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.
Though not the world's absolute fastest aircraft, the Lockheed Martin F-22 Raptor can accelerate to and sustain supersonic speeds without the use of its afterburners. The Boeing 747 has a cruise speed of 550 miles per hour, which is actually faster than the top speed combat fighters could achieve in World War Two.