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.
Although the official record is about Mach 3.3 (or 3.3 times the speed of sound), many believe the aircraft could actually fly much faster. However, it seems unlikely that the SR-71 could go much faster than about Mach 3.5, with a very slim chance of Mach 4, due to propulsion and structural limitations.