Because the air gets too thin.
Helicopters can fly directly up or down.
No, Helicopters cannot fly in Stratosphere. It is too high for them. They do not produce that much lift. But they can fly in the Troposphere.
Yes, helicopters fly high when on long journeys.
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.
They fly in California.
You can fly helicopters.
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.
so we can fly
No
Yes, there are helicopters available.