This month brings the 50th anniversary of the Boeing CH-47 Chinook's service entry - and it is entirely possible that the venerable tandem-rotor helicopter might serve with the US Army for another half-century.
The service initially signed the contract to develop the Chinook in 1959 with what was then Vertol, says Boeing business development director for mobility rotorcraft Mark Ballew. The first prototype flew two years later on 21 September 1961 - but by then, Boeing had purchased the Vertol Aircraft Corporation, the former 20-year veteran Chinook aviator says. Less than a year later, the army took delivery of its first aircraft on 16 August 1962.
"Believe it or not, that aircraft is still flying," Ballew says. "It's gone through multiple iterations from the A-model to the D-model."
Currently that aircraft is being remanufactured once again into the latest F-model configuration. "It just came back from Afghanistan, and it's going to go back to Afghanistan probably in the January timeframe," Ballew says.
Royal Air Force
The Chinook has served through various iterations in Afghanistan
Although the initial contract was signed in 1959, the origins of the Chinook date back to the 1940s, when Frank Piasecki pioneered the tandem-rotor concept.
The first operational tandem-rotor designs to see service were the Piasecki Helicopter Corporation CH-21 and CH-25 helicopters. Their successors, the CH-46 Sea Knight and the CH-47, were designed nearly concurrently in the late 1950s, after Piasecki left the renamed company, says historian Jon Bernstein, curator of the US Army Air Defense Artillery museum in Fort Sill, Oklahoma.
For the US Army, the CH-21 was a very significant aircraft, Bernstein says. But with the development of new gas turbine engines, the service wanted a machine that could take advantage of the new technology.
"The army really wanted a turbine-powered heavy lift aircraft to replace the CH-21," he says. "And that's really where the CH-47 came from."
Half a century later, there are many original A-model Chinooks that have been remanufactured multiple times, and which have been serving continually since their original roll-out. It is the Chinook's robust tandem-rotor design which allowed the aircraft to evolve over the decades, while lesser aircraft fall by the wayside.
There are a number of advantages to the tandem-rotor concept, Ballew says. Firstly, unlike in a single-rotor machine where horsepower is siphoned off to power the anti-torque rotor, 100% of the engines' output is dedicated to providing lift. That gives the aircraft outstanding high-altitude performance, he says.
The air flow from the tandem rotors is also cleaner over parts of the airframe in flight, Ballew says. The Chinook also has a large area over which the aircraft's centre of gravity is spread due to its rotor design, he says. That gives the crews more flexibility when loading or unloading the aircraft.
What impresses Bernstein the most is the Chinook's sheer power. It is the helicopter's prodigious power margins and robust design that has enabled it to adapt various roles over the years.
The Chinook is also the fastest helicopter in the US inventory, Bernstein adds. The CH-47 is significantly faster than its escorting gunships, like the Boeing AH-64D Apache.
In places like Iraq and Afghanistan - where large numbers of Chinooks are currently serving - Apache pilots are constantly radioing their charges to slow down. "It was always fun trying to keep up with them," says Bernstein, a former Apache pilot. "They are fast as anything."
It is also extremely versatile. "It's done pretty much every role," Bernstein says. But hauling cargo is where the aircraft excels. The CH-47 was originally intended as a medium-lift machine. But during the Vietnam War, the Chinook proved to be such good cargo hauler that it ultimately replaced the Sikorsky CH-54 Sky Crane as the army's heavy-lifter, he says. But the Chinook has also been used for air assault, as a mobile refueling station, for special operations and even as a gunship.
The Chinooks versatility gives it huge staying power
The Chinook made its combat debut over the jungles of Vietnam. Since then, it has served in every major combat operation that the United States has been involved in since it entered service. Perhaps its most famous mission in recent years was during the mission to eliminate terrorist leader Osama bin Laden - Operation Neptune Spear. On 2 May 2011, a number of special operations MH-47 aircraft participated in a daring night-time raid deep inside Pakistan.
While details of the operations are murky, Chinooks and a specially modified stealthy variant of the Sikorsky MH-60 Black Hawk infiltrated that country from Afghanistan. While the Black Hawk(s) flew all the way to Abbottabad, the Chinook remained in reserve half-way between the objective and the border. Ultimately, the mission was successful when an elite team of US Navy SEAL operators successfully eliminated their target, however, one of the Black Hawk(s) crashed.
Perhaps one of the most unique uses of the Chinook came during the Vietnam War, when the US Army adapted four aircraft into an experimental ACH-47A configuration in a programme dubbed Guns-a-Go-Go, Bernstein says. The concept was similar to the fixed-wing Douglas AC-47 Spooky or Lockheed Martin AC-130 gunship - both of which were developed during that conflict.
The ACH-47 served for about three years. However, though the gunship variant proved to be an effective machine, three of the four aircraft were lost either in combat or accidents, Bernstein says. The surviving aircraft is preserved in an army museum at the Redstone Arsenal, Alabama.
Ultimately, the army decided to cancel the programme because there were other, less expensive ways of carrying out the gunship mission. The emergence of the Bell AH-1 Cobra attack helicopter, for example, meant that the Chinook was not needed for that role, Bernstein says. "Using a high-value asset like a Chinook in gunship role didn't really make much sense, even though they were incredibly heavily armed," he says. "You could do the same job with [Bell UH-1] Hueys or Cobras and not risk as many people."
The Chinook has been upgraded over the years and throughout the various conflicts it has flown in. The aircraft has evolved from the original A-model through to the latest F-model and special operations standard G-model machines.
Over the years, materials and construction has changed. Engines and transmissions have been upgraded and the gross weight has increased. There has also been a quantum leap in avionics technology.
Compared to the original 33,000lb CH-47A, the F- and G-model machines weigh in at over 50,000lbs, and have state-of-the-art avionics. Boeing has added a common avionics architecture system which offers a full glass cockpit - greatly increasing a pilot's situational awareness. The company has also added a digital advanced flight control system (DAFCS), Ballew says, which vastly improves the Chinook's handling characteristics. The DAFCS offers stabilised hover capability, and a pilot can alter his position foot by foot in any direction.
Boeing is continuing to evolve the Chinook. One upcoming feature is a refined rotor blade design which will add 2,000lbs of lift, Ballew says. There are also other ongoing projects to continue improving the aircraft's performance.
The US Army is committed to flying some Chinooks till at least 2050, but unless there is some revolutionary breakthrough in propulsion technology that offers cost-efficient rotorcraft flight at high speeds, the Chinook looks to continue its dominance of the heavy-lift market indefinitely, says Richard Aboulafia, an analyst at the Teal Group.
The Chinook may not be heading off in to the sunset any time soon
"I know it's a bold statement to say we're going to be flying for [the] next 50 years," Ballew says. "But based on the army's projected usage for it until at least 2045, you going to have some residual aircraft out there flying somewhere for 100 years."