January 2018

2018 January

US Army Light Helicopter Experimental (LHX) and Light Helicopter (LH)

LHX/LH Competition

Boeing Sikorsky YRAH-66A prototype first flight: January 4, 1996

The Light Helicopter Experimental (LHX) helicopter program was launched in 1983 (after a 1980-81 Aviation Mission Area Analysis and other Army/industry conceptual design studies) to replace the US Army's aging fleet of Vietnam-era OH-1 Cayuse and OH-58A Kiowa scouts, and AH-1 Cobra light attack helicopters as well as some UH-1 Hueys in the utility role. The original requirement was for over 7,000 helicopters.

Designed with lessons learned from Vietnam and the need to fight and survive in a high-threat combat setting (threats included: man-portable air-defense systems, radar-directed anti-aircraft artillery, and the possible need to fight in a nuclear, biological or chemical environment). The US Army/Boeing Sikorsky RAH-66 Comanche was selected after further Army studies, an Advanced Rotorcraft Technology Integration (ARTI) program, a new engine development program and an industry competition.

The need for high survivability and low detectability (low radar cross-section and reduced IR and noise signatures) was the major driver for the air vehicle design.

After initially promoting their individual LHX concepts (left-to-right, small photos at bottom), Boeing Vertol’s two artist concepts; an advanced, window-less helicopter and tiltrotor, Bell’s Advanced Tiltrotor (BAT) mockup, Hughes Helicopters advanced concept featuring the NOTAR anti-torque system, Sikorsky’s Compound Co-axial concept with a ducted pusher-prop, and an early Boeing Sikorsky ‘First Team’ Light Helicopter (LH) concept along with (far right), Bell Helicopter/McDonnell Douglas ‘SuperTeam’ LH, also with the NOTAR system.

On June 21, 1988, the US Army issued the LHX request for proposal. 23-month demonstration/ validation contracts were awarded to the Boeing/Sikorsky First Team (who had started collaborative LHX work in June 1985) and the Bell/McDonnell Douglas SuperTeam.

In early 1990, the US Army renamed the program ‘Light Helicopter’, removing the ‘X for eXperimental’ tag.

After careful evaluations, and flying demonstrations by both teams on technology demonstrators in the ARTI program, the US Army announced on April 5, 1991 that it had selected the Boeing Defense & Space Group’s Helicopters Division and United Technologies Corporation’s Sikorsky Aircraft and their team of twelve major subcontractors to receive the $2.8B contract to develop the aircraft.

On May 25, 1995, the first YRAH-66 prototype was rolled out at a ceremony at Sikorsky Aircraft’s plant in Stratford, Connecticut.

The RAH-66 Comanche featured advanced integrated avionics and an automated cockpit and sensor suite in a digital Mission Equipment Package to provide unprecedented real-time situational awareness. It could acquire and distribute critical battlefield data and information to the battle group.

A bearingless five-bladed main rotor and a canted ducted-fan (FANTAIL) anti-torque system enabled high agility and a low noise signature. The Comanche prototype demonstrated 75 knots in left sideward flight, 60 knots in right sideward flight, and 70 knots in rearward flight. It had a level flight dash speed of 170 knots. While in hover, the aircraft could complete a 180-deg. turn in less than 5 seconds and at 80 knots, it was able to make a snap-turn-to-target in 4.5 seconds.

  • Wide field-of-view helmet-mounted display
  • Two 6-in. x 8-in. multi-function displays
  • Triple redundant, fly-by-wire flight control system with three-axis side-arm controllers
  • Triple redundant electrical/hydraulic systems
  • Self-healing digital mission electronics
  • Longbow fire-control AESA radar
  • Passive, long-range, high-resolution sensors
  • On-board diagnostic system
  • Retractable missile armament system
  • All-composite airframe
  • Stowable three-barrel 20-mm Gatling gun
  • Two T800-LHTEC-801 turboshaft engines
  • Advanced technology split-torque main gearbox

The YRAH-66 prototype completed its first flight on January 4, 1996 at West Palm Beach, Florida, piloted by test pilots Rus Stiles and Bob Gradle.

Despite the established need for a modern scout/attack helicopter (the Army/Bell AH-1 Cobra fleet was retired in 2001), the program suffered from cost, schedule, weight growth, and technology readiness challenges and requirements ‘creep’. Despite several program restructures, it was cancelled by the Army in February 2004 after two prototypes had flown. 

Main photo: Boeing Sikorsky
Text: Ken Bartie


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