What Is a Heading Indicator?
Aircraft are replete with instruments that ensure their optimal functionality. Gyroscopic devices are just one example which are used for measuring or maintaining orientation and angular velocity. One of the three fundamental gyroscopic devices aircraft are equipped with is a heading indicator. A heading indicator is accompanied by a magnetic compass, allowing pilots to traverse the sky with ease.
Without a heading indicator, straight flight and precise turns to headings are nearly impossible to achieve in turbulent conditions with a magnetic compass alone. Acceleration, deceleration, and the high-altitude curvature of the Earth’s magnetic field are just some of the factors that are not within a magnetic compass’ ability to handle, oftentimes generating inaccuracies as a result. As such, a heading indicator assists in these situations as it is unaffected by such pressures.
To understand the importance of heading indicators, we must cover how they function. Heading indicators work on the principle of rigidity in space. They operate by using a gyroscope that is tied by an erection mechanism to the aircraft yawing plane. The yawing plane is defined as the longitudinal and transverse axis of the aircraft.
Equally as important is having an understanding of what a flight heading is. The heading, which is also referred to as a bearing or vector, is the direction that the aircraft is pointed in. For pilots, direction is typically expressed in relation to due north on a compass and is measured clockwise. Now that we have defined important terms related to heading indicators, we must outline the differences between a heading indicator and a magnetic compass.
As previously discussed, a heading indicator and magnetic compass work hand-in-hand. Magnetic compasses provide the necessary calibration to direct aircraft properly. In fact, the majority of aircraft rely on magnetic compasses as their principal indication of direction, allowing for precise maneuvers and a steady direction.
Before being called a heading indicator, this flight instrument was called a directional gyro. While its name has changed, the essential components it is composed of has not. Heading indicators contain a main drive gear, compass card gear, gimbal, gyro, adjustment gears, and an adjustment knob. They serve to provide a straight, leveled flight, but they do face some obstacles.
One of the main obstacles heading indicators come across is the downward slope of the earth’s magnetic field, commonly referred to as a “dip.” Dip error accounts for the inaccuracies generated by the magnetic compass during banking, accelerating, and decelerating. With this in mind, the heading indicator displays the same data as the magnetic compass, but with enhanced precision.
Now, we will be covering how to read a heading indicator. To read a heading indicator, one must understand mechanical and apparent drift. Mechanical drift is the result of the friction that causes unalignment with magnetic north due to gyroscopic precession, while apparent drift is sourced from an error in the directional gyro which is impacted by the effect of the earth’s rotation and longitudinal position.
Typically, both types of drift are taken care of through the realignment of the heading indicator with reference to the magnetic compass. After being realigned, one must uncage the older heading indicator. Today, some aircraft feature heading indicators that automatically align without the need for mechanical intervention. That being said, one must make sure to check all flight instruments from time-to-time to ensure they are working optimally.
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