What in the world do all of these gauges do? That’s often the first reaction when someone sees an airplane cockpit. There is a lot of information being displayed on the various needles in an aircraft – it can be overwhelming. But every airplane has a few staple instruments – the milk, bread and eggs of the flying world, that are easy to recognize and fundamental to flight. Whether you are new to aviation or perhaps looking to gain some deeper understanding on your flight simulator, let’s look at the six basic aircraft instruments that you’ll find in just about any airplane, affectionately called the “six-pack.”
This is like your speedometer – it shows how fast you are travelling through the air. A little silver tube called the pitot (pronounced “pee-toe”) tube, which is usually affixed to the wing, takes in ram air as the airplane flies. This measures the speed that the airplane moves through the air. Keep in mind that the ground speed will likely differ from the airspeed because of wind. For example, if a boat is travelling 5 MPH down a river that is flowing 10MPH, the boat is really travelling 15MPH in relation to the shore. Similarly, an airplane will travel a certain airspeed through the air, which can be read on the airspeed indicator, and then have a different groundspeed if the wind – like a river of air – is working either with or against the airplane.
No, this doesn’t turn different colors like a mood ring and tell you when you’re mad – it’s a different kind of attitude. Have you ever played with a gyroscope? It’s basically a spinning wheel on a gimbal, but the principle of the gyro is that the spinning wheel tends to stay rigid in space. It’s hard to visualize without just spinning one up and playing with it (Hobby Lobby has them in the kids area), but the spinning gyro in the attitude indicator allows the airplane to effectively rotate around the gyro, showing the degree of pitch that the nose is high or low and the degree of bank that the wings are right or left. The pitch and bank are marked with lines, calibrating the degrees of pitch and bank. Some off road cars have a similar instrument encased in fluid that tells them when they are pitched or banked too far and risking tipping. In a nutshell, the miniature airplane (the icon in the center of the instrument that looks like a bird) gives a great visual indication of the airplane’s position in relation to the horizon.
Airplanes are known for going up, and this is the instrument that shows just how far up you are. It reads much like a clock. The long hand is the hundreds of feet, the shorter hand thousands of feet. There is also a super thin hand that reads tens of thousands of feet. By using barometric pressure to change a little balloon-like wafer inside, the needles will rise or fall when the airplane does. The altimeter will show the height above sea level, called Mean Sea Level (MSL), and because it functions off pressure, a little window on the altimeter called the Kohlsmann Window is used to input the altimeter setting (a number in inches of mercury gained from the airport’s weather station) so that it is calibrated to read accurately. Thus, if you are at an airport where the elevation is 500 feet, your altimeter will read 500 feet when calibrated correctly and sitting on the ground.
This “miniature airplane” gives you a reference of your left and right bank. Using a tilted gyro inside, it senses both the direction and quality of the bank, so when the wing of the airplane is banked and aligned with the lower mark, that indicates a standard two minute turn. This means that to complete a full 360 degree circle in this bank would take two minutes. Turning 180 degrees, then, would take one minute. The other component of the turn coordinator is the ball. It’s literally a little ball in a liquid chamber that can roll left or right and is used to show you if your bank is coordinated or not. Simply put, it shows if the rudder input is matching the bank. If the ball rolls right, more right rudder is needed and vice versa. The ball made the most sense to me when I rode in the middle of the back seat on a flight one day. I was sitting with my knees together, high to my chest (not much space in the middle) with my arms wrapped around my knees – almost like a cannonball. I was sort of balancing in that position. I noticed that if the ball rolled left, so did I. If it rolled right, so did I. In a turn, if it stayed centered, so did I. The lesson? The ball shows centripetal or centrifugal force, much like a turn in a car pushes you against the outside of the turn. The phrase “step on the ball” is used because you use your feet to apply rudder input in the direction the ball is rolling.
Going somewhere fast doesn’t much matter if you aren’t going in the right direction, and your heading indicator functions aesthetically much like a compass. Using a gyro inside, the airplane turns around the instrument, moving a card calibrated in degrees, telling you which compass direction you are heading. Why not just use the compass? Well, the compass is magnetic and in fluid, and subject to a lot of various errors unless in level flight at a constant speed. Trying to use a compass in a moving airplane reminds me a little of trying to sip a full cup of coffee on a jog. The heading indicator is pretty stable, so it is a more accurate method of telling direction through all phases of the flight. The gyro inside will precess, or drift a little over time, causing the heading indicator to need realigning with the magnetic compass every 15 minutes or so when in stable, level flight.
Vertical Speed Indicator
It’s one thing to know that you’re climbing or descending, but knowing how fast you’re climbing or descending is pretty helpful, too. By using a balloon-like wafer inside the instrument with a calibrated leak, the changing pressure that results from climbing or descending show up as a reading in feet per minute. The instrument rests at the zero mark, indicating level flight. When the needle drops below the zero, it indicates a descent. Naturally, then, a climb is the needle showing above the zero indication. It’s good to know that this instrument can lag just a bit, so while it will show a trend of a climb and descent, it will take a few seconds to settle in to an exact rate.
Glass and Steam
While airplanes will have varying orientations of the six pack, the important part of the instruments are the information that they provide. With advances in technology, many airplanes are now being built or converted to a cockpit that uses a display that looks more like a tablet or computer screen instead of the dials and gauges of the past. This is referred to as a “glass panel” cockpit, and many now refer to the older gauges as “steam gauges” when discussing the airplane’s cockpit layout. While the information gained from the instruments is the same in either a glass panel or steam gauges, it does take a bit of a transition from one to the other to get familiar with the layout – almost like driving on the opposite side of the road in a different country. While glass cockpits provide a simple and intuitive layout, many pilots feel that learning on steam gauges and then transitioning to glass is the best way to build the proper fundamentals, arguing that it’s easier to transition up to glass than trying to figure out the steam gauges if all you know is glass. Which one do you use? Do you prefer one to the other? Leave some comments below!
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