One of the most important inventions in the Aeronautical industry of the 20th century is the helicopter. What many people don't know though is that Leonardo da Vinci sketched a helicopter which was manually piloted. The genius did this around the year 1500. The first utilizable helicopter appeared much later though, in the 20th century, at the end of the 1930s.

There are many differences between an airplane and a helicopter, obviously. A plane, in order to be able to move, has to execute a forward motion. When its wings are moving in the air, they generate a force that neutralizes the gravity force. This is what causes the plane to fly.

The helicopter is a much different story though. It can hover into the air without moving, due to the continuous motion of the blades. This has a main factor, like in the case of airplane wings, the air resistance force.

When the helicopter hovers, the force generated by the rotating blades is equal to the weight of the helicopter. If the pilot wished to take the helicopter to a bigger height, the blades' positioning angle must be modified. The pilot can do this simultaneously with all the helicopter's blades.

The helicopter has a single engine, which is used to spin the rotor. Although most helicopters have a single main rotor, there are some who have two. They spin in different directions, which results in greater stability for the helicopter.

Most helicopters have a single main rotor though and a smaller one which produces a horizontal force at the tail of the helicopter. If the engine fails, the main rotor's spin will be reduced. This means that the rotor won't be able to provide the necessary ascending force for the helicopter to fly.

In this situation, a helicopter can still land safely, especially if there's an experienced pilot on board. This can be done through a method called auto-rotation. This is also one of the main advantages of the helicopter, it can bring a pilot safely to the ground even in the most difficult conditions.

Helicopters have many uses, from warfare to saving lives. The most technologically advanced ones are a menace on any battlefield, due to their sheer maneuverability and stealth. There are also big helicopters used to carry military equipment from place to place.

Then, helicopters are also used in rescuing people from difficult situations, in places where nothing else could reach. For example, countless persons have been saved from remote mountain tops or from rough seas. This could have never been possible otherwise, and this is maybe the biggest utility of a helicopter.