IFH 5-15

N W S E 33 30 24 21 15 12 6 3 Figure 3-22. A vertical card magnetic compass. Figure 5-22. Vertical card magnetic compass. Figure 3-23. The soft iron frame of the flux valve accepts the flux from the Earth’s magnetic field each time the current in the center coil reverse. This flux causes current to flow in the three picked coils. Figure 5-23. The soft iron frame of the flux valve accepts the flux from the Earth’s magnetic field each time the current in the center coil reverses. This flux causes current to flow in the three pickup coils. Figure 3-24. The current in each of the three pickup coils changes with the heading of the aircraft. Figure 5-24. The current in each of the three pickup coils changes with the heading of the aircraft. The Vertical Card Magnetic Compass The floating magnet type of compass not only has all the errors just described, but also lends itself to confused reading. It is easy to begin a turn in the wrong direction because its card appears backward. East is on what the pilot would expect to be the west side. The vertical card magnetic compass eliminates some of the errors and confusion. The dial of this compass is graduated with letters representing the cardinal directions, numbers every 30°, and marks every 5°. The dial is rotated by a set of gears from the shaft-mounted magnet, and the nose of the symbolic airplane on the instrument glass represents the lubber line for reading the heading of the aircraft from the dial. Eddy currents induced into an aluminum-damping cup damp oscillation of the magnet. [Figure 5-22] The Flux Gate Compass System As mentioned earlier, the lines of flux in the Earth’s magnetic field have two basic characteristics: a magnet aligns with these lines, and an electrical current is induced, or generated, in any wire crossed by them. The flux gate compass that drives slaved gyros uses the characteristic of current induction. The flux valve is a small, segmented ring, like the one in Figure 5-23, made of soft iron that readily accepts lines of magnetic flux. An electrical coil is wound around each of the three legs to accept the current induced in this ring by the Earth’s magnetic field. A coil wound around the iron spacer in the center of the frame has 400-Hz alternating current (A.C.) flowing through it. During the times when this current reaches its peak, twice during each cycle, there is so much magnetism produced by this coil that the frame cannot accept the lines of flux from the Earth’s field. But as the current reverses between the peaks, it demagnetizes the frame so it can accept the flux from the Earth’s field. As this flux cuts across the windings in the three coils, it causes current to flow in them. These three coils are connected in such a way that the current flowing in them changes as the heading of the aircraft changes. [Figure 5-24] The three coils are connected to three similar but smaller coils in a synchro inside the instrument case. The synchro rotates the dial of a radio magnetic indicator (RMI) or a horizontal situation indicator (HSI). Remote Indicating Compass Remote indicating compasses were developed to compensate for the errors and limitations of the older type of heading indicators. The two panel-mounted components of a typical