12.2 Helicopter flight control systems (ATA 67)

Scope

Level 2 (A) / 3 (B1.3): cyclic, collective, swashplate, yaw control (tail rotor, bleed air), main-rotor head design, blade dampers, blade construction and attachment, trim and stabilisers, manual/hydraulic/electrical/fly-by-wire operation, artificial feel, balancing and rigging. One of the heaviest-weighted M12 sub-modules (about 9 questions).

The three primary controls

Control	Pilot's hand/feet	What it changes	Result
Collective	Left hand lever	Pitch of all main-rotor blades by the same amount at the same time	Total rotor thrust — climb/descent. Throttle twist-grip or governor usually linked to it
Cyclic	Stick between the knees	Pitch of each blade cyclically (once per revolution)	Tilts the tip-path plane — direction of flight, pitch and roll attitude
Anti-torque pedals	Feet	Pitch of tail-rotor blades (or fenestron/NOTAR thrust)	Heading in the hover, balance in forward flight

Key fact: Collective changes pitch equally on all blades; cyclic changes pitch differentially around the disc.

Swashplate assembly

The swashplate transfers fixed-system control inputs to the rotating blades.

• Stationary (non-rotating) swashplate: around the mast on a uniball/spherical sleeve, connected to the cyclic and collective by push-pull rods or servo actuators. An anti-drive (anti-rotation) link stops it rotating. It can tilt in any direction and slide up and down the mast.
• Rotating swashplate: mounted on the stationary plate via a bearing, driven round with the mast by drive links (scissors), and connected to each blade's pitch horn by a pitch link (pitch-change rod).
• Collective input moves the whole assembly up or down (all pitch links move together). Cyclic input tilts it, so each pitch link rises and falls once per revolution.
• A mixing unit combines cyclic and collective inputs (and, on some types, yaw) before they reach the servo actuators.