Boeing CH-47 Chinook
Medium-Lift, Tandem Rotor Transport Helicopter
The Boeing CH-47 Chinook tandem-rotor helicopter became a widely-used and widely-exported medium-lift platform for its time - amazingly it remains in service today.
Authored By: Staff Writer | Last Edited:
The Boeing "Chinook" line of medium-lift, tandem-rotor transport helicopters has been a mainstay utility system for the United States Army (and others) for decades since its introduction in 1962. The iconic design was given a tandem-rotor approach to provide the necessary lift properties when hauling medium-class loads over the battlefield - able to transport weaponry, supplies, a full complement of combat-ready troops, and other useful components to and from operating points. Despite its 1960s origins, the CH-47 remains in service throughout the world and should continue to be one of the more versatile transport helicopters ever produced - its importance is such that the series is scheduled for retirement no sooner than 2060 while being set to become the U.S. Army's first "100 Year" aircraft.
The story of the CH-47 began in the mid-1950s with the U.S. Army looking to replace its stock of Sikorsky CH-37 "Mojave" transport helicopters. Production of this system - which was not an outright success due to operating expenses, size, and reliance on piston-driven engines - was limited to just 154 units. Service began in July of 1956 and ended relatively quickly in the late 1960s. The turbine engine soon arrived and replaced piston engines in helicopters through such successful products as the Bell UH-1 "Huey" medium-lift transport helicopter so thought was no being given to an all-new, medium-lift system based on the more powerful and capable drive units.
Various contractors were in play early on to deliver a solution to the ongoing Army requirement. To help sell the idea of a new turbine -powered platform, Vertol engineers fleshed out their "V-107" of 1957 and this was enough to prove the investment as a formal contract followed the following year to be based on the developmental "YHC-1A" designation. Three prototypes would be featured for evaluation.
However, the YHC-1A failed to sell itself to the Army after testing and was instead taken on by the USMC as the CH-46 "Sea Knight" tandem rotor transport. The decision was then made to simply develop a dimensionally larger version of that same helicopter and this formally became company Model 114 and assigned the Army designation of "HC-1B". A first flight (a hovering action) followed on September 21st, 1961.
Due to the 1962 redesignation initiative covering all aircraft then in American service, the HC-1B was redesignated to the more common "CH-47" with its initial production model now recognized as the CH-47A. It was granted the name of "Chinook" in keeping with Army tradition of naming its helicopters after Native American tribes. The CH-47A entered service in August of 1962 to begin its long and storied career.
As completed, the CH-47 was an easily identifiable aircraft with its twin main rotor design. Each rotor utilized a three-bladed assembly seated atop mast mountings, the rotors arranged as counter-rotating units which eliminated the need for a tail rotor unit (the natural occurring torque of a spinning rotor was offset by another rotor spinning in the opposite direction). The high placement of the main rotors also cleared all areas immediately around the aircraft for ground personnel - no immediate danger was to be had from a spinning tail rotor so common to other helicopter transports. The cockpit was fitted well-forward in the design with excellent vision for the two pilots. The fuselage was rectangular in its general shape as seen from the side profile and dotted with vision ports. At the rear of the fuselage was a large, powered cargo door that lowered to double as the loading ramp to provide unfettered access to the cargo hold within. The engines were fitted outboard of each rear fuselage side to provide the needed forward thrust while also driving the two main rotors. The undercarriage relied a four-legged system, fixed during flight, and wheeled. Internally, the helicopter could seat up to 55 troops, 24 medical litters with medical crew, or an equal amount of cargo. An external cargo hook allowed the helicopter to sling loads under the fuselage to double its carrying capability in-the-field. The original engines were Lycoming T55-L-7 turboshaft types of 2,650 horsepower (each) with two being fitted.
The United States Army took on a total of 354 CH-47A models and these were then followed into service by the improved CH-47B. The B-model would become a "bridge" offering of sorts between the original A-models and the much improved C-model form still to come. The CH-47B fitted 2 x Lycoming T55-L-7C engines of 2,850 horsepower each as well as new, asymmetrical rotor blades. The rear rotor mounting was redesigned and there was inherent support for the M60 General Purpose Machine Gun (GPMG) mounted at the side doors for local defense/suppression. The cargo ramp at rear was also modified to support the M60D/M41 weapon station - the CH-47B flying with its cargo ramp down to allow this gunner to engage trailing threats. Its greater overall power made it a better medium-lift performer.
The CH-47C saw its gearbox and engines upgraded while fuel stores were expanded for increased operational ranges. Its first flight was during October 14th, 1967 and 233 production units followed. Many existing A- and B-models were eventually upgraded to the C-standard in time.
The primary Army models of the Vietnam War became the CH-47A, CH-47B, and CH-47C - some Chinooks outfitted for delivering napalm loads rolled out of the rear of the aircraft while others were modified for the combat assault role. The Canadian Army took delivery of eight CH-47C aircraft beginning in 1974 (as the "CH-147") and the British Army knew the type under the "HC.1" designation. Other British variants became the HC.2, HC.3, HC.4, HC.5, and HC.6. British Chinooks saw action during the Falklands War (1982).
In February of 1982 the CH-47D first took to the air and this model incorporated uprated engines with slightly reduced hauling capabilities. There were also upgraded avionics, support for night vision equipment, and a triple cargo hook external arrangement for moving heavy loads including artillery pieces. The U.S. Army went ahead with procuring some 480 D-models for service, these simply modified from the existing stock of available A-, B-, and C-models.
A small number of Chinooks were reformed from existing C-model stocks to the D-standard for use by special forces as the "MH-47D". The MH-47E marked another special forces version - this based on an E-model prototype emerging in the early 1990s and featuring increased fuel stores. Production of this model reached 26 units. A later special operations model standard became the MH-47G following the form and function of the E-model but with all-modern systems including a full "glass" cockpit.
The Dutch government purchased ex-Canadian CH-147s and used these in the upgraded D-standard guise. This left the Canadians free to pursue purchase of D-models in 2008. The Japanese joined the foreign operators list through local-licensed production of the Chinook as the "CH-47J". The J-model was completed with different avionics and engines when compared to the American-born models. A subsequent model became the CH-47JA. Both were manufactured under the Kawasaki Heavy Industries brand label.
Many export versions have been based on the CH-47D model makeup.
The CH-47F is the newest Chinook offering, first flying in 2001. This offering incorporates newer uprated engines of 4,868 horsepower output (each) for increased field performance and the fuselage relies on milled construction for more robustness. The cockpit supports a modern digital avionics suite complete. Deliveries of this variant began in 2006.
The U.S. Army has contracted for 191 of the F-model with the Dutch following as the initial export user with six examples ordered. Other operators have become Australia and the United Kingdom. Despite its newness, the CH-47F is already slated for upgrading through the "Block 2" initiative and "Block 3" proposal which are intended to keep this mighty system a viable battlefield component into the mid-2000s. The Block 2 upgrade will see the F-model hauling capabilities return to A-model levels while Block 3 is a re-engining program in line with the Army's "Future Affordable Turbine Engine" (FATE) project tied to other helicopter products in inventory (including the Boeing AH-64 "Apache" attack helicopter). The U.S. Army has undertaken a program to replace its D-model lineup with the newer F-model, a conversion process that should be completed in 2019.
The Chinook has been seen in a few civilian market products following certification to operate in civilian airspaces - this is through the Model 234 and Model 414 variants.
Sixteen nations have been participants in the CH-47 story and over 1,200 have been built since 1962. Some of the most recent combat exposure for the Chinook has centered around the coalition involvement in Afghanistan and Iraq which have resulted in some airframe losses an fatalities. Due to the Chinooks ability to haul large numbers of personnel, the aircraft suffers from a high number of fatalities when they are shot down or crash through accidents/human error. A 2005 incident near Kabul, Afghanistan saw a special forces group flying in a Chinook shot down by enemy elements - killing all members aboard.