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.
Next up on the list is The AW189, the biggest of the AgustaWestland family of commercial helicopters. Powered by two turboshaft General Electric, GE CT7-2E1 with FADEC engines, it attains a maximum speed of 313kmh (169kn, 194.4mph) and maximum range in excess of 1,200km.