Main-rotor blades

How a composite blade is built

The Astar's blades are glass fibre and epoxy: a spar of wound glass rovings carries the loads, a light foam core fills the section behind it, and the whole is wrapped in a composite skin. A metal strip protects the leading edge from erosion.

Damage limits — how deep a dent, how long a crack — are set by maintenance documentation, not by eye.

Source 1

The leading edge

On the Astar the erosion strip is stainless steel, bonded to the blade. It takes the sand, rain and grit so the composite behind it doesn't.

The bond matters as much as the strip. EASA AD 2022-0246 followed reports of the strip debonding on certain blade part numbers, which unbalanced the rotor and produced high vibration; it requires repeated tap inspections. It lists the earlier variants (B, BA, BB, B1, B2, D) and AS355s — whether it applies is a blade part-number question for maintenance.

Sources 1, 3

Track, balance and trim tabs

For a smooth ride all three blades must fly in the same plane (track) and the rotor must be balanced around the mast. Maintenance measures both with track-and-balance equipment and corrects them — typically with pitch-link length, the small trim tabs on the trailing edge, and balance weights.

Tabs are set with tools, to measured values. A bent tab changes the track — check them on the walkaround, and never adjust one by hand.

Sources 5, 6

Reading vibration

The handbook groups vibration by frequency. Low-frequency vibration — near main-rotor speed; a blade out of track or balance gives one beat per revolution — comes from the main rotor: track, balance, a damaged blade, worn bearings or dampers. Medium frequencies come from things like cooling fans, accessories and the driveline. High-frequency vibration points to the engine or the tail rotor.

A new vibration in flight is a reason to slow down and land to have it looked at, not to press on to see if it goes away.

Source 5

Describing it to maintenance

What helps the engineer most is a good description:

• frequency — a slow beat you could count, a buzz, or a high-pitched tingle
• direction — up-and-down (vertical) or side-to-side (lateral)
• when — on the ground, in the hover, at a particular speed, in turns
• what changed — recent maintenance, a blade change, a bird strike, a hard landing

The handbook stresses direction — up and down, fore and aft, side to side — and whether it's in the controls or the airframe: that's what lets maintenance tell track from balance. Some vibration is part of any rotor's normal character; what matters is a change.

Sources 5, 7

Why slow blades sail

At flight rpm, centrifugal force holds the blades stiffly out. At low rpm it is a fraction of that, while a gust still acts with full force on blades that are flexible and long. A gust or an updraft under one side lifts the blades there and drives them down on the other — towards the tail boom.

The handbook pairs the gust with the controls: a control that moves, or sits out of position, tilts the slow disc before the wind does anything — one reason the controls are frictioned and the pilot stays on them. Rooftops, buildings and ridges make the worst gusts.

Source 4