Risk factors. Factors that increase the risk of stuttering include: 1  Having relatives who stutter. 2  Stuttering tends to run in families. 3  Delayed childhood development. 4  Children who have developmental delays or other speech problems may be more likely to stutter. 5  Being male. 6  Males are much more likely to stutter than females are. 7  Stress.
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. Keep Learning.
In addition, a hovercraft will travel faster when traveling downwind than it will when it faces a headwind. Depending upon the terrain and the weather, the average speed of a hovercraft is 35 mph (56 km/h). Today's light recreational hovercraft can reach speeds in excess of 70 mph (112 km/h).