The air gets thinner as altitude increases, which in turn decreases the amount of lift an aircraft can get. The air in the stratosphere is far too thing for helicopters and most planes.
Helicopters are typically designed to fly in the troposphere, which is closer to the Earth's surface. The stratosphere begins at around 10 kilometers above sea level, and helicopters lack the necessary design and power to operate efficiently at that altitude.
Helicopters can fly directly up or down.
Because the air gets too thin.
Helicopters are not very well suited to high altitude flight. By their very nature helicopters less suited for high altitudes than airplanes or balloons. Additionally, since the most common usages of helicopters deals in short hops or other low-altitude duties, modern helicopters aren't designed with high altitude flight in mind. The stratosphere is generally agreed to start at about 30,000 feet altitude. While this is pretty near to the helicopter altitude record (in 2005 an Ecureuil/AStar AS 350 B3 helicopter landed on Mount Everest (29,035 feet)) This is far higher than the ceiling of the average helicopter (10 to 12,000 feet).
They fly helicopters.
Because rotors are noisy and helicopters isually fly close to ground
Most helicopters fly with only one rotor. If you mean one blade, that is because it would be unbalanced.
You can fly helicopters.
They fly in California.
Stratosphere
Type your answer here... airplanes fly in the stratosphere to avoid weather problems
There are many different helicopters. Most small civilian helicopters may fly for about an hour, but large passenger or military helicopters can fly for 6 hours or more.