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Hughes OH-6 Cayuse (Loach) Light Observation / Attack Helicopter


The nimble little Hughes OH-6 Cayuse served extensively with US Army forces in the Vietnam War and, in various forms, exists today.

 Updated: 5/11/2016; Authored By Staff Writer; Content ¬©www.MilitaryFactory.com

The Hughes OH-6 "Cayuse" (popularly recognized as the "Loach") was a revolutionary light helicopter mount primarily in service with the United States Army and saw combat service during the Vietnam War (1955-1975). The type was born from the US Army Light Observation Helicopter (LOH) program (which provided its "Loach" nickname) and ultimately proved an excellent helicopter system seeing only limited service in the inventories of several American allies worldwide. Fewer than 2,000 of the type were produced though the original went on to spawn a plethora of viable performers including the Hughes 500 "Defender" and the special forces-minded MH-6 "Little Bird".

Following the close of World War 2 in 1945, rotary-wing flight entered a period of advancement and refinement to produce a viable helicopter solution for both military and civilian markets. The Korean War (1950-1953) was the first large-scale combat zone use of helicopters by United States forces who had been entertaining the prospects of vertical flight as early as the 1930s. The Korean War ushered the helicopter in as a Search and Rescue (SAR) mount and transportation of the wounded across Korea's unforgiving terrain.

Years after the close of the war, the United States Army unveiled "Technical Specification 153" in 1960, establishing its Light Observation Helicopter (LOH) program. As the title suggested, the program goal was to stock a dedicated, light-class, rotary-wing system with a multipurpose battlefield role. The helicopter would be called upon to undertake various missions including that of SAR, MEDEVAC, observation, transport, reconnaissance, escort, Close Air Support (CAS) and direct attack.

Famous American flight pioneer Howard Hughes (1905-1976), still alive by this time, was operating an aircraft division through his Hughes Tool front as the Hughes Tool Company - Aircraft Division. Understanding the potentially lucrative government contract waiting for such a system, he positioned his company to deliver. Hughes engineers developed the Hughes "Model 369" and, joining a dozen other firms, submitted their LOH proposal to the US Army.

The United States Army initially selected two designs - one from Bell Helicopters and the other from Fairchild-Hiller. However, the Hughes submission was later added to the fold and all three concerns were funded for development of five prototype vehicles. The Hughes Model 369 was outfitted with an Allison T63-A-5A series turboshaft engine of 252 horsepower and recorded its first flight on February 27th, 1963. Should the Hughes development succeed, Allison Engine Company stood to make its own fair share of profit from the long-term US Army commitment. The United States Army designated the Hughes submission as the "YHO-6A" until a complete rewrite of American military designations occurred in 1962, prompting a change to the model as the "YOH-6A" (as such, serial production would spawn the "OH-6A").

With US Army evaluations of each prototype ongoing, the underpowered Bell offering was formally dropped from contention and the US Army decision favored the Hughes design over the Fairchild-Hiller. It was deemed, based on Hughes' estimates, his units would be most cost effective in the long run. It later turned out that Howard Hughes purposely undervalued his estimate and deceptively won out against Fairchild-Hiller - his reasoning being that a long-term US Army commitment to his helicopter would, over time, make the deal profitable at some point. The US Army charged Hughes for 714 units with the serial production contract formally announced in May of 1965. Sensing its growing battlefield requirements, the US Army then raised the production ceiling to 1,300 units in all. The helicopter was inducted as the OH-6 "Cayuse" and would eventually take on the in-the-field nickname of "Loach" in reference to its "LOH" origins.




Hughes' deceptiveness would eventually come full circle for, in 1968, when the US Army sought to further strengthen its stock of light helicopters, a new competition was forced open by Fairchild-Hiller who had formally complained about Hughes' prior tactics to the US Army. While Fairchild-Hiller did not partake in the subsequent competition, this opened the door for Bell Helicopters and their new "Model 206" platform. After evaluation, the Bell submission was granted the production order and this begat the popular OH-58 "Kiowa" light observation / scout platform of 1969 detailed elsewhere on this site.

With that, production of OH-6 helicopters was limited to just 1,434 complete vehicles when all was said and done. Amidst rising manufacture costs and a slowdown in OH-6 orders, the Cayuse line and its contract was eventually terminated. In the United States, the type was utilized by the US Army and several state- and city-level police agencies as well as borders/customs elements. Globally, the OH-6 failed to achieve widespread use and was featured in the inventories of only a few select US-allied nations including the Dominican Republic, Denmark, Japan, Spain and Taiwan.

The initial production version was designated as the OH-6A and these were powered by a single Allison T63-A5A turboshaft engine of 317 horsepower. The standard operating crew was two personnel in the forward cockpit with two removable seats fitted in the passenger cabin. The fuselage utilized the iconic Hughes OH-6 teardrop shape that made the aircraft instantly recognizable. The fuselage was designed as just voluminous enough to house the needed avionics, fuel stores, crew and (optional) passenger seating. The single engine was fitted over the fuselage and coupled to a four-bladed main rotor assembly, a shaft running through the tail stem to power the two-bladed tail rotor facing portside. The tail was capped by a large vertical tail fin with another (canted outward) vertical fin offset to starboard. A smaller ventral fin was also noted at the tail unit. The engine exhausted through a simple circular port under the tail, held well low in the design arrangement. The undercarriage was of the fixed twin skid type, supported at two points, and helped to keep maintenance costs down. Doors at the cockpit sides and passenger cabin were optional though often times left off completely for increased situational awareness. The frontal panel of the aircraft was largely transparent, offering unparalleled views of the action ahead.

The OH-6B followed with the uprated Allison T63-A-720 turboshaft engine of 420 horsepower. The OH-6C was a proposed variant fitted with a five-bladed main rotor assembly coupled to an Allison 25-C20 series turboshaft engine. The OH-6D was a local, license-built (Kawasaki Heavy Industries) Japanese military model based on the Hughes Model 500D family. The OH-6A was built locally in Japan as well, this under the OH-6J designation to which Japanese factories produced 387 OH-6 helicopters in all. The US Navy operated the OH-6 as the TH-6B solely in a training role.

The American military furthered their OH-6 line through the EH-6B, an electronic warfare and command post platform for use by special forces. The MH-6B was a special forces-minded mount outfitted with specialized equipment and optional armament. The MH-6C was yet another special operations variant. The AH-6C was fielded with variable armament loadouts for the light attack role and operated by the 160th SOAR(A) (160th Special Operations Aviation Regiment (Airborne)) force - better known as the "Night Stalkers".

The MH-6 "Little Bird" proved the yet another special operations variant and originally based on the OH-6A airframe. Introduced in 1980, these were/are typically outfitted with rocket pods and minigun pods and feature a crew of two. The MH-6 was evolved through the related MD 500E platform.

With production having begun in 1965, the US Army stock grew until the aircraft was formally introduced in 1966 - in time for the American involvement in the Vietnam War (1955-1975). Back in 1964, the US Air Force took over all fixed-wing aircraft of the Army and this left only a fleet of helicopters for air service in the latter. During the Vietnam conflict, OH-6 Cayuse platforms undertook a myriad of frontline sorties and even CIA-directed covert missions, both as unarmed and armed platforms. Their vertical abilities allowed them unfettered access over the jungle canopy and across mountainous terrain of Southeast Asia while delivering all manner of support for ground troops and critically wounded. In all, sources state that some 658 Cayuse helicopters were lost to enemy fire in the war and a further 297 were lost through accident alone.

Japanese OH-6 helicopters are currently (2013) being replaced by the all-new, indigenously designed and developed Kawasaki OH-1 series of which over 30 have been produced to date. The new helicopter entered service in 2000 after years of development.

Often lost in discussions about the OH-6 is its record-setting design - capturing some 23 helicopter records worldwide including those for speed and endurance. The OH-6 certainly rewrote the light observation category and its stellar design is solidified by the fact that the airframe is still in use today - nearly 50 years since its inception.



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Hughes OH-6 Cayuse (Loach) Technical Specifications



Service Year: 1966
Type: Light Observation / Attack Helicopter
National Origin: United States
Manufacturer(s): Hughes Tool Company, Aircraft Division - USA
Production Total: 1,434


Structural (Crew Space, Dimensions and Weights)



Operating Crew (Typical): 2
Overall Length: 30.84 feet (9.4 meters)
Overall Width: 27.33 feet (8.33 meters)
Overall Height: 8.53 feet (2.60 meters)

Weight (Empty): 1,975 lb (896 kg)
Weight (MTOW): 3,549 lb (1,610 kg)

Installed Power and Standard Day Performance



Propulsion: 1 x Allison T63-A-5A OR T63-A-700 turboshaft engine developing 317 horsepower to a four-blade main rotor and two-blade tail rotor.

Maximum Speed: 175 mph (282 kph; 152 knots)
Maximum Range: 267 miles (430 km)
Service Ceiling: 15,994 feet (4,875 meters; 3.03 miles)
Rate-of-Climb: 2,067 feet-per-minute (630 m/min)

Armament / Mission Payload



Optional and variable (attack and special forces versions only). Can include a combination of the following across two fuselage wingstubs (though some weapons operated from cabin doors):

7.62mm M60 general purpose machine gun
7.62mm M134 minigun pod
12.7mm M2 Browning heavy machine gun pod
2.75" (70mm) Hydra 70 rocket pod (7 x rockets ea).
TOW Anti-Tank Guided Missile (ATGM) pod (2 x missiles ea).
AGM-114 Hellfire Anti-Tank (AT) missile pod (2 x missiles ea).

Also crew-served small arms of various kinds - sniper rifles, assault rifles and light machine guns as required.

Global Operators / Customers



Dominican Republic; Denmark; Japan; Spain; Taiwan; United States

Model Variants (Including Prototypes)



YOH-6A - Prototype Designation
OH-6A - Initial Production Model Designation; fitted with 1 x Allison T63-A5A turboshaft engine.
OH-6A NOTAR - Experimental Platform; sans tail rotor system.
OH-6B - Fitted with 1 x Allison T63-A-720 turboshaft engine.
OH-6C - Proposed Variant; fitting 1 x Allison 25-C20 turboshaft engine; five-bladed main rotor.
OH-6J - Japanese Ground Self-Defense Force Version; license-production by Kawasaki Heavy Industries; based on OH-6A production model.
OH-6D - Japanese Ground Self-Defense Force Version; license-production by Kawasaki Heavy Industries; based on Hughes 500D production model.
EH-6B - Electronic Warfare Aircraft (EWA) Platform foruse by special forces; airborne command post.
MH-6B - Special Forces Variant
TH-6B - US Navy Variant; based on the MD-369H.
AH-6C - Attack Platform; based on the OH-6A production model; provision for outboard weapons on wingstub fittings.
MH-6C - Special Forces Variant