United States Department of Defense - OH-6 Cayuse

The Hughes Helicopters OH-6 Cayuse (nicknamed Loach) is a single-engine light helicopter with a four-bladed main rotor used for personnel transport, escort and attack missions, and observation. Hughes also developed the Model 369 as a civilian helicopter, the Hughes Model 500, currently produced by MD Helicopters.

In 1960, the United States Army issued Technical Specification 153 for a Light Observation Helicopter (LOH) capable of fulfilling various roles: personnel transport, escort and attack missions, casualty evacuation and observation. Twelve companies took part in the competition and Hughes Tool Company's Aircraft Division submitted the Model 369. Two designs, those submitted by Fairchild-Hiller and Bell, were selected as finalists by the Army-Navy design competition board, but the U.S. Army later included the helicopter from Hughes as well.

The first Model 369 prototype flew on February 27, 1963. Originally designated as the YHO-6A according to the Army's designation system, the aircraft was redesignated as the YOH-6A in 1962 when the Department of Defense created a Joint designation system for all aircraft. Five prototypes were built, fitted with a 252 shp Allison T63-A-5A, and delivered to the U.S. Army at Camp Rucker, Alabama to compete against the other 10 prototype aircraft submitted by Bell and Fairchild-Hiller. During the course of the competition, the Bell submission, the YOH-4, was eliminated as being underpowered (it used the 250shp T63-A-5). The bidding for the LOH contract came down to Fairchild-Hiller and Hughes. Hughes won the bid, and the Army awarded a contract for production in May 1965, with an initial order for 714 which was later increased to 1300 with an option on another 114. Production reached 70 helicopters in the first month.

YOH-6A
Prototype version.
OH-6A
Light observation helicopter, powered by a 263-kW (317-shp) Allison T63-A5A turboshaft engine.
OH-6A NOTAR
Experimental version.
OH-6B
Re-engined version, powered by a 298-kW (420-shp) Allison T63-A-720 turboshaft engine.
OH-6C
Proposed version, powered by a 313.32-kW (400-shp) Allison 25-C20 turboshaft engine, fitted five rotor blades.
OH-6J
Light observation helicopter for the JGSDF. Built by Kawasaki Heavy Industries under licence in Japan. Based on the OH-6A Cayuse helicopter.
OH-6D
Light observation, scout helicopter for the JGSDF. Built by Kawasaki Heavy Industries under licence in Japan. Based on the Hughes Model 500D helicopter.
EH-6B
Special Forces electronic warfare, command post version.
MH-6B
Special Forces version.
TH-6B
A Navy derivative of the MD-369H, six McDonnell Douglas TH-6B Conversion-in-Lieu-of-Procurement aircraft are used as an integral part of the United States Naval Test Pilot School's test pilot training syllabus. The aircraft and associated instrumentation and avionics are used for the in-flight instruction and demonstration of flying qualities, performance and missions systems flight test techniques.
AH-6C
Modified OH-6A to carry weapons and operate as a light attack aircraft for the 160th SOAR(A).
MH-6C
Special Forces version.

For other AH-6 and MH-6 variants, see MH-6 Little Bird.