Cyclic, collective and the swashplate

Stick to blade, end to end

Follow one input all the way:

• cyclic and collective → rods and bellcranks routed beneath the cabin floor and aft
• → the mixing unit, which combines them
• → three main servos — fore-and-aft, left and right — mounted on the main gearbox
• → the stationary swashplate, which they raise and tilt
• → the rotating swashplate, turning with the rotor
• → three pitch links → the pitch horns on the sleeves → the blades

The pedals take their own path to a tail-rotor servo, and on to the tail rotor's pitch mechanism.

Sources 1, 2, 3

The mixing unit

Your cyclic and collective don't reach the servos separately. They meet in a mixing unit, which sends the combination to three main servos — two lateral, one fore-and-aft — that move the stationary swashplate. A fourth servo drives tail-rotor pitch.

Source 2

Two swashplates

The stationary swashplate doesn't turn. The servos push it up and down for collective and tilt it for cyclic.

The rotating swashplate sits on it through a large bearing and turns with the mast, driven round by a scissors-type link. It copies every tilt and lift of the plate below and passes it to the pitch links.

The bearing between the two is the hand-off from the fixed world to the rotating one — one of the parts a walkaround checks for play and condition.

Sources 1, 4

What the servos do — and don't

The rotor's feedback loads are far more than a pilot could hold, so each servo is a hydraulic jack that does the work while your stick only moves its valve. The controls feel light and dead because the servos absorb the rotor's loads.

A servo has a maximum force. Demand more than it can produce — high speed, high weight, high g, turbulence — and the rotor's load reaches your hands. That is servo transparency, the subject of its own chapter.

Lose hydraulic pressure altogether and the same loads arrive all at once: the hydraulics chapter.

Sources 2, 5

Why 90°?

A blade given less pitch doesn't drop instantly — its flapping peaks about a quarter of a revolution later. The handbook calls it gyroscopic precession.

So to tilt the disc forward, the pitch has to be least 90° earlier: on an AS350, on the left. The control rigging builds this in, so the disc goes where you push.

Source 6

Phase lag in the rigging

Because the disc answers a quarter-turn after the pitch change, the pitch links don't act in line with the stick. On a clockwise rotor, forward cyclic must give least pitch on the left — the advancing side — and right cyclic least pitch at the front.

None of this is felt in the cockpit: the swashplate and pitch-link geometry is laid out so the disc tilts the way you push. It matters when reading American material, where the offsets are mirrored, and for understanding why transverse flow and retreating-blade stall show up 90° round from their cause.

Sources 6, 7

Friction is not trim

Friction holds a control where you left it by resisting movement — both your input and the control's own drift. Too little and the collective creeps; too much and you're fighting it in the moment you need to move it fast.

Unless an autopilot or trim system is fitted, nothing holds the cyclic for you: in the hover your hand is the trim. Set friction for the phase of flight, and take it off before anything where a large, quick collective movement is likely.

Source 1

Control margins

Cyclic travel is finite. The further the centre of gravity is from the mast, the more cyclic is used just to hold attitude — and the less is left for manoeuvring.

With a forward CG, aft cyclic for a flare can run out. With a lateral CG — a heavy passenger or load on one side, a hoist, a doors-off configuration — lateral cyclic is reduced, and a crosswind from the wrong side uses up the rest.

Sources 1, 9

Autopilots and stability augmentation

Most Astars are flown by hand. Retrofit autopilots exist under supplemental type certificates, among them Garmin's GFC 600H (an FAA STC for the AS350 B2 and B3 in 2020, EASA approval in 2022) and Genesys's HeliSAS, an autopilot and stability augmentation system certified on the AS350. Which models a given STC covers is on the STC itself.

They work through the existing controls, and each comes with an RFM supplement: its modes, limits, failure indications and how to disconnect it. If the aircraft you're flying has one, that supplement is required reading before the first flight — not the brochure.

Sources 10, 11, 12, 13