How an RC helicopter works

A helicopter looks complicated, but it comes down to a handful of parts doing simple jobs very quickly. Understanding them makes flying, setting up and fixing a helicopter far easier.

The main rotor: making lift

The main blades are wings that spin. As they move through the air at an angle, they push air down and the helicopter up. Lift depends on two things:

• Rotor speed (head speed): faster blades make more lift.
• Blade angle (pitch): a steeper angle makes more lift, up to a point.

Fixed pitch helicopters control lift by speeding the rotor up and down. Collective pitch helicopters keep the rotor at a steady speed and change the angle of all the blades together, which is much faster. Coaxial vs fixed pitch vs collective pitch compares the types.

The swashplate: steering the rotor

The swashplate is a pair of plates around the main shaft: the bottom one doesn't spin and is moved by servos; the top one spins with the rotor and connects to each blade through links.

• Raise or lower the whole swashplate: every blade's angle changes together. That's collective pitch: climb or descend.
• Tilt the swashplate: each blade's angle rises and falls as it goes round. That's cyclic pitch: the rotor disc tilts, and the helicopter moves in that direction.

Three servos (sometimes four) under the swashplate make all of this happen. Setting them up correctly is covered in swashplate levelling.

The tail rotor: stopping the spin

Spinning the main rotor one way tries to spin the body the other way (torque reaction). The tail rotor pushes sideways to counter it. Changing the tail rotor's thrust turns the helicopter: that's the rudder control.

Tail rotors are driven by a belt, a shaft (torque tube), or on small helicopters a separate tail motor. Problems with the tail are behind most "my helicopter spins" questions; see tail spinning and tail wag.

The gyro and flybarless unit: staying stable

A helicopter on its own is unstable: it wants to drift, tilt and spin. Two things have tamed that:

• The tail gyro senses the body turning and corrects the tail rotor instantly.
• The flybar or flybarless unit stabilises the main rotor. Older helicopters used a weighted mechanical flybar; modern ones use electronic gyros. See flybarless vs flybar helicopters.

On beginner helicopters, the same sensors add self-levelling, altitude hold and rescue modes. The electronics are covered in gyros and flybarless units.

Coaxials: a different trick

Coaxial helicopters have two main rotors spinning in opposite directions. Their torques cancel, so there's no tail rotor; speeding one rotor up and slowing the other turns the helicopter. A small swashplate or a tail fan tilts it forward and back. That's why they're so stable, and why they can't handle wind.

The power system

A battery feeds an electronic speed controller, which drives a brushless (or on small models, brushed) motor. The motor turns the main rotor through a gear, or directly on "direct-drive" designs. On collective pitch helicopters, a governor holds the head speed steady. See ESCs and brushless motors.

Putting it together

The sticks are explained in RC helicopter controls explained. Back to the RC helicopters hub.