The OH-6A "Cayuse" is a small tactical helicopter flown by units of the 160th Special Operations Aviation Regiment [SOAR]. It can cruise at speeds of 150 mph. Hughes developed the Model 369 as a prototype for the U.S. Army in the early 1960s. The Hughes 369 was redesignated the OH-6A "Cayuse" by the U.S. Army.
The Boeing (McDonnell Douglas) (formerly Hughes model 369A) OH-6A was designed for use as a military scout during the Vietnam war to meet the US Army's need for an extremely maneuverable light observation helicopter. In 1961, twelve companies submitted proposals to meet U.S.Army requirements for a four-seat turbine-powered light observation helicopter (LOH). After evaluation, three designs were selected and 5 of each: the Bell OH-4A; the Hiller OH-5 and the Hughes OH-6, were ordered for trials by the U.S.Army Aviation Board. Hughes Tool Company Aircraft Division submitted their Model 369 to fill a US Army requirement for a Light Observation Helicopter capable of performing a number of secondary duties including escort, attack and casualty evacuation duties. This helicopter was chosen by the US Army over the proposals of a number of other helicopter manufactures, designated the OH-6A Cayuse, and entered service in 1965.
The helicopter was designed around their earlier model 269/300 making use of monocoque steel tube construction techniques, allowing a strong and compact fuselage. The small "egg-shaped" design and simplified rotorhead incorporated four rotor blades of constant chord, made of bonded light alloy. The four-passenger teardrop shaped "Flying egg" (six-passenger with rear seats folded-down) was a small, light, sturdy, maneuverable helicopter, with very low drag.
Initially fielded in Vietnam in early 1968, the Hughes OH-6A was used for command and control, observation, target acquisition, and reconnaissance. The OH-6A replaced the Korean era OH-13 Sioux and OH-23 Raven light observation helicopters. The Hughes (Model 500M) international military version was sold in ten countries and built under license in Italy and Japan. The Cayuse had a single articulated four-bladed main rotor, a metal two-bladed tail rotor, and a V-shaped tail. The OH-6A was powered by a single Allison T63-A-5A 285 shp turboshaft engine, and had a cruising speed of 144 mph (125 knots).
The OH-6A Cayuse was quite effective when teamed with the AH-1G Cobra attack helicopter as part of what were known as Pink Teams. The OH-6A Loach (for "LOH") would find targets by flying low, "trolling for fire", then marking the target with colored smoke to lead in a Cobra, or Snake, to attack. The Cayuse could absorb an extensive amount of small arms fire and still bring the crew home safely. The OH-6A could be armed with the M27 armament subsystem, the port (left) side mounting M134 six-barrel 7.62mm minigun or a 40mm grenade launcher on the XM8 armament subsystem. In addition, an M60D 7.62mm machine gun could be mounted in the front port (left) or rear starboard (right) door openings. The Cayuse was organic to division, brigade, and battalion size units. At peak production, during the Vietnam War, as many as 100 OH-6As were built a month.
The US Naval Test Pilot School (USNTPS) trains and graduates qualified engineering test pilots, flight test officers, and flight test engineers to conduct test and evaluation (T & E) at the Naval Air Warfare Center-Aircraft Division (NAWC-AD) Patuxent River Maryland and other activities. In support of the Helicopter Flight Mechanics syllabus, the USNTPS operates surplus Army OH-6B Helicopters which were refurbished by the Army National Guard, Gulfport, Mississippi in 1991. As the reserve units have continued to move away from the OH-6 as their primary scout aircraft, military technical support of the aircraft has dwindled. USNTPS plans to retain the aircraft indefinitely and continue to improve the safety, reliability, and usefulness of the aircraft in the test pilot training role.
- OH-6A/Cayuse: Developed initially by the Hughes Aircraft company (later McDonnell Douglas Helicopter Company) in the mid-1960s for the US Army. Fitted with 1x 253-shp Allison T63-A-5A turboshaft, 4 bladed main rotor, and an offset "V" tail.
- OH-6A/MD-530F Super Cayuse/Lifter: Upgraded engine to a 425-shp Allison 250- C30 turboshaft, and avionics in 1988 for the US Army.
- EH-6B, a previous version of the Little Bird, was used for command, control and radio relay.
- The "OH-6C" was the creation of the Maintenance Section of The Real Cav, B Troop 7/17th Air Cavalry Squadron, which was stationed near Pleiku in early 1972. Armed with a 40mm grenade launcher in a nose turret, and two 19-tube 2.75 inch rocket launchers, the "OH-6C" was ready to take on anything. Unfortunately, the weight of the armament kept the little bird from taking off.
- AH/MH-6J: US Army Special Operations variant derived from the MD-530MG.
- Hughes 500M: Military export version of OH-6 in mid-1970s with upgraded 278-shp Allison 250-C18 turboshaft engine, "V" tail. A recontoured nose allowed for greater leg and head room. Modifications were also made to the rotor assembly by way of a five blade main rotor which increased stability.
- MD-500MD/Scout and TOW Defender: Improved military version of the model 500 with 5 main rotor blades, 375-shp Allison 250-C20B turboshaft engine, and T-tail.
- MD-500E/MD-500MG/Defender II: Had a more elongated nose for streamlining, and an optional 4x blade tail rotor for reduced acoustic signatures. Possible mast-mounted sight.
- MD-530MG/Defender: Has a mast-mounted sight, and incorporated upgrades of all previous variants.