Unseen hypersonic airliners from the Los Angeles area, part 1: the Lockheed CL-500

In the late 1950s, aircraft manufacturers in the US with experience building passenger aircraft, including Boeing, Convair, Douglas, and Lockheed, began planning for the day when airliners capable of supersonic speeds would become US commercial aviation's wave of the future in the 1970s and beyond, presaging design of the Boeing 2707, Convair 58-9, Douglas 2229, Lockheed L-2000, and North American NAC-60. However, years before the Federal Aviation Administration (FAA) initiated the competition in 1963 for a supersonic transport that would produce the Boeing 2707 and Lockheed L-2000 designs, Lockheed was already thinking about the far-fetched notion of an airliner optimized for hypersonic speeds, and from the late 1950s to 1970s, aircraft manufacturers in the Los Angeles basin unveiled a flurry of design studies for hypersonic airliners. Therefore, I'm beginning my overview of hypersonic airliner designs conceived in the Los Angeles area with a discussion of Lockheed's idea of a VTOL hypersonic airliner.

Cutaway view of the baseline Mach 4 iteration of the CL-500 VTOL hypersonic airliner from the company documents.

In 1959, Lockheed conceived a design for an intercity airliner not only capable of speeds beyond Mach 3 but also optimized for vertical takeoff and landing (VTOL). This proposal, designated CL-500, was a very unorthodox design in that it resembled a rectangular slab with sharply swept delta wings and a vertical stabilizer whose base extended to a point on the airframe aft of the overhead main entrance door. The front nose section of the aircraft accommodated twelve turbojets fed by air intakes at the front of the nose, and lift jets were housed in efflux slots along the chines of the CL-500, with ramjet/reheat burners placed at the rear of the fuselage. The lift jets would be used during vertical takeoff, and after making a transition to forward flight, the CL-500 would use its jet engines at speeds of up to Mach 3, after which the turbojets would operate as ramjets for hypersonic flight and the supersonic ram inlet would be shut. The CL-500 had a seating capacity for 60 passengers and a flight station behind the forward fuel compartment for the jet engines for two crewmembers, and because it had no windows on the sides of the fuselage, it featured a television and periscope visual display to enable the passengers and crew to guide the aircraft in forward flight and during takeoff and landing. The baseline 60-passenger CL-500 design had a top speed of Mach 4, and other variants of the CL-500 studied by Lockheed would have traveled at Mach 7. To withstand heat friction above Mach 3, the CL-500 was to be manufactured from titanium and a few other heat-resistant metal alloys.

Unsurprisingly, the notion of a VTOL hypersonic airliner encapsulated by the CL-500 was not only a rather whacky concept but also was sure to be ridiculed by the airline industry as too far-fetched given the insurmountable hurdles to adapting the CL-500's VTOL engine nozzles to immense heat generated by flight at hypersonic speeds.