Yes they do. By pulling back on the cyclic stick the main rotor swings backwards forcing the helicopters to go backwards. -Credits Lukespill
Airplanes can have a zero or negative ground speed, but the only thing that is important to maintain flight is airspeed.
No they cannot
Yes
Normally they can't. But the Harrier can to a certain degree, as can helicopters.
They fly helicopters.
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.
They fly in California.
You can fly helicopters.
Fly backwards
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.
No
so we can fly
Helicopters can fly directly up or down.
Yes, there are helicopters available.
Yes, by changing the rotor angle.