How does a helicopter move forward?

Marshall Brain

You Asked:

How does a helicopter move forward? --- E. K., Mechanicsville, Va.

Marshall Brain Answers:

The basic idea that lets a helicopter hover in the air is easy to understand. Basically you take a pair of airplane-like wings and spin them. The spinning motion causes the wings to slice through the air at high speed, and in the process they generate lift.

For this to work you need to add one thing. It the wings are spinning one way, the body of the helicopter has the desire to spin in the opposite direction. This would be unpleasant to anyone sitting inside the body (no to mention inefficient), so most helicopters add a tail rotor. These are smaller wings on a boom and they create enough force to counteract the body's desire to rotate.

So now you have a helicopter with a stationary body that can hover in the air. How do you make it go forward? There is a part attached the rotors called the swash plate that makes this possible. You can see how a swash plate works in this brilliant little video:

It's brilliant because this is as simple as a helicopter gets, and you can see exactly what is happening.

As he describes in the video, the collective control (the bar she grabs with her left hand) moves the swash plate up and down to change the pitch of both blades together. This causes them to "take a bigger bite of air" (or a littler bite, depending on which direction you move the control), which lets the helicopter go up or down vertically.

The cyclic control (the one between her legs) tilts the swash plate. So now the pitch of the blades is greater on one side of the helicopter and less on the other side. The helicopter now tilts (in a direction dependent on which way you push the cyclic). Push the cyclic forward and the helicopter tilts forward and therefore moves forward.

For lots more info see: How Helicopters Work