For centuries men dreamed of achieving vertical flight. In 400 A.(D), Chinese children played with a【B1】______toy that spun upwa

For centuries men dreamed of achieving vertical flight. In 400 A. D. , Chinese children played with a fan—like toy that spun upwards and fell back to earth as rotation ceased. Leonardo da Vinci conceive the fast mechanical apparatus, called a "Helix", which could carry a man straight up, but this was only a design and was never tested.
    The ancient dream was finally realized in 1940 when a Russian engineer piloted a strange looking craft of steel tubing with a rotating fan on top. It rose awkwardly and vertically into the air from a standing start, hovered a few feet above the ground, went sideways and backwards and then settled back to earth. That vehicle was called a helicopter.
    Imaginations were fired. Men dreamed of going to work in their own personal helicopters. People anticipated that vertical fight transports would carry millions of passengers as do the airliners of today. Such fantastic expectations were not fulfilled.
    The helicopter has now become an extremely useful machine It excels in military missions, carrying troops, guns and strategic instruments where other aircraft cannot go. Corporations use them as airborne offices, many metropolitan areas use them in police work, construction and logging companies employ them in various advantageous ways, engineers use them for site selection and surveying, and oil companies use them as the best way to make offshore and remote work stations accessible to crews and supplies. Any urgent mission to a hard-to-get-to place is a likely task for a helicopter. Among their other multitude of uses: deliver people across town, fly to and from airports, assist in rescue work,and aid in the search for missing or wanted persons.