The washout assembly (or lower mixer) is a set of linkages in the rotor head that serve to mix out collective pitch inputs from the swashplate, and pass the remaining cyclic pitch inputs to the flybar control arm.
The washout assembly consists of three parts:
- The washout guide (often also the phase ring) that keeps the washout aligned with the rotor head;
- The washout arms that connect the swashplate to the flybar control arm linkages;
- The washout base to which the washout arms are mounted, and which slides up and down the main mast.
The washout also often serves to rotate the cam follower of the swashplate with the rotor head.
A few helicopters do not have a traditional washout, and either transmit collective inputs to the rotor head via a pushrod separate from the swashplate (such as the Falcon 3D), or use a flybar that can move up and down inside a guide (such as the Gazaur Mars).
Washout also refers to changing blade pitch or profile along the length of a rotor blade, as the tip of the blade is moving much faster than the root. Typically model helicopter blades don't have this type of washout, as the blades are symmetrical to allow for inverted flight.
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