The Boeing Sea Knight & Chinook

v1.0.1 / 01 jul 02 / greg goebel / public domain

* Frank Piasecki and his Piasecki Helicopter company were pioneers of military helicopter technology, building a series of tandem-rotor helicopters, most notably the "Flying Bananas". Piasecki left Piasecki Helicopter in 1955 to found a new company that would also carry the Piasecki name, and the original firm refashioned itself as "Vertol (Vertical Take-Off & Landing)". Vertol was bought out by Boeing in 1960, to become first "Boeing Vertol" and later simply "Boeing Helicopters".

Whatever the name, the company would only build two successful products, the "CH-46 Sea Knight" and the "CH-47 Chinook", but they would both be sold in quantity, and remain in service in the 21st century. This document provides a short history of the Sea Knight and the Chinook.

[1] ORIGINS: VERTOL V-107 & V-114
[4] US ARMY CH-47A / CH-47B / CH-47C / CH-47D / SOA CHINOOKS
[7] ACH-47A GUNSHIP / MODEL 347 / XCH-62 HLH (MODEL 301) / MODEL 360

[1] ORIGINS: VERTOL V-107 & V-114

* In 1956, Vertol began studies for a new medium-lift helicopter, with the general configuration of the company's "HUP-1 Retriever / H-25 Mule" helicopter and based on the rotor system of the company's "H-21 Flying Banana", but fitted with new lightweight turboshaft engines then in development. The new machine was given the company designation of "Vertol Model 107 (V-107)", and company management decided to go ahead with development using their own funds.

Construction of the V-107 prototype began in May 1957. The prototype was powered by two Lycoming T53 turboshaft engines, each with 860 horsepower and lent by the US Army. Initial flight of the prototype was on 22 April 1958. The machine was then put through an intensive program of flight demonstrations in the US and overseas. In June 1958, the Army awarded a contract to Vertol for ten production aircraft designated "YHC-1A".

The Army also issued a request to industry for a larger helicopter, and so Vertol began design work on what amounted to a scaled up version of the V-107, designated the "V-114". The V-114 won the Army competition in March 1959, and Vertol was awarded a contract for a mockup and five prototypes, to be designated the "YHC-1B".

Vertol was now busy trying to develop two helicopters at the same time, which severely strained the company and led to the Boeing buyout. The number of YHC-1A prototypes was reduced to three to free up resources for YHC-1B development. The first flight of the initial YHC-1B prototype was on 21 September 1961.

The Army had lost interest in the smaller YHC-1A, but Boeing Vertol still felt there was a market for it and continued development. The US Marine Corps was impressed by the machine and awarded the company a production contract in February 1961.

The Marines originally wanted to give the V-107 the military designation of "HRB-1", but in September 1962, the Pentagon introduce a new "tri-service" uniform designation scheme. The HRB-1 became the "CH-46A Sea Knight", while the HC-1B became the "CH-47A Chinook". The five V-114 prototypes became "YCH-47As".



* Initial flight of a full-specification CH-46A was on 16 October 1962, and the type went into operational service with the Marines in June 1964. The service obtained a total of 160 CH-46As.

The CH-46A had the contrarotating tandem rotor configuration of its Piasecki Retriever ancestor. The two T58-GE8-8B turboshaft engines, providing 1,250 horsepower each, were fitted on either side of the rear rotor pedestal. A driveshaft ran to the forward rotor, and either of the two engines could run both rotors in an emergency. The three-bladed rotors had a power-folding scheme for shipboard storage, though some other Sea Knight variants would delete this feature and use manually-folding rotors instead.

The cargo bay had a rear loading ramp that could be removed or left open in flight for extended cargo or for parachute drops, and a winch system and rollers in the floor to help cargo loading. A belly sling hook for external loads could be installed through a cargo hatch in the floor. There was a split passenger door on the right side, with built-in steps on the bottom half.

The CH-46A had a crew of three, and could carry 17 troops; or 15 litters with two attendants; or 1,815 kilograms (4,000 pounds) of cargo. A pintle mount for a 12.7 millimeter (0.50 caliber) Browning machine gun was fitted on each side of the machine to accommodate a self-defense capability.

The CH-46A had fixed tricycle landing gear, with twin wheels on all three units. The main gear was fitted in rear sponsons that also contained self-sealing fuel tanks with a total capacity of 1,438 liters (350 US gallons). Some Sea Knight variants would also be fitted with auxiliary external tanks, as discussed later.

The gear configuration gave the machine a nose-up attitude that made cargo easier to load and unload. Skis could be fitted to the landing gear for operation on snow and on marshy ground. The Sea Knight could float on calm waters in an emergency, though it wasn't really an amphibian.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   rotor diameter          15.24 meters        50 feet
   fuselage length         13.66 meters        44 feet 10 inches
   footprint length        25.40 meters        83 feet 4 inches
   height (rotor head)     5.09 meters         16 feet 9 inches

   empty weight            5,625 kilograms     12,405 pounds
   max loaded weight       9,705 kilograms     21,400 pounds

   maximum speed           256 KPH             159 MPH / 138 KT
   service ceiling         4,265 meters        14,000 feet
   range                   370 kilometers      265 MI / 230 NMI
   _____________________   _________________   _______________________

CH-46A production was followed by 266 "CH-46Ds", with initial delivery in September 1966. The primary improvements were uprated T58-GE-10 turboshaft engines with 1,400 horsepower each, and modified rotor blades. The greater horsepower allowed the CH-46D to lift 25 troops or 3,175 kilograms (7,000 pounds) of cargo. About 12 CH-46As were also updated to the CH-46D standard.

The final Boeing production model was the "CH-46F", with 174 obtained by the USMC from July 1968 to February 1971. The CH-46F retained the T58-GE-10 turboshafts, but had revised avionics and other modifications.

The sponsons and the nose-up attitude of the CH-46 on the ground gave the appearance of a frog ready to hop, and so the Marines nicknamed the type the "Frog". Although there was initial suspicion of the type as Marines were accustomed to Sikorsky helicopters, the Frog quickly proved itself in Vietnam after its introduction into the theater in March 1966, though the CH-46 fleet was grounded for a time in 1967 when a few of them were lost in accidents. The Frogs acquitted themselves well, particularly during the siege of Khe Sanh in early 1968.

* The US Navy also acquired the Sea Knight, though in smaller numbers, beginning with 24 "UH-46As" shipboard resupply ("vertical replenishment / vertrep") helicopters. Initial delivery of the UH-46A was in July 1965.

This order was followed by ten "UH-46Ds", with five UH-46As also updated to this configuration. Some sources mention "HH-46A" and "HH-46D" variants for "search and rescue (SAR)", an "RH-46" minesweeper, and a "VH-46F" VIP transport, but specifics are unclear.

* The Sea Knight has proven very long-lived in service. Since Vietnam it has seen action with the Marines in Lebanon, Grenada, and elsewhere. The type has been through a number of upgrades and conversions, with most Marine machines now up to "CH-46E" standard. The CH-46E features fiberglass rotor blades, airframe reinforcement, and further uprated T58-GE-16 engines with 1,870 horsepower each. Some CH-46Es have been given doubled fuel capacity and nicknamed "Bullfrogs".

The fiberglass rotor blades were also fitted to US Navy Sea Knights, and many Sea Knights in foreign service. During the 1980s, the Marine and Navy Sea Knight fleets were given a broad set of updates in the form of the "safety, reliability, and maintainability (SR&M)" program, and late in the decade they were also given an airbag flotation system to improve their seaworthiness. Many current Marine Sea Knights have defensive countermeasures, including missile warning systems and chaff-flare dispensers, but it is unclear when and how they were fitted.

The Marines are now looking to replace the Sea Knight with the new Bell-Boeing "MV-22 Osprey" tilt-rotor transport, but the Osprey is an ambitious machine and the program has run into various snags. As a result, Marine Frogs are still in service. The US Navy, confronted with rising costs for keeping the service's venerable UH-46s in the air, is now trying to phase them out. Current target date for removal from service is spring 2004, though that schedule is dependent on acquisition of a replacement.



* Boeing built 17 "V-107/IIs" for commercial service, fitted with General Electric CT58 turboshafts with 1,250 horsepower each. They were available in an airliner format, with passenger seating and a rollout baggage compartment, or in a cargolifter format, with a rear loading ramp like the military versions of the helicopter.

One of the three YHC-1A prototypes was modified to serve as the V-107/II prototype, performing its first flight on 25 October 1960. The first of 17 production V-107/IIs performed its initial flight on 19 May 1961, with the type receiving US Federal Aviation Administration (FAA) certification in January 1962.

Seven of the V-107/IIs were operated by New York Airways, the first of them going into service on 1 July 1962. The other ten were sold to Kawasaki of Japan as a prelude to Japanese license construction of the type, as discussed below.

* Boeing sold a total 18 Sea Knights to Canada, beginning with six "CH-113 Labradors" delivered to the Royal Canadian Air Force for SAR duties in 1963 and 1964. They were basically CH-46As with a search radar radome in the nose and greater fuel capacity. The Canadian Army also obtained 12 "CH-113A Voyageurs" in 1964:1965, these machines being close to stock CH-46As.

The surviving Canuck Sea Knights were given a comprehensive update by Boeing Canada in the mid-1980s. Canadian Sea Knights remain in service, tasked with the SAR mission, but are being replaced by the Agusta-Westland EH-101 helicopter.

* Following the signing of a license agreement in early 1962, Kawasaki of Japan took up production of the V-107/II, under the designation of "KV-107/II". The first Kawasaki-built Sea Knight flew in May 1962. In 1965, Kawasaki signed a follow-on agreement with Boeing that allowed the Japanese company to sell the helicopter on the world market. All commercial sales of the Sea Knight after that time were from Kawasaki production.

The KV-107/II series was fitted with by twin General Electric CT58-110-1 turboshaft engines or equivalent license-built Ishikawajima-Harima CT58-IHI-110-1 engines. Subvariants included:

Kawasaki then went on to develop a "KV-107/IIA" series with uprated CT58-140-1 or CT58-IHI-140-1 turboshafts providing 1,400 horsepower each. Boeing assisted in qualification of the new series. A number were built for the Japanese military:

Saudi Arabia took a particular interest in the type , with Kawasaki building a series of "KV-107/IIA-SM" variants for that nation, including:

The KV-107s in Japanese service are now largely or completely out of service, any of them having been replaced by Kawasaki-built CH-47s, discussed later. Status of the KV-107 in Saudi service is unclear.

* The Swedish air force obtained ten Sea Knights in 1962 and 1963, while the Swedish navy obtained three in the same timeframe. These machines were designated "HKP-4A" and "HKP-4B" respectively, where "HKP" is from the Swedish rendering of the word "helicopter". It appears that these machines were built by Boeing, since the Japanese constitution includes strong obstacles to the export of weapons systems.

These were unique variants, featuring large fuel capacity, and fitted with Rolls-Royce Gnome H-1200 turboshafts, with 1,200 horsepower each, and Decca navigation systems after arrival in Sweden.

The Air Force HKP-4A machines were used for SAR, and featured a retractable rescue hoist in the forward door. The Navy HKP-4B machines were used for antisubmarine warfare (ASW) and minesweeping. They were fitted with a search radar radome on the end of the tail ramp, of all places, and could carry dipping sonar. Offensive armament consisted of four homing torpedoes, or six depth charges specially designed for shallow water-work.

One of the HKP-4Bs crashed in 1968, and Kawasaki provided a replacement, which is said to have been a refurbishment of the initial Kawasaki KV-107/II prototype. The Swedish Navy obtained eight more KV-107s as "HKP-4Cs" in 1972:1974, with these machines fitted to a similar configuration as the HKP-4B but powered by Gnome H-1400 turboshafts with 1,400 horsepower each. Exactly how Kawasaki got over the constitutional obstacles is likely an interesting study in politics.

The Air Force HKP-4As were phased out in the late 1980s or early 1990s, with four transferred to the Navy and updated to ASW configuration as "HKP-4Ds". The Navy HKP-4s are expected to remain in service until 2005 at earliest.


[4] US ARMY CH-47A / CH-47B / CH-47C / CH-47D / SOA CHINOOKS

* Initial delivery of the CH-47A Chinook to the US Army was in August 1962. The Chinook had a similar configuration to the Sea Knight, with the same contrarotating tandem-rotor configuration and turboshaft engines mounted on each side of the the rear rotor pedestal. As with the Sea Knight, a driveshaft ran up the top of the fuselage to the forward rotor and one engine could drive both rotors in a pinch.

Initial CH-47A engine fit consisted of two Lycoming T55-L-5 turboshafts with 2,200 horsepower each. These were presently changed in production to T55-L-7 turboshafts with 2,650 horsepower each. The three-bladed rotors were set high enough to allow personnel to walk under them safely under normal circumstances. The rotors could be manually folded.

The Chinook had a rear loading ramp that could be set to any level to allow loads from truckbeds or other platforms, and could be opened in flight for dropping paratroops or parachute loads. A winch system was provided in the cargo bay to help handle loads, which were secured with deck tie-point points. A single sling attachment was fitted in the belly.

Of course, the Chinook was bigger than the Sea Knight, boxcar size rather than schoolbus size. Fairings containing the fuel tanks ran most of the length of the fuselage, and there were four fixed landing gear, rather than three. Fuel capacity of the CH-47A's self-sealing tanks was 2,350 liters (621 US gallons). There were dual wheels on the front gear, which bore most of the load, and single wheels on the back. The rear wheels were steerable. As with the Sea Knight, the wheels could be fitted with skis for operation on snow or marshy ground. The machine could land on calm waters in an emergency.

Crew consisted of pilot, copilot, and loadmaster or combat commander. There were emergency exit doors on each side of the cockpit, and a split-section personnel door behind the cockpit on the left side. The personnel door had built-in steps on the lower half. An auxiliary power unit provided ground power and operations from remote sites, and the cargo bay included a heater-blower system to keep the occupants warm.

The CH-47A could carry 33 fully-equipped troops on sidewall seating, though more could be carried by fitting center seats; or 24 casualty litters with two attendants; or 2,720 kilograms (6,000 pounds) of internal cargo. Almost 6 tonnes (13,000 pounds) of cargo could be lifted externally, though with much reduced range for very heavy loads.

354 CH-47As were built for the US Army. The Chinook went to Vietnam in 1965, where it served with distinction, particularly in retrieving thousands of downed aircraft from field locations. It was also useful for carrying stores, ammunition, and artillery pieces to remote firebases.

The Chinooks were generally armed with a single 7.62 millimeter 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.

* CH-47A production was followed by manufacture of 108 "CH-47Bs" for the US Army, with initial flight of a prototype, a modification of one of the five original YCH-47A prototypes, on 9 September 1966. Initial service delivery was in May 1967, and the type arrived in Vietnam in February 1968.

The CH-47B featured Lycoming T55-L-7C turboshafts with 2,850 horsepower each, as well as slightly longer, redesigned rotor blades. Strakes were fitted alongside the rear loading ramp to improve flight stability, a feature retained in later Chinook models.

* The CH-47B was an interim solution while Boeing worked on a more substantially improved Chinook, the "CH-47C", which was the last major new production variant for the US Army.

The CH-47C featured Lycoming T55-L-11 turboshafts with 3,750 horsepower each and a more robust power transmission system to support the greater power. One of the main drivers for the development of the CH-47C was that the earlier versions of the Chinook had troubles carrying the Army's M198 155 millimeter howitzer any distance. The CH-47C could not only handle the big howitzer, the machine also had substantially greater speed than its predecessors.

In addition, the CH-47C had greater fuel capacity of 4,273 liters (1,129 US gallons). Additional fuel bladders could be carried in the cargo bay for long ferry flights, giving the C-47C the capability to cross the Atlantic and self-deploy to Europe.

270 CH-47Cs were built, with the first flying on 14 October 1967. Initial deliveries to the US Army began in the spring of 1968, with the variant going into service in Vietnam in September of that year.

* The large Chinook fleet in US Army service remains the backbone of the service's medium-lift capability, serving in most of America's campaigns since Vietnam. Not only has the big helicopter proven useful and reliable, but it has an enviable flight safety record. It has been used for a wide range of roles, including fire-fighting with a sling-carried kit, and even for transporting the Apollo Lunar Module, used to land on the Moon, from the Grumman manufacturing plant in Tulsa, Oklahoma, to Cape Canaveral in Florida.

The Chinook has been upgraded to keep it in service. A glass-fiber rotor blade was introduced in 1969, and 182 CH-47Cs were retrofitted with the improved blades. The CH-47C fleet was also fitted with "crashworthy" fuel tanks beginning in 1973.

403 US Army Chinooks, including CH-47As, CH-47Bs, and CH-47Cs, were later upgraded to the "CH-47D" specification. The CH-47D features a refurbished airframe with some composite assemblies; single-point pressure refueling; an improved rotor transmission; fiberglass rotor blades; and improved Textron Lycoming (now Garrett) T55-L-712 turboshafts providing 3,750 horsepower each.

Lift capacity was increased to 6,300 kilograms (13,900 pounds) internally or 10,340 kilograms (22,800 pounds). The CH-47D could even lift a Cat D-5 bulldozer. One nice new feature was fit of three sling hooks, which made it much easier for the machine to lift unstable cargoes, or balance multiple loads. This was one of those ideas that in hindsight should have been implemented at the start, and it is now standard on all Chinooks.

The CH-47D program was initiated in 1976, with first flight of a prototype on 14 May 1979. The first flight of a production CH-47D was on 26 February 1982, with the variant going into service that May. The CH-47D has gone on to provide excellent service in the Gulf War and other campaigns.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   rotor diameter          18.29 meters        60 feet
   fuselage length         15.54 meters        51 feet
   footprint length        30.14 meters        98 feet 11 inches
   height (rotor head)     5.77 meters         18 feet 11 inches

   empty weight            10,150 kilograms    22,380 pounds
   max loaded weight       22,680 kilograms    50,000 pounds

   maximum speed           298 KPH             185 MPH / 160 KT
   service ceiling         6,735 meters        22,100 feet
   operational radius      185 kilometers      115 MI / 100 NMI
   _____________________   _________________   _______________________

* About 32 CH-47Ds were updated to the "CH-47D Special Operations Aircraft (SOA)" configuration for support of the US Army Special Operations Command (Army SOC). These machines were fitted with improved navigation and communications gear, including satellite communications links; countermeasures systems; and pintle-mounted machine guns. Introduction to service was in 1985.

The Army went on to obtain improved SOA Chinooks. The CH-47D SOA was followed by a dozen "MH-47D SOA" machines, with deliveries beginning in the mid-1980s. These rotorcraft were similar to the CH-47D SOA variant, but added nose radar, a forward-looking infrared (FLIR) camera mounted in the nose, a glass cockpit, inflight refueling probe, and other refinements. One crashed in 1989.

The next step was the "MH-47E SOA", which built on the MH-47D by adding a Texas Instruments APQ-174 terrain-following radar in a pod on the left side of the machine; a night vision goggle (NVG) compatible cockpit; and oversized fairings with a huge fuel capacity, along with additional internal fuel tanks.

26 MH-47Es were rebuilt from other Chinook models, with initial flight of a prototype on 1 June 1990 and service delivery in early 1994. Two MH-47Es was lost in crashes, one in 1996 and the second in 2002. The CH-47Ds have been been returned to conventional Chinook transport configuration, but the MH-47Ds and MH-47Es remain in service.

Following the American intervention in Afghanistan in late 2001, the US Army's special operations helicopter fleet was very heavily committed, and the service is now interested in expanding the fleet from 35 machines to 72 in expectation of further service in the American "war on terror". They will all be the new "MH-47G SOA" variant, which will essentially provide MH-47E-style enhancements to the new "CH-47F" variant, described in a later section, plus an improved defensive countermeasures suite.

All MH-47Ds and MH-47Es will be upgraded to the MH-47G configuration, and the Army may buy a few used Chinooks on the international market for upgrade as well. The remainder will be new production.



* Boeing announced the "Model 234 Commercial Chinook" in the summer of 1978. This variant was based on the CH-47C but incorporated features that would go into later military Chinook production, such as a "long nose" housing weather radar, and some models were fitted with oversized fairings for housing bigger fuel tanks. They were powered by Avco Lycoming AL-5512 turboshafts with 4,075 horsepower for takeoff, and could be ordered in pure airliner, cargo carrier, or mixed configurations.

The major target market for the Model 234 was support of offshore oil exploration. Six "Model 234LR" machines with the big fairings and airliner seating for 44 passengers were sold to British Airways Helicopters to support a contract from Shell Oil. However, the Model 234 suffered a serious blow to its credibility for offshore use when one was lost in the mid-1980s due to a rotor failure.

Three more Model 234LRs were sold to a Norwegian operator. All the eight surviving Model 234LRs were eventually bought up by an American operator and brought up to the "Model 234UT (utility)" configuration, with increased lift capacity and additional fuel storage.

Two new-build "Model 234ER (extended range)" machines, similar to the Model 234LR but with additional internal fuel tankage, were sold to Arco Alaska. This gives total Model 234 production of only 11 machines, trivial in contrast to the hundreds of military Chinooks sold.

* Although a number of ex-US Army CH-47As were provided to Thailand, the first new-build military export version of the Chinook was the "Model 414", essentially a CH-47C, with a dozen sold to Royal Australian Air Force (RAAF) and initial delivery in 1973. These machines were nicknamed "Chooks", Aussie slang for "chicken".

One RAAF CH-47C was lost in a crash in 1985. The other eleven were put into storage in 1989, when the Australian Army took up the battlefield support role from the RAAF. Seven of these machines found their way eventually back to the US Army, as part of a deal in which the other four were updated to CH-47D standard and returned to Australian Army service, where they were desperately needed.

The Australian Army couldn't get enough out of their small fleet of Chinooks, and so two more CH-47Ds were ordered, with delivery in 2000. While CH-47D configurations tend to vary in detail from customer to customer, the Aussie Chooks are almost identical to US Army Chinooks in order to ensure logistical compatibility.

* Canada bought nine CH-47Cs as "CH-147s", with deliveries in 1974. These machines were fitted with a power hoist above the crew door, a configuration referred to by Boeing as the "Super C". They were often fitted with skis. Two of these machines were lost in crashes, while the others were withdrawn from service in the early 1990s for cost reasons.

The Netherlands bought all seven of the surviving Canuck CH-117s, upgraded to CH-47D standards, and bought six more new-build CH-47Ds that were delivered in 1995, for a total of 13. The Dutch CH-47Ds feature a number of improvements over US Army CH-47Ds, including a long nose for Bendix weather radar, a "glass cockpit", and improved T55-L-714 engines.

Argentina bought three CH-47Cs, with one being captured by the British during the Falklands War in the early 1980s. The other two, at last notice, remain in service for Antarctic support. They have been updated to the long nose weather radar configuration.

Spain bought a batch of 13 CH-47Cs under the designation of "HT.17s". Nine of these machines were later updated to CH-47D standards, and the Spaniards also bought six new CH-47Ds.

* The British have been particularly enthusiastic users of the Chinook and have adopted it as their own. In the early 1960s, British forces operated the Bristol Belvedere tandem-rotor helicopter, but the Belvedere was one of the more regrettable British helicopters, and in 1967 the British Ministry of Defense decided to adopt the Chinook as replacement.

This was during a long and painful period of time when British defense procurement exercises tended to go more wrong than is normal for such things, and "normal" tends to be troublesome. It wasn't until 1978 that the Royal Air Force (RAF) finally ordered 33 "Chinook HC.1s", with initial flight of this variant on 23 March 1980 and introduction to service in the summer of 1981.

This initial batch of RAF Chinooks featured Lycoming T55-L-11E turboshafts with 3,750 horsepower each, but included a number of advanced features not found on other CH-47C subvariants, such as triple cargo hooks; a rotor brake; an NVG compatible cockpit; additional avionics; and a single-point pressure refueling system.

Many of the improvements introduced in the HC.1 found their way back into the US Army CH-47D upgrade. The HC.1s were also field-fitted with pintle mounts for 7.62 millimeter M60 machine guns, and Marconi radar warning receivers (RWRs) salvaged from Avro Vulcan bombers.

Eight more HC.1s were delivered to the RAF from 1984 to 1986, bringing the total to 41. Despite the fact that the designation was unchanged from the original batch, these machines had the Lycoming T55-L-712 engines of the CH-47D, with 3,750 horsepower each, and an automatic fire extinguishing system. The older HC.1s were upgraded to this specification,

The HC.1s were also refitted with fiberglass rotor blades and redesignated "HC.1Bs". Still later, in the early 1990s Boeing gave them a more comprehensive upgrade along the lines of the full CH-47D specification, turning them into "HC.2s". The engines were rebuilt to the T55-L-712F standard, featuring "full authority digital engine controls (FADEC)".

FADEC not only improves engine responsiveness and reduces pilot workload, but also provides greater engine efficiency and longer life. There were some initial problems with the FADEC software, but they were quickly resolved, and the HC.2 upgrade otherwise went well. Some of the machines were also brought up to "HC.2A" specification, featuring a strengthened forward fuselage that could allow fit of a midair refueling probe in the future.

HC.2s have countermeasures kit, and can be fitted with a pintle-mounted 7.62 millimeter "M134 Minigun" Gatling gun firing out either side of the machine, plus a pintle-mounted 7.62 millimeter machine gun firing out the rear ramp. An auxiliary fuel tank can be carried in the cargo bay.

The RAF ordered eight more Chinooks in 1995, with delivery beginning in 2000. These "HC.3s" are intended for special operations or combat SAR. They incorporate features from the US Army MH-47Es, such as large fuel tanks, midair refueling, and enhanced avionics, but they are based on the latest "Super D" Chinook specification (described later) and are possibly the most capable Chinooks now in operation.

The British are the second biggest Chinook operator, currently with 31 HC.2s, nine HC.2As, and eight HC.3s. One British Chinook, designated "Bravo November", did outstanding service in the Falklands during the war there in 1982, even lifting 81 troops on one occasion. The British Chinooks have since done sterling service in the Gulf War and the Balkan campaigns.

* The main license builder of the Chinook has been Elicotteri Meridionali (EM) of Italy, part of the Agusta helicopter group, which signed an agreement with Boeing for production of the CH-47C in 1968. EM built 38 CH-47Cs for the Italian Army, 26 of which were later upgraded to the "CH-47C Plus" standard with fiberglass rotor blades and T55-L-412E engines. One is configured as a flying surgical operating room.

EM would eventually build about 200 Chinooks. Besides Italy, the EM Chinooks were obtained by a number of other nations:

* Following CH-47C exports, Boeing went on to market new-build "Model 414 CH-47D International Chinooks". The company wanted to conduct export sales of the new model themselves and did not sign a license agreement with EM, but did sign such an agreement with Kawasaki to permit production of the type for Japanese military requirements as the "CH-47J".

Kawasaki obtained two as pattern machines in 1986 and then went on to build 54 more, with the first five assembled from kits supplied by Boeing. 40 of these CH-47Js were bought by the JGSDF, with another 16 obtained by the JASDF. Later production of JGSDF Chinooks has been to "CH-47JA" standard, with the machines fitted with enlarged saddle tanks, nose radar, an AAQ-16 FLIR in a turret under the nose, and a partial glass cockpit.

Other International CH-47D sales include:



* The Chinook is still going strong and shows no signs of fading out of service, making it one of aviation's major success stories. CH-47Ds are now being upgraded for the 21st century in the form of the "Model 414-100 CH-47SD Super D" for export, and the "CH-47F" for the US Army.

The CH-47SD features twin AlliedSignal T55-L-714A turboshafts, with 4,075 horsepower each. These engines provide greater fuel economy; are "marinized" with corrosion protection to allow operation in a salt-water environment; and are fitted with FADEC.

External cargo load has been increased to 12,700 kilograms (28,000 pounds) on the center sling hook, or 9,070 kilograms (20,000 pounds) each on the forward and aft cargo hooks. Larger fuel tanks have been fitted, giving the Super D twice the range of the CH-47D, and the airframe has been given structural changes and reinforcement. The CH-47SD has a glass cockpit with color displays and digital map, a Global Positioning System (GPS) navigation system, and nose radar. Countermeasures kit is optional.

Initial flight of the Super D prototype was on 25 August 1999. The initial announced customer was Taiwan, with deliveries of three machines beginning in 2001. These machines were designated "Model 234MLR" after an earlier unbuilt commercial variant to give them a "civilian" designation and avoid the wrath of the mainland Chinese.

As mentioned, Singapore is also buying six Super Ds to increase their Chinook fleet to twelve, and is considering upgrade of their current International CH-47Ds to the Super D standard.

* The US Army hopes to convert at least 300 of their current fleet of CH-47Ds to the CH-47F standard. The CH-47Fs are expected to remain in service until 2033 at earliest, at which time the Chinook will have been in US Army service for over 70 years.

The upgrade program was launched in May 1998 as the "Improved Cargo Helicopter (ICH)" effort, and will reduce operating costs by about 20% compared to the CH-47D. The machines will be run through depot level maintenance to be given structural reinforcements to renew service life and reduce vibration, and will also be fitted with new rotorheads; T55-714A turboshafts; an extended-range fuel system; a partial glass cockpit; other improved avionics, and a MIL-STD 1553 data bus.

The CH-47F is essentially a subset of the CH-47SD. There has been some grumbling among the Army helicopter aviation faction that the full Super D fit wasn't that much more expensive and is clearly superior, particularly with regards to a full glass cockpit and many more corrosion-proof composite assemblies, and that the CH-47F effort has been "penny wise and pound foolish".

Initial CH-47F prototype flight was in June 2001, with flight tests to be completed by the end of 2002 and deliveries to the Army shortly after that. Final deliveries are expected in 2015.


[7] ACH-47A GUNSHIP / MODEL 347 / XCH-62 HLH (MODEL 301) / MODEL 360

* There were a number of interesting excursions from the main line of Chinook development. In 1965, Boeing modified four CH-47As to the "Armed CH-47A (ACH-47A)" gunship configuration. All cargo-handling gear was removed, while 900 kilograms (a ton) of armor and armament were added. Armament included:

The ACH-47A was given the name of "Guns A Go-Go" or "Go-Go Bird". Three of the four were evaluated in combat in Vietnam in 1968, but though the Go-Go Birds had impressive firepower, the Army judged that smaller and more maneuverable dedicated helicopter gunships like the Bell AH-1 HueyCobra were the way of the future.

* One experimental machine, the "Model 347", was a prototype for a second-generation Chinook family. The program was initiated in 1969 and involved a rebuild of an existing CH-47A, featuring a fuselage stretch; four-bladed rotors; a taller rear rotor pylon; and elements borrowed from the Soviet Mil organization's heavy lift helicopters, including detachable wings to improve range and payload and a "booth" that could be extended from under the nose to house a pilot for control of crane loads.

Initial flight was on 27 May 1970. The machine was later fitted with a fly-by-wire flight control system, and was run through evaluations for several years in the early 1970s.

* While the Chinook is a big brute of a helicopter by American standards, it is dwarfed by the huge Soviet-Russian heavy-lift helicopters designed by the Mil organization, and for a long time Boeing and the US military had an urge to match or top the Mil heavy lifters.

In the late 1960s, Boeing came up with designs for machines with broad similarities to the Sea Knight and Chinook, but about twice the size of the Chinook in terms of linear dimensions. Proposed machines included the "Model 227" transport and the "Model 237" flying crane.

Following award of an Army contract for a prototype of a "Heavy Lift Helicopter (HLH)" in 1973, Boeing did move forward on building an oversized flying crane machine, the "XCH-62". Rotor diameter was to be 28 meters (92 feet), fuselage length 27.2 meters (89 feet 3 inches), and footprint length 49.5 meters (162 feet 3 inches). Its widely spaced landing gear would allow it to straddle heavy cargoes such as armored vehicles, and still carry twelve troops in its slender fuselage. Boeing also considered selling a commercial version, the "Model 301".

The XCH-62 prototype was in an advanced state of assembly in 1975, being readied for a planned initial flight the next year, when the US Congress cut funding for the program in August. The Sikorsky CH-53E Super Stallion was felt to give adequate heavy-lift capability for US forces.

The incomplete XCH-62 prototype was mothballed, to be pulled out of storage in the mid-1980s when the Army, the US National Aeronautics & Space Administration (NASA), and the Defense Advanced Research Projects Agency (DARPA) collaborated on a scheme to finish the XCH-62 for experimental flights. However, Congress put their foot down again and it didn't happen.

* In the 1980s, Boeing built an all-composite helicopter, the "Model 360", as a private venture to investigate new rotorcraft technologies. The Model 360 resembled the Sea Knight in a general way, but was more the size of the Chinook, and vastly more sophisticated and capable than either the Sea Knight or the Chinook.

The Model 360 had a fuselage length of 15.5 meters (51 feet) long and a takeoff weight of 13,835 kilograms (30,500 pounds). It was mostly built of composite materials, and featured a glass cockpit, with six CRT displays; a digital flight control system; twin Avco Lycoming AL5512 turboshafts providing 4,200 horsepower each, driving four-blade composite rotors; and retractable tricycle landing gear. Cruise speed was 370 KPH (230 MPH).



* I don't recall ever seeing a Sea Knight, but I was very familiar with the Chinook during my hitch in the Army down at Fort Hood, Texas, in the early 1970s. The distinctive slow and steady WHUMP WHUMP WHUMP sound of its rotor blades made it instantly recognizable by ear from the Hueys, Cobras, and Kiowas that buzzed around.

* Sources include:

* Revision history:

   v1.0.0 / 01 apr 02 / gvg
   v1.0.1 / 01 jul 02 / gvg / Comments on expansion of Army SOC CH-47 fleet.