Changes

A '''helicopter''' is a rotary wing [[aircraft]].  The first practical helicopter was developed in 1939 by [[Russian]]-born [[Igor Sikorsky]] (1889–1972).  

A '''helicopter''' is a rotary wing [[aircraft]].  The first practical helicopter was developed in 1939 by [[Russian]]-born [[Igor Sikorsky]] (1889–1972).  

''Helicopter flight was the first flight envisioned by man. In fact, the ancient [[Chinese]] were playing with a hand-spun toy that rose upward when revolved rapidly and as early as the mid 1500's, the great [[Italian]] inventor [[Leonardo da Vinci]] had used his fertile mind to make drawings of a machine that we now know as the helicopter.''<ref> [http://www.helis.com/ Helicopter History Site]

Helicopter flight was the first flight envisioned by man. In fact, the ancient [[Chinese]] were playing with a hand-spun toy that rose upward when revolved rapidly and as early as the mid 1500's, the great [[Italian]] inventor [[Leonardo da Vinci]] had used his fertile mind to make drawings of a machine that we now know as the helicopter.<ref> [http://www.helis.com/ Helicopter History Site]

</ref>

</ref>

''Each blade in a helicopter rotor is an [[airfoil]], a [[wing]] with a curved top and a straight bottom. As the blade spins around, air travels faster over the top surface than under the bottom. This reduces air pressure above the blade and produces an upward force called lift. The pitch of the blades (the angle they make to the incoming airflow) controls the amount of lift. During takeoff, the pilot increases the pitch with a control called the collective pitch stick. The lift produced is greater than the helicopter's weight and this makes the helicopter rise upward. If the lift exactly equals the weight, the helicopter hovers. If the weight is greater than the lift, the helicopter descends to Earth.'' <ref>[http://www.explainthatstuff.com/helicopter.html How helicopters work]</ref>

Each blade in a helicopter rotor is an [[airfoil]], a [[wing]] with a curved top and a straight bottom. As the blade spins around, air travels faster over the top surface than under the bottom. This reduces air pressure above the blade and produces an upward force called lift. The pitch of the blades (the angle they make to the incoming airflow) controls the amount of lift. During takeoff, the pilot increases the pitch with a control called the collective pitch stick. The lift produced is greater than the helicopter's weight and this makes the helicopter rise upward. If the lift exactly equals the weight, the helicopter hovers. If the weight is greater than the lift, the helicopter descends to Earth. <ref>[http://www.explainthatstuff.com/helicopter.html How helicopters work]</ref>

Bell Helicopter Textron, is a producer of commercial and military helicopters, and the pioneer of the revolutionary tiltrotor aircraft.  

Bell Helicopter Textron, is a producer of commercial and military helicopters, and the pioneer of the revolutionary tiltrotor aircraft.