RC Helicopter Controls Understanding Cyclic

Besides Lift, our RC Helicopter Rotor blades also produce thrust. This is what allows our helicopter to fly forwards, backwards, sideways, or any combination of those.

This is where an airplane wing and helicopter rotor blade take on different characteristics. The rotor is spinning just like a propeller and therefore not only produces lift it also produces thrust.

Propeller Example

If you think of a rotor as a propeller, it is really easy to understand how a helicopter can fly in all directions. OK, let’s take that complicated rotor system off our RC helicopter and replace it with a simple propeller. This propeller is on the top of our helicopter exactly horizontal to the ground so the thrust is pulling the heli straight up.

In this very simple example, the helicopter will lift off the ground and go straight up as the propeller speeds up or the pitch is increased (assuming the helicopter is not sitting on the side of a hill). If we match the amount of thrust from the propeller to the pull of gravity, the helicopter now hovers.

Now let’s tilt the propeller on the helicopter a little bit with our cyclic helicopter controls, how about tilting it forward. What happens? There is still thrust pulling the heli up but there is also a small component (or vector) of thrust pulling the heli forward now. Same idea if we tilt the propeller backward – the helicopter will move backwards. These two movements are referred to as pitching. More specifically pitching forward and pitching backward.

What about side ways, exactly the same - tilting the propeller to the right will produce thrust to pull the helicopter to the right – opposite if you want to move to the left. These movements are referred to as rolling.

Cyclic Explained

Now our helicopter controls don’t really tilt the rotor – they do something even better and it is called "CYCLIC PITCH CONTROL". How does it work? By changing the angle of pitch of each rotor blade as it makes one revolution or cycle we can tilt the helicopter in any direction. That is why it is called cyclic pitch control or just plain cyclic. Cyclic helicopter control is responsible for controlling pitch (elevator) and roll (aileron) of the helicopter.

You will often hear of aileron and elevator being used in the RC heli world since RC radios (fixed wing and heli) refer to those two channels as aileron and elevator - never cyclic roll & cyclic pitch. Helicopters of course don't have ailerons and elevators so to be correct, I always try to use the terms cyclic roll and cyclic pitch. I just wanted to mention why you will also hear aileron and elevator thrown around from time to time.

Let’s look at our forward flight example of tilting the propeller again. This time instead of tilting the propeller forward we will change the pitch angles of the rotor blade. For forward flight we will want the rotor to lift on the rear half of its travel more than the front half - in effect, tilting or pitching the helicopter forward. What do helicopter pilots (RC and real) call this – forward cyclic.

You might think to achieve more lift on the back than the front; the rotor blade will have more pitch when it is at the back half of the rotor disc than the front half. However, because of the principle of gyroscopic precession this is not exactly where these pitch changes happen, but you get the idea of how it works.

By increasing pitch on one half of the rotor disc and decreasing it on the opposite half, the rotor will want to tilt. Seeing that the rotor is firmly attached to the helicopter – the heli will follow along and also tilt in the same direction. Once the helicopter is tilted in that direction, the thrust coming off the rotors pulls it in that direction, just like tilting the propeller.

Notice I have only been talking about one rotor blade as it makes one revolution or cycle. This is to keep things simple in this explanation. Of course for balance reasons we need at least two rotor blades. The same pitch changes will occur to each rotor blade as it makes one revolution or cycle. It makes no difference if there are two, three, four, or five rotor blades – the same cyclic pitch changes occur to each rotor blade as it makes one revolution.

All these cyclic pitch changes are possible because of the rotor head and the swash plate. The swash plate is what makes much of helicopter control possible. It is basically a mechanical linkage system which mechanically joins the non-rotating helicopter control systems to the rotating control portions of the main rotor head.