Boeing Vertol CH-46 Sea Knight - Wikipedia

Origins

During the 1940s and 1950s, American rotorcraft manufacturer Piasecki Helicopter emerged as a pioneering developer of tandem-rotor helicopters; perhaps the most famous of these being the piston-powered H-21 "Flying Banana", an early utility and transport helicopter. During 1955, Piasecki was officially renamed as Vertol Corporation (standing for vertical take-off and landing); it was around this time that work commenced on the development of a new generation of tandem rotor helicopter. During 1956, the new design received the internal company designation of Vertol Model 107, or simply V-107; this rotorcraft differed from its predecessors by harnessing the newly developed turboshaft engine instead of piston-based counterparts. During that year, construction of a prototype, powered by a pair of Lycoming T53 turboshaft engines, each one being capable of producing 877 shp (640 kW), commenced.[2]

On 22 April 1958, the V-107 prototype performed its maiden flight.[3] In order to garner publicity for the newly developed rotorcraft, it was decided to use the prototype to conduct a series of publicised flight demonstrations during a tour across the United States and several overseas nations. During June 1958, it was announced that the U.S. Army had awarded a contract to Vertol for the construction of ten production-standard aircraft based on the V-107, which were designated YHC-1A.[4] However, this order was later decreased to three helicopters; according to aviation author Jay P. Spenser, the cutback had been enacted in order that the U.S. Army would be able to divert funds for the development of the rival V-114 helicopter, which was also a turbine-powered tandem rotor design but substantially larger than the V-107.[4] All of the U.S. Army's three YHC-1As were powered by pairs of GE-T-58 engines. During August 1959, the first YHC-1A-model rotorcraft conducted its first flight; independently, it was shortly followed by the maiden flight of an improved model intended for the commercial and export markets, designated 107-II.[1]

During 1960, the U.S. Marine Corps evolved a requirement for a medium-lift, twin-turbine troop/cargo assault helicopter to replace the various piston-engined types that were then in widespread use with the service.[5] That same year, American aviation company Boeing acquired Vertol, after which the group was consequently renamed Boeing Vertol.[4] Following a competition between several competing designs, during early 1961, it was announced that Boeing Vertol had been selected to manufacture its model 107M for the U.S. Marine Corps, where it was designated HRB-1.[1] During 1962, the U.S. Air Force placed its own order for 12 XCH-46B Sea Knight helicopters, which used the XH-49A designation; however, the service later decided to cancel the order due to delays in its delivery; instead, the U.S. Air Force opted to procure the rival Sikorsky S-61R in its place.[citation needed]

Following the Sea Knight's first flight in August 1962, the military designation was changed to CH-46A. During November 1964, the introduction of the Marines' CH-46A and the Navy's UH-46As commenced. The UH-46A variant was a modified version of the rotorcraft to perform the vertical replenishment mission.[1] The CH-46A was equipped with a pair of T58-GE8-8B turboshaft engines, each being rated at 1,250 shp (930 kW); these allowed the Sea Knight to carry up to 17 passengers or a maximum of 4,000 pounds (1,815 kg) of cargo.[6]

Further developments

During 1966, production of the improved CH-46D commenced with deliveries following shortly thereafter. This model featured various improvements, including modified rotor blades and the adoption of more powerful T58-GE-10 turboshaft engines,[1] rated at 1,400 shp (1,040 kW) each. The increased power of these new engines allowed the CH-46D to carry an increased payload, such as up to 25 troops or a maximum of 7,000 pounds (3,180 kg) of cargo.[6] During late 1967, the improved model was introduced to the Vietnam theater, where it supplemented the U.S. Marine Corps' existing CH-46A fleet, which had proven to be relatively unreliable and problematic in service.[7] Along with the USMC's CH-46Ds, the U.S. Navy also acquired a small number of UH-46Ds for ship resupply purposes.[8] In addition, approximately 33 CH-46As were progressively re-manufactured to the CH-46D standard.[6]

Between 1968 and 1971, the U.S. Marine Corps received a number of CH-46F standard rotorcraft. This model retained the T58-GE-10 engines used on the CH-46D while featuring revised avionics and featured a number of other modifications. The CH-46F was the final production model of the type.[1] During its service life, the Sea Knight received a variety of upgrades and modifications. Over time, the majority of the U.S. Marine Corps' Sea Knights were upgraded to the improved CH-46E standard. This model featured fiberglass rotor blades, reinforcement measures throughout the airframe, along with the refitting of further uprated T58-GE-16 engines, capable of producing 1,870 shp (1,390 kW) each; in addition, several CH-46Es were modified to double their maximum fuel capacity.[6] Starting in the mid-1990s, the Dynamic Component Upgrade (DCU) programmes was enacted, focusing on the implementation of strengthened drive systems and modified rotor controls.[citation needed]

The commercial variant, the BV 107-II, was first ordered by New York Airways during 1960. During July 1962, they took delivery of their first three aircraft, which was configured to seat up to 25 passengers.[5] During 1965, Boeing Vertol sold the manufacturing rights of the 107 to Japanese conglomerate Kawasaki Heavy Industries. Under this arrangement, all Model 107 civilian and military aircraft built in Japan were referred to by the KV 107 designation.[5] On 15 December 2006, Columbia Helicopters, Inc acquired the type certificate for the BV 107-II, and with the help of Piasecki eventually developed an original design, the Model 107-III, remanufactured from older airframes.[9] This model features new manufactured CT58-GE-16 engines, the commercial version of the upgraded engines used for the CH-46E as well as modernized avionics including a glass cockpit.[9]