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I’m going to tell you a little bit more about an important invention, the helicopter. In the 16th century, Leonardo da Vinci and other great thinkers made a lot of drawings of a machine that we now know as the helicopter but they were missing two essentials: a true understanding of the nature of lift and a competent engine so they weren’t able to build the first helicopter. Because of new techniques and better understanding of engines, Paul Cornu lifted the first helicopter in the air for a few seconds in 1907. In 1924, Etienne Oehmichen, became the first to fly a helicopter a kilometer in a closed circuit in 1924. It was a historic flight taking 7 minutes and 40 seconds. Then, in 1936, the German helicopter wulf fw 61 became the first practical helicopter and vertical flight was not a dream anymore. Nowadays helicopters have a lot of functions. For example: People use Sea-Kings for rescue operations, policeman use police helicopters and they are also used for transporting wounded people to a hospital. Modern helicopters have a rotor. Because of that rotor, vertical flight is no problem. Nowadays rotors are very strong and the quality of rotors is very good whereas the primitive helicopters had a lot of accidents because rotors weren’t strong enough. A good invention needs a good pilot. After 30 hours of lesson you can handle a helicopter but if you want to be a very good pilot you need 200 hours of lesson. The tail of a helicopter is very necessary because otherwise there is no balance and the helicopter would crash. The capacity of a normal helicopter is 4 till 6 people but there are also bigger helicopters for transporting goods to other countries or when soldiers need to go somewhere, people use a big army-helicopter. Big helicopters have generally 2 rotars because of the weight of the goods or the many people inside the helicopter. The invention of the helicopter was very successful but it’s also a dangerous invention. When you don’t pay enough attention or when there’s a defect, an accident could happen.