The average speed for a four-seat helicopter is 130 to 145 miles per hour. Because smaller helicopters have smaller engines, the average speed for a two-seat is 90 to 105 mph. The fastest helicopter on Earth as of 2014, the X3 Eurocopter, can fly at 300 mph.
Helicopters can fly because of the lift produced by the rotating blades on top of it. Because helicopters have rotating wings, they fly slowly in comparison with planes. This relatively low speed is due to airflow reversal and flap back, a phenomenon by which the advancing blade produces more lift than the receding one.