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 CH-47 Chinook in June 2005 with all aboard killed, including a 16-member U.S. Special Operations team. In May 2011, an Australian Army CH-47D crashed during a resupply mission in Zabul Province, resulting in one fatality and five survivors. The helicopter was unable to be recovered and was destroyed in place. To compensate for the loss, the ADF added two ex-U.S. Army CH-47Ds to the fleet which are expected to be in service until the introduction of the CH-47Fs in 2016. Since the type's inception, the Chinook has carried out secondary missions including medical evacuation, disaster relief, search and rescue, aircraft recovery, fire