How is the pitch of the blades of the main rotor of a helicopter controlled independently?

Posted 12May2017

The swashplate.

The best way I have explained it has been using the “Tilt-a-whirl” analogy. Most people are familiar with this carnival ride – it spins on a circuit that goes up and down a gentle incline, provoking amusement, nausea, and sometimes vomiting.

In this sense, this is what the swashplate does (the up an down, not the rest of it).

At the lower portion is the swashplate assembly, and the vertical rods are the pitch control rods. Mosul, Iraq 2010. (Source: author.)

Broken down into the stationary and rotating assemblies, the swashplate takes input from the flight controls, namely the cyclic and the collective, and mechanically transmits the desired output to the to the stationary assembly (some people differentiate them by referring them to “stationary star” and “rotating star,” but that is merely semantics). The stationary portion of the swashplate then rises accordingly – in unison for collective input, and angled by quadrant for cyclic input. The end result, when the pilot starts moving the cyclic control then resembles the aforementioned “Tilt-a-whirl” by… well, tilting. From there, the pitch control rods – connecting the rotating portion of the swashplate to the actual main rotor blade – increase and decrease the pitch of the blades in whatever phase they are in.