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.
The unofficial record speed is also inconsistent with data from the National Museum of the United States Air Force, which gives a top speed of 520 mph (840 km/h) (Mach 0.70), nonetheless, making the XF-84H the fastest single-engine propeller-driven aircraft until 1989 when Rare Bear, a highly modified Grumman F8F Bearcat reached 528 mph (850 km/h) (Mach 0.71).