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
San Francisco and Oakland Helicopter Airlines flights being operated with Bell 206 helicopters. The following destinations were served at various times by San Francisco and Oakland Helicopter Airlines during its existence: San Francisco and Oakland Helicopter Airlines San Francisco and Oakland Helicopter Airlines (also known as SFO Helicopter Airlines and SFO Helicopter) was a helicopter airline service offering scheduled passenger flights between San Francisco, Oakland, and other Bay Area cities. It was founded in 1961 but disappeared from the Official Airline Guide 15 years later before finally going out of business in 1986. San Francisco and Oakland Helicopter Airlines was one of the first helicopter airlines