In September 1958, the US Army commissioned Boeing Vertol to develop a medium transport helicopter capable of lifting a 2000kg load in all weathers. Boeing submitted a scaled-up version of its Model 107, and the new Model 114 project, the first in the very popular line of Chinook helicopters, was declared winner of the design competition in March 1959.

That it is a direct descendant of the Model 107 may be clearly seen in the broad, blunted, square fuselage section common to both aircraft. The Chinook's fuselage is in fact built around a large cargo bay, in front of which is the flight deck and above it, at either end, the pylons holding the transmission for the two rotors. The two turbine engines are installed on either side of the aft pylon. Behind the cargo bay is a hydraulically-actuated ramp which greatly facilitates loading and unloading operations. On either side of the fuselage are two large fairings, housing the fuel tanks, landing gear shock absorbers and battery for the electrical system. The cargo bay has a volume of circa 42m³ and can carry either 44 troops, 24 stretcher cases plus two medical attendants, or various items of equipment, representing a weight of between eight and 11 tonnes. A hoist at the front of the bay can be used for lifting loads vertically through a hatch in the middle of the floor or for lowering items to the ground. The Chinook also has a cargo hook at the center of gravity for carrying slung loads, enabling it to operate as a flying crane.

The contra-rotating tandem rotors comprise a hub and three blades 18.28m in diameter. The articulated blades are composed of a steel spar and light alloy honeycomb panels, with a fiberglass reinforced plastic skin.

The two turbine engines are regulated automatically by the flight deck controls and fuel control system. A 67shp Solar turbine at the base of the aft pylon drives the electric generators and hydraulic pumps. At the front end of each turbine is a 90° gearbox, from which a shaft leads to the combining transmission. The two turbine engine transmissions, apart from changing the direction of drive and reducing the r.p.m, each have a freewheel which enables the rotors to autorotate, overriding the engine in the event of engine failure. To minimize the vibrations transmitted to the fuselage by the rotors, the helicopter has five vibration absorbers, one in the nose, two under the cockpit floor and two inside the aft pylon. The landing gear consists of four non-retractable units. The front wheels are of the non-steerable type, while the rear wheels are steerable (but are locked during flight).

Five Boeing Model 114s, as chosen by the selection committee, were duly ordered by the US Army. These were followed by steadily increasing orders: the CH-47B soon replaced the original model, and came to be chosen by the US Army as the standard troop transport for the First Cavalry Division (Airmobile). The CH-47B — recognizable by the two thin fins at the base of the rear ramp — was followed by the CH-47C which had new 3802shp T55-L-11A engines, strengthened transmission and new, larger capacity fuel tanks. The first CH-47C flew on 14 October 1967 and deliveries began in spring 1968. In Vietnam, the Chinook, together with Bell helicopters, shouldered most of the burden of operations.

Over 800 Chinooks have been built in all, about half of which were still in service at the beginning of the eighties, mostly updated to the standard of the CH-47D version with 4431shp T55-L-712 turbines. As well as for the US Army, the Chinook has been built for the Royal Australian Air Force (12) and the Spanish Ejercito del Aire (12), and others have been sold to Argentina, Canada, Great Britain and Thailand. An important agreement was signed in 1968 with Elicotteri Meridionali (a company created by Agusta in 1967) to manufacture the Boeing helicopter under license in Italy. After a number of setbacks, an order was confirmed for 26 CH-47Cs for the Italian Army and the first wholly Italian aircraft were delivered in 1974. The Italian order was followed first by an order for the Iranian Army (initially 20 aircraft) and then for Libya, Morocco, Egypt, Tanzania and Greece.

G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984

Following the evaluation of submissions by five US helicopter manufacturers, the US Army selected the Boeing Vertol Model 114 as most nearly meeting its requirements for a battlefield mobility helicopter. This was expected to be suitably equipped for all-weather operations, to lift a load of 1814kg internally or of 7257kg suspended from an external sling, carry a maximum of 40 troops with full equipment, to have straight-in rear loading, be suitable for casualty evacuation roles, and be able to airlift any component of the Martin Marietta Pershing missile system. An initial contract for five YHC-1B pre-production examples was placed in June 1959, but soon after entering service these were redesignated YCH-47A and given the name Chinook.

The Model 114 was, in effect, a larger and more powerful version of the same company's Model 107 (CH-46 Sea Knight). The non-retractable landing gear is of quadricycle configuration, and the fuselage has sealed and compartmented fairing pods on each side of the lower fuselage, extending for almost three-quarters of the fuselage length to supplement the buoyancy of the sealed lower fuselage for water operations. The first YHC-1B made its initial flight on 21 September 1961, by which time the first production contract for CH-47A aircraft had been placed. These were powered initially by 1641kW Lycom-ing T55-L-5 turboshafts (subsequently by 1976kW T55-L-7 turboshafts), and deliveries of CH-47As began in December 1972.

Since that time a number of versions have been built, including the CH-47B, a development with more powerful 2125kW T55-L-7C turboshafts, redesigned rotor blades and other detail refinements, the first of two prototypes making its first flight during October 1966, with deliveries beginning on 10 May 1967. It was followed by the CH-47C (Model 234) which is powered by two 2796kW T55-L-11C turboshafts, has a strengthened transmission system, and incorporates increased fuel capacity. The first of these aircraft made its initial flight on 14 October 1967, and deliveries of production aircraft began in early 1968. Nine aircraft similar to the CH-47C have been built for the Canadian Armed Forces, under the designation CH-147; deliveries began in September 1974. The CH-147 has the latest safety features and an advanced flight-control system, with a maximum land take-off weight of 22680kg and emergency water take-off weight of 20865kg. During the war in Vietnam, four of an ACH-47A derivative were built, similar in configuration to the CH-47A, but equipped with armour and armament which included a 40mm grenade-launcher in the nose, a 20mm forward-firing cannon and a 7.62mm machine-gun or a 19-round rocket pack mounted on a pylon, one on each side of the fuselage, plus five gun positions for air gunners stationed in the cabin, each having a 12.7mm or 7.62mm machine-gun on a flexible mounting. Three of these were evaluated in Vietnam, but no further examples were built.

Chinooks operated in South East Asia proved most valuable, not only for the transport of troops and supplies, and for casualty evacuation, but also for the recovery of disabled aircraft and the airlift of refugees. Chinooks are still considered an important component of the US Army's helicopter air logistic forces, and it is planned to modernise all surviving aircraft. Under a US Army development programme, one each of the models CH-47A, CH-47B, and CH-47C were stripped down to the basic airframe, and rebuilt to an improved standard to serve as CH-47D prototypes. These upgraded CH-47Ds have more-powerful turboshaft engines and higher-rated transmissions; a redesigned avionics; and many design refinements. They also introduce an auxiliary power unit and a triple hook cargo-suspension system. Following a successful conclusion to flight testing of these prototypes by the US Army, Boeing Vertol started a programme of remanufacturing CH-47As to CH-47D standard, and the first of these was delivered in 1982.

Under the designation Chinook HC. Mk 1, the Royal Air Force ordered 33 examples similar to the Canadian CH-147. They have British avionics and equipment, and a number of special provisions. The first was handed over in August 1980, and delivery of all 33 was completed during early 1982. Since 1970 Chinooks have been built in Italy for European and Middle East customers, following acquisition by Elicotteri Meridionali of co-production and marketing rights from Boeing Vertol. Agusta, SIAI-Marchetti, and other Italian manufacturers are also involved in this programme.

Production by Boeing Vertol of new military Chinooks is now limited to orders for the Model 414, which is an international export version and the MH-47E, a Special Forces variant of the CH-47D with night/low flying avionics and an inflight-refuelling probe.

D.Donald "The Complete Encyclopedia of World Aircraft", 1997

Design of all-weather medium transport helicopter for US Army began 1956; first flight of first of five YCH-47As 21 September 1961. Performance increased in CH-47C by uprated transmissions and 2,796kW T55-L-11A; integral fuel capacity increased to 3,944 litres; first flight 14 October 1967.

VERSIONS

CH-47A: Initial production version, powered by two 1,640kW Lycoming T55-L-5 or 1,976kW T55-L-7 turboshaft engines. Withdrawn from service. Total 354 built for US Army.

CH-47B: Developed version with 2,125kW T55-L-7C turboshaft engines, redesigned rotor blades with cambered leading-edge, blunted rear rotor pylon, and strakes along ramp and fuselage for improved flying qualities. First of two prototypes flew for the first time early October 1966. Deliveries began 10 May 1967. Withdrawn from service. Total 108 built for US Army.

CH-47C: Developed version with uprated transmissions and 2,796kW T55-L-11A; integral fuel capacity increased to 3,944 litres; first flight 14 October 1967; 270 delivered to US Army from Spring 1968; 182 US Army CH-47Cs retrofitted with composite rotor blades; integral spar inspection system (ISIS) introduced 1973 together with crashworthy fuel system retrofit kit. Transmissions of some As and Bs upgraded to CH-47C standard.

Boeing 234: Commercial version, now out of production.

CURRENT VERSIONS

CH-47C: Agusta (Meridionali) built 136 by 31 December 1995. Production line open but no orders received recently.

CH-47D: US Army contract to modify one each of CH-47A, B and C to prototype Ds placed 1976; first flight 11 May 1979; first production contract October 1980; first flight 26 February 1982; first delivery 31 March 1982; initial operational capability (IOC) achieved 28 February 1984. First multiyear production contract awarded 8 April 1985 for 240 aircraft; second multiyear production contract for 144 CH-47Ds awarded 13 January 1989, bringing total CH-47D (and MH-47E) ordered to 472; further two Gulf War attrition replacements authorised August 1992 (these new-build); seven ex-Australian rebuilds funded June 1993 for delivery January to November 1995.

CH-47D update included strip down to bare airframe, repair and refurbish, fit AlliedSignal T55-L-712 turboshafts, uprated transmissions with integral lubrication and cooling, composite rotor blades, new flight deck compatible with night vision goggles (NVG), new redundant electrical system, modular hydraulic system, advanced automatic flight control system, improved avionics and survivability equipment, Solar T62-T-2B APU operating hydraulic and electrical systems through accessory gear drive, single-point pressure refuelling, and triple external cargo hooks. Principal external change is large, rectangular air intake in leading-edge of rear sail. Composites account for 10 to 15 per cent of structure. About 300 suppliers involved.

Test programme began late 1995 of Chinook with vibration-reducing dynamically tuned fuselage.

MH-47D Special Operations Aircraft: Two battalions equipped with 11 CH-47D SOA fitted with refuelling probes (first refuelling July 1988), thermal imagers, AlliedSignal RDR-1300 weather radar, improved communications and navigation equipment, and two pintle-mounted 7.62mm machine guns. Navigator/commander's station also fitted.

GCH-47D: At least 12 Chinooks grounded for engineer training.

JCH-47D: Two CH-47Ds modified for special testing.

MH-47E: Special Forces variant; planned procurement 51, deducted from total 472 CH-47D conversions but only 25 received, including 14 not covered by multiyear production contract; prototype development contract 2 December 1987; long-lead items for next 11 helicopters authorised 14 July 1989; firm order for 11, plus option on next 14, awarded 30 June 1991; Lot 2 (14 helicopters) confirmed 23 June 1992. Prototype (88-0267) flew 1 June 1990; delivered 10 May 1991; initial production aircraft flown 1992. Following mission software problems, deliveries began January 1994; last of 26 (including prototype) received April 1995.

Equipment includes IBM-AlliedSignal integrated avionics with four-screen NVG compatible EFIS; dual MIL-STD-1553 digital databusses; AN/ASN-145 AHRS; jamming-resistant radios; Rockwell Collins CP1516-ASQ automatic target hand-off system; inertial AN/ASN-137 Doppler, Rockwell Collins AN/ASN-149(V)2 GPS receiver and terrain-referenced positioning navigation systems; Rockwell Collins ADF-149; Perkin-Elmer AN/AVR-2 laser, E-Systems AN/APR-39A laser and Honeywell AN/AAR-47 missile warning systems; ITT AN/ALQ-136(V) pulse jammer and Northrop Grumman AN/ALQ-162 CW jammer; Tracor M-130 chaff/flare dispensers; Texas Instruments AN/APQ-174A radar with modes for terrain-following down to 30 m (100 ft), terrain-avoidance, air-to-ground ranging and ground-mapping; Hughes AN/AAQ-16 FLIR in chin turret; digital moving map display; Elbit ANVIS-7 night vision goggles; uprated T55-L-714 turboshafts with FADEC; increased fuel capacity; additional troop seating (44 maximum); OBOGS; rotor brake; 272 kg (600 lb) rescue hoist with 61 m (200 ft) usable cable; two M-2 0.50 in window-mounted machine guns (port forward: starboard aft); provisions for Stinger AAMs using FLIR for sighting.

MH-47E has nose of Commercial Chinook to allow for weather radar, if needed; forward landing gear moved 1.02 m (3 ft 4 in) forward to allow for all-composite external fuel pods (also from Commercial Chinook) that double fuel capacity; Brooks & Perkins internal cargo handling system. See also Chinook HC. Mk 3, below. Chinook HC. Mk 2/2A: RAF version; Mk 1 designation CH47-352; all survivors of original 41 HC. Mk 1s upgraded to HC. Mk 1B; UK MoD authorised Boeing to update 33 (later reduced to 32) Mk 1Bs to Mk 2, equivalent to CH-47D, October 1989; changes include new automatic flight control system, updated modular hydraulics, T55-L-712F power plants with FADEC, stronger transmission, improved Solar 71 kW (95 shp) T62-T-2B APU, airframe reinforcements, low IR paint scheme, long-range fuel system and standardisation of defensive aids package (IR jammers, chaff/flare dispensers, missile approach warning and machine gun mountings). Smiths Industries HUMS being installed. Requirement exists for FLIR. Conversion continued from 1991 to July 1995. Chinook HC. Mk 1B ZA718 began flight testing Chandler Evans/Hawker Siddeley dual-channel FADEC system for Mk 2 in October 1989. Same helicopter to Boeing, March 1991; rolled out as first Mk 2 19 January 1993; arrived RAF Odiham 20 May 1993; C(A) clearance November 1993. Final Mk 1 withdrawn from service, May 1994, at which time 11 Mk 2s received. Further three new-build Mk 2s ordered 1993, for delivery from mid-1995; decision to order further 14 Mks 2A/3 announced March 1995. Mk 2A has dynamically tuned fuselage. Total RAF procurement 58 CH-47C/D/Es. First HC. Mk 2A handed over in USA 6 December 1997; arrived UK for clearance trials 18 December; remainder delivered by end of 1998.

Chinook HC. Mk 3: Eight of 14 additional RAF Chinooks announced March 1995 assigned to Special Forces; configuration similar to MH-47E, including large fuel panniers, weather radar and refuelling probes. First flight mid October 1998; deliveries from March 2000.

HT.17 Chinook: Spanish Army version.

Boeing 414: Export military version; superseded by CH-47D International Chinook.

CH-47D International Chinook: Boeing 414-100 first sold to Japan; Japan Defence Agency ordered two for JGSDF and one for JASDF Spring 1984; first flight (N7425H) January 1986 and, with second machine, delivered to Kawasaki April 1986 for fitting out; co-production arrangement (see under Kawasaki). International Chinook available in four versions with combinations of standard or long-range (MH-47E type) fuel tanks and T55-L-712 SSB or T55-L-714.

CH-47SD 'Super D': Latest variant on offer for export; embodies some improvements first installed on the MH-47E for US special operations forces. AlliedSignal T55-L-714A turboshaft with FADEC chosen as standard power plant; single-point pressure refuelling and jettison capability on both sides of aircraft, with fuel contained in two ballistic and crash-resistant tanks; total usable capacity is 7,828 litres (2,068 US gallons; 1,722 Imp gallons); CH-47SD also has Smiths digital fuel quantity gauging system in place of Ragen analogue system. Simplified structure offers benefits in maintainability and reliability.

CH-47SD also incorporates modernised NVG-compatible cockpit with avionics control management system (ACMS), utilising proven military and commercial off-the-shelf equipment on single console to reduce pilot workload and with provisions for growth. Avionics suite is comparable to that of baseline CH-47D, but features two embedded INS/GPS units as well as AN/ARN-147 VOR/ILS and AN/ARN-149 ADF, plus space and power provisions for Tacan. Rollout scheduled for 31 October 1999.

CH-47F Improved Cargo Helicopter (ICH): Boeing programme for improved Chinook configuration for US Army involving the development and production of a new version that will remain operational and cost-effective until a new cargo helicopter is developed between 2015 and 2020 under the current Army Aviation Modernisation Plan.

CUSTOMERS: Total 735 CH-47A/B/C built and 479 CH-47D/MH-47E conversions authorised for US Army. Another 166 built by Boeing for export customers together with 45 kits. Agusta (Meridionali) production totals 136, with Kawasaki having built 54 by January 1999. Total Chinook orders, including civil, amount to 1,155.

DESIGN FEATURES: Two three-blade intermeshing contrarotating tandem rotors; front rotor turns anti-clockwise, viewed from above; rotor transmissions driven by connecting shafts from combiner gearbox, which is driven by rear-mounted engines. Classic rotor heads with flapping and drag hinges; manually foldable blades, using Boeing Helicopters VR7 and VR8 aerofoils with cambered leading-edges; blades can survive hits from 23mm HEI and API rounds; rotor brake optional. Constant cross-section cabin with side door at front; rear-loading ramp that can be opened in flight; underfloor section sealed to give flotation after water landing; access to flight deck from cabin; main cargo hook mounting covered by removable floor panel so that load can be observed in flight.

FLYING CONTROLS: Differential fore and aft cyclic for pitch attitude control; differential lateral cyclic pitch (from rudder pedals) for directional control; automatic control to keep fuselage aligned with line of flight. Dual hydraulic rotor pitch-change actuators: secondary hydraulic actuators in control linkage behind flight deck for autopilot/autostabiliser input; autopilot provides stabilisation, attitude hold and outer-loop holds.

STRUCTURE: Blades based on D-shaped glass fibre spar, fairing assembly of Nomex honeycomb core and cross-ply glass fibre skin.

LANDING GEAR Non-retractable quadricycle type, with twin wheels on each front unit and single wheels on each rear unit. Oleo-pneumatic shock-absorbers in all units. Rear units fully castoring; power steering on starboard rear unit. All wheels are size 24 x 7.7-VII, with tyres size 8.50-10-III, pressure 4.62 bars. Two single-disc hydraulic brakes. Provision for fitting detachable wheel/skis.

POWER PLANT: Two AlliedSignal T55-L-712 turboshafts, pod-mounted on sides of the rear pylon, each with a standard power rating of 2,237kW and maximum rating of 2,796kW. AlliedSignal T55-L-712 SSB engine has standard power rating of 2,339kW and maximum of 3,217kW; transmission capacity (CH-47D and MH-47E) 5,593kW on two engines and 3,430kW OEI; rotor rpm 225.

Self-sealing pressure refuelled crashworthy fuel tanks in external fairings on sides of fuselage. Total fixed fuel capacity 3,899 litres. Provision for up to three additional long-range tanks in cargo area, each of 3,028 litres; maximum fuel capacity (fixed and auxiliary) 6,927 litres. Oil capacity 14 litres.

From January 1991, 100 CH-47Ds fitted with engine air particle separator (also available for RAF variant). Standard in MH-47E and optional in International Chinook are two AlliedSignal T55-L-714 turboshafts, each with a standard power rating of 3,108kW continuous and emergency rating of 3,629kW. CH-47SD has T55-L-714A turboshafts with maximum continuous rating of 3,039kW. FADEC installed on late production CH-47Ds and CH-47SD. Normal fuel capacity in CH-475S and MH-47E is 7,828 litres, but MH-47E can also operate with three long-range tanks in cargo area, each containing 3,028 litres, bringing total fuel capacity to 16,913 litres. CH-47D SOA and MH-47E have 8.97m refuelling probe on starboard side of forward fuselage.

ACCOMMODATION: Two pilots on flight deck, with dual controls. Lighting compatible with pilots' NVGs (Nite-Op in RAF variant). Jump seat for crew chief or combat commander. Jettisonable door on each side of flight deck. Depending on seating arrangement, 33 to 55 troops can be accommodated in main cabin, or 24 litters plus two attendants, or vehicles and freight. Rear-loading ramp can be left completely or partially open, or can be removed to permit transport of extra-long cargo and in-flight parachute or free-drop delivery of cargo and equipment.

Main cabin door, at front on starboard side, comprises upper hinged section which can be opened in flight, and lower section with integral steps. Lower section is jettisonable. Triple external cargo hook system, with centre hook rated to carry maximum load of 11,793kg and the forward and rear hooks 7,711kg each, or 10,433kg in unison. Provisions are installed for a power-down ramp and water dam to permit ramp operation on water, for forward and rear cargo hooks, internal ferry fuel tanks, external rescue hoist, and windscreen washers.

SYSTEMS: Hydraulic system comprises a utility system, a No.1 flight control system and a No.2 flight control system. Electrical system includes two 40kVA air-cooled alternators driven by transmission drive system. Solar T62-T-2B APU drives a 20kVA generator and hydraulic motor pump, providing electrical and hydraulic power for main engine start and system operation on the ground.

AVIONICS: International CH-47D: US Army CH-47D assumed to be generally similar. Specific MH-47E avionics listed under that heading.
Comms: ARC-102 HF com radio, Collins ARC-186 UHF/AM-FM, Magnavox ARC-164 UHF/AM com; C-6533 intercom; AlliedSignal AN/APX-100 IFF.
Flight: APN-209 radar altimeter; AN/ARN-89B ADF; AN/ARN-118 Tacan; AN/ARN-123 VOR/glide slope/marker beacon receiver; and AN/ASN-43 gyromagnetic compass. AFCS maintains helicopter stability, eliminating the need for constant small correction inputs by the pilot to maintain desired attitude. The AFCS is a redundant system using two identical control units and two sets of stabilisation actuators.
Instrumentation: Flight instruments are standard for IFR, and include an AN/AQU-6A horizontal situation indicator.
Mission: Chelton 19-400 satellite communications antenna on some RAF helicopters.
Self-defence: Provision for AN/APR-39A RWR, AN/ALQ-156 missile warming equipment and Tracor M-130 chaff/flare dispensers. RAF Chinooks have Tracor M-206/M-1 chaff/flare dispensers, Marconi ARI18228 Sky Guardian RWR and (from 1990) Lockheed Martin AN/ALQ-157 IR jammers, Honeywell AN/AAR-47 missile approach warning equipment and Racal RNS252 Super TANS INS including GPS.

EQUIPMENT: Hydraulically powered winch for rescue and cargo handling, rearview mirror, plus integral work stands and step for maintenance.

ARMAMENT: Provision for two machine guns or miniguns in crew door (starboard) and forward hold window (port).

Jane's Helicopter Markets and Systems

- In the Falklands War in 1982, a British Chinook carried 82 paratroopers in a single lift and survived a minor crash.

- The MH-47E is a special operations version, with night-flying capability.

- A Chinook pilot was killed in the First Gulf War after flying into a tower.

- The new CH-47D has triple hooks, night goggle-compatible cockpit, advanced rotors and improved crash protection.

- The lower fuselage is completely sealed to allow emergency ditching in water.

- RAF Chinooks inserted teams of SAS commandos into Iraq in the First Gulf War.