In the late seventies and early eighties, Hughes Company and the David Taylor Naval Ship Research and Development Center conducted studies of a warm cycle approach similar to the Bolkow concept, but included an investigation of incorporating circulation control. A very-heavy-lift helicopter (VHLH) was designed along those lines.
In a Hot or Warm Cycle scheme, a mixture of compressed air and engine exhaust gases is produced by a generator, located in the airframe end then ductad to blade-tip nozzles, where it is discharged at basically subsonic speeds and temperatures as low as 230°C. Rotorcraft with airframe-mounted compressed air or gas generators, where gases are ducted through the blades for either direct discharge through tip nozzles or, in the case of compressed air, the flow of gases is further energized by fuel combustion in special - usually tip-mounted - burners.
This helicopter, having a gross weight of about 270,0001b powered by four low bypass-ratio Pratt & Whitney F-IO0 or G.E. F-101 engines, was designed to carry the 60-ton XM-1 Main Battle tank for a distance of 100 nautical miles in a ship-to-shore assault mission. An interesting feature of the design was incorporation of blade circulation control, thus permitting one to eliminate root pitch control and opening the possibility for use of higher harmonic inputs to reduce vibrations associated with the two-bladed rotor configuration.
In July 1996, after AAN (Army After Next) project initiation and reading "On the Need and Feasibility of a Very Heavy Lift Helicopter (VHLH) in Support of the Army's Force XXI Operations Concept," General Robert Scales (then TRADOC Deputy Chief of Staff for Doctrine) wrote: "We can conceive of a Future Combat Vehicle (FCV) of about 30-40 tons, even more lethal and mobile as the M-1, but with much greater fuel efficiency. So conjure me up an aerial lift vehicle that can transport such a load: -tactically, over 200-300 miles -a great speed - 150-250 mph - with stealth -capable of flying at a very low level, maybe even a "terrain effects vehicle" -with some survivability built in. Such a machine is the essential ingredient to our Army After Next Operational concept."
Yippie Kai Yay, Mr. Falcon.