Christmas road test 2021: RAF Chinook helicopter

Design and engineering

The clue to the Chinook’s purpose is in its Boeing model code, HC-47, with HC standing for Helicopter, Cargo. It’s not a nomenclature used by the RAF, which calls its Chinooks HC.Mk (it’s currently up to Mk6) and includes various detail specification differences from the base Boeing unit. The Chinook is a heavy-lift helicopter designed for the military, although it has found civilian uses, too, including carrying large quantities of people and equipment into and out of hard-to-reach areas.

The key to the Chinook’s success, and what sets it apart from almost all other heavy-lift helicopters, are its two sets of counter-rotating rotor blades, a straightforward enough concept that nonetheless requires some complicated engineering to put into action.

There are two sets of three blades, one set at the front, one at the back, which spin in opposing directions (anticlockwise at the front) at the steady 225rpm that gives the Chinook its distinctive ‘wokka’ sound. Interlinked so they can never touch, each rotor balances out the other’s yaw moment, negating the need for a tail boom and vertical rotor to act against the turning force of the main rotor, as on a conventional helicopter. Without those, and with the main rotors mounted high on pylons, the entire back end of the Chinook can be given over to cargo.

Beside the rear pylon are two turboshaft engines, each making 4168 shaft horsepower (shp). Each has a gearbox, from which shafts go to a combining gearbox in front of the rear pylon. A two-piece shaft takes drive from there to a gearbox for the rear rotor, while a seven-piece shaft takes drive to the front rotor’s gearbox. Which means there are five transmissions, reducing the engines’ speed from around 15,000rpm to the rotors’ much calmer rotational speed.

The Chinook’s aluminium airframe is relatively unstressed because the aircraft is unpressurised. It’s a 30.14m-long aircraft, including rotors. (The fuselage is 15.25m long.) The cockpit is at the front and there is a door each side, a hatch underneath and a ramp that opens at the back. The bulges along each lower side hold the fuel tanks; there’s a regular 3000kg-tank version and a ‘fat-tank’ variant that carries 6000kg of fuel.

A Chinook sits on a non-retractable undercarriage. Beneath the airframe are three external hooks that can be used individually or together.

Interior

If there’s a purpose to the Chinook, it’s the interior and the cargo hooks that are monitored from within it. Take a step up on to the hydraulic ramp at the rear and into the load bay and it’s pretty dark and functional. There are some small porthole windows and an aluminium floor with hooks for securing loads, coupled with non-slip walkways. There’s a row of uncomfortable folding/removable canvas and webbing seats along each side.

A Chinook can carry 55 troops in addition to its crew of three to five: two pilots, plus one to three air crew, or ‘loadmasters’. But in combat, RAF Chinooks are known to have transported more than 70 troops at a time. “We’ll usually bulk out before we weight out,” a loadmaster told us.The Chinook’s cargo bay is 9.3m long, 2.29m wide and 1.98m tall, so big enough to take a vehicle, and it has a 10-tonne load capacity. It can hold up to 24 stretchers, or be fitted with a roller flooring system to make it easier to load pallets. It can also be fitted with rubberised Medical Emergency Response Team (MERT) f looring – blood mats, informally – when evacuating casualties, partly for hygiene but also because bodily fluids can be corrosive to the airframe. Ultimately, whatever needs transporting, if they can, they’ll carry it. “We’ve taken everything from Range Rovers, pallets of dollars and gold bars to donkeys,” we were told.

Loaded from the outside, but controlled by a loadmaster from the cabin, are the three load hooks, rated for more than the Chinook is meant to lift. The forward and rear ones have a capacity of 7711kg each or 10,433kg together. The centre hook, visible directly beneath the opening hatch in the f loor, through which the loadmaster will supervise operations while giving instructions to the pilots, is rated for 11,793kg. All three loads can be jettisoned by the loadmaster in an emergency: “We wouldn’t put anything underneath that we wouldn’t give to the enemy.”

Access to the cockpit from the cargo hold is through an open doorway, but it’s a delicate step across low-mounted switch panels and into the seats. Once in, forward visibility is very good from the two side-by-side seats. To the back, not so much, hence the importance of the air crew.

Early Chinooks had analogue displays and controls but all have been upgraded to digital glass cockpits, and this year the last of them was also upgraded with Boeing’s DAFCS (Digital Automatic Flight Control System). Behind the right-sided pilot is another jet-fuelled turbine, but this one is a cabin heater.

Performance

One of the advantages of a tandem- rotor helicopter like a Chinook is that all of its power can be used for lift: it doesn’t use any power driving a vertical tail rotor to prevent itself spinning round in circles.

If there’s a downside to this, it’s that in forward flight, the front rotor disrupts the air behind it, reducing the rear rotor’s efficiency. So the rear pylon is taller than the front one, to partially counter the effect.

There are inevitable losses between the Honeywell T55-L-714A engines’ combined 8336shp and the lift the 18.29m-diameter rotors generate. But still, they can lift this 12,100kg fully fuelled aircraft, plus a maximum payload of 10,580kg, to give a maximum take-off weight of 22,680kg. In the field, Chinooks are known to have carried more.

Chinooks can climb as high as 15,000ft but tend not to, as you’ll know if you’ve heard them pass over your house at night. The Chinook’s ‘never exceed’ speed (beyond which it’s considered dangerous to the aircraft) is 180kt, or 207mph, but the RAF tends to cruise at 120kt (138mph) because, as one of the crew told us, “it’s easier maths”.

At a 120kt cruising airspeed, the Chinook is burning 1200kg of fuel an hour, giving the standard-tank Chinook a range of two and a half hours, or double that for a fat-tank version. How much distance it will cover in that time depends on which way the wind is blowing, what with air speed and ground speed being two different things. On the way to a casualty, though, pilots will max out the Chinook to as fast as it will go.

Ride and handling

The Chinook is a big aircraft, but although it lacks the manoeuvrability of a smaller, lighter, single-main- rotor helicopter, if you’ve seen the RAF’s Chinook display team you’ll know it can be surprisingly agile. The controls are similar to those of other helicopters, although how theyact isn’t quite the same. Each pilot gets two foot pedals, which control yaw, clockwise or anticlockwise. There is a collective – a bit like a throttle – which adjusts rotor pitch to provide lift. And there’s a cyclic stick, which tilts the helicopter to get things moving. Through a combination of rotor pitch changes and changing the angle of the rotors, the Chinook has respectable manoeuvrability and excellent stability.

That stability is key to one of the Chinook’s trademark moves, the ‘pinnacle’, which lets troops on or off the helicopter while it hovers, rear wheels set onto a ridge or cliff edge. It’s particularly useful for getting troops on or off high ground. The rear brakes are locked and pilots make tiny adjustments to keep the aircraft stable – apparently easier when really close to the ridge, rather than when a few metres away, because the airflow becomes more stable. While it’s hovering, troops can step off onto firm ground, but the pilots could have thousands of feet of air beneath them.

When you think of dogfighting, you don’t really think of RAF Chinooks, but if you’re at home when one whoops low overhead, don’t think that it is necessarily just on a navigation mission. In an operational theatre, it could be a target for other aircraft and, while no fighter jet, it will have a crack at defending itself. Along its sides are sets of chaff and flare countermeasures.

More likely, though, is attack from the ground. The Chinook is lightly armoured and has those physical and some electronic countermeasures, and in theatre it usually has an M134 minigun pointing out of each side door and a machine gun at the rear.

Buying and owning

The cost of a Chinook is estimated at £30m but, defence procurement, unique equipment and ongoing maintenance and supply contracts being what they are, it isn’t quite so straightforward. Put it this way: the MOD has just approved a £1.4bn programme to buy 14 new helicopters. (Hopefully, it will go more smoothly than what the Commons Public Accounts Committee called “one of the most incompetent procurements of all time”, a series of orders that left eight Chinooks sat in a hangar, unusable, 13 years after being ordered, at a cost of nearly £500m.)

Away from central procurement and in the hands of experts, things run rather more smoothly. The RAF gets more efficiency out of its Chinooks, in terms of hours flown to time spent in repair, than any other operator in the world. And while RAF pilots are assigned to a squadron, they do not have their own aircraft (as US pilots tend to): they’ll fly any and all helicopters in their squadron.

Most of the Chinook fleet, all run by the RAF but under the control of Joint Helicopter Command, live at RAF Odiham, with the exception of half a squadron operating from RAF Benson in Oxfordshire. At any given moment, we have at least one Chinook within an hour’s readiness for anti- terrorism operations or disaster relief. In 2019, a Chinook dropped 400 tonnes of ballast onto Whaley Bridge dam to secure it; in 2020, one dropped special forces troops onto a hijacked tanker in the Solent.

For all of its durability, though, many Chinooks, as one engineer said, “are old aircraft”, and they take some looking after. The RAF is rightly proud of its engineering integrity and the careers it supports. It takes 180 people to keep one Chinook squadron flying, and there are four and a half of them. There is a reason the Chinook is a survivor – and it’s as much to do with the people supporting it as it is the aircraft itself.

Verdict

A century’s service is mapped out, with no better option in sight

The RAF knows its earliest Chinooks are elderly aircraft, but there’s still no rush to replace them. Besides, what would you replace them with? In the 1960s, Boeing hit on a winning formula that’s as relevant today as it was at the time.

If you designed from scratch a vehicle to do what the Chinook already does, you’d likely end up with something just like this: great visibility, a broad load bay big enough to hold a Land Rover, ample fuel capacity and rotor blades pulled high out of harm’s way. Throw in a ramp at the back and make it a size that fits in a huge military transporter plane, and there you go. That’s the formula.

So with an engineering team providing regular maintenance and various upgrades and orders in the pipeline, the plan for the Chinook is to keep it running and make it more efficient, but otherwise just make the most of its devastating effectiveness.

All photographs are by the UK MOD © Crown copyright 2021, and very nice they are too.

Road test rivals

RAF CHINOOK Unrivalled versatility and practicality. Reliability, durability and a sturdy airframe make it still the best and first choice for military lifting.

207mph 1399 miles 10,580kg

BOEING VERTOL CH-46 SEA KNIGHT Chinook’s predecessor first flew in 1958 and is still used in a few places. The US abandoned some in Afghanistan recently.

166mph 690 miles (unladen) 3975kg

BELL BOEING V-22 OSPREY The world’s only production tilt- rotor blends best of helicopter and fixed-wing traits. Fast and can hover but expensive and dislikes imbalanced loads.

351mph 1012 miles (unladen) 9070kg (internal), 6800kg (external)

MIL MI-26 Russian commercial and military helicopter is the world’s largest and most powerful chopper. Has even airlifted downed Chinooks to safety.

183mph 1190 miles (with auxiliary tanks) 20,000kg

ERICKSON S-64 AIR CRANE Civil version of a ’60s military lifter still does service, mostly in wildfire suppression. Legacy fleets upgraded while Erickson plans a new version.