Flight Instruments

South NORTH N OBS Figure 3-21. The effects of acceleration error. N 3 3 3 3 0 6 W E 4 1 2 2 1 2 5 1 S Figure 8-38. Vertical card magnetic compass. 8-27 E S W 30 42 3 1 3 2 NAVGS 3 5 1 6 2 1 View is from the pilot’s perspective, and the movable card is reset after each turn. Figure 8-37. The effects of acceleration error. indication toward north; deceleration causes an indication toward south. Oscillation Error Oscillation is a combination of all of the errors previously mentioned and results in fluctuation of the compass card in relation to the actual heading direction of the aircraft. When setting the gyroscopic heading indicator to agree with the magnetic compass, use the average indication between the swings. The Vertical Card Magnetic Compass The vertical card magnetic compass eliminates some of the errors and confusion encountered with the magnetic compass. The dial of this compass is graduated with letters representing the cardinal directions, numbers every 30°, and tick marks every 5°. The dial is rotated by a set of gears from the shaft- Eddy Current Damping mounted magnet, and the nose of the symbolic aircraft on In the case of a vertical card magnetic compass, flux from the instrument glass represents the lubber line for reading the the oscillating permanent magnet produces eddy currents in heading of the aircraft from the dial. [Figure 8-38] a damping disk or cup. The magnetic flux produced by the eddy currents opposes the flux from the permanent magnet Lags or Leads and decreases the oscillations. When starting a turn from a northerly heading, the compass lags behind the turn. When starting a turn from a southerly heading, the compass leads the turn.