November 2015

2015 NovemberUS Army/Hughes XV-9A
Hughes Model 385 experimental helicopter with hot-cycle rotor system
First flight: November 5, 1964

In 1962 Hughes Helicopters was awarded an Army contract for the development and construction of a research helicopter utilizing a hot-cycle propulsion system. The resulting XV-9A (serial 64-15107) made its first flight in November 1964.

The XV-9A was constructed of various “off the shelf” parts to save both time and reduce costs. It used the cockpit of an OH-6A and the landing gear of a Sikorsky H-34, along with a typical cylindrical fuselage with a twin-rudder V-tail.

The XV-9A's experimental propulsion system was constructed around two stub wing-mounted General Electric YT64-GE-6 engines on either side of the fuselage, directly below the main rotor hub. Each engine's turbine section was removed, allowing hot exhaust gases to be ducted directly through the rotor hub and be ejected at near-sonic speeds through vaned cascades in each of the three blade tips. Smaller exhaust ports on either side of the tail boom just forward of the rudders provided additional directional stability.

The XV-9A's flight test program was completed in August 1965, with a total of 19.1 hours having been flown. The hot-cycle propulsion system, however, had proven to be overly complex and the aircraft itself had been plagued by stability problems. The Army therefore returned ownership of the XV-9A to Hughes and abandoned any further hot-cycle research.

XV-9A Specs:
  • Crew: 2
  • engine: 2 x General Electric YT64-GE-6 gas turbines rated at 2850 hp (2125 kW) each
  • rotor diameter: 55 ft (16.8 m)
  • fuselage length: 45 ft (13.7 m)
  • height: 12 ft (3.7 m)
  • empty weight: 8,483 lb (3,848 kg)
  • loaded weight: 15,268 lb (6,925 kg)
  • maximum weight: 25,447 lb (11,542 kg)
  • rotor loading: 6.45 lb/sq ft (31.5 kg/sq m)
  • maximum cruising speed: 120 kt (222 km/hr)
  • range: 150 miles (241 km)

(Photo by Boeing; text by Pete Noell)

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