The Hughes OH-6 Cayuse is a single-engine light helicopter designed and produced by the American aerospace company Hughes Helicopters. Its formal name is derived from the Cayuse people, while its "Loach" nickname is derived from the Light Observation Helicopter (LOH) program, under which it was procured.
The OH-6 was developed to meet United States Army Technical Specification 153, issued in 1960 to replace its Bell H-13 Sioux fleet. The Model 369 submitted by Hughes competed against two other finalists, Fairchild-Hiller and Bell, for a production contract. On February 27, 1963, the first prototype conducted its maiden flight. The Model 369 had a distinctive teardrop-shaped fuselage that was crashworthy and provided excellent external visibility. Its four-bladed full-articulated main rotor made it particularly agile, and it was suitable for personnel transport, escort and attack missions, and observation. During May 1965, the U.S. Army awarded a production contract to Hughes.
During 1966, the OH-6 began service with the U.S. Army, and promptly entered active combat in the Vietnam War. In theater, it was commonly operated in teams with rotorcraft such as the Bell AH-1 Cobra attack helicopter, using so-called "hunter-killer" tactics to flush out and eliminate hostile ground targets. The OH-6 would act as bait to draw enemy fire and mark targets for other platforms such as the AH-1 to attack. In one clandestine incident in 1972, known as the Vinh wiretap, a pair of OH-6As were heavily modified and used by the Central Intelligence Agency (CIA) via Air America to infiltrate Vietnamese high level communications, providing valuable intelligence. Reportedly, 964 out of the 1,422 OH-6As produced for the U.S. Army were destroyed in Vietnam alone.
During 1967, following price escalations for the OH-6, the U.S. Army reopened the program to bids for as many as 2,700 additional airframes beyond the 1,300 OH-6s already contracted. Following a competitive fly-off and a sealed bidding process, Hughes lost the contract to Bell, resulting in the competing Bell OH-58 Kiowa being produced. The OH-6/Model 369 was license-produced overseas by the Japanese aerospace company Kawasaki Heavy Industries for both military and civilian operators. It was also developed into a civilian helicopter, the Model 500, produced into the 21st century by MD Helicopters as the MD 500.
Development Background
During 1960, the United States Army issued Technical Specification 153 for a Light Observation Helicopter (LOH) capable of fulfilling various roles on the battlefield, including personnel transport, escort, casualty evacuation, observation, and attack missions. These would be used to replace its fleet of Bell H-13 Sioux, a compact first generation rotorcraft. Twelve companies opted to participate in the competition, Hughes Tool Company's Aircraft Division being one of them, submitted the Model 369 as its response. Two of these designs, those submitted by Fairchild-Hiller and Bell, were selected as finalists by the Army-Navy design competition board. However, the U.S. Army subsequently chose to include Hughes's Model 369 for further consideration as well.
In terms of its basic configuration, the Model 369 had an atypical teardrop-shaped fuselage, a feature that led to personnel sometimes referring to it as the "flying egg". This shaping, combined with the provision of internal bulkheads, has been attributed as giving the rotorcraft its uncommonly strong crashworthiness properties. This aspect was further bolstered by the use of self-sealing fuel tanks that lowered the likelihood of a post-impact fire breaking out. The pilot was provisioned with excellent external visibility via its large plexiglass windscreen, while its four-bladed fully-articulated main rotor meant it was considerably more agile than the preceding H-13 Sioux. It would often be crewed by a pilot and an observer; up to five passengers or up to 1,000lb of cargo could be carried internally.
Into flight On February 27, 1963, the first Model 369 prototype performed its maiden flight.McGowen 2005, p. 105. 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. A total of five prototypes were built, all of which were powered by a single Allison T63-A-5A turboshaft engine, capable of producing . The prototypes were delivered to the U.S. Army at Fort Rucker, Alabama, where they competed against the other ten prototype aircraft produced by Bell and Fairchild-Hiller. During the course of the competition, the Bell submission, the YOH-4, was eliminated as being underpowered (it was powered by the T63-A-5).McGowen 2005, p. 107. Accordingly, the bidding for the LOH contract came down to Fairchild-Hiller and Hughes. Ultimately, Hughes was selected as the winner of the competition.
During May 1965, the U.S. Army awarded a production contract to Hughes; this initial order for 714 rotorcraft was subsequently increased to 1,300 along with an option for another 114. Hughes's price was $19,860 per airframe, without the engine, while Hiller's price was $29,415 per airframe, also without the engine.Hearings on military posture and H.R. 13456, p. 7832. The Hiller design, designated OH-5A, had featured a boosted control system, while the Hughes design did not, a difference that accounted for some of the price increase. Hughes is reported to have told his confidant, Jack Real, that he lost over $100 million to construct 1,370 airframes.Cefaratt 2002, p. 77.Real, Jack. "The Real Story." Vertiflite, Fall/Winter 1999, pp. 36–39. It was reported that Howard Hughes had directed his company to submit a bid at a price beneath the actual production cost of the helicopter in order to secure this order. Accordingly, this tactic had resulted in substantial losses being incurred on the contract with the U.S. Army; the company had allegedly anticipated that an extended production cycle would eventually make the rotorcraft financially viable.
Due to price escalations for both the OH-6 and spare components, the U.S. Army opted to reopen bids for the program in 1967.McGowen 2005, p. 112. Accordingly, during 1968, Hughes submitted a bid to build a further 2,700 airframes. Stanley Hiller complained to the U.S. Army that Hughes had used unethical procedures; therefore, the Army opened the contract for rebidding by all parties. While Hiller did not participate in the rebidding, Bell opted to, submitting their redesigned Model 206. Following a competitive fly-off, the Army requested the manufacturers to submit sealed bids. Hughes bid $56,550 per airframe, while Bell bid $54,200. Reportedly, Hughes had consulted at the last moment with Real, who recommended a bid of $53,550. Hughes, without informing Real, raised the bid by $3,000, and thus lost the contract to Bell. 1,420 of the OH-6A would be produced, not counting the other derivatives.Francillon 1990, p. 248.
Japanese production
A total of 387 OH-6/Hughes 369s were produced under license in Japan by the Japanese aerospace company Kawasaki Heavy Industries. These rotorcraft were operated by several different organisations, the majority of which were based in Japan. Military operators included the Japanese Ground Self-Defense Force (JGSDF), Japanese Maritime Self-Defense Force (JMSDF), and the Japanese Coast Guard. Furthermore, a number of civilian customers also flew Kawasaki-built OH-6s for a variety of missions, including emergency medical services (EMS), law enforcement, and agricultural work.Aoki 1999, pp. 37–44.McGowen 2005, p. 106. Beginning in 2001, the JGSDF OH-6s were supplemented by the Kawasaki OH-1, a more advanced observation helicopter.McGowen 2005, pp. 215-216.
Operational history
Entry into service and world records
During 1966, the OH-6 entered service with the U.S. Army. Its first overseas deployment, as well as into frontline combat, was the Vietnam War. The pilots dubbed the new helicopter Loach, a word created by pronunciation of the LOH (light observation helicopter) acronym of the program that spawned the aircraft. (Loach is also the name for numerous stream-dwelling carnivorous or insectivorous fishes, especially common in South-East Asia, which specialise in hunting among substrates and dense cover.) During 1964, the U.S. Department of Defense issued a memorandum directing that all U.S. Army fixed-wing aircraft be transferred to the U.S. Air Force, while the U.S. Army transitioned to solely operating rotor-wing aircraft. Accordingly, the U.S. Army's fixed-wing airplane, the Cessna O-1 Bird Dog, which was utilized for artillery observation and reconnaissance flights, would be replaced by the incoming OH-6A.Adcock 1998, p. 32.
Early on in the OH-6's career, the type demonstrated its performance in a particularly prominent manner via the setting of 23 individual world records for helicopters during 1966 in the categories of speed, endurance and time to climb."History of Rotorcraft World Records, List of records established by the 'YOH-6A'." Fédération Aéronautique Internationale (FAI). Retrieved: January 11, 2011. On March 26, 1966, Jack Schwiebold set the closed circuit distance record in a YOH-6A at Edwards Air Force Base, California, flying without landing for 1,739.96 mi (2,800.20 km)."FAI Record ID #11656 – Absolute Rotorcraft World Record, Distance over a closed circuit without landing " ID 786 Fédération Aéronautique Internationale (FAI). Retrieved: November 28, 2013. Subsequently, on April 6, 1966, Robert Ferry set the long-distance world record for helicopters by flying from Culver City, California, with over a ton of fuel to Ormond Beach, Florida, covering a total of 1,923.08 nm (2,213.04 mi, 3,561.55 km) in 15 hours, and near the finish at up to altitude. As of 2021, these records still stand."FAI Record ID #11655 – Absolute Rotorcraft World Record, Distance without landing " Fédération Aéronautique Internationale (FAI). Retrieved: November 28, 2013.Porter, Don. "Now, That’s Good Mileage" Air & Space/Smithsonian, May 2011. Accessed: April 9, 2014.Ristine, Jeff. "Obituary: Robert G. Ferry; Air Force veteran was record-setting test pilot" San Diego Union-Tribune, February 2, 2009. Accessed: April 9, 2014.
Vietnam War
In December 1967, the first OH-6As arrived in South Vietnam. Its straightforward design made it easier to maintain than most other helicopters, its relatively compact main rotor made it easier to use tight landing zones. While its light aluminum skin could be easily penetrated by small arms fire, it also crumpled and absorbed energy in a crash while the rugged structure protected key systems and its crew. The OH-6 was relatively difficult to shoot down, and its occupants would often survive forced landings that would have likely been fatal onboard other rotorcraft. The remaining H-13s were promptly withdrawn in favour of the OH-6s. Typically missions were flown during the daylight, starting at dawn; common roles included the clearance of landing zones and general intelligence/observation flights.