The Chinook is one of the most iconic aircraft ever produced, yet even now it remains a valuable asset on the field. In this video we look at the history of the Chinook, from it’s first prototype to the latest proposed upgrade.

In 1943, Frank Piasecki and Harold Venzie invented the PV-2 helicopter, which became the second successful helicopter to fly in the U.S. In 1946, the company became Piasecki Helicopter Corporation which in turn became Vertol Aircraft Corporation when Piasecki stepped down as chairman in 1955.
By March 7, 1945 the company had created the PV-3 – the largest helicopter in the world at the time and first successful use of the tandem-rotor design. During the late 1940s a few other designs improved on the tandem-rotor concept, such as the HUP-2 and HUP-3 – paving the way for a most remarkable airframe. A helicopter that has a proven record of being crucial in the field, with few, if any, alternatives capable of fulfilling the same role. From the battle fields of Vietnam to today’s conflicts, this multi-role, vertical-lift platform, serves more than 20 countries, and just keeps getting better!

ORIGIN

The origins of the Chinook dates back to the 1950s. Following the Korean War and the success of the helicopter, Aircraft designer Vertol had committed to designing a tandem rotor aircraft capable of fulfilling multiple roles, including heavy lift. In 1956, the US Army announced its plans to hold helicopter design competitions, seeking to expand and modernise its fleet of rotary wing aircraft. One such competition would be held to find a replacement for the Sikorsky CH-37 – which at the time was the primary heavy lift helicopter used by the Army. The Sikorsky was good, but following trials of newer helicopter designs – including the Bell UH-1 Huey – it was realised that turbine powered helicopters were the future. The Sikorsky was piston powered. Thus, the competition entailed designing a heavy lift helicopter which integrated a turbine engine.

By 1958 the Army had noticed potential in Vertols design – which was now known as V-107, or YHC-1A – and awarded a contract to produce several prototypes. However, there was dispute within the Army over the role the helicopter should prioritise. Some believed it should be a troop transport – like the earlier tandem rotor Piasecki H-21 – while others believed it should be larger, powerful enough to supersede the Sikorsky CH-37. These disputes resulted in several decisions: firstly, the Vertol 107 would not be scrapped, but instead be improved to lean towards the role of medium lift helicopter, while the job of troop transport would be reallocated to Bell helicopter, who mentioned that their UH-1 Huey could be used in that role.

The improved Vertol 107 design would be designated CH-46 Sea Knight, and was given to the Marines. For the Army however, things still needed improvement. A request was sent to Vertol for an even larger and more powerful V-107, which would be designated HC-1B. Powered by two Lycoming T55 turbines producing over 2000 horsepower each, and utilising two counterrotating rotors – which evened out the torque – the aircraft was able to produce massive amounts of lift. Not only that, but a twin engine design such as this meant that if one engine failed, the other could take over driving both propellers. Then, on September 21st 1961, the first HC-1B would take to the air. These initial tests proved successful, thus the US Army designated the aircraft as CH-47A Chinook.

VARIANTS

First entering limited use in 1962, the Chinook would finally enter large scale service in 1965, being sent to Vietnam in the role of Medium transport. Initially, skepticism surrounded the aircraft. However, as time passed, pilots and crew in Vietnam began to realise the true utility of the Chinook. It’s ability to lift massive amounts of equipment, including artillery, was unmatched in other modern helicopters such as the Huey. Not only that, but it proved highly capable in rescuing downed aircraft, including many Hueys. In fact, by the end of the Vietnam War, the Chinook had rescued roughly 12,000 downed aircraft, a monumental achievement.

CH-47B

The Ch-47B model arrived in 1968. The Bravo model featured several improvements, among them being an improved transmission and fuselage. Previously, in the Alpha model, pilots in Vietnam had noticed that the high temperature and its subsequent effect on air density had a substantial effect on the Chinooks lift capacity, in some cases producing a 30% reduction in power. This fluctuation based off of humidity was further exacerbated by a dangerous issue in which the transmission would fail to sustain the turbines when running at full power. The Bravo model was thus designed as an interim aircraft whilst the massively improved Charlie model was still under development.

The Bravo featured a slightly improved engine, the T55-L-7C – which produced 2800 horsepower – while also featuring mounting points for M60 machine guns on both side doors and on the rear ramp.

CH-47C

The Charlie model would arrive shortly after the Bravo. Featuring an improved engine and better transmission, the C model sought to overcome all major problems found in the original Alpha variant. This model also sought to improve the gross weight limitations of the previous variants. To achieve this, certain Charlie models were fitted with the T55-L-11 engine – capable of producing 3700 horsepower – while others retained the L-7C engine. The more powerful L-11 engine was initially found to be unreliable, thus resulting in a temporary rollback to the L-7C engine whilst further improvements were made.

Despite this, the Charlie model would see wide use in the Vietnam war from the time of its introduction onwards.

ACH-47A

One of the most interesting Chinook variants emerged in 1965, and were later sent to Vietnam. These were the ACH-47A gunships. Four were produced, with three being lost. These aircraft were developed for test and evaluation in Vietnam. Further Chinook gunship conversations were halted following this, since all available aircraft were needed in their respective transport roles, and evidently the gunship design was not necessary. These aircraft were armed with a 40mm grenade launcher, two 70mm rocket pods, two M24 cannons, and five machine guns, either M60s or M2 Brownings.

CH47D

Primarily created by converting older models, particularly the Charlie variant, although A and B models were also used, the Delta is closer to what we would now consider the modern Chinook.

It would feature new and improved engines – the T55-GA-714A – which both improved speed and lift capability. It also saw the implementation of a triple hook cargo load system. This was an important upgrade. Earlier models of the Chinook – featuring single hook systems – had to fly far slower while carrying cargo, as the load was prone to spin due to it only having one point of stabilisation. Thus, a triple hook system would prevent spin and allow for easier transport of artillery, vehicles, and other heavy loads.

The Delta was also the first Chinook to see the proper adoption of a GPS system for navigation, which was quickly booming a necessity amongst modern aircraft.

MH-47D

The success of the Delta variant in modernising the Chinook lead to the development of the MH-47D. This helicopter – which was designed by upgrading older Alpha and Charlie models – was designed specifically for special forces use.

MH-47E

Following the success of the MH-47D, a newer model – the MH-47E – was designed as a replacement. It would still be converted from Charlie model aircraft, but would possess further small upgrades, many of which were found in the latest base model CH-47D.

In keeping with its goal of providing specifically for special forces use, the MH-47D features a terrain following radar, modified avionics, and an increased fuel capacity for longer missions.

CH-47F

From the Delta model came the CH-47F, or Foxtrot, the latest of the base model Chinooks currently serving in an operational capacity. Developed on the Delta model, the Foxtrot features several new upgrades. As per usual, the primary improvement is the implementation of newer engines, which are both more powerful and have better serviceability. Alongside this, the aircraft also features a modernised avionics system integrated with CAAS.

One of the main selling points of the Foxtrot model is its focus on improving service life, while decreasing the amount of maintenance needed to keep the helicopter airworthy. This is important, as the Chinook up to this point had always been a maintenance heavy aircraft.

Such aims also played into the decision to redesign certain elements of the aircraft to reduce vibration. According to ex RAAF pilots we have spoken to, newer Delta and Foxtrot Chinooks do indeed vibrate less than the Charlie model at cruising speed, however when pushed up to higher speeds, the larger rotor blades cause the Delta or Foxtrot to vibrate more violently than the older Charlie model would at the same speed. This is obviously one of the trade offs of having these larger rotor blades.

Sub-variants of the Foxtrot have now also been designed. A Block 2 variant began entering service in 2020, and featured further improvements, including improved payload capabilities, further improved rotor blades, a larger fuel capacity, more powerful engines, and improved avionics systems aimed at increasing efficiency.

And now, there are plans for a Block 3 variant sometime in the coming years. This would once again seek to improve lift capabilities, serviceability, and reliability. Current plans include a larger fuselage, as well as designing a completely new engine, transmission, and driveshaft.

MH-47G

Alongside the latest the Foxtrot variant is the MH-47G, the most modern Chinook variant aimed at special forces use. Created by upgrading existing special forces MH-47 Delta and Echo variants, the MH-47G features the same upgrades found in the newer CH-47F model, alongside other smaller features such as a specialised avionics system.

As it stands, a Block 2 variant of the MH-47G is currently being developed, which further modernises the Chinook with even better avionics systems, terrain following radar, and other such improvements, and this will likely remain in service for many years once fully implemented.

What truly sets the Chinook apart from other helicopters – and indeed other aircraft in general – is its airframe. It has remained relatively similar over the years, with overhauls primarily being focused on things such as avionics and onboard technology. This is rather rare in an aircraft. For example, the airframes of fighter aircraft show their age as air to air technology and principles changes. An F4 Phantom can be overhauled with newer internal technology, but the airframe itself is optimised for high speeds, not the low radar profile required in modern warfare. In contrast, the Chinook retains its core features, and remains relatively unparalleled in its abilities.

A timeless airframe such as the Chinooks is rare to come across. Other examples of such airframe designs would include the C-130 Hercules, C-47, Bell UH-1, Boeing 707, and to some extent the B-52.

TODAY

Today, the Chinook has become a necessity on the field, with capability which are unmatched by other helicopters. The MH-47G Block 2 will remain in service as a special forces helicopter until the next upgrade is designed, since few other proposals are on the table for a replacement any time soon. Likewise, the yet to be implemented CH-47F Block 3 will certainly future proof the design. As it stands, the Chinook will continue to serve until some time beyond 2060, making the design over 100 years old.