What Is The Difference Between the Airspeed Indicator, Altimeter, and Vertical Speed Indicator?
When first learning how to pilot an aircraft, one will have to familiarize them self with the various cockpit instruments that they will rely on during flight to maintain safety and efficiency. There are many instruments that are provided, each offering readings on different aspects of operation. The measurements provided by the airspeed indicator, altimeter, and vertical speed indicator will all regularly be used by the pilot to effectively manage a flight path. It is paramount that one understands the differences between each instrument as they perform separate tasks. In this blog, we will discuss the differences between the airspeed indicator, altimeter, and vertical speed indicator, allowing you to have a better grasp on the importance of each.
The airspeed indicator is a necessary instrument for any aircraft, and it is a flight instrument that performans the role of measuring the airspeed of an aircraft as it traverses the atmosphere. The readings provided by the airspeed indicator may vary by country, but standard units of measurement include kilometers per hour, knots, miles per hour, and meters per second. While the ICAO recommendation is to use kilometers per hour, knots is the most common measurement. With an airspeed indicator, the pressure differential between static pressure and total pressure is measured, both values being derived from the static port and pitot tube respectively. Based on the difference in pressure, a diaphragm within the instrument casing will expand or retract, resulting in the movement of a needle on the dial face which will then indicate a reading. The airspeed indicator is the only instrument that relies on both the pitot and static system, and any blockage of either will alter readings by a significant degree.
With the altimeter, a pilot can determine just how high the aircraft is above a fixed level, that of which is generally sea level. In order to conduct altitude readings, the altimeter relies on an aneroid barometer that measures atmospheric pressure provided by the static port on the fuselage. On average, air pressure will adjust by around one inch of mercury per 1000 feet of altitude change, or 100 hectopascals per 800 meters of change. As the aircraft moves up and down, the needle on the altimeter will adjust in response, always indicating the height the aircraft is above sea level. As many operations are conducted over land that reaches much higher altitudes, it is important that pilots take this into consideration when flying.
While the vertical speed indicator sounds similar to the airspeed indicator, it performs a much different role. Whereas the airspeed indicator provides readings on forward momentum, the vertical speed indicator is concerned with the rate at which an aircraft climbs or descends in the air. Generally, these readings are provided in meters per second, feet per minute, or knots. In order to conduct a reading, the vertical speed indicator is also attached to the static pressure source, utilizing a diaphragm to detect changes so that a needle can be adjusted across the face of an instrument.
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