Unlike navigating a land vehicle, navigating an aircraft poses unique challenges as there are few reference points that can be used to indicate one’s location in the sky. Instead, pilots mainly rely on navigation devices like those used to indicate direction like compasses or magnetometers. All certified aircraft are required to be equipped with at least one magnetic direction indicator, those of which function by means of the Earth’s magnetic core. For your better understanding, this blog will explore the functions of a few popular aircraft direction indicating instruments.
The most basic of the magnetic direction devices you will find on aircraft is the magnetic compass. This instrument has been used for hundreds of years on land and then in the air. The working principle of this device is a simple magnet floating in a liquid similar to kerosene. This design ensures that vibrations are dampened, the assembly can oscillate freely, and friction is minimized. Additionally, the liquid allows the magnet to stay parallel to the horizontal plane and therefore align with the Earth's magnetic field. The exterior of the instrument is marked with directional degrees to indicate the aircraft’s position relative to the Earth's magnetic North pole.
While this simple design might appear fail proof on paper, magnetic compasses are prone to a few errors. One accuracy issue that poses a threat to magnetic compasses is the interference of nearby magnetic fields leading to magnetic deviation. A pilot can avoid this issue by “swinging the compass,” which means counterbalancing these forces by adjusting setting screws. Another issue with magnetic compasses is the phenomenon of magnetic variation caused by the difference in location of geographic North and magnetic north. In other words, the difference between Earth’s magnetic poles and geographic poles must be accounted for by pilots in order to produce an accurate reading of their location. Depending on the location of the aircraft, airmen must add or subtract degrees from the magnetic indication to obtain true geographic location information.
Additional issues with basic magnetic compasses include dip errors and reverse rotations. The former is caused by acceleration or turning motions causing inertia that alters the magnet’s position in the liquid. The latter occurs during left turns due to the compass card rotating opposite to the direction of the intended turn. This is because, from the pilot’s seat, you are actually looking at the back of the compass card.
As is common with all important technology, innovations have been made to overcome these errors and make operating magnetic compasses easier for the pilot. One example of this is the vertical magnetic compass, that of which eliminates the reverse rotation issue. By mounting the main indicating magnets of the compass on a shaft rather than a float, a compass card can be made to turn about a horizontal axis. In other words, when turning right, increasing numbers are to the right; when turning left, decreasing numbers rotate in from the left. A second example of innovative compass designs is the remote indicating compass; this design removes the need for swinging the compass. By using a synchro remote indicating system, a remote indicating compass relies on a transmitter to alter the magnetic field in the cockpit preventing interference.
Of course, developments in compass technology did not stop there. Known as the slaved gyro compass or fluxgate compass system, this elaborate and accurate design combines the use of a gyro, a magnetic compass, and a remote indicating system. The Earth’s magnetic field flows through the iron core of this device to all three of its legs in different magnitudes. Some designs even include radio navigation aids. As designs become more complex, they also become more reliable, and pilots should opt for the device that offers the most benefits and easy use during flight. With many popular options, it can be difficult to decide which device makes sense for you; however, one navigation instrument that can be found in most aircraft is the solid state magnetometer.
Unlike magnetic compasses, this device has no moving parts and uses very little power to sense not only the direction to the earth’s magnetic poles, but also the angle of the flux field. Additionally, these devices are free from oscillation that plagues a standard magnetic compass. As all instruments have an ideal time and place, it is important for any prospective buyer to fully understand both the functions of the instrument and the needs of their aircraft before making a purchase. As there are many reliable designs on the market for modern aircraft, it is hard to go wrong, but making an informed decision will ensure the most benefits to any pilot.
To learn more about the magnetic compasses, gyroscopes, amplifiers, and other aircraft direction instruments we carry at One Click Purchasing, visit our website to explore our comprehensive inventory. With an easy-to-browse database comprising a myriad of new, used, obsolete, and hard-to-find parts, we are your one stop shop for all of your aviation needs. Get started today by calling or emailing us at any time; we are available 24/7x365!
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