The Boeing CH-47 Chinook is an American twin-engine, tandem rotor heavy-lift helicopter. Its primary roles are troop movement, artillery placement and battlefield resupply. It has a wide loading ramp at the rear of the fuselage and three external ventral cargo hooks. With a top speed of 170 knots (196 mph, 315 km/h) the helicopter was faster than contemporary 1960s utility helicopters and attack helicopters, and is still one of the fastest helicopters in the US inventory. The CH-47 is among the heaviest lifting Western helicopters. Its name is from the Native American Chinook people.
The Chinook was designed and initially produced by Boeing Vertol in the early 1960s; it is now produced by Boeing Rotorcraft Systems. It is one of the few aircraft of that era – along with the fixed-wing Lockheed C-130 Hercules cargo aircraft – that remain in production and frontline service, with over 1,200 built to date. The helicopter has been sold to 16 nations with the U.S. Army and the Royal Air Force (see Boeing Chinook (UK variants)) being its largest users.
Design and development
In late 1956, the United States Department of the Army announced plans to replace the Sikorsky CH-37 Mojave, which was powered by piston engines, with a new, gas turbine-powered helicopter. Turbine engines were also a key design feature of the smaller UH-1 "Huey" utility helicopter. Following a design competition, in September 1958, a joint Army–Air Force source selection board recommended that the Army procure the Vertol medium transport helicopter. However, funding for full-scale development was not then available, and the Army vacillated on its design requirements. Some in Army Aviation thought that the new helicopter should be a light tactical transport aimed at taking over the missions of the old piston-engined Piasecki H-21 and Sikorsky H-34 helicopters, and be consequently capable of carrying about fifteen troops (one squad). Another faction in Army Aviation thought that the new helicopter should be much larger to be able to airlift a large artillery piece, and have enough internal space to carry the new MGM-31 "Pershing" Missile System.
HC-1B during in-flight evaluation
Vertol began work on a new tandem-rotor helicopter designated Vertol Model 107 or V-107 in 1957. In June 1958, the U.S. Army awarded a contract to Vertol for the aircraft under the YHC-1A designation. The YHC-1A had a capacity for 20 troops. Three were tested by the Army for deriving engineering and operational data. However, the YHC-1A was considered by most of the Army users to be too heavy for the assault role and too light for the transport role. The decision was made to procure a heavier transport helicopter and at the same time upgrade the UH-1 "Huey" as a tactical troop transport. The YHC-1A would be improved and adopted by the Marines as the CH-46 Sea Knight in 1962. The Army then ordered the larger Model 114 under the designation HC-1B. The pre-production Boeing Vertol YCH-1B made its initial hovering flight on 21 September 1961. In 1962 the HC-1B was redesignated the CH-47A under the 1962 United States Tri-Service aircraft designation system. It was named "Chinook" for the Chinook people of the Pacific Northwest.
A CH-47 in a training exercise with US Navy Special Warfare, in July 2008
The CH-47 is powered by two Lycoming T55 turboshaft engines, mounted on each side of the helicopter's rear pylon and connected to the rotors by driveshafts. Initial models were fitted with engines rated at 2,200 horsepower each. The counter-rotating rotors eliminate the need for an anti-torque vertical rotor, allowing all power to be used for lift and thrust. The ability to adjust lift in either rotor makes it less sensitive to changes in the center of gravity, important for the cargo lifting and dropping. While hovering over a specific location, a twin rotor helicopter has increased stability over single rotor when weight is added or removed; for example when troops drop from or begin climbing up ropes to the aircraft, or when other cargo is dropped. If one engine fails, the other can drive both rotors. The "sizing" of the Chinook was directly related to the growth of the Huey and the Army's tacticians' insistence that initial air assaults be built around the squad. The Army pushed for both the Huey and the Chinook, and this focus was responsible for the acceleration of its air mobility effort.
Improved and later versions
A CH-47F practicing the Pinnacle maneuver whereby soldiers are deposited without the helicopter landing.
Improved and more powerful versions of the CH-47 have been developed since the helicopter entered service. The U.S. Army's first major design leap was the now-common CH-47D, which entered service in 1982. Improvements from the CH-47C included upgraded engines, composite rotor blades, a redesigned cockpit to reduce pilot workload, improved and redundant electrical systems, an advanced flight control system and improved avionics. The latest mainstream generation is the CH-47F, which features several major upgrades to reduce maintenance, digitized flight controls, and is powered by two 4,733-horsepower Honeywell engines.
A commercial model of the Chinook, the Boeing-Vertol Model 234, is used worldwide for logging, construction, fighting forest fires, and supporting petroleum extraction operations. On 15 December 2006, the Columbia Helicopters company of the Salem, Oregon, metropolitan area, purchased the Type certificate of the Model 234 from Boeing. The Chinook has also been licensed to be built by companies outside the United States, such as Elicotteri Meridionali (now AgustaWestland) in Italy, and Kawasaki in Japan.
The Army finally settled on the larger Chinook as its standard medium transport helicopter and as of February 1966, 161 aircraft had been delivered to the Army. The 1st Cavalry Division had brought their organic Chinook battalion with them when they arrived in 1965 and a separate aviation medium helicopter company, the 147th, had arrived in Vietnam on 29 November 1965. This latter company was initially placed in direct support of the 1st Infantry Division.
The most spectacular mission in Vietnam for the Chinook was the placing of artillery batteries in perilous mountain positions inaccessible by any other means, and then keeping them resupplied with large quantities of ammunition. The 1st Cavalry Division found that its CH-47s were limited to a 7,000-pound (3,200 kg) payload when operating in the mountains, but could carry an additional 1,000 pounds (450 kg) when operating near the coast. The early Chinook design was limited by its rotor system which did not permit full use of the installed power, and users were anxious for an improved version which would upgrade this system.
As with any new piece of equipment, the Chinook presented a major problem of "customer education". Commanders and crew chiefs had to be constantly alert that eager soldiers did not overload the temptingly large cargo compartment. It would be some time before troops would be experts at using sling loads. The Chinook soon proved to be such an invaluable aircraft for artillery movement and heavy logistics that it was seldom used as an assault troop carrier. Some of the Chinook fleet were used for casualty evacuation, due to the very heavy demand for the helicopters they were usually overburdened with wounded. Perhaps the most cost effective use of the Chinook was the recovery of other downed aircraft.
Troops unload from a CH-47 in the Cay Giep Mountains, Vietnam, 1967
The CH-47s are generally armed with a single 7.62-millimeter M60 machine gun on a pintle mount on either side of the machine for self-defense, with stops fitted to keep the gunners from firing into the rotor blades. Dust filters were also added to improve engine reliability. At its peak employment in Vietnam, there were 22 Chinook units in operation. Of the nearly 750 Chinook helicopters in the U.S. and South Vietnam fleets, about 200 were lost in combat or wartime operational accidents. The U.S. Army CH-47s supported the 1st Australian Task Force as required.
During the 1970s, the United States and Iran had a strong relationship, in which the Iranian armed forces began to use many American military aircraft, most notably the F-14 Tomcat, as part of a modernization program.After an agreement signed between Boeing and Elicotteri Meridionali, the Imperial Iranian Air Force purchased 20 Elicotteri Meridionali-built CH-47Cs in 1971. The Imperial Iranian Army Aviation purchased 70 CH-47Cs from Elicotteri Meridionali between 1972 and 1976. In late 1978, Iran placed an order for an additional 50 helicopters with Elicotteri Meridionali, but that order was canceled immediately after the revolution; but 11 of them were delivered after multiple requests by Iran.
Imperial Iranian Air Force CH-47C in France before delivery in 1971
In the 1978 Iranian Chinook shootdown, four Iranian CH-47Cs penetrated 15–20 km into Soviet airspace in the Turkmenistan Military District. They were intercepted by a MiG-23M which shot down one, killing eight crew members, and forced a second one to land. Chinook helicopters were used in efforts by the Imperial Iranian loyalist forces to resist the 1979 Iranian revolution.
During the Iran–Iraq War, Iran made heavy use of its US-bought equipment, and lost at least 8 CH-47s during the 1980–1988 period; most notably during a clash on 15 July 1983, when an Iraqi Mirage F1 destroyed three Iranian Chinooks transporting troops to the front line, and on 25–26 February 1984, when Iraqi MiG-21 fighters shot down two examples. On 22 March 1982, in Operation Undeniable Victory, a key operation of the war, Iranian Chinooks were landed behind Iraqi lines, deployed troops that silenced their artillery, and captured an Iraqi headquarter; the attack took the Iraqi forces by surprise.
Despite the arms embargo in place upon Iran, it has managed to keep its Chinook fleet operational. Some of the Chinooks have been rebuilt by Panha. Currently 20 to 45 Chinooks are operational in Iran.