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| A table of the five CL-1725 HYCAT design configurations studied by Lockheed. The HYCAT-1A was derived from the HYCAT-1 iteration shown in the topmost row. |
In early 1979, under contract from NASA, Lockheed-California initiated the Hypersonic Cruise Aircraft Propulsion Integration Study to investigate the feasibility of a long-range hypersonic airliner capable of traveling at Mach 6 over a distance of 5,754 miles (9,260 km) with a seating capacity of 200 passengers and powered by a turbojet/scramjet propulsion system. Five designs, collectively called "HYCAT", were investigated by Lockheed, and the internal designation CL-1725 was applied to the HYCAT designs, all of which were to be fueled by liquid hydrogen. The first design, the HYCAT-1, had a long, slender fuselage, a single vertical stabilizer, and delta wings with forward swept trailing edges running along the length of the rear fuselage and terminating just ahead of the tail empennage, and it had six turbojets situated below the fuselage with tandem turbojet and scramjet inlets. The HYCAT-2 was a double-deck iteration which was powered by four turbojets fed by air flowing into intakes mounted atop the rear fuselage ahead of the vertical stabilizer and had scramjet inlets below the rear fuselage, and the HYCAT-3 design was also a double-decker but featured high-mounted backswept wings with twin vertical stabilizers at the wingtips and four symmetric vectoring turbojets below the rear fuselage, with scramjets mounted on the sides of the rear fuselage. The HYCAT-4 design featured a semi-blended wing body hypersonic airliner with an area-ruled fuselage featuring a double-deck seating layout, a conventional tail empennage, and four turbojet engines fed by air passing through air intakes atop the wings along with scramjets below the wings. The HYCAT-5 design, like the HYCAT-2, was a double-deck hypersonic airliner powered by four turbojet engines housed in air intakes atop the rear fuselage ahead of the vertical stabilizer and four scramjets below the rear fuselage, but it differed in having a compound delta wing and canards near the nose for low-speed trim. The HYCAT-1 to HYCAT-5 were truly gigantic aircraft designs, even bigger than the swing-wing Boeing 2707-100 and -200, with the HYCAT-1 measuring 395 feet 4.8 in (120.5 meters) long with a wingspan of 114 feet 4.92 in (34.87 meters) and a gross weight of 677,649 lb (307,382 kg), and the HYCAT-4 measuring 340 feet (103.6 meters) in length with a wingspan of 146 feet 9 in (44.73 meters) and a gross weight of 959,426 lb (435,196 kg).
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| A three-view drawing of the HYCAT-1A design marrying the HYCAT-1's wing planform with the HYCAT-4's tail empennage |
After carefully analyzing the operational, technical, and aerodynamic advantages and trade-offs of the five HYCAT designs, Lockheed decided to adopt a refined iteration of the HYCAT-1, the HYCAT-1A, as the baseline HYCAT design. The HYCAT-1A had the wing planform of the HYCAT-1 but differed in having a stretched rear fuselage and the tail empennage of the HYCAT-4, and Lockheed judged these characteristics essential to provide trim for relative change in the center of pressure through the speed range and enabled the use of drooped ailerons for low-speed lift. The HYCAT-1A featured a passenger cabin with two mid-fuselage decks as in the HYCAT-2, and it was powered by four 75,000 lb (34,019 kg) thrust turbojet engines housed below the rear fuselage and ten scramjets. The baseline HYCAT-1A design was 344 feet 10.8 in (105.12 meters) long with a wingspan of 98 feet 1.92 in (29.92 meters) and a gross weight of 600,000 lb (272,155 kg), and it would use the turbojets at speeds of up to Mach 4.5, after which the turbojet inlets would be closed and the scramjets would be ignited to allow the aircraft to reach Mach 6. The final general arrangement for the HYCAT-1A had a slightly longer fuselage 389 feet 4.32 in (118.68 meters) meters, and it featured a wingspan of 109 feet 2.76 in (33.29 meters), and a gross weight of 773,700 lb (350,944 kg). Both separate inlet turbojet/scramjet and common variable-geometry inlet turbojet/ramjet propulsion systems were investigated for the HYCAT-1A point design, and the latter propulsion arrangement was seen as creating increased inlet air flow and thrust after the turbojets shut down as well as reduced fuel consumption during acceleration and subsonic cruise. The design of the HYCAT-1A would form the basis of the Lockheed CL-2103 hypersonic bomber project envisaged in 1980, which was bigger than any of the CL-1725 HYCAT designs.
For more info on Lockheed's HYCAT designs, see the following links:
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