Marine gyrocompass lab

Meridian

Damped gyro motion — the spin axis spirals from a displaced attitude into settling point S, where all four forces balance.

Settling spiral

Click or drag to set a start

Four forces on the spin axis

A gravity-controlled gyro hunts true north, but without damping it traces a closed ellipse about the meridian. Damping in tilt adds a precession toward the horizon, so the path spirals into settling point S. In the northern hemisphere S lies above the horizon and slightly east of the meridian — the latitude / damping error.

  • Tilting · red

    15° cos φ sin α per hour. North end rises east of the meridian, falls west of it. Zero on the meridian.

  • Drifting · blue

    15° sin φ per hour. Constant at a given latitude — always the same length and direction on this chart.

  • Control precession Pc · green

    From the pendulous control. Westward when the north end is up. Zero on the horizon. At S, Pc cancels drift.

  • Damping precession Pd · gold

    Acts toward the horizon (damping in tilt). Zero on the horizon. At S, Pd cancels tilting — which is why S cannot sit on the meridian.

dα/dt = D − Pc    dβ/dt = T − Pd    At S: D = Pc and T = Pd