Supersonic airliner designs from southern California

Much has been written about the Anglo-French Concorde and Tupolev Tu-144 supersonic airliners with some mention of the larger but unbuilt triple-sonic Boeing 2707 as well as 1980s and 1990s projects for new-generation supersonic airliners to replace the Concorde and Tu-144. However, almost lost in talk about supersonic civil aviation is the fact that a number of aircraft manufacturers in southern California were working on their own supersonic airliner designs, either comparable to or faster than the Concorde and Tu-144. Therefore, this post is tailored to discuss supersonic airliner projects conceived by the aircraft industry in southern California during the 1950s and 1960s.

Left: Lockheed CL-823 design, 1963
Right: Douglas Model 2229

In the late 1950s, a number of American aircraft manufacturers from southern California, including Lockheed and Douglas, conceived the notion of an airliner capable of traveling at supersonic speeds, fresh off their long-standing pedigree in airliner development. Before long, the delta wing had been selected as the best planform for high supersonic flight thanks to the transonic area rule developed in 1952 by aeronautical engineer Richard T. Whitcomb. Even though the aerospace industry was striving for the "higher, faster" realm of air travel, they had to confront one issue: unlike the delta wings of supersonic military aircraft, the most advanced wing designs for supersonic transports were around 9, in contrast to the wings of subsonic airliners. In 1958, Lockheed initiated design studies for a supersonic airliner capable of reaching Mach 3, including one with a tapered straight wing (similar to the one seen on the Lockheed F-104 Starfighter) and a delta canard, and another with a delta wing. However, these initial proposals were judged aerodynamically unsatisfactory judging from wind tunnel tests, and by 1962 a proposal was drawn up featuring canards and a highly swept cranked-arrow wing with four individual turbojets buried in the wings. In 1963, Lockheed unveiled a design for an SST with a double delta wing, called CL-823, which featured a double delta wing with an extended leading edge, a nose that could droop during landing, and four Pratt & Whitney turbofans arranged individually under the delta wing. The CL-823 was 223 feet (70 meters) long and could carry up to 210 passengers. Douglas's SST design study, the Model 2229, was similar to the B-70 Valkyrie but had a compound delta wing stretching from the single vertical rudder at the rear almost to the front of the fuselage, and it had an MTOW of 420,000 lb (190,508 kg) and a seating capacity for 100 passengers. Four turbojets were mounted in a nacelle under the wing that used two shock cones at the front of the intake, creating a single large duct with three-part variable-profile walls that slowed the intake air to subsonic speeds. Behind this duct were separate ducts leading to the engines, and the landing gear folded into space beside the duct. 

Left: Drawing of the Convair Model 58-9
Right: Artist's rendering of the North American NAC-60 in United Airlines colors

In the early 1960s, Convair and North American proposed the Model 58-9 and North American NAC-60 designs based on B-58 Hustler and B-70 Valkyrie supersonic bombers respectively. The Model 58-9, envisaged in 1961, was similar to the unbuilt B-58C (which Convair had proposed as a cheaper alternative to the B-70 Valkyrie) in the delta wing design and in having four Pratt & Whitney J58s (used on the SR-71 Blackbird) but differed in having an entirely new fuselage and tail empennage, and it had a length of 150 feet (45.72 meters), a seating capacity for 52 passengers, a maximum take-off weight of 190,000 pounds (86,000 kg), a range of 2,900 miles (4,600 km) and a speed of Mach 2.4. Convair saw the Model 58-9 as a follow up on route-proving using an unmodified B-58, with a version of the bomber using a five-passenger version of its unique external weapons pod being an intermediate step, and the first flight was planned for 1964, with expectations that the Military Air Transport Service would perform simulated airline flights with the Model 58-9. The NAC-60, on the other hand, had the delta wing planform and nose-mounted canards of the B-70 Valkyrie but differed in having a single vertical stabilizer, a less tapered fuselage, and a more compound wing. It was to be 195 feet (59 meters) long, with a wingspan of 121 feet (37 meters), a range of 3,900 miles (6,276 km), a top speed of Mach 2.65, an MTOW of 480,000 lb (217,724 kg), and accommodations for 187 passengers and four crew. 

Top: Lockheed L-2000 model at Planes of Fame Museum

Bottom: L-2000-7 full-scale mockup

On June 5, 1963, US President John F. Kennedy announced the launch of the National Supersonic Transport (NST) competition for a supersonic airliner with a top speed of Mach 3 while delivering a speech to the US Air Force Academy. The Federal Aviation Administration (FAA) sent out a Request for Proposals (RFP) to Boeing, Lockheed, and North American for the airframes, and Curtiss-Wright, General Electric and Pratt & Whitney for engines. The Lockheed CL-823 and North American NAC-60 were submitted to the FAA on January 15, 1964 along with Boeing's swing-wing Model 733 proposal; Convair's Model 58-9 failed to garner interest from the airlines and military and thus never left the drawing board, and Douglas chose not to enter the Model 2229 into the NST contest because it was financially preoccupied with the DC-8 and DC-9 jet airliners. As 1964 progressed, the NAC-60 design was rejected by the FAA due to it being slower and smaller than the Boeing and Lockheed submissions, and the CL-823 and Model 733 were selected for further design study. To meet a slate of revised requirements for the NST contest, in November Lockheed proposed the L-2000, of which three initial designs were worked out for Phase IIA studies: the 214 foot (65.23 meter) long L-2000-1 (170 seats), the 225.7 foot (68.8 meter) long L-2000-2 (221 seats), and the 245.7 foot (74.9 meter) long L-2000-3 (250 seats). The L-2000-1 and L-2000-2 were intended for intercontinental routes, while the L-2000-3 was optimized for domestic routes, and all were to be powered by four Pratt & Whitney JTF17 turbofans. During Phase IIB studies in 1965, a modified version of the L-2000-2 was envisaged as the L-2000-4, while the L-2000-5 and L-2000-6 had slightly cranked wings. By 1966, Lockheed unveiled its final design for the L-2000, the L-2000-7, of which a full-scale mockup was built at the Lockheed plant in Burbank. Two L-2000-7 variants were conceived, the L-2000-7A and L-2000-7B, both of which weighed 590,000 lb (267,600 kg), a larger delta wing, and an aerodynamic lift-to-drag ratio of 8:1, differing only in length and seating (the L-2000-7A was 273 feet [83 meters] long and carried 230 passengers, while the L-2000-7B was 293 feet (89 meters) long and carried 250 passengers).

On December 31, 1966, the FAA declared the swing-wing Boeing 2707-200 (an enlarged derivative of the earlier Model 733) the winner of the NST competition; the Lockheed L-2000, despite its simpler delta wing design, had slightly lower performance during takeoff and at high speed. The Boeing 2707-200, however, ran into developmental problems because tests with the swing-wing mechanism meant that the aircraft would be much heavier than Boeing engineers had expected, so in 1968, the Boeing 2707 was reworked into a slightly smaller delta wing aircraft, the 2707-300. Even so, the Boeing 2707-300 design faced opposition from environmentalists and the cost of making titanium for the aircraft was very astronomical, and in 1971, the Boeing 2707-300 was canceled without having flown.