how do the propellers on a helicopter actually make the vehicle able to fly?
In: Engineering
There are a few elements that need to work together to make a helicopter fly. The simplest is probably the big rotor on the top – this pushes air down and lifts the helicopter into the air. Once the helicopter is off the ground though, there is nothing to hold it straight, so the rotor spinning would start to make the body of the helicopter spin too.
To counteract this they put a second, smaller rotor at the back pointing sideways – when the torque from the main rotor tries to twist the body one way, the tail rotor pointing the other direction pushes in the opposite direction to balance out.
That gives you a helicopter that goes up and down, which is cool but not entirely useful.
The more complicated bit comes when you want to travel sideways – this is done by adjusting the pitch (angle) of the blades as they rotate. Changing the pitch of a blade changes how effective it is. So if you have the blade pitched to be effective when it is on the rear of the helicopter, and less effective when it is at the front, this will naturally lift up the back of the helicopter and cause it to move forwards. Reverse that so the blades are pitched to be more effective on the front and you will go backwards (and the same to the sides).
By manipulating the speed of the main rotor you can go up and down, by manipulating the pitch you can move forwards, backwards or side to side, and by manipulating the tail rotor you can rotate on the spot. Combine them all together and you can fly.
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