In late 1956 the Department of the Army announced plans to replace the CH-37 Mojave, which was powered by piston engines, with a new, turbine-powered helicopter.[3] Turbine engines were also a key design feature of the smaller UH-1 utility helicopter. Following a design competition, a joint Army-Air Force source selection board recommended in September 1958 that the Army procure the Vertol medium transport helicopter. However, funding for full-scale development was not available and the Army vacillated on its design requirements. Some in the Army felt that the new helicopter should be a light tactical transport aimed at the mission of the old H-21s and H-34s and, consequently, sized for approximately fifteen troops. Another faction believed that the new transport should be much larger to serve as an artillery prime mover and have minimum interior dimensions compatible with the Pershing Missile System. This sizing problem was a critical decision.[3]
Vertol began work on a new tandem rotor helicopter designated Vertol Model 107 or V-107 in 1957.[4][5] In June 1958, the US Army awarded a contract to Vertol for the aircraft under the YHC-1A designation.[6] The YHC-1A had a capacity for 20 troops.[3] Three were tested by the Army to derive 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.[3] The decision was made to procure a heavier transport helicopter and at the same time upgrade the 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.[7] The Army then ordered the larger Model 114 under the designation HC-1B.[8] The pre-production Boeing Vertol YCH-1B made its initial hovering flight on September 21, 1961. In 1962 the HC-1B was redesignated the CH-47A under the 1962 United States Tri-Service aircraft designation system.
The name "Chinook" alludes to the Chinook people of the Pacific Northwest. The CH-47 is powered by two turboshaft engines, mounted on either side of the helicopter's rear end and connected to the rotors by driveshafts. Initial models were fitted with engines of 2,200 horsepower. 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 role. If one engine fails, the other can drive both rotors.[9] 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 airmobility effort.[3]
Improved and later versions
Improved and more powerful versions of the CH-47 have been developed since the helicopter entered service. The US 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.[10] The latest mainstream generation is the CH-47F, which features several major upgrades to reduce maintence, digitised flight controls, and is powered by two 4,733-horsepower Honeywell engines.[11]
A commercial model of the Chinook, the Boeing-Vertol Model 234, is used worldwide for logging, construction, fighting forest fires and supporting petroleum exploration operations. As of December 15, 2006 Columbia Helicopters, Inc. of Aurora, Oregon has purchased the Type Certificate of the Model 234 from Boeing.[12] The Chinook has also been licensed to be built by companies outside of the US, such as Elicotteri Meridionali (AgustaWestland) in Italy and Kawasaki in Japan.
CH-47F
The CH-47F, an upgraded D model, first flew in 2001. The first production model was rolled out on June 15, 2006 at the Boeing facility in Ridley Park, Pennsylvania, and had its maiden flight on October 23, 2006.[43] The CH-47F was designed to extend the service life of the Chinook class beyond 2030. Among its upgrades are new 4,868 shaft horsepower Honeywell engines, improved avionics, and an upgraded airframe with larger single-piece sections to reduce part count and need for fasteners.[44] The new milled construction will reduce vibrations, eliminate points of joint flexing, and reduce the need for inspections and repairs, and reduce maintenance costs. It is also expected to increase service life.[45] The CH-47F can fly at speeds of over 175Â mph (282Â km/h) with a payload of more than 21,000Â lb (9,530Â kg).[46] The improved avionics include a Rockwell Collins Common Avionics Architecture System (CAAS) cockpit, and BAE Systems' Digital Advanced Flight Control System (DAFCS).[44]
Boeing has delivered 48 F-model helicopters to the United States Army; on 26 August 2008, Boeing announced that the Army has signed a five-year contract, worth over $4.8 billion for 191 more, plus 24 options.[46] In February 2007, the Netherlands were the first international customer to order the F model; six helicopters were ordered to expand their current fleet to 17. These helicopters will be equipped with an upgraded version of the Honeywell Avionics Control Management System (ACMS) cockpit.[47] On 10 August 2009, Canada signed a contract to purchase 15 CH-47Fs for delivery in 2013-14.[48][49]
On 15 December 2009 the British government announced its Future Helicopter Strategy including the purchase of 24 new CH-47F Chinooks to be delivered from 2012.[50] In April 2009, Australia requested seven CH-47Fs,[51] and placed an order for seven CH-47Fs on 20 March 2010. These aircraft are scheduled to replace the Australian Army's six CH-47Ds between 2014 and 2017.[52]
Specifications (CH-47D)
Data from Boeing CH-47D/F,[74] Army Chinook file,[75] International Directory[76]
General characteristics
- Crew: 3 (pilot, copilot, flight engineer)
- Capacity: ** 33-55 troops or
- 24 litters and 3 attendants
- 28,000 lb (12,700 kg) cargo
- Length: 98 ft 10 in (30.1 m)
- Rotor diameter: 60 ft 0 in (18.3 m)
- Height: 18 ft 11 in (5.7 m)
- Disc area: 2,800 ft² (260 m²)
- Empty weight: 23,400 lb (10,185 kg)
- Loaded weight: 26,680 lb (12,100 kg)
- Max takeoff weight: 50,000 lb (22,680 kg)
- Powerplant: 2× Lycoming T55-GA-712 turboshaft, 3,750 hp (2,796 kW) each
Performance
- Maximum speed: 170 knots (196 mph, 315 km/h)
- Cruise speed: 130 kt (137 mph, 220 km/h)
- Range: 400 nmi (450 mi, 741 km)
- Ferry range: 1,216 nmi (1,400 mi, 2,252 km[77])
- Service ceiling: 18,500 ft (5,640 m)
- Rate of climb: 1,522 ft/min (10.1 m/s)
- Disc loading: 9.5 lb/ft² (47 kg/m²)
- Power/mass: 0.28 hp/lb (460 W/kg)