Helicopter rotor of gravity fore-aft. However, it requires the expense of two large rotors rather than the more common one large main rotor and a much smaller tail rotor. The Boeing CH-47 Chinook is the most common tandem rotor helicopter. Coaxial rotors are a pair of rotors mounted one above the other on the same shaft and turning in opposite directions. The advantage of the coaxial rotor is that, in forward flight, the lift provided by the advancing halves of each rotor compensates for the retreating half of the other, eliminating one of the key effects of dissymmetry of lift: retreating blade
Boeing Chinook (UK variants) Operation Granby in the 1991 Gulf War, attached to large peace-keeping commitments in the Balkans, the continued British presence in Afghanistan, and in Operation Telic in the 2003 Iraq War. They provide routine supply and support missions to the British military, notably in Operation Banner in Northern Ireland. The helicopter has also been of use in military humanitarian missions and the extraction of civilians from warzones, such as the evacuation of Sierra Leone in 2000, and the evacuation from Lebanon in 2006. One Chinook in particular, known by its original squadron code "Bravo November", has come to widespread public recognition