Every infantry man in a combat zone loves to hear a Chinook. Wop, wop, wop, you can hear the characteristic sound, you know what it is but you can’t see it. The twin rotor helicopter is coming in at 160 mph with 10 tons of stores and ammunition or re-enforcements. Once it lands, it will be there for 60 seconds, there will be no departure delays, no last calls for passengers, no check in queues. What isn’t taken off or loaded within the time is left where it is.
For the pilot, that 60 seconds is an anxious time. Can the enemy get the range with a few mortars, loose off a rocket propelled grenade or mount a machine gun attack? There is often a small attack helicopter hovering above, looking for trouble, keeping the heads of the enemy pinned down.
Meanwhile, at the back, the door is already open, pallets slide off, fully equipped troops jog out and form a defensive ring. Casualties are loaded and any returning troops. If it can be done in less than 60 seconds, the loadmaster will tell the pilot to ‘get the hell outta here’. At about £60 million each, we can’t afford to lose a Chinook, we only have 60 of them anyway.
Flying a Chinook
Chinook pilots must be able to fly low, under 100 ft, to avoid tall buildings, power cables, TV and telecoms masts, small hills and tall trees. They must be able to do it in rain, snow, sandstorm, fog and gales and at night. Then they must be able to land anywhere or to hover if there is no flat surface. They need clearance for the 10 M rotor blades but any space, in jungle, deserts, on mountains, cliffs, bogs and sea shore but easiest of all, back home at Odiham, Hampshire. They are part of our essential defences. One was ready to fly within 30 minutes of the terrorist attack in Manchester.
The proximity of Odiham to Lasham Gliding Club means that we glider pilots see a lot of Chinooks and we need to avoid one another. A swipe from a rotor blade could affect a glider’s flying capability. Group Captain P J Robinson, Station Commander at RAF Odiham invited a group of us from Lasham to attend a briefing on their flying practices, flight circuits and safety precautions. To hold our attention, anyone who was awake at the end could have a flight in a Chinook.
Unique trip around Hampshire
Equipped with flying helmet and visor, I trotted out to our Chinook. The unwary might be blown over by the downdraught of the rotors and cough at the heat and smell of the turbine exhausts but, once inside, the little canvas seats were more comfortable than expected.
We sat, backs to the wall, but with large windows opposite. My seat was up front next to the gun port which was open throughout the flight. Lap straps held us in place but there was no in-flight entertainment. Leg room amounted to a couple of yards.
There are two cabin crew. One up front next to where I was sat to man the machine gun, operate the winch, check navigation and observe the ground. The second, at the rear, acts as a flight engineer, operates the door and supervises loading and unloading. He also has a machine gun.
Off we flew around Hampshire, west between Basingstoke and Lasham and on towards the A34 at Whitchurch. Then we flew a couple of large holding loops and returned to Odiham. The flight was smoother than I imagined but the craft was swayed a little by the freshening wind. We all had ear defenders in our helmets so noise was not a problem. Being next to the gun port, I could stick my head out but as the machine gun man was careful not to do that, neither did I.
Chinooks can fly on one engine and have often had to do so in Afghanistan. One pilot lost an engine while loading troops and could not lift off. However, there is a ground effect increasing the lift when close to the ground so he managed a few feet then, once he had got some forward speed, the lift increased and he managed to get back to base.
The two turbines look quite small but generate 4000 h.p. each. They drive the rotors through a fixed gearbox so that the blades can never collide with one another. As the rotors counter-rotate, there is no need for a vertical tail rotor. The rear rotor is mounted higher to avoid the turbulent air made by the front rotor. Because of its size and relative slowness, the Chinook is vulnerable to enemy fire. To counter this, it has many electronic jamming gadgets and warnings of incoming missiles. It manoeuvrability helps but the main defence is to fly low, below radar and below the horizon of ground observers. It can dodge behind tree lines, hills and villages.
There are several flight stabilisers on board to ease the load on the pilot. It can be flown without these under VFR (Visual Flight Rules) but one of the problems is that the rear rotor tries to overtake the front one so the aircraft yaws sideways. With lift provided on each side, there is considerable torque on the fuselage and early models suffered from metal fatigue. An advantage of twin rotors as opposed to single rotor craft is that two centres of lift and one centre of gravity make it easier to keep stable when loading in the hover.
It takes a gang of engineers, mechanics and electronics engineers to service a Chinook. When deployed on active service, changes are made; Kevlar armour is fitted inside to stop small arms fire, filters over the air intakes are needed in the desert and perhaps additional fuel tanks are necessary. Some situations need more than the two and a half hours flight duration. Suspension slings underneath can be used for heavy equipment up to 10 tons.
How many miles per gallon? Not a lot; fuel load is 3 tons, about 4,000 litres to fly at 160 mph for two and a half hours works out about 176 yards per litre or about 2 gallons per mile. And I thought my car consumed a lot. How fast do the rotors go? About 120 rpm so each rotor tip travels 120 x 2πr metres per minute where r is 10 M. That works out at 425 Km per hour assuming no forward movement or something like 675 allowing for that. Then the forward moving tip must move faster through air than the aircraft. Complicated, I know there are mathematicians out there but probably the answer is close to the speed of sound but still subsonic. The speed of sound in air is about 1220 Km/Hr or 730 mph or 340 M per sec.
Thank you RAF Odiham. I know where to look for Chinooks when flying. Last birthday my son bought me a T shirt with the logo ‘Adventure till Dementia.’ Seems a good plan to me and I am doing what it says but I won’t advertise by wearing the shirt.
- Chinook people are native Americans living in the north-west across the US Canada border. Their language is Chinookan.
- Chinook wind blows down the Rockies into Alberta, Canada. Warm and dry.
- Chinook – A breed of honey coloured dog.
- Chinook – Used as a place name in NW America
- Chinook – A name used for several aircraft.
- Chinook – Name chosen by Boeing for their CH47 twin-rotor helicopter.