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.
Commercial airlines cruise at approximately 500 - 600 mph. (804.672 kilometre/hour) Additional InformationFighter jet aircraft fly at speeds in the low mach numbers. Mach one is roughly 750 miles per hour, give or take, and military jets can fly at well over a thousand miles per hour. Back in the day (July of 1976), the SR-71 set the jet speed record.