Flight Control Systems

The swashplate, collective/cyclic/pedal control, hydraulic servos, mixing and stability augmentation.

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Main ideas

The SWASHPLATE is the heart of helicopter control: a non-rotating (lower) plate and a rotating (upper) plate. The pilot's collective and cyclic move the non-rotating plate; the rotating plate turns with the shaft and drives the blade pitch links.
COLLECTIVE raises or lowers the whole swashplate, changing all blades' pitch equally (total thrust). CYCLIC tilts the swashplate, so each blade's pitch changes cyclically once per revolution — tilting the rotor disc to move the aircraft (the input is applied ~90° ahead because of precession).
The PEDALS change the tail-rotor blade pitch for anti-torque and yaw; a mixing unit combines collective, cyclic and pedal inputs mechanically before the servos.
Powered helicopters use IRREVERSIBLE hydraulic servos (the pilot cannot feel or be back-driven by rotor loads); loss of hydraulic power makes the controls heavy and may limit manoeuvring, so dual/independent hydraulic systems are common.
The helicopter is inherently unstable, so a STABILITY AUGMENTATION SYSTEM (SAS/SCAS) and/or autopilot continuously damps and stabilises it; rotor RPM is held by a governor coordinating collective and throttle.
⚠ Exam trap: the SWASHPLATE (stationary + rotating halves) converts fixed collective/cyclic inputs into rotating blade-pitch changes; cyclic changes each blade's pitch ONCE PER REVOLUTION to tilt the disc, and the input leads the desired result by ~90° (precession).

Solved examples

How does moving the cyclic forward cause the helicopter to pitch forward and accelerate?
Forward cyclic tilts the (non-rotating) swashplate, which cyclically varies each blade's pitch once per revolution. Because of gyroscopic precession the maximum pitch change is applied about 90° before the point where the disc should drop, so the rotor disc tilts forward. The tilted total-rotor-thrust vector now has a forward component, pulling the helicopter forward.

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