopter technology modifying one of the three prototypes of the XH-51 into a compound helicopter and flight testing it in his iteration in the 1964-1965. The impetus for Lockheed to took a serious look at the idea of a commercial gyroplane lay in forecasts that the bulk of a huge increase in the population would take place in urban areas by 1980, a recognition that the airports serving the main metropolitan areas of the US had to increase in size and move further from population centers to provide adequate space for long-distance travelers, and increased congestion on urban highways.

Left: Artwork of the Lockheed CL-879 gyroplane in flight
Right: Two-view drawing and specifications for the CL-879-8 from company documents.

The first Lockheed-California proposal for an intercity passenger gyroplane to be worked out, designated CL-879, was conceived in 1964. It featured seating capacity for 76-95 passengers and was intended for airport shuttling, intercity transport, and utility purposes. The CL-879-8 configuration was 102 feet (31 meters) long with a wingspan of 47 feet (14.32 meters), a height of 22 feet (6.7 meters), and a main rotor diameter of 94 feet (28.65 meters). Cruising speed was 287 mph (362 km/h), and operating range was to be 250 miles (402 km), while power would come from four 3,130 shp (2,302 kW) General Electric T64-GE-16 turboshafts housed in two paired underwing nacelles. In a confined area situation, the CL-879 would have a gross weight of 68,500 lb (31,071 kg) and a payload of 15,200 lb (6,895 kg), while gross weight and payload of the aircraft in a clear area situation were to be 79,800 lb (kg) and 19,000 lb (kg) respectively. Lockheed estimated that the CL-879 would be ready for airline service in the 1970s, and it suggested that the CL-879 itself could be optimized for cargo transport if a market demand for a short-haul commercial rotorcraft developed.

Artwork of the CL-1026 passenger compound helicopter 

Even as flight testing of its new AH-56 Cheyenne compound attack helicopter was underway, in 1967 Lockheed undertook design of the CL-1026 passenger derivative of the Cheyenne. Like the AH-56, the CL-1026 had a rigid main rotor, a four-blade anti-torque tail rotor, and a three-blade pusher propeller but was powered by two 3,435 shp (2,526 kW) Lycoming T55 turboshafts mounted side-by-side and had a deeper fuselage. It measured 60 feet 6.9 in (18.46 meters) long with a height of 15 feet 3 in (4.65 meters), a main rotor diameter of 51 feet 2.4 in (15.6 meters), a gross weight of 22,500 lb (10,206 kg) and seating for 30 passengers and three crewmembers. The CL-1026 would have a range of 225 miles (362 km/h) and a cruise speed of 230 mph (370 km/h), while it was primarily designed for intercity operations, it also could be convertible to cargo configuration in a matter of minutes.

Left: The Lockheed CL-1060 concept
Right: Artist's conception of the CL-1090 design

Although the earlier CL-879 project did not progress beyond the design phase, Lockheed capitalized on its work on the CL-879 to envisage two more large passenger gyroplane designs in 1967, the CL-1060 and CL-1090. These designs were powered by four turboshaft engines paired in two underwing nacelles and driving two propellers and a huge five-blade main rotor, and they had a crew of four. The CL-1060 proposal was 87 feet 6 in (26.67 meters) long with a wingspan of 49 feet 6 in (15.088 meters), a height of 15 feet 3 in (4.65 meters), and a main rotor diameter of 82 feet 6 in (meters), and it was intended to carry 60 passengers. The CL-1090, on the other hand, measured 124 feet 6 in (37.9 meters) in length and had a height of 30 feet 10.2 in (9.4 meters), a main rotor diameter of 102 feet (31 meters), a gross weight of 80,000 lb (36,287 kg), and seating for 95 passengers. 

Despite being pitched by Lockheed as commercial remedies to increasingly crowded US airports and congestion on urban highways, the CL-1026, CL-1060, and CL-1090 concepts, like the CL-879, did not progress to full-scale development, largely due to a lack of serious interest from commuter airlines.

For more on Lockheed's passenger gyroplane designs, see the following links:

https://www.secretprojects.co.uk/threads/various-lockheed-helicopter-projects.4153/

https://www.secretprojects.co.uk/threads/lockheed-ah-56-cheyenne-and-derivatives.941/

References:

Federal Aviation Administration, 1969. Heliport Design Guide. Washington, DC: Government Printing Office. (PDF) 

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

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.